Boolean Logic

Basic useful Boolean terms include AND, OR, NOT, and ( ). These terms are used to connect the words in a search. They can be used by themselves or in combination to specify your search terms. Although Boolean terms can be used in the "Author" field (with last names only), they are most commonly used in the "Word(s)" fields. Words within a field are assumed to be connected by OR unless otherwise specified. The OR connector is not often used since it is the default expression between terms. However, it can be helpful in organizing a complex query.

The AND connector limits the search results to articles that contain all of terms that are connected by AND. For example, a search for

"human diseases"

will return all articles that contain the term "human" or the term "diseases" (and depending on the journal, this could cause an error). In practice, this will retrieve articles as diverse as human evolution and avian diseases. Inserting an AND statement like so:

"human" AND "diseases"

ensures that only articles that mention both "human" and "diseases" will be returned.

The NOT term can be used to exclude articles containing certain terms. For example, if you wanted to search for articles about the gene called "sos" that did not deal with "Drosophila", the search would be constructed as such:

"sos" NOT "drosophila"

For more complex searches, these operators may be combined with one another, optionally using parentheses to group terms to avoid ambiguity in a complex query. For example,

("signal transduction" AND ("phosphorylation" OR "kinase")) NOT "xenopus"

finds only articles that use the phrase "signal transduction" and either the word "phosphorylation" or the word "kinase", but do not mention the word "Xenopus".

NOTE that when using boolean terms, it does not matter if you select Any, All or Phrase from the Words section. They will all produce the same result when combined with boolean operators.