Perhaps you should try some spelling variations:
"improving thermal performance contract." » "improving thermal performance contracts.", "improving external performance contract.", "improving animal performance contract.", "improving erm performance contract."
"improving mental performance evidence." » "improving general performance evidence.", "improving senegal performance evidence.", "improving annual performance evidence.", "improving maternal performance evidence.", "improving fiscal performance evidence.", "improving gender performance evidence."

Try widening your search to All Fields.

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 evidence.") or ("improving thermal performance contract."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving mental performance evidence.") OR ("improving thermal performance contract.")).
• Removing quotes may allow a broader search: (( improving mental performance evidence. ) or ( improving thermal performance contract. )).
• Adding a wildcard symbol may retrieve word variants: (("improving mental performance evidence.") or ("improving thermal performance contract."))*.