Journal articles come in different types, depending upon the field and specific type of journals. Usually, academic journals include:
Letters/Communications: These are short descriptions of important latest study or research findings which are usually considered urgent for immediate publication. Examples of these would be important breakthroughs regarding cures or treatments for previously incurable conditions, or cure for a particular outbreak of disease, like for example swine flu.
Research Notes: Research notes are typically short descriptions which are considered less urgent compared to Letters. These contain information on current research findings of an expert or a researcher.
Articles: These are usually around 5-20 pages and are complete descriptions of current original research findings.
Supplemental Articles: These mostly consist of large-volume tabular data that details all the results of current research.
Review Articles: Review articles, unlike the previous types, do not cover original research but instead accumulate results of multiple articles on a particular field or topic into a coherent narrative about the state of the art in the said field. They provide information about the subject and at the same time provide journal references to the original research.