Dynamic Comparison of Free Radical Scavenging Abilities of Hypericum Perforatum L., Herba Verbenae Officinalis, and Valeriana Officinalis L. Extracts, Li, Yi-ming, Liu Yan-Ru, Xiao Bing-Kun, Yang Jian-Yun, and Huang Rong-Qing , Pharmacognosy Journal, 01/2015, Volume 7, Issue 3, p.198-204, (2015)