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

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

• Performing a fuzzy search may retrieve terms with similar spellings: (("modified network approximation algorithms") OR ("defined network optimization algorithm"))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"modified network approximation algorithms\") OR (\"defined network optimization algorithm\"))".
• Removing quotes may allow a broader search: (( modified network approximation algorithms ) OR ( defined network optimization algorithm )).
• Adding a wildcard symbol may retrieve word variants: (("modified network approximation algorithms") OR ("defined network optimization algorithm"))*.