Use Google Scholar to find articles from a wide variety of academic publishers, professional societies, preprint repositories and universities, as well as scholarly articles available across the Web. A drawback is that not all articles are free.
Directory of Open Access Journals: Search scholarly journals by title or topic.
Find Articles: Search 10-million-plus articles from "leading academic, industry and general interest publications."
Free Medical Journals: Medical journals that are free now and those that are free 1-6 months after publication. You may browse by title or by specialty area.
High Wire Press: Hosted by Stanford University Libraries, HighWire Press provides more than 1.3 million full-text, peer-reviewed articles from 900-plus journals.
Public Library of Science: The Public Library of Science is an excellent open access site for biological and medical research articles.