[R] Change the default resolution for plotting figures?

[jtang at mappi.helsinki.fi]

Hi,
I want to save a plot in the windows device as png and the default  
resolution is 72dpi. Is it possible to increase the default resolution  
to for example 300 dpi?
I have thought of using function png(..., res=300), but the problem is  
that the figure produced this way looks different than the one shown  
in the windows device. One notable difference is the missing of some  
ticks in the x axis. Therefore I would rather to produce the figure in  
a window device and then save it as a png. Unfortunately in the device  
window there is no such an option to change the resolution.
Little information can be found so far. Any ideas are appreciated!

Best,
Jing