Perhaps you should try some spelling variations:
"improving land performance contract." » "improving land performance contracts.", "improving plant performance contract.", "improving fund performance contract.", "improving und performance contract."
"improving tax performance studies." » "improving tax performance audits.", "improving tax performance audit.", "improving tax performance standards.", "improving box performance studies.", "improving cta performance studies.", "improving dam performance studies.", "improving trade performance studies.", "improving data performance studies.", "improving care performance studies."

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

• Performing a fuzzy search may retrieve terms with similar spellings: (("improving tax performance studies.") or ("improving land performance contract."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving tax performance studies.") OR ("improving land performance contract.")).
• Removing quotes may allow a broader search: (( improving tax performance studies. ) or ( improving land performance contract. )).
• Adding a wildcard symbol may retrieve word variants: (("improving tax performance studies.") or ("improving land performance contract."))*.