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

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