Perhaps you should try some spelling variations:
"donauschwabische schrifttum heft 1" » "dopnauschwabisches schrifttum heft 1" (Expand Search), "donauschwabisches christentum heft 1" (Expand Search), "donauschwabische schrifttum heft 3" (Expand Search)
"donauschwabisches schrifttum heft 10" » "donauschwabisches schrifttum heft 12" (Expand Search), "donauschwabisches schrifttum heft 19" (Expand Search), "donauschwabisches schrifttum heft 30" (Expand Search), "donauschwabischen schrifttum heft 10" (Expand Search)

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• Performing a fuzzy search may retrieve terms with similar spellings: (("donauschwabisches schrifttum heft 10") OR ("donauschwabische schrifttum heft 1"))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"donauschwabisches schrifttum heft 10\") OR (\"donauschwabische schrifttum heft 1\"))".
• Removing quotes may allow a broader search: (( donauschwabisches schrifttum heft 10 ) OR ( donauschwabische schrifttum heft 1 )).
• Adding a wildcard symbol may retrieve word variants: (("donauschwabisches schrifttum heft 10") OR ("donauschwabische schrifttum heft 1"))*.