Please check the PHP documentation.
If you want to use include with URL, you need to provide the full URL, e.g. <?php include "http://www.yoursite.com/index.php?option=com_content&view=article&id=112&Itemid=346"; ?>
However, please take note that you are including the entire content of another article. This will include the complete header, body, etc. And note that you are using DirectPHP within another article, too. So with two headers, body, etc., it will be a "mess". (Just do a view source of both articles and you will know what I mean.)
DirectPHP is not developed for this purpose. It's for running simple and straight-forward PHP scripts. It's not for including one complete article into another.
If you simply want to include the content of one article into another, you can use another plugin that I've written: the include_content_item plugin http://www.kksou.com/php-gtk2/Joomla/Include-Content-Item-plugin.php