Perhaps you should try some spelling variations:
"amateur symbiotic association" » "amateur symbiotic associations", "nature symbiotic association"
"amateur semantic association" » "amateur semantic annotation", "amateur genetic association", "amateur semantic classification", "paper semantic association", "another semantic association", "answer semantic association"

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

• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"amateur symbiotic association\") OR (\"amateur semantic association\"))".
• Removing quotes may allow a broader search: (( amateur symbiotic association ) OR ( amateur semantic association )).
• Adding a wildcard symbol may retrieve word variants: (("amateur symbiotic association") OR ("amateur semantic association"))*.