Perhaps you should try some spelling variations:
"introduction frontier region" » "introduction fourier region", "introduction front region", "production frontiers region", "introduction frontal region"
"production frontier second" » "production frontier section", "production frontiers section", "reproduction frontier second"
"production frontier region" » "production frontal region", "reproduction frontier region"

Try widening your search to All Fields.

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: (("production frontier second") OR ((("production frontier region") OR ("introduction frontier region")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"production frontier second\") or (((\"production frontier region\") OR (\"introduction frontier region\"))))".
• Removing quotes may allow a broader search: (( production frontier second ) or ((( production frontier region ) OR ( introduction frontier region )))).
• Adding a wildcard symbol may retrieve word variants: (("production frontier second") or ((("production frontier region") OR ("introduction frontier region"))))*.