NASA ADS (Astrophysics Data System)
The free, comprehensive index for astronomy and physics — the field's shared memory.
Tier 2 Open AccessFree
Research Database Directory
Every research database, reviewed.
zbMATH Open
The open, reviewed index of mathematics — MathSciNet's free counterpart.
Tier 2 Open AccessFree
INSPIRE-HEP
The free index high-energy physics runs on — literature, authors, data, and jobs in one place.
Tier 2 Open AccessFree
ERIC
The free, authoritative index for education research and practice.
Tier 2 Open AccessFree
CORE
The world's largest aggregator of open-access research — full text at scale.
Tier 2 Open AccessFree
BASE
Bielefeld Academic Search Engine — one of the largest indexes of the academic open web.
Tier 3 Open AccessFree
Lens.org
Scholarship and patents in one place — the open platform linking research to innovation.
Tier 2 Open AccessFreemium
HathiTrust
A massive digital library of scanned books — the scholarly record, digitized.
Tier 3 Open AccessFreemium
Europe PMC
The open, full-text gateway to biomedical and life-sciences literature — PubMed's more open cousin.
Tier 1 Open AccessFree
OpenAlex
The fully open, CC0 index that set out to replace Scopus and Web of Science — bigger, free, and built for the Global South.
Tier 1 Open AccessFree