arXiv is a free distribution service and an open-access archive for more than two million scholarly articles in the fields of physics, mathematics, computer science, quantitative biology, quantitative finance, statistics, electrical engineering and systems science, and economics.
A free online archive of pre-published manuscripts, modelled after aRxiv and medRxiv, bioRxiv helps users to stay current in biology research, including medicine. It facilitates search by topic or by date. bioRxiv is maintained by Cold Spring Harbor Laboratory, a non-profit educational organization. Though articles are not peer reviewed, basic screening and plagiarism checks are undertaken.
A free online archive and distribution server for unpublished manuscripts (preprints) in the field of medicine and related health sciences. Though not peer-reviewed, these manuscripts represent the up to date research trends in the field of health sciences, and they also undergo basic screening for research integrity. This archive is maintained by Yale University, the BMJ and Cold Harbor Laboratory.
Psychology Archive(external link)
A free preprint service for the psychological sciences like aRxiv and medRxiv. It is maintained by the Society for the Improvement of Psychological Science.
This archive(external link) provides free, open access platform for social scientists to upload their pre-prints as well as published papers, allowing readers for free download of these resources.
Social Science Research Network
(external link)SSRN is designed as a pre-print archive that provide access to research papers even before their inclusion in journals and books. Even when the published articles go under paywall, often the original working papers remain as freely downloadable through this network, which features more than one million research papers in more than 60 disciplines.