Perhaps you should try some spelling variations:
"support trade integration theories." » "support trade integration theorems.", "support trade integrationstheorie 2.", "support trade integration theory.", "support trainer integration theories.", "export trade integration theories.", "import trade integration theories."
"support drip irrigation schemes." » "support drip irrigation scheme.", "support drip irrigation systems.", "support deep irrigation schemes.", "support during irrigation schemes.", "support crops irrigation schemes."

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 trade integration theories.") OR ("support drip irrigation schemes."))~.
• Removing quotes may allow a broader search: (( support trade integration theories. ) or ( support drip irrigation schemes. ))~.
• Adding a wildcard symbol may retrieve word variants: (("support trade integration theories.") or ("support drip irrigation schemes."))*.