ResearchGate is considered an open database (you need a login, but anyone can get one). For that reason, general copyright rules apply;
- If you have published in an open access journal, you own the copyright yourself. You may then publish the articles wherever you choose, including on ResearchGate.
- Many journals are not open yet, and then the author has transferred their copyright to the publisher. This generally means you cannot add the article to any database. Many publishers do have specific rules regarding parallel publishing, though: they may allow uploading of a copy after a certain amount of time, often a year or two. Or they may allow distribution of earlier versions of the article, so called preprints. You can find information for specific journals in the Sherpa/Romeo database.
- There are also journals where you can choose to pay for making the article open access, even if the journal itself is not. This is called paid open access.
