IEEE Xplore Digital Library
IEEE's research library of journal articles, conference papers and standards across computing, electrical engineering, AI and robotics.
From the site: Search and browse IEEE journals, conference proceedings and standards; abstracts are free, full text usually requires a subscription or purchase.
Why I recommend it: Paywall warning: searching and reading titles, abstracts and citations is free, but most full papers need a subscription, an institutional login or a per-article purchase. Some papers are open access and free in full. Check your school or public library for access before paying, and look for the same paper on the author's own site or arXiv first.
