The so-called keywords refer to the non-standard natural language and characters which are extracted from the title, text and abstract of the paper, can prompt (or express) the theme characteristics of the paper, and have substantive significance.

Keywords, also known as descriptive words or indexing words, are mainly used to index or help readers retrieve documents, as well as computer information retrieval and other secondary literature retrieval.

Keywords are used to express the theme of literature, not only for scientific papers, but also for scientific reports and academic papers. Thesis is the carrier of creative ideas in scientific research. Its primary task is to transmit scientific research information, and it also has the significance of cultural storage and accumulation. No matter from the perspective of transmitting information or storing information, the indexing of subject words or keywords will bring great convenience to the storage and retrieval of documents.