These sources can range from chapters within books or entire books, or journal articles, but all have common characteristics that can help you recognize that type of information. These characteristics include:

Produced by experts or researchers in a specialized field or discipline.
Purpose is to present new or unpublished research.
Articles reviewed by experts for scholarly content or quality, or peer reviewed
Written using formal language and structure: abstract, literature review, methodology, results, conclusion, footnotes, endnotes and/or bibliography.
Articles always cite source information.
May include tables or graphs to support research.