Perhaps you should try some spelling variations:
"modified oxygen optimization algorithms" » "modified oxygen optimisation algorithm", "modified oxygen estimation algorithms", "modified oxygen estimation algorithm", "modified stage optimization algorithms"
"modified notion approximation algorithms" » "modified network approximation algorithms", "modified time approximation algorithms", "modified one approximation algorithms"

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