What's the difference between the entrance to Guoan?

The admission to Tai 'an cannot use letters to represent different universities. From Guotai Anjin, you will see many entrances, each of which represents a different university database, such as DY for university of international business and economics, BEY for Beijing Foreign Studies University, BJ for Beijing Normal University, SD for Shandong University and ZJ for Zhejiang University. Some special databases that are not available in other portals are marked, such as BEY (patent download), which indicates that there is a library of patent research. For each school, there will be several entrances and some entrances to prevent hanging up.