One of the key differences between scholarly journals and popular sources like magazines is that articles submitted for publication in scholarly journals go through the "peer review" process. It's after this review of the article by the experts in the field (the authors' peers) that the journal editors, based on the reviewers' comments, determine if the article should be accepted or rejected. They could also accept pending minor revisions, or request more substantial revisions and then review it again.
Some of the Library databases index all or mostly scholarly sources, while others index primarily popular sources like our newspaper databases. Others like Academic Source Complete index both types of sources, in which case you can easily limit your searches to the peer-reviewed articles only. To find out if a journal is peer-reviewed, it is typically stated on their website, as part of the "about this journal" section or the instructions for authors who are interested in submitting an article for the journal.