According to Open Culture, Zentrum has put 3,900 pages of Paul Klee’s personal notebooks online, presenting his Bauhaus teaching from 1921-1931.
Introductory notes (translatable by Google) and a link to the notebook are here. I found that Google translation was, for once, unhelpful on the notebook pages. If your German is inadequate (as mine is), your best bet is to click on this icon 
and scroll down, clicking on any thumbnail that grabs your fancy.
Their online collection of Klee’s work are listed here (see the menu of links on the right).
via Peter Verheyen