Perhaps you should try some spelling variations:
"conservacion de recurso naturales" » "conservacion de recursos naturales", "conservacion de recurso natural", "conservacion de recursos materiales", "conservacion de rerecursos naturales", "conservation _ recurso naturales", "conservacion del recurso naturales", "conservacion el recurso naturales"
"conservacion del curso naturales" » "construccion del curso naturales", "conservacion y curso naturales", "conservation _ curso naturales", "conservacion del recursos naturales", "conservation _l curso naturales", "conservacion del cuerpo naturales", "conservacion del discurso naturales"

Try widening your search to All Fields.

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

• Performing a fuzzy search may retrieve terms with similar spellings: (("conservacion del curso naturales") or ("conservacion de recurso naturales"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("conservacion del curso naturales") OR ("conservacion de recurso naturales")).
• Removing quotes may allow a broader search: (( conservacion del curso naturales ) or ( conservacion de recurso naturales )).
• Adding a wildcard symbol may retrieve word variants: (("conservacion del curso naturales") or ("conservacion de recurso naturales"))*.