Perhaps you should try some spelling variations:
"improving air performance based." » "improving air performance measures.", "improving firm performance based.", "improving a performance based.", "improving ii performance based.", "improving water performance based.", "improving land performance based.", "improving _ performance based."
"improving plant performance risk." » "improving bank performance risk.", "improving loan performance risk.", "improving port performance risk.", "improving plant performance size.", "improving plant performance _.", "improving plant performance data.", "improving land performance risk.", "improving laws performance risk.", "improving payment performance risk."

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