The first author is the person who has completed the main scientific research of sci, and the second and third works are the second and third authors of the paper. It is certainly useful to sign after the first author, and the second and third authors, especially the second and third authors of sci papers. After all, sci papers are extremely valuable academic papers. If you are the second or third author of an ordinary paper, it depends on the actual situation. The significance and function of the second and third authors of ordinary papers are not great.