Perhaps you should try some spelling variations:
"central based research _ series." » "central case research _ series.", "central kasese research _ series.", "central bank research _ series."
"central mode research project survey." » "central model research project survey.", "central more research project survey.", "central modern research project survey.", "central node research project survey.", "central nodes research project survey.", "central body research project survey.", "central mode research projects survey."

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

• Performing a fuzzy search may retrieve terms with similar spellings: (("central based research _ series.") or ("central mode research project survey."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("central based research _ series.") OR ("central mode research project survey.")).
• Removing quotes may allow a broader search: (( central based research _ series. ) or ( central mode research project survey. )).
• Adding a wildcard symbol may retrieve word variants: (("central based research _ series.") or ("central mode research project survey."))*.