Perhaps you should try some spelling variations:
de investigaciones » de investigacion, la investigacion
pacis estudios » pacis studies
estudios de » estudio de
estudios y » estudios en, studios _, estudios del
studios a » studios _, studios fast

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: (( de ((estudios y) OR (studios a)) investigacion ) OR ( pacis estudios de investigaciones )).
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( de ((estudios y) OR (studios a)) investigacion ) or ( pacis estudios de investigaciones ))".
• Adding a wildcard symbol may retrieve word variants: (( de ((estudios y) OR (studios a)) investigacion ) or ( pacis estudios de investigaciones ))*.