In scholarly/peer reviewed articles:
Some databases have all scholarly material. Others have an option to search for only scholarly/peer-reviewed articles.
To learn how to tell the difference between popular and scholarly articles by looking at them, see Anatomy of a Scholarly Article.
To learn how peer review works, see Peer Review in 5 Minutes.
Note that many nursing journals are not peer reviewed, but editorially reviewed (it's a slight procedural difference but has the same results.) They are still scholarly!