Dear Tianyu Zhou,
I just checked access via the library account. It worked for me. Could you please check, does the portal recognize your login, i.e. you can see "Welcome staab 德国联盟!" in the upper right corner?
If not, please try the Login via IP Login.
In the hit list, do you see yellow or green arrows for the download link?
Just to make sure, we do not provide access to all materials in the Knowledge Ressource Integrated Database. You do not have access to any materials at all?