Classification
600 - Technology
330 - Economics
559
320 - Political science
252
304 - Factors affecting social behavior
123
610 - Medicine & health
123
333 - Economics of land & energy
117
370 - Education
106
363 - Other social problems & services
96
380 - Commerce, communications & transportation
58
630 - Agriculture & related technologies
39
336 - Public finance
20