Postgraduate dissertations belong to dissertations reports. Dissertation is a research report or scientific paper written by the author to obtain a certain degree. It is divided into three levels: bachelor's thesis, master's thesis and doctoral thesis. Among them, the doctoral thesis is of the highest quality, which is an original scientific research work and the focus of collection and utilization. Dissertation represents different levels of knowledge and is one of the important sources of literature information. Not published in publications, can only be obtained through degree-granting units, designated collection units and private channels.