When looking for articles I found abstracts for where full articles were behind a paywall not covered by my school, I have occasionally found them on here in full posted by one of the authors. It doesn't mean every article here has already been peer-reviewed, but I think it is a worthwhile search as long as you double-check whether the one you found was peer-reviewed somewhere else or not and cite it correctly. Follow the DOI.

ResearchGate itself does not peer review articles, but it hosts peer-reviewed articles originally published in academic journals, as well as preprints and other research outputs.