There are some effective tools you can use in keyword searching.

Connectors

Connectors (Boolean operators) link together two or more terms or concepts. The most commonly-used connectors are: AND and OR.

AND narrows a search; you get fewer records, because both terms must be present in the records found. Use AND to combine different terms in one search.

OR broadens a search; you get more records because OR searches for each of the terms separately, as well as both concepts when found together. OR casts the net widely for related concepts.

computer AND history AND mathematics

computer OR history OR mathematics