QD Chemistry 677 QD1-999 Chemistry 54 TP Chemical technology 51 Extraction (Chemistry) 50 Physical and theoretical chemistry 42 Analytical chemistry 30 Organic chemistry 26 Q Science (General) 23 Botanical chemistry. Phytochemicals 21 Inorganic chemistry 15 Soils. Soil science. Including soil surveys, soil chemistry, soil structure, soil-plant relationships 14 TA Engineering (General). Civil engineering (General) 14 L Education (General) 13 Chemical elements 11 QA Mathematics 11 TK Electrical engineering. Electronics Nuclear engineering 11 QC1-999 Physics 10 LB Theory and practice of education 9 LB2300 Higher Education 8 Laboratories. General works 8 TJ Mechanical engineering and machinery 8 Bacteria 7 Oxidation 6 QC Physics 6 Biochemistry 5 Biotechnology 5 Catalysis 5 Chemicals 5 Conditions and laws of chemical reactions 5 Fertilizers and improvement of the soil 5