Perhaps you should try some spelling variations:
"improving maternal performance series." » "improving national performance series.", "improving lanterns performance series.", "improving water performance series.", "improving maternal performance metrics.", "improving maternal performance reviews.", "improving maternal performance review.", "improve maternal performance series."
"improving thermal performance series." » "improving thermal performance metrics.", "improving thermal performance reviews.", "improving thermal performance review.", "improving rural performance series.", "improving human performance series.", "improving mental 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 thermal performance series.") or ("improving maternal performance series."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving thermal performance series.") OR ("improving maternal performance series."))*.
• Removing quotes may allow a broader search: (( improving thermal performance series. ) or ( improving maternal performance series. ))*.