Perhaps you should try some spelling variations:
"sobre variables." » "sobre variantes.", "entre variables.", "sobre varias."
"sobre distritos." » "sobre distintos.", "sobre diarios.", "sobre distintas."
"serie diarios." » "serie dietarios.", "sobre diarios.", "sur diarios."
"sobre caries." » "sobre cargas.", "sobre carlos.", "sobre carne."

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

• Performing a fuzzy search may retrieve terms with similar spellings: (("serie diarios.") or ((((("sobre caries.") or ("sobre variables."))) or ("sobre distritos."))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("serie diarios.") OR ((((("sobre caries.") OR ("sobre variables."))) OR ("sobre distritos.")))).
• Removing quotes may allow a broader search: (( serie diarios. ) or ((((( sobre caries. ) or ( sobre variables. ))) or ( sobre distritos. )))).
• Adding a wildcard symbol may retrieve word variants: (("serie diarios.") or ((((("sobre caries.") or ("sobre variables."))) or ("sobre distritos."))))*.