arXiv.org (from Cornell University Library) - Open access to 1,325,087 e-prints in Physics, Mathematics, Computer Science, Quantitative Biology, Quantitative Finance, Statistics, Electrical Engineering and Systems Science, and Economics.
Digital CSIC Open Science - Institutional repository of the Spanish Research Council. SPANISH
DOAJ (Directory of Open Access Journals) - "DOAJ
is a community-curated online directory that indexes and provides
access to high quality, open access, peer-reviewed journals."
Oxford OPEN - Journals from Oxford University Press in arts & humanities, law, medicine, science & mathematics and social sciences.
Public Library of Science - Journals in science and medicine.
Recolecta FECYT - Repository for science and technology. SPANISH
SciELO (Scientific Electronic Library Online) - Journals in science from Spanish and Portuguese speaking countries. SPANISH AND PORTUGUESE