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

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