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

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

• If you are trying to use Boolean operators, they must be ALL CAPS: (("endogenous pyrogen sulfide") OR ("exogenous estrogen sulfide")).
• Removing quotes may allow a broader search: (( endogenous pyrogen sulfide ) or ( exogenous estrogen sulfide )).
• Adding a wildcard symbol may retrieve word variants: (("endogenous pyrogen sulfide") or ("exogenous estrogen sulfide"))*.