BASE is a multidisciplinary search engine for scholarly internet resources which have been harvested from several hundred scientific repositories. Some of the indexed resources in BASE are subject to license, while most material is free available ("open access").
The EZB is a huge directory of electronic journals which mirrors the central Max Planck Society subscriptions as well as the local licensing situation of the institutes. Access rights to the contents of the individual journals are indicated with "traffic lights". Entries are searchable on journal level.
Google Book Search is a service from Google that searches the full text of books that Google scans, converts to text using optical character recognition, and stores in its digital database.
The Max Planck Journal Index provides holdings of a great range of printed journals available within the Max Planck Society. Besides, it contains metadata of electronic journals as loaded from the EZB. The database is updated regularly from the ZDB (twice a year) and the EZB (monthly).