LIBER: http://www.kb.dk/guests/intl/liber/
SPARC: http://www.arl.org/sparc/home/index.asp?page=0
EBSCO: http://www-nl.ebsco.com/home/default.asp or http://www.ebsco.com/ess/
ESF: http://www.esf.org/index.htm