Mapping knowledge domains analysis of research topics of doctoral dissertations on Library Science in Europe and the United States

Europe and the United States are considered to be the leaders in the field of Library Science research.Their doctoral dissertations have an irreplaceable role for studying and tracking the development of Library Science.In this study,3 973 doctoral dissertations in the database of PQDD from year1925 to 2013 are used as the research object.Keywords co-occurrence analysis and