Perhaps you should try some spelling variations:
"improving basic performance series." » "improving basic performance studies.", "improving basic performance size.", "improving based performance series.", "improving music performance series.", "improving baseline performance series.", "improving air performance series.", "improve basic performance series."
"improving rural performance contracts." » "improving euract performance contracts.", "improving larval performance contracts.", "improving pupil performance contracts."

Try widening your search to All Fields.

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• Performing a fuzzy search may retrieve terms with similar spellings: (("improving basic performance series.") or ("improving rural performance contracts."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving basic performance series.") OR ("improving rural performance contracts.")).
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