Do you know some websites/applications useful by looking for the transport?

oh, you can just ask help for TravelChinaGuide.
Their warm service and high efficiency will make you feel comfortable. You can trust them.
For booking trains, you can write to bookingtravelchinaguide.com;
for rent vehicles, you can write to traveltravelchinaguide.com

In addition, you can found out the train&flight schedules on this website. And the timetable is updated.