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   11497篇
  免费   338篇
  国内免费   1217篇
林业   2356篇
农学   741篇
基础科学   2697篇
  1440篇
综合类   4565篇
农作物   206篇
水产渔业   172篇
畜牧兽医   365篇
园艺   388篇
植物保护   122篇
  2024年   32篇
  2023年   108篇
  2022年   238篇
  2021年   292篇
  2020年   336篇
  2019年   386篇
  2018年   225篇
  2017年   347篇
  2016年   448篇
  2015年   396篇
  2014年   658篇
  2013年   586篇
  2012年   1083篇
  2011年   950篇
  2010年   757篇
  2009年   815篇
  2008年   706篇
  2007年   904篇
  2006年   751篇
  2005年   581篇
  2004年   486篇
  2003年   340篇
  2002年   266篇
  2001年   191篇
  2000年   175篇
  1999年   136篇
  1998年   117篇
  1997年   130篇
  1996年   94篇
  1995年   110篇
  1994年   84篇
  1993年   62篇
  1992年   60篇
  1991年   57篇
  1990年   54篇
  1989年   33篇
  1988年   26篇
  1987年   17篇
  1986年   9篇
  1982年   1篇
  1981年   1篇
  1980年   1篇
  1978年   1篇
  1977年   1篇
  1973年   1篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
41.
机电产品的包装需要耗费大量的原木,对环境造成了极大的影响,也增加了机电产品的生产经营成本。文章从低碳和成本约束的角度,对机电产品包装概念设计的模型进行了分析和探讨。  相似文献   
42.
人们关注的中心为“图”,背景的部分为“底”,“图形”与“基底”的关系指一个封闭的式样与另一个和它同质的非封闭的背景之间的关系。图底关系理论在城市建筑设计中大有可为。  相似文献   
43.
为解决网络驱动的协同设计三维几何模型共享技术的实现问题,提出一种基于特征流的混合式3D几何模型共享机制,提出了基于多粒度的产品几何模型数据结构描述方法和面向模型局部操作的"游历-查询"特征的历史记录来重构模型的特征建模方法。建立了网络驱动的、基于CORBA/JAVA中间插件的3D几何模型特征信息同步传输和共享平台,CORBA/JAVA平台支持多用户、分布数据管理、消息传输、网络通讯以及可扩展性,通过该平台实现了三维模型的实时传输和共享。  相似文献   
44.
45.
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   
46.
In urban design, only by continuous and dynamic research work from design to finally putting it into practice, can we made good control on city appearance. This article analyzes nowadays defects in our urban design from two aspects as the result establishment and validated control, and tries to conceive a feasibility plan to solve the problem.  相似文献   
47.
According to the needs of setting up a professional system based on motorcycle design,the CBR(case based reasoning) and RBR(rule based reasoning) methods are introduced.After discussing the difference between the two kinds of reasoning,a method of integrating them into the motorcycle design flow is put forward to realize the design reusable technology and improve the design efficiency,by using the CBR in the step of selecting the similar motorcycle and the RBR in project's modification according to correlative rules.  相似文献   
48.
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   
49.
The green is as a symbol of no pollution,no public harm and environmental protection. The green automobile is the inevitable results that the automobile technique continuously developes. A new style vehicle--the green automobile is the urgent solicit of environmental protection is developed. The automobile industry can develop continuously. This article mainly discusses the importance of the green auto_mobile's research and development,the development status in quo and prospect of the green auto_mobile technique in the world,and states the relationship between the green automobile technique and environmental protection from green technical system theoretically clarify the study of green automobile,including its design and the system,the manufacture and its technology,the energy,the rebuild engineering and a series of subjects. How to evaluate the cycle and the evaluable mark of the green automobile,the prospect of green automobile are pointed out.  相似文献   
50.
This paper analyzes the structure and line current waveform of 3-phase AC voltage regulation circuit. As an application of 3-phase AC voltage regulation circuit, a high-frequency welding device's simulation model and harmonic analysis of line current are presented. Results of simulation are compared to field measurements. The two are in a good agreement, so this simulation model is correct. Two single-tuning filters and one second-order HPF are designed according to the device's harmonic condition. Simulation results of the circuit with filters indicate decrease of the harmonics in current of power supply, and the waveform is close to sinusoidal wave, which prove correctness of the solution to harmonics pollution.  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