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

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 fourier region")))).
• Removing quotes may allow a broader search: (( production frontier second ) or ((( production frontier region ) or ( introduction fourier region )))).
• Adding a wildcard symbol may retrieve word variants: (("production frontier second") or ((("production frontier region") or ("introduction fourier region"))))*.