Different databases index different sets of journals. Use the one (or a couple) that best suits the kind of information you're looking for. DO NOT limit to "full text only" (use the Find It! button) but DO limit to peer-reviewed journal articles if you are looking for those specific sources.
When you search a database for a "Full Text" item, you are only searching through that particular database for the document in full-text, and not our entire collection. An item may exist as a "Full Text" selection within a different database.
If you don't find an item as full-text in the database you're searching, use the "Find It" button to cross-search other databses for that same item. You may discover that we have electronic access to that material after all.
Your BEST resource for citing any of your sources in proper APA style is to use the Publication Manual of the American Psychological Association, 7th Edition which you can find at King Library. Most databases offer a citation, but be sure to take those as suggestions as they are often incorrect.