There are many things to consider when identifying a scientific paper, but the following can be used as guidelines:
Note: With the exception of peer-review, meeting the criteria above does not say anything about the credibility or reliability of a paper. You should still consider the guidelines for Evaluating Sources.
It is often necessary to read a paper multiple times before completely understanding it. As you are reading, pay attention to the following:
It can be helpful to take notes and highlight key findings while reading the paper, then write down a summary of major points after finishing the paper. The inforgraphic How to Read a Scientific Paper provides more information on this process.
Finally, after you have read a paper and feel confident that you understand it, ask yourself the following three questions: