Perhaps you should try some spelling variations:
"modified multiobjective optimization algorithms" » "modified multiobjective optimisation algorithm", "modified multiobjective estimation algorithms", "modified multiobjective estimation algorithm"
"modified bi1 approximation algorithms" » "modified time approximation algorithms", "modified _ approximation algorithms", "modified one approximation algorithms"

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• Performing a fuzzy search may retrieve terms with similar spellings: (("modified bi1 approximation algorithms") or ("modified multiobjective optimization algorithms"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("modified bi1 approximation algorithms") OR ("modified multiobjective optimization algorithms"))*.
• Removing quotes may allow a broader search: (( modified bi1 approximation algorithms ) or ( modified multiobjective optimization algorithms ))*.