Perhaps you should try some spelling variations:
"modified df approximation algorithm" » "modified df approximation algorithms", "modified _ approximation algorithm", "modified one approximation algorithm", "modified time approximation algorithm", "modified adam approximation algorithm", "modified bi1 approximation algorithm"
"modified adaptive solution algorithm" » "modified adaptive evolution algorithm", "modified adaptive convolution algorithms", "modified adaptive evolutionary algorithm", "modified passive solution algorithm"

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• If you are trying to use Boolean operators, they must be ALL CAPS: (("modified df approximation algorithm") OR ("modified adaptive solution algorithm"))~.
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