All of the databases and search engines discussed on this guide will respond best to keyword searches using Boolean operators. Things to keep in mind when choosing keywords:
There are three Boolean operators in database searching: AND, OR, and NOT. These operators form relationships between words and establish parameters by which database search engines populate results.
Combining terms with AND directs a search engine to provide you with all results that contain all words connected with AND. So, for example, a search for:
two-stroke AND emissions AND reduction
will only return articles that mention all three keywords.
In general, use AND to connect all of the key concepts in a research question or topic.
Combining terms with OR directs a search engine to provide results that contain at least one of the terms provided. For example, a search for:
two-stroke OR two-cycle OR internal combustion
will return articles that mention one, two, or all of these terms.
In general, use OR to connect synonyms and related terms.
NOT directs a database to exclude any results that mention a certain term. For example, a search for:
two-stroke NOT four-stroke
would eliminate any resources that mentioned "four-stroke" engines.