Perhaps you should try some spelling variations:
"conservacion de recursos materiales" » "conservacion de recursos naturales", "conservacion de recursos minerales", "conservacion de hechos materiales", "conservation _ recursos materiales"
"conservacion en recurso naturales" » "conservacion en recursos naturales", "conservacion en recurso natural", "conservacion en recursos culturales", "conservacion del recurso naturales", "conservacion y recurso naturales", "conservation _ recurso naturales", "conservacion el recurso naturales", "conservacion un recurso 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 en recurso naturales") or ("conservacion de recursos materiales"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("conservacion en recurso naturales") OR ("conservacion de recursos materiales")).
• Removing quotes may allow a broader search: (( conservacion en recurso naturales ) or ( conservacion de recursos materiales )).
• Adding a wildcard symbol may retrieve word variants: (("conservacion en recurso naturales") or ("conservacion de recursos materiales"))*.