Content Provider
Directory of Open Access Journals: DOAJ Articles
12
Unknown
9
Defense Technical Information Center: DTIC Technical Reports database
5
DataCite Metadata Store (German National Library of Science and Technology)
2
Cambridge University Press
1
Istituto Nazionale di Fisica Nucleare (INFN): Open Access Repository
1
Oxford University Press (via Crossref)
1
Queen's University Belfast Research Portal
1
SAGE Publications
1
Utrecht University Repository
1