Perhaps you should try some spelling variations:
"export trade integration theories." » "export trade integration theory.", "export trade integration through.", "export trade integration efforts.", "export share integration theories.", "export taxes integration theories.", "export price integration theories."
"support large irrigation schemes." » "support large irrigation scheme.", "support large irrigation systems.", "support farm irrigation schemes.", "support drip irrigation schemes.", "support scale 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: (("export trade integration theories.") OR ("support large irrigation schemes."))~.
• Removing quotes may allow a broader search: (( export trade integration theories. ) or ( support large irrigation schemes. ))~.
• Adding a wildcard symbol may retrieve word variants: (("export trade integration theories.") or ("support large irrigation schemes."))*.