Credo is an online reference that includes dictionaries, general and subject-specific encyclopedias, and links to full-text articles. Definitely a good place to start!
https://s3.amazonaws.com/libapps/accounts/4358/images/Credo_Physics_MindMap.PNG
https://ezproxy.library.und.edu/login?url=http://search.credoreference.com/search/visual?concepts=954556&institutionId=5753