Primary sources in the sciences are a little bit different than primary sources in history, humanities, or social sciences.
In the sciences, the focus is on the research. Primary sources are ones written by the scientists who performed the experiments - these articles include original research data.
So how can you tell if a science article is a primary source?
Primary research articles will usually include sections about:
A sample of what a primary research article might look like:
Secondary sources interpret and analyze the original event documented in a primary source.