Google Scholar is a great place to begin a literature search, but it is not the only place to search. It does not search everything, and when doing a literature review or looking for gaps in the literature, it is important to scope out as much as possible. Here are ideas about finding other places to search.
Use Databases A-Z to locate databases
I know how to use Google Scholar, so why would I use a database?
A database often has articles and information that are for a specific subject. Examples include EconLit (Economics), Sociological Abstracts (Sociology), Education Full Text (Education), PsycINFO (Psychology). Plus, databases often have more detailed search interfaces that let you be more precise in your searching. An example is limiting to scholarly, peer reviewed articles.
Google Scholar is a helpful research tool, but it searches many subjects at once. Consider using it along with a subject specific database.
Also, while Google Scholar has a lot, it doesn't have everything.