Perhaps you should try some spelling variations:
"improving basic performance contract." » "improving basic performance contracts.", "improving based performance contract.", "improving music performance contract.", "improving baseline performance contract.", "improve basic performance contract."
"improving air performance series." » "improving air performance studies.", "improving air performance size.", "improving zur performance series.", "improving bar performance series.", "improving der performance series.", "improving _ 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 air performance series.") or ("improving basic performance contract."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving air performance series.") OR ("improving basic performance contract.")).
• Removing quotes may allow a broader search: (( improving air performance series. ) or ( improving basic performance contract. )).
• Adding a wildcard symbol may retrieve word variants: (("improving air performance series.") or ("improving basic performance contract."))*.