Entrez databases use a search syntax closer to natural language than does z39.50 databases. Enter key words, and the Entrez server will generate a custom set of search results based on its retrieval algorithms. Note that when searching PubMed for personal author names, `,' should not be entered between first names and last initials, and that first initials (as opposed to first names) are typically used, as in `wright s' or `fisher ra'.
For more focused searching, Entrez allows terms to be combined using Boolean operators. According to the Entrez documentation, available at Boolean Operators, these must be entered as follows.
Combine two search terms together to find all documents that contain BOTH terms.
Combine two search terms together to find all documents that contain EITHER term.
Combine two search terms together to find all documents that contain search term 1 BUT NOT search term 2.
The Entrez search rules and syntax for using Boolean operators are:
Another way in which searches can be focused in PubMed is by the use of extensions to the search terms. For instance, to search for `random genetic drift' in the MeSH terms field only, enter the following:
random genetic drift [hm]
into the search field. Note that the extension appears in brackets after the search key (`random genetic drift,' in this case).
Other useful extensions include the following.
Last author name
Language (use the first three letters of the language's name, but note that "ja" means "japanese".)
Publication date in YYYY/MM/DD format. Month and day are optional.
Title or abstract
Complete documentation of the extensions is provided at Search Field Description and Tags.