各位大神,这段话什么意思啊?小弟实在看不懂!

各位大神,这段话什么意思啊?小弟实在看不懂!
The absence of direct experimental data has given rise to the coexistence in the literature of very different hypothesis ranging from models based on a totally random distribution of ionic bonds to those based on zones rich in modifier cations which alternate with less rich zones.