PUBMED search      Boolean operators
General advice:  always use one of these three operators between words:   AND, OR, NOT
(or automatic phrase searching will be carried out, without finding much of what you want)
      AND retrieves results that include all the search terms.
      OR   retrieves results that include at least one of the search terms.
      NOT excludes the retrieval of terms from your search.
phrase =   "little tiny blue bugs"
truncation (wild card) = *     an asterisk
truncation means cut off from the right-hand end, such as:
which retrieves chemistry, chemical, chemist, and variants you have not thought of
    ("john smith") OR ("john * smith")       which retrieves all John Smiths including all middle initials and middle names
Are parentheses needed when quotation marks are already in place?
Can parentheses be nested as in:
    (("john smith") OR ("john * smith")) AND (bugs OR insects)
Boolean operators must be used when combining tagged search terms as follows: search term [tag] BOOLEAN OPERATOR search term [tag]. (See Search Field Descriptions and Tags)

In a multi-word search PubMed will use Automatic Term Mapping to identify concepts. For example, for the search air bladder fistula, PubMed will search "air bladder" as a phrase, which works ONLY for common medical expressions that it recognizes; note that the search without tags will NOT find the ordinary human bladder, but instead will find only the air bladders of lower animals like fish. You shake your head and say "what the heck is all this crap about fish?"
If you do not want this automatic phrase parsing, enter each term separated by the Boolean operator AND, e.g.,
air AND bladder AND fistula.

With no tag [ ], means search everywhere within a citation (including full article text or just the abstract held in PubMed?), which will often swamp you with results that you don't want. A much more relevant search is to limit the search to article titles using the title tag [ti]

I use these more than any other ways of narrowing a search: To search only titles, put this anywhere in your search line:
To search only titles and abstracts, put this anywhere in your search line:

PubMed processes searches in a left-to-right sequence. Use parentheses to “nest” concepts that should be processed as a unit and then incorporated into the overall search.

Click Advanced search Details to see how PubMed translated your search strategy.


Find citations on DNA that were authored by Dr. Crick in 1993:
    dna [mh] AND crick [au] AND 1993 [dp]

Find articles on the effects of heat or humidity on multiple sclerosis:
    (heat OR humidity) AND multiple sclerosis

Find citations about arthritis excluding the Publication Type Letter:
    arthritis NOT letter [pt]

    common cold AND (vitamin c OR zinc)
Why are "common cold" and "vitamin c" not in quotation marks?

    (piling OR clumping) AND (rats OR mice)
    (piling AND rats) OR (clumping AND mice)