Perhaps you should try some spelling variations:
"improving job performance contract." » "improving job performance contracts.", "improving court performance contract.", "improving co performance contract.", "improving food performance contract.", "improving crop performance contract."
"improving tax performance series." » "improving tax performance studies.", "improving tax performance size.", "improving box performance series.", "improving cta performance series.", "improving dam performance series.", "improving trade performance series.", "improving data performance series.", "improving care performance series."

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