User interfaces (Computer systems) 2,650 User Interfaces and Human Computer Interaction 2,496 Universities and colleges 2,361 Urbanization 1,032 Urban policy 699 Urban renewal 634 Urology 567 Urban Sociology 497 Utopias 482 Urban economics 403 Unemployment 377 Urban ecology (Sociology) 367 Unemployed 353 Underground movements 332 United States 309 Urban poor 261 Urban ecology (Biology) 211 Utopias in literature 206 United States of America 201 Ultrasonics 184 Usage 180 Uncertainty 174 Upper class 165 Underwater archaeology 154 Urban transportation 154 Urban Economics 149 United States -- Race relations 148 Utilitarianism 144 U.S. states 138 USA 138 United States -- Politics and government 134 Unemployment insurance 131 Urban Ecology 131 Usury 115 Urban youth 100 United States -- Military policy 99 Underground Railroad 94 Urban schools 91 Urologic Diseases 89 Urban anthropology 88 Ubiquitous computing 86 Utilization 82 Ukiyoe 78 United States -- Politics and government -- 2001-2009 75 UNITED STATES 74 United States -- Foreign relations 74 Urban health 74 Unmarried mothers 72 Ut pictura poesis (Aesthetics) 70 Ukrainians 68 Ultrasonic imaging 67 Underground literature 67 UE/CE Etats membres 63 United Nations 62 Underground press publications 61 Unitarianism 60 Union catalogs 58 Urban geography 58 United States -- Ethnic relations 56 Universals (Philosophy) 56 Upper class women 56 United States -- Foreign relations -- 2001-2009 55 United States -- Religion 54 Unity 54 Uncertainty (Information theory) 53 Universities 53 Ultrasonography 52 United States -- Politics and government -- 1945-1989 51 United States. -- Supreme Court 51 Utopian socialism 51 United States -- Economic policy 50 Urine 50 Unmarried couples 49 Urbanisme 49 United States -- Foreign relations -- 1945-1989 48 United States -- Foreign relations -- 1989- 48 United States -- Politics and government -- 1989- 48 United States -- Social policy 48 United States -- Social conditions 46 Universalism 46 Universal algebra 45 Urban Indians 45 Urban landscape architecture 45 Urban women 45 Unskilled labor 44 Ultrastructure (Biology) 43 Urban beautification 43 United States -- History 42 United States -- History -- Civil War, 1861-1865 -- Campaigns 42 United States -- Economic conditions 41 United States -- Emigration and immigration 41 United States -- Foreign relations -- 20th century 41 Use 41 United States -- History -- Civil War, 1861-1865 40 Unidentified flying objects 39 United States -- Politics and government -- 20th century 39 Urban Health 39 Urban transportation policy 39 Urban-rural migration 39 User charges 39