Perhaps you should try some spelling variations:
"modified multiobjective approximation algorithms" » "modified multiobjective optimization algorithms"
"modified _ optimization algorithms" » "modified _ optimisation algorithm", "modified _ estimation algorithms", "modified _ estimation 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 multiobjective approximation algorithms") or ("modified _ optimization algorithms"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("modified multiobjective approximation algorithms") OR ("modified _ optimization algorithms"))*.
• Removing quotes may allow a broader search: (( modified multiobjective approximation algorithms ) or ( modified _ optimization algorithms ))*.