1. The title of the paper is too unpopular: if the title of the paper is too unpopular or specific to a small field, it may lead to the inability to find relevant information in the existing literature database. In this case, we can try to expand the scope of paper search and cover more related fields and topics.
2. Incorrect paper format: If the paper format does not meet the requirements, it may cause the document database to be unable to identify and retrieve the paper. Please ensure that the paper follows the correct citation format, such as APA, MLA, etc.
3. Incomplete or irregular cited materials: When quoting materials, please ensure that the cited sources are complete and standardized. For example, if you use online resources, make sure that the link or URL is complete and valid. At the same time, please make sure that the citation source is correctly marked, such as author, year, literature type, etc.
4. Inaccurate or excessive paper keywords: Paper keywords are an important basis to help the literature database retrieve related papers. If the keywords are inaccurate or too many, the search results may be inaccurate. Please re-examine the keywords to ensure that they are closely related to the theme of the paper and accurate.
5. Network or database failure: Sometimes, there may be network or database failure, resulting in the paper can not be retrieved. Please try to change the search engine or consult other databases to see if you can find relevant information.
6. The document library is not updated in time: even if the paper is new at the current time, the document library may not be updated in time. In this case, it is recommended to wait patiently for a period of time before trying to search for papers.
7. Unpublished paper: If the paper is unpublished, relevant information may not be found in the existing literature database. Please pay attention to the publishing progress of the paper and upload it to the corresponding academic database in time.
If none of the above methods can solve the problem, please try to contact the thesis advisor or professionals in related fields for their advice and help.