Content Provider
DataCite Metadata Store (German National Library of Science and Technology)
6
PubMed Central (PMC)
4
CyberLeninka (Scientific Electronic Library)
3
Defense Technical Information Center: DTIC Technical Reports database
3
MDPI Open Access Publishing
3
Copernicus Publications: E-Journals
2
Unknown
2
University of Nebraska-Lincoln: DigitalCommons@UNL
1
Université du Québec à Chicoutimi (UQAC): Constellation
1