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Microbiology and Molecular Biology: Searching PubMed

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Greg Nelson
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PubMed Basics from NCBI (Tri-fold PDF)

Tips for Refining a PubMed Search

Search field operators called Boolean Operators will help to narrow or broaden out a search. In PubMed, operators should be written in ALL CAPS.



The AND operator conjoins two search terms. Each of the search terms or associated concepts must be somewhere in the record. You will have fewer search results.

Search terms Results
cardiovascular disease




Combining the two terms with an AND narrows the search results
cardiovascular disease AND chocolate



The OR operator links two or more search terms separated with the 'OR'. At least one of the search terms must be somewhere in the record. You will have more search results.

Search terms Results




Combining the two terms with an OR broadens the search results
chocolate OR cacao


Nested Searching

A search that uses multiple terms, usually with an "OR" separating the terms, in conjunction with an "AND", should contain the OR'ed terms within parenthesis.

Search terms Results
chocolate OR cacao


cardiovascular disease 2,418,733
Refining a search by combining the AND and OR operators
cardiovascular disease AND (chocolate OR cacao)


Field Descriptions and Tags

One way to narrow a broad search is to add a field tag that indicates to PubMed exactly where you want it to look for your keyword. Two of the most useful field tags are [title] and [title/abstract]. PubMed will only look in those locations for your exact keyword or phrase.

Search terms Results
chocolate [title]


 cacao [title/abstract] 1,059
 chocolate [title] OR cacao [title/abstract] 2,331
Refining a search as above with the title and title/abstract tags
cardiovascular disease AND (chocolate [title] OR cacao [title/abstract])



PubMed Simple Subject Search Tutorials and Videos