Google Scholar crawls the Web for articles, government and technical reports, open access material. It is good for Cited Searches. It can be starting place for your research but to find "the good stuff" that is vetted by experts you need to use the Library Subscription Databases.
Many publishers do NOT want to partner with Google and their materials will ONLY be in the Library Databases. Google Scholar has poor searching capabilities compared to library databases. You will save time by using the Databases with advanced searching.