TP Chemical technology 49 TK Electrical engineering. Electronics Nuclear engineering 39 TJ Mechanical engineering and machinery 26 TA Engineering (General). Civil engineering (General) 19 T Technology (General) 15 QD Chemistry 7 Q Science (General) 6 QA75 Electronic computers. Computer science 5 TD Environmental technology. Sanitary engineering 5 TC Hydraulic engineering. Ocean engineering 4 TH Building construction 4 NA Architecture 3 QA76 Computer software 3 QH301 Biology 3 GE Environmental Sciences 2 QH Natural history 2 SB Plant culture 2 T58.5-58.64 Information technology 2 Unspecified 2 GV Recreation Leisure 1 HC Economic History and Conditions 1 HD Industries. Land use. Labor 1 HD28 Management. Industrial Management 1 HJ Public Finance 1 QA Mathematics 1 QC Physics 1 QH426 Genetics 1 QK Botany 1 QR Microbiology 1 R Medicine (General) 1