Don't forget subject terms!
There can be many ways to label the same thing, particularly in the sciences, so how do you know what to search for?
When in doubt, use Subject Terms!
Subject Terms (or Subject Headings) are keywords that librarians agree on as the best way to research certain topic. Catalogers apply these terms to records, whether or not the author used that exact word or phrase when writing. Click on subject terms in a record to do a search for that specific term. Using subject terms is also a great way to find more resources similar to one you like!
MeSh terms follow the same idea.
The circles above represent the records in a database available with two key words, Lycopene and Synthesis. Some records only have one key word, others have both.
If you connect your search terms with the Boolean operator AND, you might think you are making your search result pool larger, but you're actually shrinking it, because you are asking the database to only return records that include both words. You'll want to use the AND operator when connecting two parts of your research question. You don't just want information on Lycopene, you would have to wade through too many results to find the ones you want, those that deal with lycopene synthesis.
The OR operator sounds like it should exclude results, but it doesn't. In fact, using OR is a great way to get more results when you are having a hard time finding what you need. Usually, you'll use OR for two keywords that describe similar ideas to account for authors using different words for the same idea, like (Lycopene OR "2,6,10,14,19,23,27,31-
We don't use the NOT operator very often, but it can come in very handy. Sometimes, the keyword you are using is used so often with an idea unrelated to your research question that you are swamped in unrelated results and can't find the information you need. When that happens, look through the false records to find the offending idea, and exclude that keyword(s) from your search.