The full text is a paper in a general sense, with a long length and substantial content, including my own ideas and detailed calculation flow. The length of some periodical papers can reach 8000 words. Generally speaking, a complete science and engineering paper should include title, abstract, key words, introduction, methods and skills, results, discussion, conclusion, thanks, references and supplementary materials. There are many pictures, tables and even some video software, which can fully express the author's ideas.

Letter is a smaller version of paper, which is more concise, but it occupies different positions in different fields. Some letters are actually more influential, just like the summary in the paper has higher citation times and impact factors. The general length is 2-4 pages, with about 3,000 words (for reference, different journals have different requirements). The most important thing in a letter is to highlight your ideas in a limited space, which is actually a manifestation of your basic skills. SCI and NATURE also have letters. Some people think that letters are not SCI, in fact, as long as they are retrieved by SCI. The format is also more casual.