Perhaps you should try some spelling variations:
"primitive general theorems" » "primitives generic theorems", "positive general theorems", "primitive neural theorems", "primitive general theory"
"positive energy theorems" » "positive energy theory"

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: (("positive energy theorems") OR ("primitive general theorems")).
• Removing quotes may allow a broader search: (( positive energy theorems ) or ( primitive general theorems )).
• Adding a wildcard symbol may retrieve word variants: (("positive energy theorems") or ("primitive general theorems"))*.