Perhaps you should try some spelling variations:
"central american research firm series." » "central americans research firm series.", "central african research firm series.", "central numerical research firm series.", "central america research firm series.", "central american research from series.", "central american research field series.", "central american research final series.", "central american research film series.", "central american research forum series."
"central climate research team series." » "general climate research team series.", "cultural climate research team series.", "centered climate research team series.", "central climate research stem series.", "central climate research nejm series.", "central climate research tilsm series."

Try widening your search to All Fields.

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• Performing a fuzzy search may retrieve terms with similar spellings: (("central american research firm series.") or ("central climate research team series."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("central american research firm series.") OR ("central climate research team series.")).
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• Adding a wildcard symbol may retrieve word variants: (("central american research firm series.") or ("central climate research team series."))*.