Indexes and online databases often provide citations that present the journal title in abbreviated form, for example: J. Am. Psychoanal. Assoc.
Sometimes it's possible to find the full title of a journal simply by searching for the abbreviated title in a search engine like Google. For example, if you search for: J. Am. Psychoanal. Assoc. inGoogle, the first result is a listing for the Journal of the American Psychoanalytic Association.
It's also sometimes possible to find the full title of a journal by searching its abbreviated title directly in Omni using the Journal Search option. For example, if you search for:j soc biol struct in Omni's Journal Search, you will get an entry for the Journal of Social and Biological Structures. However this will only work sometimes, if the abbreviation is included in the journal description.
Below are some general and subject-specific websites that can help convert journal abbreviations to full journal titles.