Perhaps you should try some spelling variations:
"introduction frontier second" » "introduction fourier second", "introduction front second", "production frontiers second", "introduction frontier section", "introduction frontiers section"
"production frontier second" » "production frontier section", "production frontiers section", "reproduction frontier second"
"production frontier region" » "production frontal region", "reproduction frontier 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 ("introduction frontier second"))) OR ("production frontier region")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"production frontier second\") OR (\"introduction frontier second\"))) or (\"production frontier region\"))".
• Removing quotes may allow a broader search: (((( production frontier second ) OR ( introduction frontier second ))) or ( production frontier region )).
• Adding a wildcard symbol may retrieve word variants: (((("production frontier second") OR ("introduction frontier second"))) or ("production frontier region"))*.