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 quantization algorithm" » "modified adaptive estimation algorithm", "modified adaptive ventilation algorithm", "modified passive quantization algorithm"

Try widening your search to All Fields.

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (("modified df approximation algorithm") or ("modified adaptive quantization algorithm"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("modified df approximation algorithm") OR ("modified adaptive quantization algorithm")).
• Removing quotes may allow a broader search: (( modified df approximation algorithm ) or ( modified adaptive quantization algorithm )).
• Adding a wildcard symbol may retrieve word variants: (("modified df approximation algorithm") or ("modified adaptive quantization algorithm"))*.