I. Philosophy           II. Mathematics          III. SCIENCE           IV. Humanities

I. Philosophy

http://www.philosophypages.com/dy/

http://www.refdesk.com/philos.html

http://www.ipl.org/ref/RR/static/hum70.00.00.html

http://plato.stanford.edu/contents.html

http://www.ditext.com/encyc/frame.html

http://www.utm.edu/research/iep/

II. Mathematics

http://www.ipl.org/ref/RR/static/sci40.00.00.html

http://www.alcyone.com/max/reference/maths/

http://euclid.math.fsu.edu/Science/math.html

http://www.hoxie.org/math/title.htm   

http://crh.choate.edu/Math/Math%20Reference/Math%20Reference%20Page.htm

http://www.stg.brown.edu/~rog/GS96/GS96ref.html

III. Science

http://www.eurekalert.org/resources/definitions.html

http://www.asu.edu/lib/noble/scirefrm/

http://www.physlink.com/reference.cfm

http://www.ncstrl.org/

http://mel.lib.mi.us/science/sciref.html

http://www-hpcc.astro.washington.edu/scied/sciref.htm 

http://www.lib.uchicago.edu/e/crerar/db/ref/home.html

IV. Humanities

http://www.lib.virginia.edu/reference/humanities/humindex.html 

http://www.nyu.edu/library/bobst/research/hum/

http://www.sil.org/humanities/index.html

http://www.ipl.org/ref/RR/static/hum00.00.00.html