Classification
330 - Economics
630 - Agriculture & related technologies
4
333 - Economics of land & energy
3
363 - Other social problems & services
2
301 - Sociology & anthropology
1
320 - Political science
1
380 - Commerce, communications & transportation
1
500 - Natural sciences & mathematics
1
581 - Specific topics in natural history
1
600 - Technology
1
620 - Engineering & allied operations
1
900 - History & geography
1