Load right place that i have just operate before

Question

Hi everybody! My problem is i want to use ajax to load my page again but it must load  exactly position of the page that have just display on the screen.
For example :A website always have the height higher than the screen and we have to use scroll bar to see all.
Example i'm watching at middle of the page and i have a operation with the page(press button) and it load page again ,so after page load again i want it display exactly at middle of the page as previous page.
Hope anyone know it ,please talk for me know.Thanks!!