Perhaps you should try some spelling variations:
"modified allocation approximation algorithms" » "modified allocation optimization algorithms"
"modified parameter estimation algorithms" » "modified parameter estimation algorithm", "modified parameter optimization algorithms", "modified parameter optimisation algorithm", "modified parameter estimates 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: (("modified parameter estimation algorithms") or ("modified allocation approximation algorithms"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("modified parameter estimation algorithms") OR ("modified allocation approximation algorithms")).
• Removing quotes may allow a broader search: (( modified parameter estimation algorithms ) or ( modified allocation approximation algorithms )).
• Adding a wildcard symbol may retrieve word variants: (("modified parameter estimation algorithms") or ("modified allocation approximation algorithms"))*.