Perhaps you should try some spelling variations:
"modified multiobjective estimation algorithm" » "modified multiobjective optimization algorithm"
"modified passive optimisation algorithms" » "modified passive optimisation algorithm", "modified passive optimization algorithms", "modified passive estimation algorithms", "modified adaptive optimisation algorithms"

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

• If you are trying to use Boolean operators, they must be ALL CAPS: (("modified multiobjective estimation algorithm") OR ("modified passive optimisation algorithms"))~.
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