Perhaps you should try some spelling variations:
"introduction frontier region" » "introduction fourier region", "introduction front region", "production frontiers region", "introduction frontal region"
"reproduction frontier region" » "production frontiers region", "introduction frontiers region", "reproduction printing region", "reproduction frontal region"
"production frontier second" » "production frontier section", "production frontiers section"
"production frontier region" » "production frontal 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"))) OR ("reproduction 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\"))) or (\"reproduction frontier region\"))))".
• Removing quotes may allow a broader search: (( production frontier second ) or ((((( production frontier region ) OR ( introduction frontier region ))) or ( reproduction frontier region )))).
• Adding a wildcard symbol may retrieve word variants: (("production frontier second") or ((((("production frontier region") OR ("introduction frontier region"))) or ("reproduction frontier region"))))*.