Does anyone can help me the Bus schedule Beijing - Erlian

Dear travelers,

I am a happy Catalan girl coming to China! :D
I cannot wait for visiting your country... this trip is making me be very very excited :)
These days, I am planning each detail because my time will be very very limited...
Currently the information that is missing is the schedule of the buses going from Beijing to Erlian. I heard that I can take a bus from three different bus stations: Muxiyuan 木樨园, Liuliqiao 六里桥, and Jiandemen 健德门. Is it true?

Does anyone can help me? Do you know whether there are many buses per day?

Thanks a lot! I wish you a nice summer! :)

Anna.