There is usually a delay of several months after an article is written before it is published in a paper journal and this makes journals not an ideal format for disseminating the latest research. In some fields such as astronomy and some parts of physics, the role of the journal at disseminating the latest research has largely been replaced by preprint databases such as arXiv.org.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.