1. Primary literature: refers to monographs, academic papers, patent specifications, scientific and technological reports, etc. What has been published, distributed and used in social circulation is created or compiled by the author according to his own research results.
2. Secondary literature: products that collate and process primary literature information resources, such as catalogues, indexes, abstracts and various bibliographic databases. Provides clues to literature information resources.
3. Three documents: based on certain purposes and needs, on the basis of a large number of primary and secondary documents and information resources, the information resources are synthesized, analyzed, experienced and reorganized.