1, direct method: also known as common law, refers to the method of directly using retrieval systems (tools) to retrieve literature information. It is also divided into sequential investigation, reverse investigation and spot check.

2. Follow-up retrieval method: Follow-up retrieval method refers to the method of searching literature information from far to near in time sequence by using retrieval system. This method can collect systematic documents of a certain discipline and is suitable for document retrieval of larger disciplines. For example, if we know the initial age of a subject and need to know the whole process of its development, we can use the sequential search method to search from the initial age.

3. Backward retrieval method: Backward retrieval method is a method to retrieve documents from near to far, from new to old and in reverse time sequence by using retrieval tools. Using this method, you can get the latest information as soon as possible.

4. Spot-check method: Spot-check method refers to selecting the most likely or most likely time period of document information related to the project according to the characteristics of the project, and using retrieval tools for key retrieval.

5. Traceability method: refers to the method of tracing the source text (cited literature) one by one by using the references listed at the back of the literature without using the general retrieval system, and then expanding the scope of literature information one by one from the references listed at the back of these original texts and tracing the source one by one. It can snowball and get better retrieval results according to the citation relationship between documents.

6. Circular method: also known as subsection method or comprehensive method. It uses direct method and backtracking method alternately in stages to learn from each other's strong points and cooperate with each other to obtain better retrieval results.