Perhaps you should try some spelling variations:
"agricultural introduction" » "agriculture introduction", "agricultural productions", "agricultural involution"
"agricultural instruction" » "agriculture instruction", "agricultural institution", "agricultural reconstruction"
"agricultural production" » "agricultural reproduction"

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: (("agricultural production") OR ((("agricultural introduction") OR ("agricultural instruction")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"agricultural production\") or (((\"agricultural introduction\") OR (\"agricultural instruction\"))))".
• Removing quotes may allow a broader search: (( agricultural production ) or ((( agricultural introduction ) OR ( agricultural instruction )))).
• Adding a wildcard symbol may retrieve word variants: (("agricultural production") or ((("agricultural introduction") OR ("agricultural instruction"))))*.