Operations research 514 Production and operations management--Product management 291 Operating systems (Computers) 176 Operating systems 161 Engineering & allied operations 120 Operational calculus-- Functional analysis-- Mathematics 109 Operations Research-- Information management-- Executive management 106 Operations management 100 Production and operations management 85 Operations Research--Information management--Executive management 80 Co-operative management 76 Co operation 67 Operator theory 61 Management 55 Linear operators 50 Operating system 46 Computer science 44 Production management 32 Travel Management --Travel agency and tour operations managmenet 29 Applied physics 27 Tourism travel--Travel Management --Travel agency and tour operations managmenet 25 Mathematics 23 Operation research 23 Operational amplifiers 22 Economics 21 Linear programming 20 Functional analysis 17 Programming (Mathematics) 17 Co-operation 16 International co-operation 16