OK, I spent way too much time browsing around the site Fori linked above, and now I know way more than I knew there was about Chinese porcelain. I found your mark! Here's the cliff notes:

There is commonality in the markings of the Chinese porcelain. The markings are read right to left and top to bottom, so yours reads Da qing tong zhi nian zhi.

Da qing and nian zhi are common to all. Da qing refers to the Qing Dynasty and nian zhi means "period made" with the middle 2 characters getting specific on what period within Qing it comes from.

So yours was made in the Tong Zhi period. Go to this page and scroll down until you see Tong Zhi, who was an emperor during the Qing Dynasty, from 1862-1874 (and died ignominiously of either smallpox or syphillis).

So yeah, I think you've got yourself a piece of Qing porcelain! I have no clue what it's worth, but a quick search on ebay for "tongzhi porcelain" should give you an idea.

Have fun!