Todd C. Will Anand Srinivasan Michael Bieber Il Im Vincent Oria Yi-Fang Wu GRE: hybrid recommendations for NSDL collections. 457-458 2009 JCDL http://doi.acm.org/10.1145/1555400.1555511 conf/jcdl/2009 db/conf/jcdl/jcdl2009.html#WillSBIOW09