There are several ways to find primary and secondary source articles. One option is OneSearch, which contains both kinds of articles:
Depending on your topic, it may make sense to search one database at a time. These database contain both primary and secondary sources in the science and medical fields:
In the sciences, primary and secondary sources may look very similar at first glance. It may be helpful to use a database that clearly labels primary vs. secondary sources, or gives you a way to search for only one or the other. The following databases have options that make this process easier for you: