[The course and achievement of maize variety improvement in the 20th-century in China].
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D000383:Agriculture / Q000191:economics / Q000193:education / Q000266:history / Q000331:legislation & jurisprudence; D001947:Breeding / Q000191:economics / Q000266:history / Q000331:legislation & jurisprudence; D002681:China / Q000208:ethnology; D018556:Crops, Agricultural / Q000191:economics / Q000266:history; D049673:History, 20th Century; D010944:Plants; D012106:Research / Q000191:economics / Q000193:education / Q000266:history / Q000331:legislation & jurisprudence; D003313:Zea mays / Q000191:economics / Q000266:history