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41.
42.
标准溶液的不确定度对农药残留检测起着非常重要的作用,影响着检测结果的准确性。笔者以实际应用的14种有机磷农药混合标准溶液为例,采用配制混合标准溶液过程单元操作的不确定度计算方法(top down),分析了在配制混合标准溶液过程中的所有影响因素,得到了最终的扩展不确定度。最终结果显示使用精准的移液器将储备液配置为混合标液,得到最终的扩展不确定度相对小。 相似文献
43.
C. M. Geraldson 《Journal of plant nutrition》2013,36(8):1091-1098
The concentration and balance of nutrients in both the hydroponic or soil solution has been evaluated with relevance to tomato productivity. Yields of 200 mt/ha have been produced in greenhouse, hydroponic culture in a 9 to 10 month period. Yields of more than 100 mt/ha of field grown tomatoes have been produced in Florida in a 4 to 5 month period. Within the limitations of either culture, it is possible per unit of time to provide the nutrients required to produce equivalent yields. It is most significant that field grown tomatoes in Florida can be grown with minimal management and at a fraction of the cost of those grown hydroponically. The validity of the Florida fresh market tomato industry is based on the production efficiency of the field culture. There are annually 16,000 ha of tomatoes grown in Florida, perhaps less than 40 ha grown in hydroponic cultures. 相似文献
44.
方聪娜 《厦门水产学院学报》2012,(4):297-300
利用指数型二分性理论及相关分析技巧,研究了一类具有有限时滞的非算子型的中立型泛函微分方程的概周期解问题,得到了方程存在唯一稳定的概周期解的新结果. 相似文献
45.
46.
《Communications in Soil Science and Plant Analysis》2012,43(5):483-495
Abstract When sugarbeet seedlings are transferred from a complete nutrient solution to one from which Ca has been withheld, the rootlets and tops fail to develop. The same transfer at the eight‐leaf stage causes the rootlets to become stubby and swollen at the tips and blade expansion becomes modified; particularly the upper portions of the blades attaining nearly full development, which pucker and often develop a cupping or hooding effect; a unique symptom characteristic of Ca deficiency. As each new leaf develops, the blade area becomes smaller until only a black tip remains at the apex of the petiole, which is the symptom referred to as tip‐burn for this petiole and the successively . shorter petioles formed as Ca deficiency increases in severity. Strangely, these symptoms also appear during periods of rapid growth when the nutrient solution contains as much as 10 to 28 milliequivalents per liter of Ca or when soils are high in Ca. This implies that Ca absorption and possibly translocation limits the Ca supply at the growing point. Increasing Mg in the nutrient solution decreases Ca uptake and increases Ca deficiency. Potassium deficiency, unexpectedly, induces Ca deficiency apparently by decreasing the translocation of Ca to the growing point. These phenomena suggest the hypothesis that when ion absorption takes place from the root exchange site that has the affinity for H > Ca > Mg > K > Na, then the H generated internally replaces, and the roots absorb, Na, K and Mg preferentially. Externally, Ca would be adsorbed preferentially from the nutrient solution by the exchange complex, and with the addition of Mg, it would compete for the common adsorption site of Ca and limit Ca absorption internally. Under these conditions potassium‐deficient nutrient solutions would not induce Ca deficiency by decreasing Ca absorption but rather by decreasing Ca translocation. Theoretically, Ba would replace H more readily than Ca on the exchange complex, and therefore, Ba would be adsorbed preferentially and Ca uptake would increase. This effect of Ba was verified experimentally. Since the translocation of 45Ca to the growing point was found to be unrestricted under Ca‐sufficient and Ca‐deficient conditions and since the formation of insoluble Ca compounds such as phosphate or oxalate did not account for the Ca deficiency at the growing point, the cause of the Ca deficiency at the growing point is most likely the higher priority of the storage root for Ca over tops when leaf blades and storage root are both expanding rapidly. However, Ca retransport from older to younger parts of the sugarbeet plant may be restricted by the formation of Ca phosphate under Ca‐deficient conditions and Ca oxalate under Ca‐sufficient conditions. Calcium deficiency increases net photosynthesis per unit blade area initially, probably because of blade puckering, but not on a per unit chlorophyll basis. 相似文献
47.
从生产实习的现状入手,以石河子大学电气工程及其自动化专业为例,分析了生产实习的重要性,并就存在的问题提出了解决方案。 相似文献
48.
彭沉 《农业图书情报学刊》2012,24(12):208-211
公共图书馆员职业倦怠是中国图书馆行业中普遍存在的问题,分析图书馆员职业倦怠的成因,以广州图书馆为例,探析解决公共图书馆员职业倦怠的对策。 相似文献
49.
西部欠发达地区农村图书馆建设对策研究 总被引:1,自引:0,他引:1
李强 《农业图书情报学刊》2010,22(3):42-44
面对建设社会主义新农村的重大历史任务,本文通过对西部欠发达地区农村图书馆建设现状及发展滞后的原因分析.提出了适合西部农村图书馆发展的对策和建议。 相似文献
50.
灌溉对心底土积盐层的溶解作用 总被引:1,自引:0,他引:1
1.心底土积盐层是引起土壤次生盐渍化不可忽略的原因土壤次生盐渍化是干旱、半干旱地区作物正常生长和发展农业生产的一个重要限制因素,综合目前的研究资料,人们对土壤次生盐渍化的发生和防治作了大量的研究工作,但对心底土积盐层与土壤次生盐渍化研究得较少,忽略了这个问题。正如罗赞诺夫指出:“人们往往忽略了土壤以及底土的原始含盐量在灌区土壤次生盐渍化中的作用,因此,我们愿意再一次强调指出,必须重视自然条件特别是土壤的原生盐渍化在次生盐渍化中的重大意义和作 相似文献