The third kind of literature is a general literature that systematically sorts out and summarizes the first kind of literature, and analyzes and comprehensively compiles it on the basis of making full use of the second kind of literature. The National Bibliography is the only annual catalogue in China. Compiled year by year from 1949, including all kinds of books published that year. It is a necessary reference book for publishing houses, libraries, information materials and scientific research and teaching departments. So the national bibliography belongs to three documents.

The concept of three documents:

Third-level literature, also known as third-level literature, is a literature compiled from a large number of related documents after comprehensive analysis and research. Usually, it is formed by collecting a large number of relevant documents around a certain topic through secondary literature retrieval and deeply processing its contents.

It is a document that comments, summarizes and predicts the development trend of existing achievements, including review, summary, progress and dynamics. In literature research, we can make full use of this kind of literature to understand the research history, development trend and level of the research topic in a short time, so as to grasp the technical background of the topic more accurately.

Refer to Baidu Encyclopedia-National Bibliography for the above contents? Baidu Encyclopedia-Three Documents