TP Chemical technology 647 QD Chemistry 72 TA Engineering (General). Civil engineering (General) 63 TJ Mechanical engineering and machinery 31 T Technology (General) 28 Q Science (General) 24 QC Physics 19 TK Electrical engineering. Electronics Nuclear engineering 14 Chemical engineering 11 QA Mathematics 9 Chemical elements 8 Unspecified 8 Analytical chemistry 7 QH301 Biology 7 Extraction (Chemistry) 6 Physical and theoretical chemistry 6 Q Science 6 QA75 Electronic computers. Computer science 6 Chemicals 4 Oils, fats, and waxes 4 Organic chemistry 4 QA76 Computer software 4 QP Physiology 4 RA0421 Public health. Hygiene. Preventive Medicine 4 TD Environmental technology. Sanitary engineering 4 TS Manufactures 4 Adsorption 3 GE Environmental Sciences 3 HD28 Management. Industrial Management 3 LB Theory and practice of education 3