Perhaps you should try some spelling variations:
irrigation system » irrigation systems, irrigation water, irrigation scheme
gray irrigation » grain irrigation, gravity irrigation, murray irrigation
a integration » 3 integration, 2 integration, 10 integration
4 integration » 3 integration, 2 integration, 4.1 integration
supply gray » supply great, supply gap, supply gas

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: (( support ((a integration) OR (4 integration)) theories. ) OR ( supply gray irrigation system. ))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( support ((a integration) OR (4 integration)) theories. ) or ( supply gray irrigation system. ))~".
• Adding a wildcard symbol may retrieve word variants: (( support ((a integration) OR (4 integration)) theories. ) or ( supply gray irrigation system. ))*.