1. Books: refers to long paper documents published by publishing houses with specific topics as the main content, including textbooks, professional books, novels, biographies, etc.
2. Periodicals: refers to the paper documents with a specific subject or field as the theme and papers, research reports and comments as the main contents in a fixed period of time, including academic journals, magazines and newspapers.
3. Report: refers to the paper documents compiled by government agencies, enterprises and research institutions. Taking specific topics as the content, including investigation reports, research reports, annual reports, etc.
4. Essays: refers to the paper documents that academic institutions or individuals collect many papers with a certain subject or field as the theme.
5. References: refer to other documents cited in papers, research reports and other documents, including books, periodicals and reports.
6. Map: refers to documents that record information such as geography, topography and climate by printing or hand drawing with paper or other substances as the carrier.
It should be pointed out that with the development of digital technology, more and more documents exist in electronic form, such as e-books, electronic journals and electronic reports. Readers can choose paper documents or electronic documents according to their specific needs and actual situation when consulting documents, so as to obtain more convenient, fast and accurate information.