zbMATH Open
The open, reviewed index of mathematics — MathSciNet's free counterpart.
Tier 2 Open AccessFree
Research Database Directory
Every research database, reviewed.
INSPIRE-HEP
The free index high-energy physics runs on — literature, authors, data, and jobs in one place.
Tier 2 Open AccessFree
RePEc / IDEAS
The volunteer-built open bibliography of economics — with IDEAS as its main front door.
Tier 2 Open AccessFree
AGRICOLA
The U.S. National Agricultural Library's free index for agriculture and the food sciences.
Tier 3 Open AccessFree
PhilPapers
The comprehensive, community-curated index and archive of philosophy.
Tier 2 Open AccessFree
SciELO
The open-access library of Latin American, Caribbean, and allied science — free, full-text, multilingual.
Tier 2 Open AccessFree
Redalyc
The open-access index of Ibero-American scholarship — diamond open access at scale.
Tier 2 Open AccessFree
J-STAGE
Japan's national platform for scholarly journals — much of it open, much of it in English.
Tier 2 Open AccessFree
ResearchGate
The academic social network where researchers share papers — and their metrics.
Tier 3 ToolsFree
ERIC
The free, authoritative index for education research and practice.
Tier 2 Open AccessFree