There are a few ways to ensure that the articles in your results list are published in scholarly sources.
If the database you are searching has this capability, check the box to limit the results to Scholarly or Peer-Reviewed Journals.
See this example from SPORTDiscus:
Two more tips:
Limiting to Scholarly Journals may still retrieve articles from sources that do not meet the professor's specifications for sources. If in doubt, consider the following: