Perhaps you should try some spelling variations:
"scale irrigation studies." » "scale irrigation sources.", "scale irrigation services.", "scale segregation studies."
"scale migration studies." » "male migration studies.", "female migration studies.", "trade migration studies."
"can migration studies." » "main migration studies.", "von migration studies.", "urban migration studies."

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (("scale irrigation studies.") or ((("scale migration studies.") or ("can migration studies."))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("scale irrigation studies.") OR ((("scale migration studies.") OR ("can migration studies.")))).
• Removing quotes may allow a broader search: (( scale irrigation studies. ) or ((( scale migration studies. ) or ( can migration studies. )))).
• Adding a wildcard symbol may retrieve word variants: (("scale irrigation studies.") or ((("scale migration studies.") or ("can migration studies."))))*.