Seasonal Variation in Water Use of Ziziphus jujuba in the South Aspect of Taihang Mountains with Deuterium Isotope Signature Synthesis of Five Deuterium Substituted 2-pyrimidinyloxy- N-arylbenzylamines with Herbicidal activity Study on Hydrogen and Oxygen Stable Isotopes in Precipitation in Wolong Nature Reserve,Sichuan Province Review and Perspective on Hydrogen Stable Isotopes Technique in Tracing Plant Water Sources Researches