Perhaps you should try some spelling variations:
"central action research nejm series." » "central national research nejm series.", "central section research nejm series.", "central nation research nejm series.", "centric action research nejm series.", "central action research new series.", "central action research need series.", "central action research needs series."
"central cgiar research firm series." » "central asia research firm series.", "central asian research firm series.", "central city research firm series.", "central cgiar research from series.", "central cgiar research field series.", "central cgiar research final series.", "central cgiar research film series.", "central cgiar research forum series."

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

• If you are trying to use Boolean operators, they must be ALL CAPS: (("central cgiar research firm series.") OR ("central action research nejm series."))~.
• Removing quotes may allow a broader search: (( central cgiar research firm series. ) or ( central action research nejm series. ))~.
• Adding a wildcard symbol may retrieve word variants: (("central cgiar research firm series.") or ("central action research nejm series."))*.