Perhaps you should try some spelling variations:
"endogenous estrogen sulfide" » "exogenous estrogens sulfide", "endogenous hydrogen sulfide", "endogenous pyrogen sulfide", "endogenous nitrogen sulfide", "endogenous dinitrogen sulfide"
"exogenous estrogen sulfide" » "exogenous estrogens sulfide", "exogenous nitrogen sulfide", "exogenous hydrogen sulfide", "exogenous dinitrogen sulfide"

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: "((\"endogenous estrogen sulfide\") OR (\"exogenous estrogen sulfide\"))*".
• Removing quotes may allow a broader search: (( endogenous estrogen sulfide ) OR ( exogenous estrogen sulfide ))*.