Perhaps you should try some spelling variations:
"modified coverage approximation algorithms" » "modified average approximation algorithms"
"modified a classification algorithm" » "modified _ classification algorithm", "modified gas classification algorithm", "modified image classification algorithm", "modified df classification algorithm", "modified adam classification 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 coverage approximation algorithms") OR ("modified a classification algorithm"))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"modified coverage approximation algorithms\") OR (\"modified a classification algorithm\"))*".
• Removing quotes may allow a broader search: (( modified coverage approximation algorithms ) OR ( modified a classification algorithm ))*.