Perhaps you should try some spelling variations:
integration theory » integration through, information theory, innovation theory
irrigation schemes » irrigation scheme, irrigation systems
a irrigation » _ irrigation, 4 irrigation, 5 irrigation
import trade » export trade, import price, import taxes
support a » support _

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (( support a irrigation schemes. ) or ( import trade integration theory. ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( support a irrigation schemes. ) OR ( import trade integration theory. )).
• Adding a wildcard symbol may retrieve word variants: (( support a irrigation schemes. ) or ( import trade integration theory. ))*.