In the sciences, primary sources are documents written by the person(s) who conducted the original research. For example, a primary source would be a research article where scientists describe their methodology, results, and conclusions about the genetics of tobacco plants. A secondary source would be an article commenting or analyzing the scientists' research on tobacco.
Primary sources
These sources are where the results of original research are usually first published in the sciences. This makes them the best source of information on cutting edge topics. However the new ideas presented may not be fully refined or validated yet.
Secondary sources
These sources tend to summarize the existing state of knowledge in a field at the time of publication. Secondary sources are useful places to learn about your topic in depth. They are useful places to find comparisons of different ideas and theories and to see how they may have changed over time.
Tertiary sources
These types of sources present condensed material, generally with references back to the primary and/or secondary literature. They can be a good place to look up data or to get an overview of a subject, but they rarely contain original material.
In the sciences, primary research articles have a similar basic structure. Most will have these sections or a subset of them, but all should have a "methods" section and a "results" section.
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