Basically, for our purposes, there are two types of scientific journals: popular and scholarly.

	Popular Magazines	Scholarly Journals
Purpose	Persuade, inform or entertain and sell advertised products; produce a profit.	Report original research; usually with a narrow subject focus
Examples	Time, Newsweek, Sports Illustrated	Cell, Behavioral Ecology, Lancet
The Four R's of Journal Evaluation
Reliability	Written by freelance writers or members of the magazine's staff.	Written by researchers who have conducted research in the field and are usually affiliated with a university or research center; author's credentials are included with the article.
Readability	Articles are short and written in language aimed at a broad, general audience.	Written in the language of the discipline.
Refereed	Usually edited by staff editor.	Edited by scholars; before publication, article is reviewed by scholars or researchers in the field.
References	Seldom footnoted; source for the information is rarely provided.	Articles are documented, with all references provided.

There are some journals that do not fall into either category:

• Hybrids are journals such as Science and Nature that have characteristics of both types....research articles and shorter, more newsy type articles.
• Trade journals are published by professional or trade associations aimed at practitioners of those professions or trades.
• Other periodicals, such as Scientific American and Psychology Today can be considered scholarly publications, although their articles are usually written by staff or freelance journalists for an educated but general audience.
• Gray literature includes government reports, research reports and technical reports.