SHANGHAI — Land sales in China fell sharply in value last year, while half the country’s listed real estate developers saw a fall in net profits, and more than 10 percent lost money, Chinese media reported. It is further evidence of the pressures on China’s property sector, one of the main engines of the nation's growth over the past two decades, which has slowed significantly in the last three years — despite recent signs of a recovery and official hopes that it will stimulate the nation’s slowing economy.