Authors may wonder if they can make their articles freely available online.
Since the publishers surely prefer to have the least quantity of free version available on the web, they rarely inform the authors about their rights for sharing their papers. Find below some basic information (disclaimer: which is, obviously, not exhaustive).
Most publishers actually allow authors to post a version of their papers on their personal website. However, not any version can be freely posted. The “accepted version” is usually authorized. While the definition of this version may vary from one publisher to the other, it is usually the last version that the authors have submitted for peer review, after revision, major and minor corrections, but before any edition from the publisher itself.
The very final version edited by the publisher, which can be bought on the webiste, can not be posted, obviously, on any website.
For more details:
Concerning Elsevier, this is surely the best approach for dealing with Author Posting.