No. PubMed is a database that provides search and abstract of biomedical papers and free search. The database source is MEDLINE. Its core theme is medicine, but it also includes other fields related to medicine, such as nursing or other health disciplines. Citation retrieval in pubmed database cannot only retrieve one citation at a time. Citation retrieval is the mutual citation of documents, which directly reflects the communication and connection between academic research. Through citation retrieval, we can find the early, then and recent academic literatures on related research topics, and understand the internal relations between the literatures.