"Bibliographic databases" are the best sources for finding unknown journal articles (remember, the Catalog does not contain records of journal articles). These databases are generally related to specific disciplines or subject areas, though Articles+ is a single database that attempts to be as comprehensive as possible. These databases are searched much like the Catalog (by title, author, subject, etc.), but use the "keyword" option to start. The results of your search will be records of particular articles, of which many will have direct links to an HTML or PDF copy.