Perhaps you should try some spelling variations:
"modified coverage approximation algorithms" » "modified average approximation algorithms"
"modified early convolution algorithms" » "modified early evolution algorithm", "modified early solution algorithm", "modified early evolution algorithms", "modified learning convolution algorithms", "modified male convolution algorithms", "modified near convolution algorithms"

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• Performing a fuzzy search may retrieve terms with similar spellings: (("modified coverage approximation algorithms") or ("modified early convolution algorithms"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("modified coverage approximation algorithms") OR ("modified early convolution algorithms"))*.
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