Gale Encyclopedia of Medicine, 4th Ed. by 
Encyclopedia of Sport and Exercise Psychology by Primary vs. Secondary Resources
There are some great resources available on the web for determining whether a resource is considered primary or secondary.
Check these out:
Primary vs. Secondary Sources from the Borough of Manhattan Community College Library
http://lib1.bmcc.cuny.edu/help/sources.html
How to Distinguish Between Primary and Secondary Sources from the University of California, Santa Cruz Library
http://library.ucsc.edu/ref/howto/primarysecondary.html
