Perhaps you should try some spelling variations:
performance series » performance studies, performance size
mental performance » general performance, senegal performance, annual performance
improving thermal » improving external, improving animal, improving erm
performance risks » performance risk
improving mental » improving maternal, improving fiscal, improving gender

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (( improving mental performance series. ) or ( improving thermal performance risks. ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( improving mental performance series. ) OR ( improving thermal performance risks. )).
• Adding a wildcard symbol may retrieve word variants: (( improving mental performance series. ) or ( improving thermal performance risks. ))*.