TJ Mechanical engineering and machinery 126 QA Mathematics 105 TP Chemical technology 52 Q Science (General) 25 T Technology (General) 23 TA Engineering (General). Civil engineering (General) 22 Q Science 14 TK Electrical engineering. Electronics Nuclear engineering 13 QC Physics 5 TD Environmental technology. Sanitary engineering 5 QD Chemistry 4 TN Mining engineering. Metallurgy 3 Unspecified 3 QA75 Electronic computers. Computer science 2 QH Natural history 2 QH301 Biology 2 TC Hydraulic engineering. Ocean engineering 2 TL Motor vehicles. Aeronautics. Astronautics 2 VM Naval architecture. Shipbuilding. Marine engineering 2 G Geography (General) 1 H Social Sciences (General) 1 HE Transportation and Communications 1 L Education (General) 1 QB Astronomy 1 QM Human anatomy 1 R Medicine (General) 1 T Technology 1 TH Building construction 1