How do plants intake minerals through their leaves?
They absorb minerals through pores in the leaves known as stomata, this is some what similar to the way a medicine patch is absorbed on human skin except for the fact that the human skin has sweat pores instead of stomata.

Here is a animation of them opening and closing on a tomato plant provided by Wikipedia:  

sources:


  A nice review by Wocjik (2004) (from the comments)
  
  http://www.wisegeek.com/what-is-foliar-feeding.htm
  
  http://en.wikipedia.org/wiki/Foliar_feeding
  
  http://cronodon.com/BioTech/Plant_Transport.html