MeSH (Medical Subject Headings) 这里有详细的说明
http://www.ncbi.nlm.nih.gov/books/NBK3827/#pubmedhelp.Searching_by_using_t主要就是相关的术语检索（term）
MeSH (Medical Subject Headings) is the NLM controlled vocabulary thesaurus used for indexing PubMed citations.
Use the MeSH database to find MeSH terms, including Subheadings, Publication Types, Supplementary Concepts and Pharmacological Actions, and then build a PubMed search. The MeSH database can be searched by MeSH term, MeSH Entry Term, Subheading, Publication Type, Supplementary Concept, or MeSH Scope Note.
More information about the MeSH database:
An autocomplete feature is available from the search box.
Search results are displayed in relevance-ranked order, therefore, when a user’s search exactly matches a MeSH Term, that Term is displayed first.
Click the MeSH term from the Summary display or choose Full from the Display Settings menu to view additional information and search specifications, such as Subheadings, restrict to Major MeSH Topic, or exclude terms below the term in the MeSH hierarchy.
Year Introduced is the year the term was added to MeSH. If more than one year is shown, the term was available for indexing back to the earliest year noted. Articles are indexed using the vocabulary in place at the time of indexing, therefore, the year introduced for a term and the date of publication of a citation indexed with that term may not agree.
Launching PubMed searches from MeSH
To build a PubMed search from MeSH, run a search, select terms using the check boxes, and then click "Add to search builder" in the PubMed search builder portlet. You may continue searching and including additional terms to the PubMed search builder using the “Add to search builder” and Boolean pull-down menu. When you are finished, click “Search PubMed.”
追问比如你想查一个蛋白的或基因相关的文献，选哪种搜索范围比较好呀。
追答你就先用Pubmed查，结果可能多一些，但不容易漏掉