Perhaps you should try some spelling variations:
"methode ion based / gtt" » "methods ion based / gtt", "methode iii based / gtt", "methode im based / gtt", "methode action based / gtt", "methode lesion based / gtt"
"methode von based / gtt" » "methode von basel / gtt", "methode von basen / gtt", "methode lon based / gtt"

Try widening your search to All Fields.

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• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"methode von based / gtt\") OR (\"methode ion based / gtt\"))".
• Removing quotes may allow a broader search: (( methode von based / gtt ) OR ( methode ion based / gtt )).
• Adding a wildcard symbol may retrieve word variants: (("methode von based / gtt") OR ("methode ion based / gtt"))*.