Perhaps you should try some spelling variations:
"seis estudios americanos." » "seis estudios latinoamericanos.", "los estudios americanos.", "dos estudios americanos.", "dios estudios americanos."
"series estudios urbano." » "serie estudios urbano.", "tres estudios urbano.", "sociales estudios urbano.", "series estudio urbano.", "series estudios peruanos.", "series estudios hispano."
"leyes estudios urbanos." » "leyes estudio urbanos.", "leyes estudios peruanoss.", "leyes estudios hispanos.", "los estudios urbanos.", "tres estudios urbanos."

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

• Performing a fuzzy search may retrieve terms with similar spellings: (((("series estudios urbano.") or ("leyes estudios urbanos."))) or ("seis estudios americanos."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (((("series estudios urbano.") OR ("leyes estudios urbanos."))) OR ("seis estudios americanos."))*.
• Removing quotes may allow a broader search: (((( series estudios urbano. ) or ( leyes estudios urbanos. ))) or ( seis estudios americanos. ))*.