Perhaps you should try some spelling variations:
"modified orca approximation algorithm" » "modified orca approximation algorithms", "modified one approximation algorithm", "modified _ approximation algorithm", "modified time approximation algorithm"
"modified objective optimization algorithm" » "modified multiobjective optimization algorithm", "modified objective optimization algorithms", "modified objective optimisation algorithm", "modified objective estimation algorithm"

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