Perhaps you should try some spelling variations:
"production frontier functions" » "production wannier functions"
"production frontal region" » "production front region", "production fractals region", "production final region", "production orbital region", "production frontal sections"
"production frontier section" » "production frontiers section", "production frontier second", "production frontal sections"

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") OR ("production frontal 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\") OR (\"production frontal region\"))))".
• Removing quotes may allow a broader search: (((( production frontier section ) or ( production frontier functions ))) or ((( production frontier region ) OR ( production frontal region )))).
• Adding a wildcard symbol may retrieve word variants: (((("production frontier section") or ("production frontier functions"))) or ((("production frontier region") OR ("production frontal region"))))*.