How do you decide if the article you are reading is appropriate to include in your paper?
First, some terminology.
Periodical means something that is published repeatedly. A magazine that is published once a month is a periodical. Journals and newspapers are also periodicals. A book that is published once is not a periodical, it is a monograph.
When you search in Omni, you will see results from all sorts of publications: magazines, academic articles, theses, books, reports, and more!
Learn how to distinguish between scholarly and popular resources in the following video: