I am sometimes asked what academic journals I would recommend for research in terrorism and political violence studies from an interdisciplinary social science perspective. Two stand out, although unfortunately neither is open source - each is published by Taylor and Francis. However, from the standpoint of both citation counts and, FWIW, my own experience, these two are the leaders in the field and have been for a long time. (The links go to the editorial board pages at T&F.)
Journal of Terrorism and Political Violence. Started in the mid-1980s by two leading political scientists studying terrorism, David Rapoport (UCLA) and the late Paul Wilkinson (University of St Andrews), it publishes in a distinctly interdisciplinary mode. The editorial board has many outstanding people, including Marc Sageman, Amy Zegart, Martha Crenshaw, and many more. Max Taylor (University of St Andrews) has joined Professor Rapoport at the editorial helm. (Full disclosure: I have been on the editorial board of the journal since its earliest days. My own work on terrorism dates back to 1980s, well before attending law school - the first article I published, in fact, was on Bader-Meinhoff and the Red Brigades - and David Rapoport was my professor at UCLA, where I took his courses on terrorism and political theory. I have written articles for the journal over the years, and do peer-review for the journal.)
Studies in Conflict and Terrorism. Dating back to 1977 under the title "Terrorism," the editor-in-chief is the well-known terrorism expert Bruce Hoffman, who currently heads the RAND office in Washington DC. The editorial board has many distinguished academics and experts known to Lawfare readers and beyond - Dan Byman, Peter Bergen, Christine Fair, and Marc Lynch, among many others.