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

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 e investigacion ) OR ( pacis estudios de investigaciones )).
• Adding a wildcard symbol may retrieve word variants: (( de estudios e investigacion ) or ( pacis estudios de investigaciones ))*.