Perhaps you should try some spelling variations:
"modified using classification algorithm" » "modified blind classification algorithm", "modified binary classification algorithm", "modified _ classification algorithm", "modified caging classification algorithm"
"modified average approximation algorithms" » "modified coverage approximation algorithms"

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

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