Project Euclid hosts digital copies of mathematics and theoretical physics journals and conference proceedings.
Repository of research papers and scientific data from institutions worldwide.
Publisher of peer-reviewed mathematics and physics journals.
Premier science journal publishing original research papers; requires subscription or institutional access.
Living Reviews publishes peer-reviewed survey articles on modern physics topics.
Royal Society Publishing distributes peer-reviewed scientific journals.
Hindawi publishes peer-reviewed open-access journals across science and engineering.
European Physical Society publisher; primarily a journal archive, not a teaching or problem-solving resource.
SSRN preprint and working paper repository for economics, finance, and social sciences research.
SDSS provides spectroscopic and imaging data from a large-scale sky survey, used primarily by researchers rather than students solving problems.
A wiki cataloguing unsolved research problems in mathematics and computer science, not exercise material.
Personal website of a mathematician with research materials.