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