Books or just introductions, individual chapters, or summaries provide indepth thinking on a topic.
These two collections of scholarly journal articles are easy to use, and have search features not found in GoogleScholar.
These works provide lengthly articles & bibliographies, which can clarify a concept, term, person, or phenomena that is important to your paper topic.
Companions are books that provide overviews on a topic. Every chapter is written by a different scholar and can be read like an individual article in a journal.