https://books.google.com/books?id=PetvCQAAQBAJ&pg=PT27&lpg=PT27&dq=1820年中国国内生产总值(GDP)占世界GDP的28.7%25&source=bl&ots=2QKoNHj-o6&sig=3Qcej8-_Lr_m1NMWJAn8pgmrOq4&hl=en&sa=X&ved=0ahUKEwj9tdGXt4LPAhVFRCYKHTnkA7AQ6AEIHDAA#v=onepage&q=1820%E5%B9%B4%E4%B8%AD%E5%9B%BD%E5%9B%BD%E5%86%85%E7%94%9F%E4%BA%A7%E6%80%BB%E5%80%BC(GDP)%E5%8D%A0%E4%B8%96%E7%95%8CGDP%E7%9A%8428.7%25&f=false