History 250 Analysis 190 Enzymes 181 History and criticism 104 Social aspects 102 Mathematical models 101 Data processing 93 Mathematics 77 Research 69 Politics and government 63 Design and construction 58 Criticism and interpretation 50 Environmental aspects 50 Methodology 50 Psychological aspects 50 Design 46 Economic aspects 39 Materials 38 Social conditions 38 Food 36 Management 36 Signal processing 34 Study and teaching 34 Economic conditions 33 Philosophy 32 Chemistry, Organic 31 Synthesis 31 Political aspects 30 Psychology 30 Pollution 29