History 27 Refuse and refuse disposal 21 Women 20 History and criticism 19 Fiction 15 Research 14 Social conditions 14 Education 13 English literature 12 Microbiology 12 Philosophy 12 Sewage disposal 12 Bioinformatics 11 Genetics 11 Methodology 11 Viscosity 11 Engineering 10 Biography 9 Environmental protection 9 Management 9 Motion pictures 9 Pollution 9 Religious aspects 9 Biology 8 Computer security 8 Feminism 8 Human rights 8 Literature 8 Soil chemistry 8 Waste disposal 8