Ron's right on the money in his post. I'd add another layer though that perhaps is simplistic but it worked for me when I was starting out and this publicity stuff seemed a bit overwhelming. It might not be scholarly-type journals. It might be more consumer oriented.
Point is have primary media and secondary media targets.
Concentrate on the primary, and not as much on the secondary. Too often in the beginning people give up on publicity. They say it doesn't work. Heard it a 1000 times. After you've thought out your strategy mail releases on a regular basis.