The basic study period of doctoral students in Nankai University is based on the flexible academic system of four years, and the longest study period (including student status retention and suspension time) is six years. The basic study period of undergraduate direct students is 5 years, and the longest study period (including student status retention and suspension time) is 7 years. The basic study period for postgraduate students with master's degree and doctoral degree is 4 years, and the longest study period for doctoral students (including staying in school and dropping out of school) is 6 years. Graduation requirements are two core journals of Peking University, and doctoral students should publish at least two papers in the core journals during their studies. The scope of core periodicals is in accordance with the catalogue of Chinese core periodicals of Nankai University.