1, key words are the focus and highlight of the core content of the article. Generally, keywords can be selected from the following two directions. First, it is selected from the content repeatedly emphasized in the title, abstract, titles at all levels and text of the article.

2. Paper keywords are extracted as follows: The number of paper keywords is 3-8, which is located at the lower left of the abstract. In order to meet the requirements of document indexing or retrieval, the selection of keywords has certain standardization. It includes two parts: subject words and free words.

3. The selection of keywords in scientific papers can be considered from the following four aspects: finding from the topic; Seek from the abstract; Search from the hierarchical title of the paper; Look for it from the conclusion. Keywords are words or combinations of words with substantial meaning extracted from the conclusion, abstract and title of the paper to express the theme of the article.

4. Paper keywords should be extracted according to the topic and theme of the paper.