全文获取类型
收费全文 | 9360篇 |
免费 | 500篇 |
国内免费 | 1247篇 |
专业分类
林业 | 881篇 |
农学 | 814篇 |
基础科学 | 2823篇 |
1837篇 | |
综合类 | 3176篇 |
农作物 | 292篇 |
水产渔业 | 357篇 |
畜牧兽医 | 411篇 |
园艺 | 108篇 |
植物保护 | 408篇 |
出版年
2024年 | 72篇 |
2023年 | 186篇 |
2022年 | 333篇 |
2021年 | 313篇 |
2020年 | 353篇 |
2019年 | 413篇 |
2018年 | 298篇 |
2017年 | 451篇 |
2016年 | 504篇 |
2015年 | 409篇 |
2014年 | 530篇 |
2013年 | 559篇 |
2012年 | 755篇 |
2011年 | 736篇 |
2010年 | 569篇 |
2009年 | 556篇 |
2008年 | 535篇 |
2007年 | 581篇 |
2006年 | 489篇 |
2005年 | 415篇 |
2004年 | 275篇 |
2003年 | 322篇 |
2002年 | 221篇 |
2001年 | 176篇 |
2000年 | 175篇 |
1999年 | 134篇 |
1998年 | 117篇 |
1997年 | 117篇 |
1996年 | 94篇 |
1995年 | 77篇 |
1994年 | 62篇 |
1993年 | 58篇 |
1992年 | 53篇 |
1991年 | 30篇 |
1990年 | 50篇 |
1989年 | 26篇 |
1988年 | 29篇 |
1987年 | 17篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1956年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
联合国粮食及农业组织2018年向全球发布草地贪夜蛾Spodoptera frugiperda是重要的预警害虫。据报道,2019年我国已有26个省(区、市)的作物受到草地贪夜蛾为害。目前已经发现草地贪夜蛾幼虫对某些化学农药产生抗性的现象,为缓解其抗药性产生,具有主动寻找寄主害虫的昆虫病原线虫为草地贪夜蛾的生物防治提供了应用潜能。该文从昆虫病原线虫高效侵染种(品系)及其浓度、共生菌、草地贪夜蛾幼虫易感龄期、田间致死力及影响防控效果的因素等方面进行综述,以期为田间有效利用昆虫病原线虫防治草地贪夜蛾提供参考。 相似文献
72.
Ruirui Zhang Andrew J Hewitt Liping Chen Longlong Li Qing Tang 《Pest management science》2023,79(11):4123-4131
The application of pesticides is not simply delivering chemicals to the target area. It also involves considering the negative aspects and developing strategies to deal with them during the application process, to ensure the maximization of pesticides use efficiency and the maintenance of the ecosystem. Unmanned aerial vehicle (UAV) sprayers demonstrate unique advantages compared to traditional ground sprayers, particularly in terms of maneuverability and labor intensity reduction, showed great potential for chemical application in pest control. It is undeniable that there exist challenges in the practice of UAV spraying, such as higher potential risks of pesticide drift or pathogen transmission, uncertainty canopy deposition for different crops, and unexpected leaf breakage induced by downwash flow. Maximizing the utilization of downwash flow while avoiding lateral air movement outside the intended target crop area is a major issue for chemical application with UAV sprayers, particularly in light of the increasingly apparent consensus on the need for enhanced environmental protection during the chemical application process. It must be considered that the operation strategy in different scenarios and for different crop targets is not the same, unique requirements should be given on nozzle atomization, flight parameters, adjuvants and aircraft types in specific working situations. In future, the implementation of spray drift prediction, technical procedures development, and other solutions aimed at reducing pesticide drift and improving deposition quality, is expected to promote the adoption of UAV sprayers by more farmers. © 2023 Society of Chemical Industry. 相似文献
73.
高寒草甸斑块的根-土复合体对局部水土流失过程具有调控作用,为研究其特征及抗侵蚀效应,本研究选取三江源区达日县境内典型中度退化草甸的植被斑块为研究对象,调查草甸斑块中心与边缘植物群落特征,测定斑块边缘0~10 cm土层和斑块中心0~20 cm土层的容重、含水率、毛管孔隙度等土壤物理性质,并开展单根拉伸和根-土复合体直剪试验。结果表明:受优势种矮嵩草的分布影响,地上生物量主要分布在斑块中心,根系主要分布在0~10 cm土层;斑块中心区域土壤抗剪强度、内摩擦角和粘聚力均随土层深度的增加而减小;斑块边缘区域土壤粘聚力,抗剪强度明显高于斑块中心区域,草甸斑块植物根系是土壤抗剪强度的主要影响因素。草甸斑块根-土复合体能明显增加退化草甸土壤的抗侵蚀能力,研究结果可为深入研究高寒草甸根系固土功能及水土流失调控提供科学依据。 相似文献
74.
75.
76.
对砌石拱坝的加高倍厚中新、老坝体结构面,用有限元软件ANSYS结合接触理论进行计算,并分析结果得出:温升、水压力和淤沙压力使结合面上的接触压力增大,从而接触摩擦应力较大,有利于结合面的结合,而结合面在温降的作用下有脱离的趋势。 相似文献
77.
In order to analyze the reason why the Spiral Up-flow Reactor system has excellent removal effect of COD, N and P, the authors use PHOENICS, a computational fluid dynamics program, to investigate the hydraulic characteristics and flow model of the anaerobic part of Spiral uP-flow reactor. The result shows that the fluid in the reactor unit flowed upward by the spiral way, and that flow pattern was combined by plug flow and complete-mix flow, and that the percentage of plug flow was about sixty-five percent. Spiral Up-flow Reactor units the Characteristics of PFR and CSTR, which makes it work well. 相似文献
78.
79.
The processing characteristics of the front bumper bracket are analyzed,and a reasonable process scheme is worked out.The three-dimensional sheet metal forming analysis software PAM-STAMP are adopted to simulate the bracket's drawing process.Then the surface of die is proved fine through analyzing the FLD diagrams and the forming results.An economical and optimized die structure is decided,and a complete set of dies of the bracket is designed.The spacing block is added in the sizing mold,which control the size precision of end products and assembling columns actively,and finally the certified products.The material utility and the labor productivity are raised,the production cost is saved,and the mold design quality and the efficiency are improved effectively. 相似文献
80.
Boiler is an important facility in power plant , the safety and economy of unit is affected by it. Studying the dynamic of boiler can improve the knowledge about boiler , which is important for. Features of MMS are introduced based on MMS simulation setting, and the real time capable module and non real time capable module are compared from principle. Real time capable dynamic model of boiler and non real time capable dynamic model of boiler of 330 MW unit are established . The experimental results show that the dynamic process of two type model accords with the mechanism of the object , at the same time, the validity of real time capable module is discussed . 相似文献