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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• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"modified multiobjective optimization algorithms\") OR (\"modified bi1 approximation algorithms\"))~".
• Removing quotes may allow a broader search: (( modified multiobjective optimization algorithms ) OR ( modified bi1 approximation algorithms ))~.
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