Classification
551 - Geology, hydrology & meteorology
3
577 - Ecology
3
304 - Factors affecting social behavior
2
333 - Economics of land & energy
2
001 - Knowledge
1
300 - Social sciences
1
507 - Education, research & related topics
1
621 - Applied physics
1
630 - Agriculture & related technologies
1
910 - Geography & travel
1