Perhaps you should try some spelling variations:
"gerke wilhelm friedrich engels" » "gehrke wilhelm friedrich engels", "werk wilhelm friedrich engels", "menke wilhelm friedrich engels"
"berg wilhelm friedrich hegel" » "berger wilhelm friedrich hegel", "georg wilhelm friedrich hegel", "bei wilhelm friedrich hegel"

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: (("berg wilhelm friedrich hegel") OR ("gerke wilhelm friedrich engels")).
• Removing quotes may allow a broader search: (( berg wilhelm friedrich hegel ) or ( gerke wilhelm friedrich engels )).
• Adding a wildcard symbol may retrieve word variants: (("berg wilhelm friedrich hegel") or ("gerke wilhelm friedrich engels"))*.