In the flipped classroom teaching mode, it is not necessary to flip all the contents [9], but only partially flip the key and difficult knowledge of the teaching content. For example, acid-base electrolyte balance and blood gas analysis, the key and difficult parts in medical teaching, can not only reduce the learning burden of students before class, but also enable students to concentrate on the key and difficult knowledge points for targeted learning and exploration. There is evidence that students also prefer to divide the curriculum into traditional classroom and flipped classroom [9]. In a study on engineering major, students pointed out that 30% of the flipped classroom and 70% of the traditional classroom are the best composition proportion [15]. In the teaching process, it is difficult for students to master the key and difficult knowledge points in each chapter efficiently, and some difficult points even perplex students and weaken their learning enthusiasm. Therefore, this study will focus on the key and difficult knowledge plate as the teaching content of the study, to explore the application of flipped classroom teaching mode based on rain classroom technology in the teaching of key and difficult content.
Compared with FC group, the students in fr group performed better (75.40 ± 11.82 vs. 80.07 ± 9.46, P = 0.020, effect dose = 0.437). It should be noted that, Compared with FC group, the students in fr group performed better (75.40 ± 11.82 vs. 80.07 ± 9.46, P = 0.020, effect dose = 0.437). It should be noted that, as shown in the pre-test, the acid-base electrolyte balance was comparable to the theoretical knowledge baseline of blood gas analysis in both groups before the study. These results are particularly encouraging to encourage educators to consider using rain classroom technology, as we have shown that it is very effective in helping students master and apply knowledge of acid-base electrolyte balance and blood gas analysis. From the perspective of "knowledge internalization", this paper analyzes and discusses the influence of flipped classroom teaching mode and rain classroom technology on teaching effect. Students watch the teaching video before class and solve the related problems raised by the teacher before class, so as to have the students' first knowledge internalization; in the classroom link, according to the feedback of students' watching the video before class, the teacher discusses and interacts with students in class to solve the problems that students don't understand The second knowledge internalization occurred, and students' knowledge internalization plays an important role in flipped classroom teaching effect [16–17]. The internalization of a concept, especially the internalization of complex and ill structured knowledge concepts that cannot be established spontaneously, is far from enough only through one internalization, and it can be mastered skillfully only after multiple internalization [18].as shown in the pre-test, the acid-base electrolyte balance was comparable to the theoretical knowledge baseline of blood gas analysis in both groups before the study. These results are particularly encouraging to encourage educators to consider using rain classroom technology, as we have shown that it is very effective in helping students master and apply knowledge of acid-base electrolyte balance and blood gas analysis. From the perspective of "knowledge internalization", this paper analyzes and discusses the influence of flipped classroom teaching mode and rain classroom technology on teaching effect. Students watch the teaching video before class and solve the related problems raised by the teacher before class, so as to have the students' first knowledge internalization; in the classroom link, according to the feedback of students' watching the video before class, the teacher discusses and interacts with students in class to solve the problems that students don't understand The second knowledge internalization occurred, and students' knowledge internalization plays an important role in flipped classroom teaching effect [16–17]. The internalization of a concept, especially the internalization of complex and ill structured knowledge concepts that cannot be established spontaneously, is far from enough only through one internalization, and it can be mastered skillfully only after multiple internalization [18].
Compared with the FR group, the FC group had lower high scores. Many of the students who got high scores were students who actively participated in the teaching. In the flipped classroom, only some students participate in the classroom speech, which improves the enthusiasm and participation of these students, and facilitates them to internalize their knowledge better. However, most of the students who did not participate in the speech lacked enough enthusiasm and opportunities for knowledge internalization. If these students who are not active enough to complete the task of self-study before class are not up to standard, lack of enthusiasm for interaction with teachers and students in class, and do not participate in the designated pre class or classroom activities, flipped classroom will not be able to support effective learning [19–20]. Rain classroom scientifically covers every teaching link from before class to after class, providing complete and three-dimensional data and technical support for teachers and students [7]. The application of rain classroom technology in flipped classroom teaching mode can help to form a new knowledge structure and improve students' learning efficiency by decomposing the difficulty of knowledge internalization and increasing the times of students' internalization. Compared with FC group, the use of rain classroom technology promoted the internalization of students' knowledge and improved the theoretical test scores of FR group. At the same time, the subjective evaluation of FR group on the improvement of learning ability was also higher. It highlights the advantages of rain Classroom: firstly, to improve students' interest in learning, enthusiasm and active learning ability, secondly, it helps to achieve personalized autonomous learning, thirdly, it helps to build a "relaxed and pleasant" classroom atmosphere.
Using rain class, teachers can push the preview materials with exercises, voice and MOOC video to students' mobile phones for self-study. Students' pre class learning situation can be fed back to the teacher, which plays a certain role in supervising and urging students' pre class self-study. At the same time, teachers can teach students according to their aptitude according to their learning conditions. In class, the functions of random roll call, real-time answer, bullet screen contribution, exercise push and red packet in class can realize the efficient interaction between teachers and students, which greatly improves the participation of all students Enthusiasm provides a perfect solution for the interaction between teachers and students in classroom teaching: ① real time answer in class, teachers can push exercises to the whole class in real time. On the one hand, it can improve students' concentration in class, and at the same time, it can also test students' mastery of knowledge points. The teacher can also cast all the students' answers on the screen for the whole class to browse. Students can compare their answers in the class to reflect on their own learning deficiencies. ② Bullet screen interaction and contribution: the teacher can select any time point to open the barrage function, all students can speak freely and actively express their personal opinions. The bullet screen content sent by students will be displayed on the large screen of lectures, and both teachers and students can browse. Therefore, the bullet screen function provides most students who have not been on stage to express their opinions and opinions to the whole class Space and opportunity. If you are worried that the opening of the barrage will affect the students' concentration in class, the teacher can turn off the function of the barrage in class and open it between classes, so that students can also activate their thinking during the break time. Students can also send their opinions or questions to the teacher in the form of contribution, and the content will not be directly displayed on the large screen. After receiving the contribution, the teacher can decide whether to put it on the lecture screen. ③ Exercise push: teacher can push time limited (or unlimited) exercises to students at any time point before class, class and after class, as an evaluation test of students' learning situation. Students submit answers after answering questions, and teachers can check students' answers on the teacher's side and make corrections. ④ Classroom red packets: teacher can reward students with excellent performance in class by giving them red envelopes. While activating the classroom atmosphere, they can fully attract and mobilize the attention of students and put them into classroom learning. After class, the rain classroom will send personalized reports of classroom teaching to teachers. Teachers can refer to the classroom reports to further understand the students' learning situation and make targeted suggestions students to solve doubts, find out the missing.
Flipped classroom is a deeper and more open teaching mode, and it may need to update the evaluation system to better evaluate the effectiveness of flipped classroom [21]. The results showed that there was no significant difference between FC group and FR group (62.74 ± 10.41 vs. 65.81 ± 8.67, P = 0.085, effect amount = 0.321) (Figure 2(f)). When more complex evaluation indicators are included, for example, there are not only standardized multiple-choice questions, but also open subjective discussion questions; the evaluation level is not only the mastery of theoretical knowledge, but also includes learning ability, critical and creative thinking, students' reactions and opinions. The results are shown in Figure 2 (e). The final conclusion is that the teaching effect of the experimental group is better than that of the control group and the teaching effect of flipped classroom can be significantly improved with the help of rain classroom technology. Students have changed from traditional passive acceptance learning to active autonomous learning, and the evaluation depth and representativeness of standardized multiple-choice questions are insufficient, such as the improvement of students' learning ability, especially the cognitive ability of higher-order thinking, the improvement of problem-solving ability, inquiry ability and critical creative thinking [22]. This may be the main reason why some studies [23–24] have concluded that flipped classroom has little or no improvement in teaching income compared with traditional classroom.
This study also has some limitations. First of all, the teaching content of this study is the key and difficult knowledge in medical education. Due to the particularity and complexity of medical education [25], when it is extended to other teaching fields, the teaching mode of flipped classroom + rain classroom may not achieve good results. It is expected that more research will make up for this blank in the future. Secondly, the scoring standard of argumentative questions in the after-school theoretical evaluation is to score according to the key points. The reviewers may attach their own subjective judgment when marking, which may lead to certain scoring errors. However, all our papers are graded by the same reviewer, so as to avoid different scoring standards of different people, and strictly follow each score point, specific to each score detail, and reduce the error to the lowest.
To sum up, in the flipped classroom teaching of the key and difficult chapters of the teaching content, by using rain classroom software, compared with the simple use of flipped classroom teaching, more students can obtain greater teaching benefits.