Trends in the evolution of sustainable development research in China: a scientometric review

Because of the extensive attention of global scholars on the sustainable development in China, much research has been published over the past 30 years. Based on the 12,635 journal papers from the Web of Science database, we explore the trends in the evolution of China’s sustainable development research by a knowledge graph. The result indicates that the attention of China’s sustainable development research increased exponentially during 1991–2021, and it continues to shift from a macroperspective to the exploration of specific methods and implementation paths. During 2001–2005, China’s sustainable development research developed rapidly and formed a complete cluster structure. In addition, China’s sustainable development research has experienced three stages and two topic drifts. Staged development and topic drifts lead to a wide range of disciplinary drifts. In general, the trends in the evolution of China’s sustainable development research mainly focus on three aspects: research methods, research scope, and theoretical innovation. China’s sustainable development provides a case or a path for other developing countries. Economic incentives and policy promotion remain important measures to promote sustainable development.


Introduction
Climate change caused by excessive greenhouse gas emissions has become a major threat to global sustainable development (Geissdoerfer et al. 2017;Murray et al. 2017). For nearly half a century, countries around the world have been trying to explore sustainable development paths that are suitable for them (Merli et al. 2018;Sarkodie and Strezov 2018). The same is true for China, whose special experience in the field of sustainable development has attracted widespread attention from scholars around the world (Bloch et al. 2015;Cervero and Day 2008;Cherry and Cervero 2007;Mathews and Tan 2011;Murray et al. 2008). The special features of China's experience in sustainable development are the world's largest population base, the high GDP growth rate in the past 2 decades, and the huge urbanization and poverty alleviation process. The resulting huge energy demand (Bai et al. 2012;Wu et al. 2014;Zhang et al. 2011) and expanding pollution problems (Bai et al. 2012;Cervero and Day 2008;Guan et al. 2018;Lin and Ouyang 2014) restrict China's sustainable development to a certain extent and become a special feature of China's path of sustainable development that is different from other countries. Today, how to complete the transformation of the energy structure system as soon as possible, reduce greenhouse gas emissions, and achieve sustainable social development while ensuring rapid economic development is becoming a challenge for China to fulfill its commitment to achieving carbon neutrality by 2060 (Zhang et al. 2022(Zhang et al. , 2021. The related theoretical exploration of sustainable development in China can be traced back to the signing of the Rio Declaration (1992). After that, China raised the strategic status of sustainable development through three actions: taking sustainable development as the national basic development strategy (1996), taking ecological civilization as a new requirement for building a well-off society in an all-around way (2007), and committing to the "30-60" goal (2021). The actions have directly promoted China's extensive development in three aspects: economic development mode, social and public welfare, and ecological protection; because of these achievements, many of China's sustainable development practices have attracted the attention of scholars around the world, and "the evidence from China" has begun to appear frequently in the titles of international academic journals (Li et al. 2017;Yin and Shi 2019).In view of the particularity of China's sustainable development, it is necessary to summarize a large amount of "China evidence" through scientometric analysis methods. Although there have been many studies on global sustainable development-related topics (Kajikawa et al. 2017;Leong 2021;Zhou et al. 2019), no systematic summary of the trends in the evolution of sustainable development in China has been found, especially visual analysis based on knowledge graphs. This restricts us in further exploring the special experience and development law of China's sustainable development process and is not conducive to the horizontal comparative study of sustainable development experience between regions. Based on the research shortcomings, we extracted the data of international journals with "China" in the title through the Web of Science (WOS) database and systematically summarized the trends in the evolution of China's sustainable development research through scientometric methods. This will provide effective experience for the differentiated analysis of global sustainable development models.
We focus on how China-related sustainable development research has evolved over the past 3 decades from a scientometric perspective. Based on the motivation of this research, this study is elaborated step-by-step through six parts. Following the introduction, we report on the research methodology, analytical procedures, and data processing. Next, the evolution characteristics of China's sustainable development research are analyzed from five perspectives, namely, overall trend analysis, research hotspot analysis, cluster analysis, topic drift analysis, and disciplinary drift analysis. On this basis, we further summarize the trends in the evolution of China's sustainable development research from the perspectives of key stages and methodology. Finally, we provide the principal conclusions, implications, and future research directions.

Methods and process
To review the trends in the evolution of China's sustainable development research over the past 30 years, a combination of scientometrics and knowledge graphs can be sued for retrieval, summary, and visual analyses. As a popular scientific and technological text mining tool, scientometric analysis can quantitatively analyze the literature or database in the target field and then explore the characteristics of knowledge base, research frontier, and topic distribution (Chen 2004). As an emerging tool in the field of scientometrics and knowledge graph research, CiteSpace visually analyzes trends and patterns in the scientific literature. It can find turning points and key points in the development of a certain topic (Chen 2006), and it has functions such as co-occurrence analysis and cluster analysis of keywords (Chen 2017). In view of the matching of scientometric methods and tools, we try to use CiteSpace (V5.8.R3) to conduct scientometric analysis and visual interpretation of the evolution of China's sustainable development research. This study mainly used the following five analysis methods: cluster analysis (Chen 2017), timeline and time zone analysis (Chen 2006), burst detection (Kleinberg 2003), journal overlay-map analysis (Chen and Leydesdorff 2014), and co-word analysis (Chen 2006). The specific research methods are explained in Table 1.
This study uses the above five methods to analyze the trends in the evolution of China's sustainable development research. First, a descriptive statistical analysis is conducted based on data to analyze the overall characteristics of China's sustainable development research during 1991-2021. Next, the research hotspots in the target domain are summarized through co-word analysis, burst detection, and time zone analysis. Further, cluster analysis can determine the main structural features and knowledge domain distribution. Finally, the timeline graph and journal overlay-map analysis are used to analyze the drift process of topics and disciplines and then help us identify the transfer process between knowledge units.

Literature search and data processing
To maximize access to literature on sustainable development research in China, we searched the WOS Core Collection by "topic-search" combined with "title-search." Since some scholars use "sustainability" to discuss the issue of sustainable development, we use the indistinct search method of "sustainab*" to cover the two categories of "sustainable development" and "sustainability." Due to the broad scope of the topic search, we further added the indistinct title search condition "China" (covering Chinese, China's, etc.), that is, to extract sustainable development research results related to China. The above search method can effectively focus the search scope on those published papers that explore China's sustainable development experience, which is helpful for us to summarize research directions and scholars' viewpoints. To a certain extent, this method draws on the perspective of "re-statistics" in the meta-analysis method, that is, a higher-dimensional econometric analysis based on existing opinions and data. Based on the above search settings, the time span of searched data is 1991-2022. Since the literature for 2022 is incomplete, the data cut-off is set to 2021. On this basis, we set the document type to "Articles" and obtained a total of 12,894 data items. Given the broad scope of the topic search, we further proofread and screened the data. By excluding data such as reports, news/interviews, book chapters, and items with missing information, we finally obtained a total of 12,635 valid data items (an effective rate of 98%). The time range of the data is 1991-2021, a total time span of 31 years. The specific search settings and information are displayed in Table 2.

Overall characteristic analysis
Through the descriptive statistical analysis of the data, the annual publication distribution and word frequency of China's sustainable development research are drawn (Fig. 1). We also plotted an exponential curve matching annual publication volume and found significant overlap between the two. This proves that from 1991 to 2021, the annual publication volume of China's sustainable development research showed exponential growth. This trend will continue for the foreseeable future as China pays more attention to sustainable development and the construction of its ecological civilization (Wu and Bai 2022). Based on the key points of the annual publication volume, it takes about 10 years to go from 10 to 100, and then from 100 to 500. However, from 500 to 1000 and then from 1000 to 2000, this time is shortened to only about 2 years. This also confirms the trend of exponential growth from the side, which is especially obvious after 2015. Based on word frequency analysis, the word frequency trends of the two core keywords "sustainable development" and "sustainability" are extracted as shown in parts A and B in Fig. 1. The word frequency trend of the two is similar to the distribution trend of the annual publication volume, and both show exponential growth. It is Table 1 Analysis methods and expected purposes

Brief description
Expected purposes 1 Cluster analysis The cluster analysis refers to the analysis process of grouping a collection of physical or abstract objects into multiple classes composed of similar objects, which is based on analyzing the similarity of the objects Identify key structural features and knowledge domain distributions (see the "Knowledge structure analysis" section) 2 Timeline and time zone In the timeline view, documents belonging to the same cluster are placed on the same horizontal line, which can reflect the time characteristics of the cluster and the time span of the articles in the cluster. In the time zone view, the nodes of same time are put in the same time zone, which can reflect the development trend of the topic in different time zones Timeline: identify the transition process between topics (see the "Topic drift analysis" section) Time zone: identify the transition process between research hotspots (see the "Research hot-spot analysis" section) 3 Burst Detection CiteSpace provides the Burst Detection function to detect large changes in the number of citations during a certain period, and to find the decline or rise of a certain topic, keyword, articles, or author, etc. Therefore, the Burst Detection can be used to analyze the emerging trends of a certain node Identify emerging research hotspots and key research directions (see the "Research hot-spot analysis" section) 4 Co-word analysis The basic principle of co-word analysis is to count the number of times they appear in the same set of articles for a group of words and measure the close relationship between them through this number of co-occurrences Identify the relevance of research hotspots (see the "Research hot-spot analysis" section) 5 Journal overlay-map analysis The journal overlay-map analysis elaborates the knowledge sources and contribution destinations of carbon footprint research by analyzing all the subject categories of citing and cited papers Identify the transfer process of knowledge units between disciplines (see the "Knowledge transfer analysis" section) worth noting that the keyword "Sustainable Development" exhibited a burst feature during 2006-2008 (bold line), that is, the keyword was widely used by scholars and appeared frequently in academic publications (Chen 2006). This finding shows that the topic of sustainable development has been widely recognized by the Chinese government, scholars, and society during this period and began to form a rapidly growing research field. The burst features of sustainable development during 2006-2010 are closely related to China's "Eleventh Five-Year Plan" policy to build a resource-saving and environment-friendly society during this period. Similarly, the keyword "sustainability" has also become a hotspot for scholarly attention from 2009 to 2010 and shows a high word frequency (see part A). After a brief retreat, the attention of this topic has also experienced exponential growth. In the past 15 years, China's sustainable development research has received rapid development and widespread attention, which is reasonably validated in the above analysis. Furthermore, a descriptive statistical analysis is performed based on four indicators: country/region, institution, fund source, and source journal as shown in Table 3. Besides China (f = 11,970) itself, the country most concerned about China's sustainable development is the United States (f = 1821). Australia, the UK, and Canada are also continuing to pay attention to China's sustainable development issues. In addition to the mainstream role of English in the international academic community, the extensive network of academic exchanges and cooperation between China and the above four countries can also provide an explanation for this. In terms of institutions, five research institutions from China occupied the top 5 in the number of publications. The Chinese Academy of Sciences provided the most research evidence for sustainable development research in China (f = 2572), more than the sum of the contributions of the last four institutions. Many academic achievements in sustainable development research in China in recent years have benefited from diversified funding. Nearly half of the 12,653 publications used in this study were funded by the National Natural Science Foundation of China (NSFC), which are twice the number of funds that ranked 2-5. In terms of journals, journals such as Journal of Cleaner Production and Science of the Total Environment have received a wide range of submissions and have become the most important platforms for showcasing sustainable development research in China.

Research hotspot analysis
To a certain extent, keywords can reflect the core theme and knowledge base of an article (Chen 2006). To this end, this paper conducts a co-occurrence network analysis of keywords. Based on 12,635 data items, parameters such as the node type of keywords, the cosine algorithm, and the top 50 threshold setting are used to conduct the co-occurrence network analysis of keywords. The time range we set is January 1991 to December 2021, and the time slice is 1 year. The visualization of the analytical results is shown in Fig. 2, which is divided into four parts, namely, the keyword cooccurrence network (right side), part A (burst strength > 10), part B (word frequency > 200), and the word frequency curve of the keyword "impact" (bottom right). The cooler colors in the picture are trending toward 1991, while the warmer colors are trending toward 2021. Based on 12,635 data items, we identified a total of 1262 keyword nodes and 6251 links among them, and the density of the entire network structure was 0.0079. As the keyword with the highest word frequency (F = 1782), the word frequency curve of "impact" is like the curve of annual publication volume, and both show a certain exponential trend. From the top 10 word frequency rankings (Table 4), the word frequency of the keyword "impact" is about three times that of the tenth keyword "urbanization" (F = 599). In addition, the word frequency of the keywords "management," "model," and "sustainability" all exceeded 1000 occurrences; all of which are the main topics of sustainable development research in China. In terms of the first appearance time of keywords, "sustainable development" was the earliest keyword in the top 10 word frequency rankings (1995); relatively speaking, "policy" appeared the latest (2004). This reflects from the side that China has experienced 10 years (1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004) from the introduction of the concept of sustainable development to the beginning of formation of relevant policies. As a comparison, we obtained the top 10 keywords with burst strength through burst detection. "Trend" became the keyword with the highest burst strength (S = 32.13) and continued to play an important role during 2009-2017. The next was "vegetation," which had a strong representation during 2006-2015, and its burst strength (S = 31.96) also exceeded 30. Judging from the duration of burst, the keyword "winter wheat" continued to be the main topic in China's sustainable development research during 2005 to 2015 (11 years). This, to a certain extent, explains the importance of agricultural development and grain output to the social stability of China (Gong, Yan, Wang, Hu, and Gong et al. 2009). Relatively speaking, the two topics of "greenhouse gas emission" and "driving force" have become relatively short-lived topics in China's sustainable development research (2018-2019).
The time zone perspective is further used to interpret the co-occurrence network of keywords and the time zone distribution of key nodes (Fig. 3). We still use two indicators, frequency and burst strength, to explore the distribution characteristics of keywords. Based on the threshold of word frequencies of more than 100 occurrences, we found that high-frequency keywords were concentrated between 1991 and 2010. Keywords such as "pollution," "loess plateau," and "land use" to "carbon emission," "indicator," and "technology," to a certain extent, reflect that the focus of scholars is constantly shifting from a macro-perspective to indicators and paths (Liu 2018). There was a decline in research attention during 2011-2015. Subsequently, emerging topics and research perspectives such as "innovation" and "life cycle assessment (LCA)" began to appear from 2016 to 2021 (Umaret al. 2020). Judging from those eight keywords with a burst strength of over 20, their time zone distribution is like that of high-frequency words. Five high-strength burst keywords such as "trend," "vegetation," "basin," "ecosystem," and "winter wheat" were mainly concentrated during 2005-2010. Keywords such as "carbon emission," "greenhouse gas emission," and "innovation" also appeared among the emerging themes. From the above two perspectives, China's sustainable development research has gradually shifted from macro-perspectives such as ecological pollution, vegetation protection, and geographical features to specific implementation methods and paths such as indicators, technologies, and innovation. In addition, China has paid great attention to climate change caused by greenhouse gases in recent years (Sarkodie and Strezov 2018), which is of great significance to global sustainable development.

Knowledge structure analysis
To elucidate the group characteristics of the keyword cooccurrence network and the knowledge structure of China's  sustainable development research, keyword-based clustering analysis (K-clusters) and link walkthrough are conducted on the network (Fig. 4). Figure 4 mainly includes two parts, namely, the K-cluster view (center) and the link walkthrough diagrams (both sides). The modularity value Q = 0.6079 (Q > 0.3), which is an evaluation index reflecting the modularity of the network, indicates the significant effect of the network clustering structure. The silhouette value S of the evaluation index reflecting the homogeneity of the network is 0.8822 (S > 0.7), indicating that the clustering results have high reliability (Chen and Song 2019). Through K-cluster analysis, the keyword co-occurrence network of sustainable development research in China is identified as having 21 clusters. Except for three clusters (#18, #19, and #23), which are far from the center, the network structure formed by the remaining 18 clusters is relatively concentrated, which all are closely related to the topic of sustainable development. In order to further identify the development context of China's sustainable development research, we show the cluster evolution process from 1991 to 2021 through time slicing. It can be seen from the link walkthrough diagrams that the cluster structure diverged from the center to the periphery during 1998-2008, indicating that this stage is the key formation stage of China's sustainable development research. During 2001-2005, the fields and topics of China's sustainable development research have been greatly expanded, providing a foundation for the subsequent formation of the main structure. Therefore, we call this stage the "expansion area." Interestingly, this phase coincides in time with China's "Tenth Five-Year Plan" (2001)(2002)(2003)(2004)(2005). The "Tenth Five-Year Plan" is an important milestone in China's sustainable development research. This promotes the production of much scientific research and the publications, which in turn provide the basis for the formation of the expansion area.
In the information table for the K-clusters, the cluster IDs, size, annual average, and the top 3 cluster labels based on the LLR algorithm are given (Table 5). As the largest cluster, "China" (#0, S = 141) closely fits the topic of this study, which verifies the effectiveness of data search from the side. Topics such as "sustainable development" and "energy consumption" involved in this cluster also outline the main directions of sustainable development research in China as a whole. The next three clusters, "water use efficiency" (#1), "soil organic matter" (#2), and "water resources" (#3) all have a size of over 70. Their topics all involve basic science and key resources related to sustainable development, such as soil, water, and plants. Relatively speaking, "institutional measures" (#18), "Delphi method" (#19), and "control strategy" (#23) become the three smallest clusters. It can be seen from the cluster labels that all three involve sustainable development strategies for policy control through    Fig. 4. Scholarly focus on topics such as dynamic perspectives and nutrient cycling makes "dynamics" (#7) the earliest cluster to form and the only one to form before 2000. The subsequent two clusters of "loess plateau" (#6) and "township and village enterprises" (#10) make sustainable development research more in line with China's scenarios and specific national conditions (Jia et al. 2017). The thematic differences between clusters represent the localization process of sustainable development in China to a certain extent. The three clusters "institutional measures" (#18), "China" (#0), and "industrial ecology" (#16), which were formed later, pay more attention to industries and policies (Mathews and Tan 2011), as well as the shaping of sustainable development systems (Zhang et al. 2008). The analysis of cluster formation also proves that the establishment of China's sustainable development research system is short-lived and rapid.

Topic drift analysis
The process of topic drifts is identified based on a further combination of timeline and link walkthrough (Fig. 5).
Based on the timeline of the annual slice, China's sustainable development research has gone through three stages and two significant topic drifts: (1) The budding stage (1991)(1992)(1993)(1994)(1995)(1996). First, in this stage, scholars focus on the contradiction between rapid development and ecological carrying capacity in the process of urbanization, such as "pollution," "land use," "vegetation restoration," and "loess plateau" (Hershkovitz 1993;Li 1992;Zhang and Jack 1992). The research method is relatively simple, and scholars tend to adopt qualitative research methods such as conceptual analysis or case analysis. The link walkthrough indicates that the research scope in this stage is relatively focused, and there are no significant topic drifts, as shown in part I of Fig. 5. (2) The primary stage (1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015). With the approach of the expansion area, China's sustainable development research began to experience a large-scale topic drift. This process is obvious in the link walkthrough, that is, many longitudinal connections extend from part I to part II. This drift lasted for nearly 20 years and mainly manifested as a shift from basic pollution issues in the budding stage to macro-themes such as climate change and biodiversity. The global ecological crisis caused by climate warming in the first decade of the twenty-first century has promoted human societal awareness of the need for ecological protection (IPCC 2013(IPCC , 2021, which has also brought about significant effects on China's sustainable development. In this stage, scholars tend to use quantitative research methods (such as index or quantitative analysis) to estimate the specific impact of climate change on the sustainable development of China's society and economy (Geng et al. 2012). Different from the more focus on water resources protection in the budding stage, the research in this stage focuses more on the assessment of soil (Liu et al. 2010;Teng et al. 2014) and air pollution (Jim and Chen 2008) and the analysis of potential impacts (such as research on cardiovascular, cerebrovascular, and respiratory diseases) (Hu et al. 2017). The resulting attention to environmental strategies at the macro-and meso-levels is also reflected in China's environmental policy-making process (Lu et al. 2012). Based on the above analysis, we refer to the topic drift between the budding stage and the primary stage as the "buddingto-primary" transition.
(3) The mature stage (2016-2021). As the Chinese government and scholars continue to pay attention to ecology, emerging hotspots and controversial topics continue to emerge, and the process of topic drift follows. The drift process is obvious in the link walkthrough. That is, since 2016, many horizontal connections have been extended from part I to part III. Although the "smog problem" has become a social hotspot in China as early as 2013 (Sueyoshi and Yuan 2015), the in-depth control of air pollution has only become a topic of extensive attention and in-depth research by the Chinese government and academia in this stage (such as the "Blue Sky Defense" campaign). In this stage, scholars began to adopt a more systematic approach to scientific research and environmental assessment. For example, the wide application of data envelopment analysis (DEA) based on the multi-index system and the environmental assessment system based on the LCA provides effective tools for China to deeply analyze ecological carrying capacity and track carbon footprints (Liu et al. 2022;Sueyoshi and Yuan 2015;Sun et al. 2022). In the above process, the wide application of environmental information disclosure system and emission testing facilities from the perspective of macro-environmental regulation has played a key role (Li et al. 2018). In addition, the application of new technologies (5G, Internet of Things) and the practice of emerging environmental governance models (public-private-partnership, sharing economy, carbon trading market, and green finance) provide a guarantee for China to move toward comprehensive and sustainable development (D'Orazio and Valente 2019; Wang et al. 2016;Xiaer et al. 2022;Zhang et al. 2015). Based on the above analysis, we refer to the topic drift between the primary and mature stages as the "primary-to-mature" transition.

Knowledge transfer analysis
Instead of topic drift, we try to explore the development and practice of China's sustainable development research from a more macroscopic perspective. Based on the journal overlaymap analysis, the disciplinary drift paths of China's sustainable development research from 1991 to 2021 are studied, which will help to identify the transfer process of knowledge units between disciplines, as shown in Fig. 6 which can be divided into three parts: part A is the original layer and the layers are marked with different colors representing the categories of the journals in the WOS database; part B is the result of disciplinary drift after journal overlay-map analysis and the line represents the transition from citing to citied literature in an article; part C demonstrates the results of merging repeated paths through the Z-score method and then identifies the drift paths of key disciplines (Chen and Leydesdorff 2014). Figure 6 shows that China's sustainable development research has experienced a significant and large-scale disciplinary drift process from 1991 to 2021. Combined with the results of Z-score analysis, the disciplinary drift of China's sustainable development research can be summarized into the following eight key paths: from the perspective of discipline sources, the most important source of knowledge in China's sustainable development research is the "ecology, earth, and marine" discipline. The discipline became the source of knowledge for the four key paths (4/8). Relatively speaking, the main destination of China's sustainable development research results is "economics, economic, and political," which has become the knowledge attribution of the three key paths (3/8). Interestingly, the direct transition between the main source and destination is not the most important disciplinary drift path of China's sustainable development research (the third one). There are still many indirect transfer or secondary drifts in the process of disciplinary drift in China's sustainable development research. Based on the Z-score, the transformation from the discipline "economics, economic, and political" to "economics, economic, and political" has become the most important disciplinary drift path (Z = 5.099, F = 16,548). This is the drift path of the self-iteration of the "Economics, Economic, and Political" discipline and, at the same time, makes it the discipline that is most closely integrated with China's sustainable development research. Relatively speaking, the knowledge transfer process from the discipline "ecology, earth, and marine" to "environmental, toxicology, and nutrition" is the lowest scoring path among the eight key paths. Overall, seven of the eight key paths have undergone disciplinary transitions, which shows that China's sustainable development research has experienced many disciplinary drifts during 1991-2021. Based on the above analysis, the key paths of disciplinary drift and the transfer process of knowledge units are further summarized ( Table 6).

Key stages and development context
We summarize the trends in the evolution of China's sustainable development research from four perspectives: keywords (high-frequency and burst), clusters, topics, and disciplines ( Fig. 7). First, the time difference between high-frequency keywords and burst keywords provides a reasonable perspective for longitudinally observing the trends in the evolution of sustainable development research in China. The time of appearance of high-frequency keywords is mainly concentrated in the period of 1995-2004, which relates to the period (2005-2021) of the emergence of burst keywords. This finding shows that after extensive exploration and discussion in the first 15 years (1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004), China's sustainable development researchers began to focus on core topics gradually. The transition of the above two stages also led to the formation of many clusters in this stage, that is, the "expansion area" (2001)(2002)(2003)(2004)(2005). That is to say, the process of China's sustainable development research from quantitative  to qualitative change is accompanied by the formation of many clusters, which further forms the core structure of China's sustainable development research. The drift perspective allows us to further expand the scale of China's sustainable development research, that is, to view the evolution trend of China's sustainable development research from a more macroscopic level. In the budding stage, scholars began to pay attention to issues such as sustainable development, ecological carrying capacity, and water pollution based on the pollution problems brought about by China's rapid urbanization, and their research methods tended to rely on qualitative analysis. With the continuous emergence of more pollution problems and the rise of sustainable development to the strategic level, the establishment of a statistical system in the field of sustainable development at the national level has made scholars begin to pay attention to the solution of specific industries and problems in sustainable development. At this time, quantitative analysis methods were widely adopted in the primary stage. Quantitative analysis methods based on the extensive application of data and indicators have been rapidly developed at this stage. Diversified environmental governance models and relatively new international environmental assessment methods (e.g., DEA and LCA) have pushed China's sustainable development model into a mature stage. The two topic drifts also provide impetus for the disciplinary drifts in China's sustainable development research. Continued attention to economic impacts and policy measures has become the main thread and key driver of sustainable development research in China. How to coordinate the development of the economy and the environment with the assistance of policies and then bring the greatest social welfare is an important experience and typical case provided by China for global sustainable development.

Trends in the evolution based on methodological perspectives
After 30 years of rapid development, China's sustainable development research has also shown clear evolution at the methodological level. Based on research hotspots, clustering networks, and drift analysis, we summarize the trends in the evolution of China's sustainable development research in three aspects: research methods, research scope, and theoretical innovation (Fig. 8).  In terms of research methods, China's sustainable development research has begun to pay more attention to the application of data in research methods after going through three stages of qualitative analysis, quantitative analysis, and systematic evaluation. Thanks to the rapid development and wide application of big data analysis models, China's sustainable development governance model reflects more and more intelligent application scenarios. Diversified data push China's sustainable development research toward datadriven research methods such as testing, verification, and simulation based on data modeling. This research method not only can adapt to the increasingly complex social operation, intelligent manufacturing, and supply chain adjustment but also provide the possibility for the effective implementation of environmental risk management and control, environmental information disclosure, and full lifecycle governance based on the circular economy system.
In terms of research scope, the focus of China's sustainable development research has begun to pay more attention to the global perspective under the climate crisis after experiencing cities, provinces (or watersheds), and countries. The focus of this perspective change is such that China is striving to coordinate the environment and climate governance and explores the path of sustainable development under the global climate crisis from the perspective of a "community with a shared future for mankind." While systematically evaluating domestic sustainable development issues, China has continuously adopted new measures to promote the green transformation of the supply chain and the optimization of production layout, and to connect with the global emission reduction system through green financial measures such as the establishment of a national carbon trading market platform. Such measures have prompted China's sustainable development research to begin to focus on more macroscopic issues such as how to promote the green transformation and sustainable development of the entire industrial chain and how to promote regional sustainable development from the perspective of finance and trade.
In terms of theoretical innovation, China's sustainable development research, after experiencing theoretical explorations from the perspectives of economics, sociology, and ecology, has begun to move toward theoretical breakthroughs from the perspective of systematics. In the past 3 decades, China's sustainable development research has  Fig. 8 External context, evolution trends, and exploration frontier focused on one of the following three aspects: technological progress and the improvement of marginal benefits (economic significance), economic efficiency and social equity (sociological significance), and economic development and environmental carrying capacity (ecological significance).

Research Methods
With the expansion of research scope and the advancement of research methods, China's sustainable development research has begun to explore a sustainable development path that is more conducive to the comprehensive synergy of human, society, and nature. From "harmonious society" to "ecological civilization," China has continuously explored the origin and evolutionary law of sustainable development and then promoted the maximization of the overall benefits of the sustainable development system. This breaks through the inherent meaning of economics, sociology, and ecology, and begins to examine the theoretical connotations of sustainable development with a complex and dynamic system view.  (1991)(1992)(1993)(1994)(1995)(1996), the primary topics focused on the contradiction between urbanization and ecological carrying capacity, and related research mainly focused on issues such as land use, vegetation restoration, and urbanization. In the primary stage (1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015), scholars try to use quantitative research methods to perform the analysis of biodiversity, soil pollution, air pollution, and the potential effects thereof. In the mature stage (2016-2021), the environmental information disclosure system, the scenario-based application of new technologies, and the emerging environmental governance model make it possible for China to shape a unique model of sustainable development. The transformation process among the three stages has formed two topic drifts in China's sustainable development research. Based on the journal overlay-map analysis, we found eight key paths in China's sustainable development research in the process of disciplinary drifts.

Conclusion and discussion
Third, the trends in the evolution of China's sustainable development research are mainly concentrated in three directions: research methods, research scope, and theoretical innovation. After going through three stages of qualitative analysis, quantitative analysis, and systematic evaluation, data-driven research has become an obvious tendency in China's sustainable development research. After experiencing the perspectives of cities, provinces (or watersheds), and countries, China's scholars begin to switch to the perspective of globalization under the perceived climate crisis. After the exploration of three theoretical perspectives of economics, sociology, and ecology, China's sustainable development research is more inclined to the theoretical research from the perspective of systematics.

Discussion
The sustainable development research in China has developed rapidly in the past 30 years, and the annual publication volume of the two core keywords "sustainable development" and "sustainability" has shown an exponential growth trend. The 2001-2005 period is an important window period; the coincidence between this period and China's "Tenth Five-Year Plan" (2001)(2002)(2003)(2004)(2005) reflects that policy orientation can dominate the direction of sustainable development to some extent. This is also reflected in the path of discipline drifts. The knowledge self-iteration of the "economics, economic, and political" discipline has become the main driving force for the continuous development of sustainable development research in China and further promotes the interdisciplinary research and diversified development. At the same time, the concentrated appearance of practical problems such as air pollution and ecological destruction provides the basis for the formulation of the Chinese government's environmental policy and strategies. These further pushed Chinese scholars to adopt more systematic environmental assessment methods such as DEA and LCA since 2016 instead of quantitative analysis based on single indicators. The wide application of data-driven research pushes the shifting tendency to digital and intelligent paradigms, which in turn influences the rapid progress of big data, Internet of Things, and digital economy on social operation mechanism, intelligent manufacturing system, and supply chain adjustment.
In recent years, more and more attention has been paid to the integrity between domestic environmental governance and international climate governance. Scholars tried to explore the path of sustainable development under the global climate crisis from the perspectives of "a community with a shared future for mankind" and "Belt and Road." On this basis, China tries to promote the formation of a global emission reduction system through the perspectives of supply chain transformation, carbon trading market, and green finance. Based on the advancement of research methods and the expansion of research scope, scholars have begun to explore a sustainable development path that is more conducive to the comprehensive integrity of human, society, and nature. The purpose of this exploration is to examine the theoretical connotations and evolution of sustainable development from the perspective of a system and then to promote the maximization of the overall benefit of the sustainable development.

Implications
China's sustainable development process provides a special case for a comparative analysis of regional differences in sustainable development models. It took China only 10 years from introducing the concept of sustainability to form systematic theoretical research. The entire development process has gone through three stages of "introduction-digestionpractice." China's practical experience in the field of sustainable development provides a good reference for other developing countries, especially the populous countries such as India, Pakistan, and Brazil. Although China's sustainable development path has strong "Chinese characteristics," it still has guiding significance especially in policy designation and economic measures. In addition, the horizontal comparison between "China's experience" and "developed countries' experience" will also provide a feasible theoretical support for the sustainable development path selection. This is one of the directions that we should focus on in the future study.
Economic incentives and policy promotion are important boosters for sustainable development. National development policies such as the "Tenth Five-Year Plan" and the "Tenth Five-Year Plan for National Environmental Protection" provide rigorous and effective standards and norms in all regions of China, which in turn provide the impetus for the implementation of sustainable development strategies. Relatively speaking, the "invisible hand" of economic incentives will provide impetus for sustainable development on a larger scale. Measures such as green finance, the carbon trading market, a carbon tax, and ESG concepts have facilitated sustainable development in many countries and regions while improving the supply chain system and the way of life of residents to a certain extent. We will continue to focus our research on the positive role of market mechanisms such as carbon emission trading, China Certifies Emission Reduction (CCER), and Clean Development Mechanism (CDM) for China's sustainable development. The design and experience of market mechanisms in developed countries such as the EU-ETS should also be regarded as an important reference for China's sustainable development. In addition, the role of technological innovation in promoting low-carbon economy has gradually become the hot research topic. Therefore, the issues that need to be focused on include but are not limited to (a) the incentive effect of environmental regulation on technological innovation, (b) the verification of "Porter's hypothesis" in various situations, and (c) how to realize the "double dividend" of economy and environment.
This study provides a new perspective for scientometrics using meta-analysis to conduct bibliometric analysis. The data for scientometric analysis in this study comprised 12,635 published papers on sustainable development research in China. Each paper discussing China's experience in sustainable development becomes one of the items of data for the scientometric analysis of this study. We further analyze the scholars' viewpoints by using meta-analysis of the hot topics. Therefore, this analytical approach provides a new perspective for systematic review analysis in specific subject areas, and subsequent studies should be conducted on this basis for further attempts and validation.
This study still has some limitations. First, the data used in this study include 12,635 items; however, most of them are journal papers and do not cover other types of documents such as dissertations, conference papers, book chapters, and newspaper reports. In addition, since CiteSpace method cannot analyze both English and Chinese data simultaneously, Chinese journal data was not included in this study, which also becomes one of the limitations of this article. Next, this study analyzes China's sustainable development research from a relatively macro-annual perspective, so it is difficult to find the details of quarterly or monthly research changes and progress. In that case, the division method of research nodes should be further refined, and multi-level and multiperspective analysis should be conducted in combination with different research tools. In addition, this study has a certain degree of subjectivity in drawing and interpreting knowledge graphs, especially in terms of indicator setting, threshold selection, and graph interpretation. In the future study, it should consider conducting a horizontal comparison of the results among different indicators and threshold selections to mine the behavioral trends underpinning the data.