UC Library Search is the University of California’s unified discovery and borrowing system. Use it to find books, articles, media, archival collections, and more across most UCB libraries (notable exception: Berkeley Law Library), as well as the collections of other UC libraries.
You can:
See the UC Library Search user guide.
Here are other guides to look at when you want library resources specific to your major or subject area - for example, recommendations for article databases are listed in the 'articles' tabs. The guides are geared towards grad students and others doing research in these subject areas, so there's a lot of information.
And a couple more: