Primary sources in the sciences are different than primary sources in the humanities or social sciences.
In the sciences, the focus is on the research.
Primary sources are written by the scientists who performed the experiments -- these articles include original research data.
Secondary sources summarize or compare previous research in a particular subject area.
So, how can you tell if a scientific article is a primary source? It's not always clear.
Helpful Tip! Read the Introduction and/or Methodology section of the article carefully to see if the authors actually conducted the research or if they are only writing/summarizing research conducted by others.