is it possible to connect the serial port of 8051 to the RS485 network?

Yes, use SN75176 chip

As the 8051 serial port is full duplex, while the Rs485 is half-duplex. Half these two standard working together?

RS-485 is a hardware standard, you will have to define your communication protocol or obey the existing network's protocol.

do i need to set some flow control/protocol to it. It is a little bit difficult to me.

Yes, you will have to. It is not difficult

Can i have some example above Rs485 and 8051 on the web?

Oh, I will look for some stuff.

BTW: Search this forum for RS-485 and I am sure, you will find useful info.

Good Luck