1. PubMed Central. [
http://www.pubmedcentral.org
]
2. Potsdam. [
http://www.uni-potsdam.de/over/homegd.htm
]
3. INIST. [
http://www.inist.fr/index_en.php
]
4. e-Depot. [
http://www.kb.nl/
]
5. Which funding agencies explicitly allow direct use of their grants to cover article processing charges?. [
http://www.biomedcentral.com/info/about/apcfaq#grants
]