What does a plus sign mean in journal abbreviations? On this journal title abbreviation list, some abbreviations are followed by a plus sign (+).  For example, "Thermophysics and Aeromechanics" is abbreviated "THERMOPHYS AEROMECH+".

What is the significance of the plus sign, and is it to be included when creating a reference list?
Web of science doesn't explain it on the page you quote, but you can find it in another page with detailed explanation: "The plus sign on this last abbreviation indicates that cites to the original language journal are unified with cites to the translation title"

From here: http://wokinfo.com/essays/cited-title-unification/