Perhaps you should try some spelling variations:
"modified network approximation algorithm" » "modified network approximation algorithms", "certified network approximation algorithm", "defined network approximation algorithm", "modified near approximation algorithm"
"modified parameters estimation algorithms" » "modified parameter estimation algorithms", "modified parameter estimates algorithms", "modified parameter optimization algorithms", "modified parameters estimation algorithm", "modified parameters optimization algorithms", "modified parameters optimisation algorithm"

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