If you're only looking for magazine and journal articles using your usual search engines then you're missing out on a ton on articles you have to pay to read. Lesley Library pays for subscriptions to journal/magazine databases so you don't have to!
Journal and magazine articles are written by experts in their field, just like books are, but it takes a lot longer to publish a book so journal articles offer the most up-to-date information on a subject.
EBSCOhost is a company that offers a lot of different databases. Some of them are for specific subjects, like their Art Full Text database, which searches only art journals/magazines.
Academic Search Premier is another EBSCO database that searches a wide variety of journals/magazines. Because it covers a broad range of subjects, it's a good place to go to start your research.
Go to the Academic Search Premier database and try searching for Robert Mapplethorpe.
Notice how the results compare to a Google search. You have popular news/magazine articles, but you also have in-depth scholarly articles. For example instead of just finding background info on his life and art, you find articles like "Public Welfare, Artistic Values, and the State Ideology: The Analysis of the 2008 Japanese Supreme Court Obscenity Decision on Robert Mapplethorpe". This would be a more scholarly examination, with a more global perspective than a lot of the stuff you find with Google.
Play around with the search result limiters.