If you are searching for a phrase, such as spontaneous combustion or greater rice weevil, put the entire phrase in double quotes. This will tell the search engine to only find results that contain the exact phrase, rather than one or two of the individual words.
If you have two or more words or concepts that you want to find, use AND (must be capitalized) to tell the search engine to only look for items that contain both words.
Often, there is more than one way to talk about your topic. For example, if you are looking at the study habits of college students, you could look for "study strategies," "study habits," "ways of studying," "study methods" etc. Some phrases might be better than others. If you want to try looking for multiple variations of the same word or phrase in a single search, use OR (all capitals) to tell the search engine to find material with any of the words you've included.
You can even get fancy and use both AND and OR:
Secondary sources are materials which provide an interpretation, analysis or discussion of information originally presented elsewhere. This is in contrast to primary materials which provide first-hand evidence. What counts as a secondary source depends heavily on the topic you are writing about and the discipline you are working within.
Scholarly articles are a common type of secondary source:
Contains summaries of the world's journal literature, of dissertations and technical reports, and of English-language chapters and books in psychology and related disciplines. No full text content within PsycInfo, but there are links to full text in other databases, including PsycARTICLES. Also includes psychology articles from related disciplines such as sociology, linguistics, education, medicine, law, physiology, business, psychiatry, and anthropology.
Note: Beginning June 1, 2021, users of NCBI services will need to login with their MSU Net ID instead of a NCBI-generated account. The NLM has more information about this change and how to link your existing NCBI account with your MSU Net ID. A Microsoft Word document containing step by step instructions is avaialble for download.