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

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

• If you are trying to use Boolean operators, they must be ALL CAPS: (("modified time approximation algorithms") OR ("defined network optimization algorithm"))~.
• Removing quotes may allow a broader search: (( modified time approximation algorithms ) or ( defined network optimization algorithm ))~.
• Adding a wildcard symbol may retrieve word variants: (("modified time approximation algorithms") or ("defined network optimization algorithm"))*.