If you would like to re-publish ("self-archive") a journal article or another paper via the "Green Road" of Open Access in the Research Collection, you need to comply with the copyright policies of the original publisher.
Many publishing houses permit the publication of either preprints or postprints (also called Author's Accepted Manuscript, short AAM) of published articles in an institutional repository such as the Research Collection.
A preprint is the manuscript version of an article as submitted to the publisher, i.e. before peer review.
A postprint is the accepted manuscript after the peer review process. The postprint...
Publishing houses rarely allow the use of the publisher PDF for publication in a repository.
Some publishing houses only permit the publication of articles in repositories after a so-called embargo from the first publication date. The embargo generally varies between 6 to 36 months.
You can nevertheless submit your article at any time to the Research Collection. When uploading the file, indicate the embargo end date - your file will then be automatically made available to external users on this day while only metadata will be visible immediately.
The SHERPA/RoMEO database provides information on self-archiving guidelines of many scholarly journals and publishers.
Please consider however, that in case of doubt only those regulations actually stipulated in your publishing contract (Copyright Transfer Agreement, Licence to Publish) are legally binding.
In the absence of a publishing contract, the publisher's general terms and conditions apply.
The following example of an entry in SHERPA/RoMEO for the journal "Advances in Intelligent Systems and Computing" tells you that...
Ideally, you should always make sure whether and to which extent self-archiving in an institutional repository is permitted before signing a publishing contract.
If your publisher does not allow self-archiving, you can try to negotiate the right to self-archive, for example by adding and having the publisher sign an author addendum to the publishing contract (see eg. SPARC Author's Addendum.
Moreover, you can also obtain the publisher's consent to making a work accessible via the Research Collection retrospectively.
Some publishers have special conditions for reusing content within doctoral theses that are more generous than what is documented in Sherpa/Romeo. You can find more information on this topic on the page Cumulative doctoral theses.