Perhaps you should try some spelling variations:
"export prices integration theories." » "export prices integration theorems.", "export prices integrationstheorie 2.", "export prices integration theory.", "export price integration theories.", "export process integration theories.", "export policies integration theories.", "import prices integration theories."
"efforts policies heating services." » "effects policies heating services.", "export policies heating services.", "forms policies heating services.", "efforts policies dealing services.", "efforts policies meeting services.", "efforts policies sealing services.", "efforts policies testing services.", "efforts policies hunting services.", "efforts policies leasing services."

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: (("export prices integration theories.") OR ("efforts policies heating services."))~.
• Removing quotes may allow a broader search: (( export prices integration theories. ) or ( efforts policies heating services. ))~.
• Adding a wildcard symbol may retrieve word variants: (("export prices integration theories.") or ("efforts policies heating services."))*.