For books and periodicals in the public domain (printed before 1927), links go to the Hathi Trust whenever possible. No login is required to read them onscreen, but if you want to download a PDF of the whole book, log in by selecting UNLV from the institutional access drop-down menu and you'll be redirected to use your ACE account.
Some online links to books still under copyright go to the Internet Archive Open Library. These books cannot be downloaded but can be viewed on screen for one hour. Create a free Internet Archive account to borrow books for one hour viewing sessions. The controlled digital lending model only allows online viewing of corresponding print copies owned by the Open Library, so if the book you want can't be borrowed because it is in use, search to see if there's another copy scanned. Some publishers may require you to use Adobe Digital Editions instead of your browser to view a borrowed book.
UNLV Libraries subscriptions
Items with red UNLV icons will require your ACE login for off-campus access. These are behind a paywall and the publishers or distributors rely on libraries and universities to pay for access for students and faculty.