Perhaps you should try some spelling variations:
"survey based immunization systems." » "survey based communication systems.", "survey based immunization rates.", "survey based immunization costs.", "survey basic immunization systems.", "survey mass immunization systems.", "survey measles immunization systems."
"supply crop irrigation schemes." » "supply crop irrigation scheme.", "supply crop irrigation systems.", "supply drip irrigation schemes.", "supply scale irrigation schemes.", "supply canal irrigation schemes.", "supply crowd irrigation schemes.", "supply curve 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: (("supply crop irrigation schemes.") OR ("survey based immunization systems."))~.
• Removing quotes may allow a broader search: (( supply crop irrigation schemes. ) or ( survey based immunization systems. ))~.
• Adding a wildcard symbol may retrieve word variants: (("supply crop irrigation schemes.") or ("survey based immunization systems."))*.