Journal articles that report first-hand observations of an event or that report discoveries, experiments, or the the results of studies are considered primary sources.
They often include sections with the following headings: Introduction, Methods, Results, Discussion.
Journal articles that comment on or analyze primary sources are considered secondary sources of information. However, these articles may also contain some primary source material.
For example, a journal article analyzing the text of a literary work may include scanned images of the original text of the literary work or excerpts from the text. Or, an article about the history of political humour in the press may include images of political cartoons from various newspapers.