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"

Try widening your search to All Fields.

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• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"endogenous estrogen sulfide\") OR (\"exogenous estrogen sulfide\"))".
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