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