Perhaps you should try some spelling variations:
"modified notion approximation algorithms" » "modified network approximation algorithms", "modified time approximation algorithms", "modified one approximation algorithms"
"modified a validation algorithm" » "modified a estimation algorithm", "modified a predation algorithm", "modified a estimation algorithms", "modified _ validation algorithm", "modified a valuation algorithm", "modified _ validating algorithm", "modified df validation algorithm", "modified adam validation algorithm"

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

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