Much of the research on bullying covers bullying in schools and among young people, and if that is your area of research databases on education would be most helpful. For mobbing and bullying in the workplace, the psychological and business literature will be most helpful, although in the psychological literature bullying among young people will still need to be filtered out. The Academic Search Complete database is a good, comprehensive source covering areas including psychology and business. For the most serious and clinical treatments PsycINFO would be best, while Business Source Complete and LexisNexis Academic will provide organizational and managerial treatments. Most research in the English language covers bullying while mobbing prevails as the topic in continental Europe, so you may expect the research in the listed databases to cover mainly bullying.