1. The number of keywords in the paper is 3-8, 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.
Subject words are words or phrases selected from the main vocabulary of natural language and standardized for indexing or retrieving documents; Free words are words or phrases that are not standardized, that is, they are not included in the thesaurus. When determining the subject words, it is necessary to analyze the theme of the paper and convert it into standard words in the thesaurus according to the rules of indexing and matching.
2. The title of a paper usually comes straight to the point and directly explains the content of the paper, so one or more central words in the intercepted title can be directly used as the key words of the paper. For example, keywords such as "safety and principles of drug use for the elderly" and "rational drug use" can be extracted.
3. Most of the words with the highest frequency in a paper can be directly used as keywords. However, it should be noted that there are many high-frequency words because of the large number of words and information in the paper. At this time, we should pay attention to screening and grasp the main contradictions. You can sort the high-frequency words roughly and choose the first few. At the same time, we should arrange keywords according to their relevance to the paper.