Perhaps you should try some spelling variations:
"improving indoor performance series." » "improving indoor performance studies.", "improving indoor performance size.", "improving outdoor performance series.", "improving poor performance series.", "improving floor performance series.", "improving india's performance series.", "improving food performance series.", "improving gender performance series."
"improving donor performance series." » "improving donor performance studies.", "improving donor performance size.", "improving poor performance series.", "improving motor performance series.", "improving monitor performance series.", "improving food performance series.", "improving gender performance series.", "improving export 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 indoor performance series.") OR ("improving donor performance series."))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"improving indoor performance series.\") OR (\"improving donor performance series.\"))".
• Removing quotes may allow a broader search: (( improving indoor performance series. ) OR ( improving donor performance series. )).
• Adding a wildcard symbol may retrieve word variants: (("improving indoor performance series.") OR ("improving donor performance series."))*.