There is one wordpress plugin called “Search ads” that lets you do this. You can show adsense ads only to search engine users, which usually click on ads. As for regular readers from sources like bookmarks and manual address typing, ads will not show. Another plugin is “ad injection“.
If you wish to do adsense tracking on any website then you have to connect google adsense with google analytics profile. You have to use the tracking code of that profile on site which has adsense enabled.