Can I prevent archive pages from being indexed without damaging post indexing?

Hi, I hope somebody would be kind enough to help.
I’d like to prevent the pages “mysite.com/year” from being indexed on Google (ex: mysite.com/2011; mysite.com/2012; ecc).
I thought i should set “Disallow:/2011” in my robots.txt, but i’m afraid that all my posts will be blocked from indexing, because the URL format of my posts is “mysite.com/year/month/day/postTitle”. For example: if I prevent from being indexed the directory /2011, i’m afraid that all the posts published in 2011 will be blocked from indexing, because they are in the same directory… is it right?
If this logic is right, Can you help me to find the right way to do this job?

I hope I’ve been clear, my english is a little rusty.

Thanks so muck for your help!