Perhaps you should try some spelling variations:
"modified df classification algorithm" » "modified _ classification algorithm", "modified a classification algorithm", "modified gas classification algorithm", "modified adam classification algorithm", "modified bi1 classification algorithm"
"modified average approximation algorithms" » "modified coverage approximation algorithms"

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

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