Most of the databases have tools to help you limit your search. In OneSearch and the EBSCO databases for example, you can limit your search by publication date or source type. You can limit your results to Scholarly (Peer Reviewed) Journals using the tools on the left-hand side of the screen. However, do NOT limit your search at the beginning of your research. You should use limiters like "scholarly peer-reviewed articles" after you've looked at all types of results for keywords and ideas that will help you construct the most effective searches.
You can also click on Show More above to limit to your choice of publication sources.