Wal-Mart Stores Inc has taken full ownership of Chinese e-commerce firm Yihaodian.com, buying out the 49 percent stake that it did not already own to accelerate its push online, the U.S. retail giant said on Thursday. The investment will help Wal-Mart target China’s fast-growing online market at a time when largely brick and mortar retailers are feeling the pinch of competition from online rivals and a slowing of the world’s second-largest economy.