Perhaps you should try some spelling variations:
"modified _ approximation algorithm" » "modified _ approximation algorithms"
"modified parameters optimization algorithms" » "modified parameter optimization algorithms", "modified parameter estimation algorithms", "modified parameters optimisation algorithm", "modified parameters estimation algorithms", "modified parameters 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 _ approximation algorithm") OR ("modified parameters optimization algorithms"))~.
• Removing quotes may allow a broader search: (( modified _ approximation algorithm ) or ( modified parameters optimization algorithms ))~.
• Adding a wildcard symbol may retrieve word variants: (("modified _ approximation algorithm") or ("modified parameters optimization algorithms"))*.