首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   24210篇
  免费   1490篇
  国内免费   2856篇
林业   2417篇
农学   2105篇
基础科学   3254篇
  5097篇
综合类   10509篇
农作物   865篇
水产渔业   981篇
畜牧兽医   1703篇
园艺   342篇
植物保护   1283篇
  2024年   324篇
  2023年   702篇
  2022年   995篇
  2021年   931篇
  2020年   1019篇
  2019年   1097篇
  2018年   748篇
  2017年   1109篇
  2016年   1332篇
  2015年   1178篇
  2014年   1280篇
  2013年   1387篇
  2012年   1767篇
  2011年   1817篇
  2010年   1476篇
  2009年   1382篇
  2008年   1311篇
  2007年   1370篇
  2006年   1176篇
  2005年   977篇
  2004年   759篇
  2003年   624篇
  2002年   488篇
  2001年   385篇
  2000年   365篇
  1999年   329篇
  1998年   315篇
  1997年   293篇
  1996年   261篇
  1995年   260篇
  1994年   209篇
  1993年   181篇
  1992年   170篇
  1991年   159篇
  1990年   145篇
  1989年   101篇
  1988年   64篇
  1987年   28篇
  1986年   12篇
  1985年   3篇
  1984年   4篇
  1981年   1篇
  1980年   9篇
  1979年   2篇
  1978年   2篇
  1976年   1篇
  1963年   2篇
  1962年   2篇
  1956年   2篇
  1955年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
Magnetorheological materials are a class of smart materials whose reological properties may be rapidly varied by application of magnetic field. By a simple mechanical mold, a visco-plastic model for the materials is developed. It is shown that the model can describe the variation of the mechanical properties for the Magnetorheological materials in the different magnetic field. The result is shown that the model can characterize the mechanical properties of Magnetorheological Materials in plastic and viscous variation.  相似文献   
182.
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   
183.
This paper analyzes the limitation of regarding the weighted average cost of capital as the optimal standard of capital structure in the traditional capital structure decision-making method, and analyzes the view that the capital structure is affected by many factors,such as earning power, long-term stability of operating, the attitudes held by owners and operators, the attitudes held by creditors and financial risk. With the example, the affecting factors of the capital structure is analyzed. The fuzzy synthetic evaluation model are employed to decision-making of the capital structure. This article also shows the key point of its application.  相似文献   
184.
The high-precision displacement measuring technology of optic-measuring mechanics is, for the first time,successfully applied on the similar model of the model land-layer with a new-type variable modulus of elasticity. The angle of movement and the distributed displacement of upper and lower rock-layers are measured. The technology is a combination of laser's technology and the modern chemical sticker-it is called the sticking moire interferometry. Compared with the measured values, the result is very satisfactory.  相似文献   
185.
Aero-elastic model design is the precondition of full bridge aero-elastic model tunnel tests. The full aero-elastic bridge model design of long span arch bridge is discussed. The effect on the model design of different transverse rod space and bend stiff is analyzed in detail. Different scheme need to be designed according to the transverse rod stiff. Considering the changing section dimensional arches, the method of projecting the spatial arches to the plane arches, then designing the plane arches, at last projecting the plane arches to the spatial arches is proposed at first. The results show that the method is effective.  相似文献   
186.
The characteristics of pretreatment and cyclic control stream are analysed:the form of cyclic embedded hardware circuit,the idea for designing the pretreatment program.The chart model of the system is established preliminarily.  相似文献   
187.
Additional time delay of arrival resulted from non-line of sight(NLOS)propagation and muti-path effect in(cellular) environment is the dominant factor resulting in TDOA location error,study on the statistical property of TDOA error is useful for improving the accuracy of TDOA location.Based on the exponential distribution property of NLOS propagation delay,and considering the system error resulted from the signal detection,the authors establish a statistical model of arrival time and a model of TDOA error distribution by statistics when non-light of sight and multi-path propagation exist.The models reflect the statistical property of arrival time and TDOA error in cell network,the simulation shows that the proposed models have a good accuracy and a satisfactory behavior.  相似文献   
188.
In this paper, taking a D1201 spindle as an example, we discuss the dynamic analysis of spindle by using the theory of the complex model, we also analyse the factors which effect the dynamic characterics of spindle and give results which arc reference value to improving the structure of spindle,  相似文献   
189.
190.
To research the problem of plastic art design and emulation of products with the virtual reality technology can short the product development cycle and reduce the cost. This paper discusses the information based on the product feature ,solid model with parameters, the structure and function of this system. Combined the product properties with its solid model. Proposed a method with CAD to create the model of the product based on features in the product design. Expressed its feature parameter and shape of model fully .In the case for a deceleration box the feature model has solved the problem of physical information ,geometry information and the informative process in its production management system efficiently.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号