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