Unlike in the humanities, primary sources are not diaries, artwork, or 1st hand accounts.
In the sciences, primary sources (also called research articles or empirical articles) report on original research. They will typically include sections such as an introduction, methods, results, and discussion.
The databases often provide a search limiter of methodology, research article, or empirical study.
If they do not have the limiter, use the words study, clinical-trial, or case-study, as a search term:
Also, unlike in the humanities, "review" in the sciences doesn't mean a "book review" or judgement of a particular resource.
In the sciences, review articles (sometimes called literature reviews or secondary sources) synthesize or analyze research already conducted in primary sources (original research). They generally summarize the current state of research on a given topic.
So searching for review articles is often just searching for scholarly, often peer-reviewed journal articles. You can also search more specifically with limiters for reviews, systematic reviews, or meta-analysis.
