排序方式： 共有12条查询结果，搜索用时 13 毫秒
1.
水稻立枯病对旱育秧田危害十分严重,特别是遇到持续低温或气温忽高忽低时发病尤重,可造成秧苗大量死亡.
1.症状识别因病原种类、为害时期和环境条件不同,从而引起的症状也不同,常见的症状有以下几种类型:
芽腐在出苗前或刚出土时发生.幼苗的幼芽或幼根变褐色,病芽扭曲、腐烂而死.在种子或芽基部生有霉层. 相似文献
2.
3.
参数化的设计方法在车身设计中得到了大量的应用。利用Catia v5进行了某轿车车身总布置参数化设计,在其基础上使用Visual Basic进行二次开发,构建了知识驱动的车身硬点布置参数化设计系统,然后根据GB1589-1989《汽车外廓尺寸界限》中常见的轿车尺寸关系以及限制的要求,对车身硬点尺寸进行了检查,获得了符合要求的车身总体造型。 相似文献
4.
【目的】针对土石坝坝体沉降存在多变量、强耦合、强干扰的复杂问题,建立基于KPCA-RVM的土石坝沉降预测模型。【方法】利用核主元分析(KPCA)对输入向量进行降维处理,以减少因子个数,随后利用相关向量机(RVM)模型对土石坝沉降进行预测,并以平均相对误差为指标对预测精度进行评价。【结果】实例应用表明,KPCA-RVM模型将输入向量由14个降低到7个,预测结果的平均相对误差仅为0.9%,预测效果得到明显提升。【结论】利用KPCARVM模型对土石坝进行沉降预测,不仅可以减少输入向量个数,而且可以提高预测精度,可在实际工程中推广应用。 相似文献
5.
6.
7.
This research explored the effect of different levels of phosphorus application on diurnal variation in photosynthesis and partitioning of photosynthetic products in alfalfa under drip irrigation. In particular, the relationship between photosynthetic product levels in the plant and leaf photosynthetic parameters of alfalfa was clarified. Four phosphorus（P2O5）application levels of 0（CK）,50（P1）,100（P2）and 150 kg·ha-1（P3）were used as treatments in a field experiment. Leaf photosynthetic parameters were measured with a Li-6400 portable photosynthesis instrument on sunny days from 10：00-20：00 during the early flowering stage,together with environment factors and sugar and starch content in the leaves,stems and roots. A feature of the results was a ‘photosynthetic noon-break’phenomenon across all phosphorus application treatments,and stomatal limitation was the main factor responsible for the mid-day decline of net photosynthetic rate （Pn）. Photosynthetically active radiation had the greatest impact on the Pn of alfalfa leaves,while atmospheric CO2 concentration,atmospheric temperature,and atmospheric environmental factors such as relative humidity and vapor pressure deficit based on leaf temp also affected Pn. Principal component analysis showed that alfalfa photosynthetic efficiency in the four P-treatments ranked P2>P1>P3>CK. At the 100 kg·ha-1 phosphorus level（compared to CK）,the hay yield of alfalfa was increased significantly,the soluble sugar contents of leaves,stems,and roots were increased by 11. 6%,5. 0% and 4. 6%,respectively,and the starch contents were increased by 15. 2%,9. 6% and 5. 3%,respectively. Higher overall levels of soluble sugar and starch typically manifested as greater concentration increases in leaves,and relatively smaller increases in roots and stems. The diurnal troughs in Pn,transpiration rate,leaf internal CO2 concentration and water use efficiency（WUE）of alfalfa leaves were less marked in the P treatments,compared with the control treatment. Therefore,appropriate phosphorus application can increase the photosynthetic efficiency of alfalfa leaves,thereby significantly promoting crop growth and development. At the phosphorus（P2O5）application rate of 100 kg·ha-1（P2）,the alfalfa photosynthetic enhancement effect was the most pronounced. © 2022 Editorial Office of Acta Prataculturae Sinica. All rights reserved. 相似文献
8.
林业资源是重要的自然资源之一,对社会经济的建设和林业产业发展都有着较大的影响。想要使林业产业带来更好的经济效益,高质量的管理工作必不可少。如今我国的科学技术水平已经逐渐走到了世界的前列,林业产业也基本实现了机械化,为各个环节工作的顺利实施提供了很大的帮助。机械设备的使用一方面提升了日常工作的效率和质量,另一方面也造成了大量的资源消耗。机械的操作对工作人员的专业能力要求较高,阻碍了林业机械化程度的进一步提高,由此可见在林业机械中应用节能改造技术的重要性。文章对林业资源对社会发展的重要意义进行了阐述,研究了如何融合林业机械和节能技术,希望能为我国林业机械化进程的推进有所帮助。 相似文献
9.
一、农业技术推广工作存在的问题1、推广体系断层,技术服务难以到位。2、是行政指令推广,服务对象难以接受。3、农民素质偏低,应用科技难以普及。4、服务环节单一,推广效果难以提高。5、技术人员知识提高和技术更新难,技术人员外出学习考察的机会少,仅通过杂志、书籍、电视介绍的新技术、新品种,了解一些抽象的信息,没有实地感受,更没有 相似文献
10.