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