Technically speaking the version http://www.domain.de does not exist. The reason for this is that each request must always be specified in a path. The shortest possible path is indicated between two „slashes“(/). Therefore, the shortest possible path of a domain is „http://www.domain.de/ (same goes for https).
Therefore, Google evaluates the URL http://www.domain.de as it would have a trailing slash http://www.domain.de/. This is a special case and can only be used in case of the homepage URL of a domain and can not be transferred to other directories.
Optimally, the URL http://www.domain.de/ is indexable and is canonicalized by the homepage URL without the backlash http://www.domain.de. If you are using both versions of homepage URL, one with and one without backslash, and one page is indexable, google will treat both versions as one and will index your homepage URL.