Perhaps you should try some spelling variations:
"modified bi1 approximation algorithm" » "modified bi1 approximation algorithms", "modified time approximation algorithm", "modified _ approximation algorithm", "modified one approximation algorithm"
"defined network optimization algorithm" » "defined network optimization algorithms", "defined network optimisation algorithm", "defined network estimation algorithm", "designed network optimization algorithm"

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