Ai2 Asta
Open agentic literature search from the lab behind Semantic Scholar.
Tier 2 Open AccessFree
Research Database Directory
Every research database, reviewed.
OpenCitations
Citation data as public infrastructure — CC0, queryable, no licence required.
Tier 2 Open AccessFree
Scilit
A fast, free scholarly index — MDPI's comprehensive metadata search.
Tier 3 Open AccessFree
Fatcat
The Internet Archive's open catalog of scholarship — the editable backbone under IA Scholar.
Tier 3 Open AccessFree
DOAB
The Directory of Open Access Books — DOAJ's counterpart for scholarly monographs.
Tier 3 Open AccessFree
LILACS
Latin American and Caribbean health literature — the regional index PubMed misses.
Tier 3 Open AccessFree
PubMed Central (PMC)
The free full-text archive behind PubMed — biomedical papers you can actually read.
Tier 2 Open AccessFree
Retraction Watch
The database of retractions — know when a paper has been pulled.
Tier 2 Open AccessFree
Internet Archive Scholar
Full-text search of the preserved scholarly record — including the hard-to-find.
Tier 3 Open AccessFree
Paperity
An aggregator of open-access papers — one search across gold and hybrid OA.
Tier 3 Open AccessFree