Topogràfic
S - Agriculture
1,009
T - Technology
576
Q - Science
151
A - Treballs generalss
112
H - Social Science
112
L - Education
24
G - Geography, Anthropology, Recreation
14
Z - Library Science
14
P - Language and Literature
11
N - Fine Arts
10
B - Filosofia, Psicologia, Religió
9
J - Political Science
8
R - Medicine
8
K - Law
6
F - General American History
4
C - Historical Sciences
2
D - World History
1
U - Military Science
1