The KOBV Portal is the regional library portal for Berlin and Brandenburg. It contains almost all the library holdings from the KOBV libraries in Berlin and Brandenburg (Status of the data).
With the current version 3.5.0 of the KOBV portal you have a daily updated index based on Crossref at one's disposal. Crossref provides interdisciplinary data from numerous magazines. Especially articles can be found here. The crossref data is shown as a second tab "Online articles" in the KOBV portal.
Furthermore 78 libraries and their holdings are listed in the KOBV portal.
More detailed information about the portal can be found in the KOBV portal help.