1. extract keywords according to the theme of the paper. A paper has its own discussion content and direction, and sometimes scientific attributes can be summarized as keywords. For example, the key word of a law-related paper can be "law-related".

2. Extract keywords according to the title of the paper. Usually, the title of the paper is the most commonly used keyword. Many students learn to intercept some words in the title as keywords. This method is not infeasible.

3. Choose terms that can be expanded or reduced. The selected keywords can be expanded or reduced according to the main content of the paper, so as to select the terms within the scope of the keyword paper.

4. Extract keywords according to high-frequency words. The words with the highest frequency in the paper can be used as keywords. It should be noted that due to the large number of words and information in the paper, sometimes there are more high-frequency words, so attention should be paid to screening and so on.