In the sciences, a primary source describes original research, while a secondary source analyzes or comments on a primary source or sources. For example, a research article is primary literature because it describes an original experiment and its results, while a review article is secondary literature because it collates multiple research articles to describe the current state of the field.
Examples of primary sources:
Examples of secondary sources:
The databases below can help you find primary literature in the sciences. While searching, you can narrow your results to primary literature by using filters on the left of the page.