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

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