arXiv.orgOne of the first online scholarly repositories, this re-print server provides “open access to 1,486,542 e-prints in Physics, Mathematics, Computer Science, Quantitative Biology, Quantitative Finance, Statistics, Electrical Engineering and Systems Science, and Economics.” This is perhaps the oldest, and most well-established and respected scholarly open access site.
ChemIDplusChemIDplus is a free, web search system that provides access to the structure and nomenclature authority files used for the identification of chemical substances cited in National Library of Medicine (NLM) databases.
ChemSpiderChemSpider is a free chemical structure database published by the Royal Society of Chemistry that provides text and structure search access to over 100 million structures from hundreds of data sources.
GeneReviewsGeneReviews, an international point-of-care resource for busy clinicians, provides clinically relevant and medically actionable information for inherited conditions in a standardized journal-style format, covering diagnosis, management, and genetic counseling for patients and their families.
NASA Technical Reports ServerAn online database to technical reports published by various NASA centers and programs. Full text PDFs of many NASA technical reports are available from 1958 onward. In addition, full text PDFs of reports from NASA's predecessor, the National Advisory Committee for Aeronautics or NACA are available from 1917-1958.