Perhaps you should try some spelling variations:
"conferencia internacional." » "convencion internacional.", "comercial internacional.", "experiencia internacional."
"conferencia ministerio." » "conferencia ministerial.", "conferencia magistral.", "conferencia monetaria."
"referenda nacionales." » "referendo nacionales.", "referencia nacionales.", "referendum nacionales."

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

• Performing a fuzzy search may retrieve terms with similar spellings: (((("referenda nacionales.") or ("conferencia internacional."))) or ("conferencia ministerio."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (((("referenda nacionales.") OR ("conferencia internacional."))) OR ("conferencia ministerio."))*.
• Removing quotes may allow a broader search: (((( referenda nacionales. ) or ( conferencia internacional. ))) or ( conferencia ministerio. ))*.