"not only demonstrates" is correct and usable in written English.
You can use it to emphasize that something does more than one thing. For example, "This book not only demonstrates the power of language but also highlights the importance of connection."
The case not only demonstrates a weakness in Googlemail accounts, but how electronic crimes are not taken seriously.
This study not only demonstrates a direct effect on microbes but also has an influence on immune cell recruitment.
It suggests that singing not only demonstrates how healthy a bird is, but how healthy it was.
It not only demonstrates to abusers that their behaviour is wrong, but crucially, it signals as much to everyone else, too.
This not only demonstrates an individual's commitment and drive to a prospective employer, but it also gives an insight into the realities of working in a specific sector.
Saying "Here's a pattern we've observed" not only demonstrates the kind of reciprocity that's inherently motivating but helps us understand if we're drawing valid conclusions.
One such example is the Occupy movement, which not only demonstrates a method of combatting issues, but also demonstrates the evolution of the method of protests.
Our experiment not only demonstrates a new protocol to measure out-of-time ordered correlations, but also provides new insights in the study of quantum thermodynamics.
This result not only demonstrates a possible avenue to increase the amount of foundry waste recycled annually, but it also reduces the demand for virgin aggregates for PCC.
Also, not only demonstrates high tough performance in various conditions such as water and temperature but also shows an ease in shape change by using water.
Our preliminary work at Santa Elena not only demonstrates the great potential of these techniques at this site, but at historic sites in general.
