It has been argued that peer-reviewed paper journals are in the process of being replaced by electronic publishing. There is usually a delay of several months after an article is written before it is published in a journal and this makes journals not an ideal format for disseminating the latest research. In some fields such as astronomy, the role of the journal at disseminating the latest research has largely been replaced by preprint databases such as archivX.org. However, scientific journals still provide an important role in quality control, archiving papers, and establishing scientific credit. In general, the electronic material uploaded to preprint database are still intended for eventual publication in a peer-reviewed journal.
There is an article titled "Online or Invisible" (see link at end of article) which provides statistical evidence that electronic publishing provides wider dissemination. A number of journals have, while retaining their peer review process, established electronic versions or even moved entirely to electronic publication.
There are four types of journal articles. Letters (which should not be confused with letters to the editor) are short usually one or two page descriptions of current research findings. Articles are usually between five and twenty pages and are a complete descriptions of current original research finding. Supplemental articles contain a large volume of tabular data that is the result of current research and may be dozens or hundreds of pages with mostly numerical data. Review articles do not cover original research but rather are long in-depth overviews of current research work on a particular topic.
The format of letters and articles are generally fixed. They begin with an abstract which is a two to four paragraph summary of the paper. An introduction which describes the background for the research including a discussion of similar research. A results and discussion section which describes the results and implications of the research, and a conclusion section which places the research in context and describes avenues for further exploration.
In addition to the above, some scientific journals such as Science will include a news section where scientific developments (often involving political issues) are described. These articles are often written by science journalists and not by scientists. In addition some journals will include an editorial section and a section for letters to the editor. Interestingly, while these are articles published within a journal, they are not generally regarded as scientific journal articles because they have not been peer reviewed.
See List of scientific journals for a listing of significant journals.