You can search any books at
www.baidu.com, its pretty much the Google in China. I searched 本草纲目 and this came up as the first link.
http://www.qisuu.com/Shtml1924.html
I should caution you that many of those ebook sites (you can search 电子书) give you tons of free content, however, I'm not sure if they have the legal rights to publish them.
Hope it helps
