Classification
577 - Ecology
172
634 - Orchards, fruits & forestry
161
333 - Economics of land & energy
49
630 - Agriculture & related technologies
27
581 - Specific topics in natural history
24
580 - Plants (Botany)
22
631 - Techniques, equipment & materials
15
304 - Factors affecting social behavior
12
660 - Chemical engineering
12
571 - Physiology & related subjects
11
363 - Other social problems & services
9
551 - Geology, hydrology & meteorology
8
579 - Microorganisms, fungi & algae
8
578 - Natural history of organisms
7
621 - Applied physics
6
592 - Invertebrates
5
628 - Sanitary & municipal engineering
5
910 - Geography & travel
5
338 - Production
4
519 - Probabilities & applied mathematics
4
572 - Biochemistry
3
595 - Arthropods
3
620 - Engineering & allied operations
3
320 - Political science
2
344 - Labor, social, education & cultural law
2
500 - Natural sciences & mathematics
2
550 - Earth sciences
2
570 - Life sciences; biology
2
305 - Social groups
1
327 - International relations
1
530 - Physics
1
539 - Modern physics
1
560 - Paleontology; paleozoology
1
582 - Plants noted for characteristics & flowers
1
590 - Animals (Zoology)
1
612 - Human physiology
1
624 - Civil engineering
1
658 - General management
1
664 - Food technology
1
690 - Buildings
1