Perhaps you should try some spelling variations:
maternal performance » materials performance, external performance, national performance
improving maternal » improve maternal, improving water
performance series » performance studies, performance size
improving thermal » improving external, improving animal, improving erm

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. )).
• Adding a wildcard symbol may retrieve word variants: (( improving thermal performance series. ) or ( improving maternal performance series. ))*.