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 estudios urbanos.", "series estudio urbano.", "series estudios peruanos."
"leyes estudios urbano." » "leyes estudios urbanos.", "leyes estudio urbano.", "leyes estudios peruanos.", "los estudios urbano.", "tres estudios urbano."

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 urbano."))) or ("seis estudios americanos."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (((("series estudios urbano.") OR ("leyes estudios urbano."))) OR ("seis estudios americanos."))*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"series estudios urbano.\") OR (\"leyes estudios urbano.\"))) or (\"seis estudios americanos.\"))*".
• Removing quotes may allow a broader search: (((( series estudios urbano. ) OR ( leyes estudios urbano. ))) or ( seis estudios americanos. ))*.