When it comes to finding the right keywords remember that iteration is key. If a likely word doesn't turn up the articles you need try synonyms or closely related concepts. Sometimes finding good results is just a matter of finding the right way to "talk" to a database.
LESS IS MORE
Don't search sentences or complex phrases. Isolate the most relevant words and search those instead. Strip out prepositions and speech articles.
Use them to return results containing an exact phrase or concept. For example, "Captain America," not "captain" and "America."
a.k.a. limiters or filters. Use them wisely! Limiters narrow the scope of your search, so be sure you aren't inadvertently overlooking useful resources. Begin broadly, ensure that your keywords are well chosen, then narrow by one or more variables.