Perhaps you should try some spelling variations:
"modified multiobjective approximation algorithms" » "modified multiobjective optimization algorithms"
"modified cover optimisation algorithm" » "modified cover optimization algorithms", "modified cover estimation algorithm", "modified cover estimation algorithms", "modified qoe optimization algorithm"

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

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