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

Try widening your search to All Fields.

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

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