One of the main criteria scholars use for determining the importance of a journal is the number of times articles that appear in the journal get cited or used as references by authors of other articles.
Citation counts become the scoring system for the importance of a journal. That is not to say that import research does not appear in other journals. It is just that research is more likely to be noticed and influence the field when it appears in a journal with a history of publishing highly cited articles because that is where other scholars look first.
The database Web of Science is the main tool for finding out what these highly cited journals are.
In fact, Web of Science is limited to the most cited journals and is a good starting point if you want to limit your search to articles from journals with recognized importance. PsycINFO covers many more journals-- as well as books, dissertations, and reports-- and requires that you have some familiarity with journals in a field-- and what journals are even relevant to a field.
Web of Science also has search tools from the record of an article, such as Related Records, Citation Analysis and Citation Map, that help you discover the invisible college of researchers interested in a topic.