arXiv.org is an electronic archive and distribution server for research articles. Covered areas include physics, mathematics, computer science, nonlinear sciences, quantitative biology, quantitative finance, statistics, electrical engineering and systems science, and economics.
PMC is a free archive for full-text biomedical and life sciences journal articles. is is a digital counterpart to the NLM extensive print journal collection. Although the articles are free, they are still protected by copyright. It includes final, peer-reviewed author manuscripts by scientists and others who receive research funding from NIH and other funding agencies.