Perhaps you should try some spelling variations:
"central station research firm surveys." » "central mutation research firm surveys.", "central situations research firm surveys.", "central taxation research firm surveys.", "central state research firm surveys.", "centralisation _ research firm surveys.", "central station research from surveys.", "central station research field surveys.", "central station research final surveys.", "central station research firm survey."
"central bank research firm series." » "central bank research from series.", "central bank research field series.", "central bank research final series.", "central bank research film series.", "central bank research forum series."

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

• Performing a fuzzy search may retrieve terms with similar spellings: (("central bank research firm series.") OR ("central station research firm surveys."))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"central bank research firm series.\") OR (\"central station research firm surveys.\"))".
• Removing quotes may allow a broader search: (( central bank research firm series. ) OR ( central station research firm surveys. )).
• Adding a wildcard symbol may retrieve word variants: (("central bank research firm series.") OR ("central station research firm surveys."))*.