Primary Sources in the Sciences are not exactly like primary sources in history or literature.
They are most often found as journal articles, and:
Research studies or scientific experiments
Papers and proceedings from scientific conferences or meetings
Dissertations and Theses
lab notebooks published online
Secondary sources may also be useful, but you should be able to distinguish them from primary sources. These typically involve reviews of the primary literature, meta-analysis of data from multiple primary sources, or editorial writing.
Publications about the significance of research or experiments
Reviews of the results of several experiments or trials
Analysis of a clinical trial
Letters to the editor, editorials, perspectives, or historical summaries