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 invasive convolution algorithms" » "modified invasive evolution algorithm", "modified invasive solution algorithm", "modified invasive ventilation algorithms", "modified passive convolution algorithms"

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 invasive convolution algorithms") or ("modified df approximation algorithm"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("modified invasive convolution algorithms") OR ("modified df approximation algorithm")).
• Removing quotes may allow a broader search: (( modified invasive convolution algorithms ) or ( modified df approximation algorithm )).
• Adding a wildcard symbol may retrieve word variants: (("modified invasive convolution algorithms") or ("modified df approximation algorithm"))*.