In order to access MathSciNet, it is first necessary to find the resource in the Libraries web pages.
In the case of MathSciNet, it is here: https://search.library.wisc.edu/catalog/999774961902121
Click Online Access (to the right)
You'll be taken to
https://mathscinet-ams-org.ezproxy.library.wisc.edu/mathscinet
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