Perhaps you should try some spelling variations:
integration theories » integration theory, integration through, integration efforts
spate irrigation » scale irrigation, water irrigation, surface irrigation
import trade » export trade, import price, import taxes
supply spate » supply system, supply side, supply water
systems. » system.

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: (( import trade integration theories. ) OR ( supply spate irrigation systems. ))~.
• Adding a wildcard symbol may retrieve word variants: (( import trade integration theories. ) or ( supply spate irrigation systems. ))*.