Perhaps you should try some spelling variations:
"improving central performance contract." » "improving central performance contracts.", "improving contract performance contract.", "improving sectoral performance contract.", "improving entry performance contract.", "improving mental performance contract.", "improving critical performance contract.", "improving energy performance contract."
"improving hiv performance series." » "improving hiv performance metrics.", "improving hiv performance reviews.", "improving hiv performance review.", "improving miv performance series.", "improving high performance series.", "improving ii performance series.", "improving air performance series.", "improving child performance series.", "improving civil 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 central performance contract.") or ("improving hiv performance series."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving central performance contract.") OR ("improving hiv performance series."))*.
• Removing quotes may allow a broader search: (( improving central performance contract. ) or ( improving hiv performance series. ))*.