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It is not always enough to enter your keywords into a search. You may also need to show the database how you want your keywords to combine. To show the database how you want to bring your keywords together, you use something called Boolean operators.
Boolean operators are simple words (AND, OR, and NOT) used to join your keywords in a more focused way.
AND requires both terms to be present.
OR either terms may be present in the search. OR is the Boolean operator you use to allow for word variations (e.g. spinal cord OR backbone).
NOT excludes that keyword from search.