Perhaps you should try some spelling variations:
"improving air performance series." » "improving air performance metrics.", "improving air performance reviews.", "improving air performance review.", "improving firm performance series.", "improving a performance series.", "improving ii performance series.", "improving water performance series.", "improving land performance series.", "improving _ performance series."
"improving basic performance evidence." » "improving based performance evidence.", "improving bank performance evidence.", "improving past performance evidence.", "improve basic performance evidence.", "improving public performance evidence."

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 evidence."))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"improving air performance series.\") OR (\"improving basic performance evidence.\"))".
• Removing quotes may allow a broader search: (( improving air performance series. ) OR ( improving basic performance evidence. )).
• Adding a wildcard symbol may retrieve word variants: (("improving air performance series.") OR ("improving basic performance evidence."))*.