Scholarly journals, sometimes called academic or professional journals, are specialized periodicals that publish articles for study and research in a particular subject area.
Many scholarly journals have a system of peer review: they must first be reviewed by a group of scholars who make sure that the article meets high standards for study and research in the subject area.
As you review bibliographies, reference lists, etc., you will discover additional sources to possibly use.
Find them using the CitationLinker.
When searching for articles, be more specific with your searching. Articles tend to cover very specific or niche topics, and are also published more quickly than books, meaning the information is typically more current than the general information you can gather from books.
Google Scholar is a great resource for articles. It searches across many disciplines and sources. Link your Google Scholar to your library account to get access to articles that might be behind a paywall. Here's how: