How to negotiate for clinical vs protected research time in academic job offer? I am a doctor, with specialty in psychiatry and a subspecialty in mood disorders. 

I have been offered an academic position at a larger university, but the letter of offer does not specify any research time - only clinical time. I want to negotiate clinical time (number of patients to see per week), which will be my main source of income, vs protected research time (for which the Hospital/University will provide compensation). I want to be able to do research but need the department to commit to paying me for it.

It is my understanding that this will be the only time I will be in a position of power to negotiate something, but I don't know where to start. I have other 2 offers in place as well. 

The clinical aspect may make this negotiation different from other junior faculty members, e.g. as in Evaluating and negotiating a start-up package.
It really depends on your professional goals.
if a purely clinical position is not an option for you, and if your research credentials (publications, etc) back up your ambition, then you should make that clear to the department and work with them on adapting the offer.

It is not just about salary, but would likely involve a start up package for your research, reserved physical space for research (lab space), possibly a joint appointment in a research department. etc.
if none of these can be part of the offer, this would mean your research activity is not supported.