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

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 changing approximation algorithms") OR ("defined network optimization algorithm"))~.
• Removing quotes may allow a broader search: (( modified changing approximation algorithms ) or ( defined network optimization algorithm ))~.
• Adding a wildcard symbol may retrieve word variants: (("modified changing approximation algorithms") or ("defined network optimization algorithm"))*.