PRODUCTION OF WHEAT HAPLOIDS USING ANTHER CULTURE AND WHEAT×MAIZE HYBRIDIZATION TECHNIQUE A Study on the Yield Potential in Maize Hybrids with Different Leaf Angles Changes of Grain Yield and Nitrogen Use Efficiency of Maize Hybrids Released in Different Eras in Shaanxi Province Genotype differences on nitrogen use efficiency among maize hybrids Isozyme Studies in Predicting the Potential Yield of Heterosis in Maize Effects of Seedling Shading and Light Intensity Transfer on Photosynthetic Efficiency of Different Maize (Zea mays L.) Hybrids