[R] x-axis annotation

[array chip]

Hi, I have a simple plot by plot(x,y, log='xy'). However, due to the large range 
of values of x, the x-axis annotation is printed as "2e+02  1e+03  5e+03  2e+04  
1e+05" instead of "200  1000   5000 20000   100000". How can I make it printed 
as in the later one?

Thanks

John