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   8811篇
  免费   468篇
  国内免费   774篇
林业   1198篇
农学   775篇
基础科学   923篇
  1447篇
综合类   3559篇
农作物   314篇
水产渔业   355篇
畜牧兽医   631篇
园艺   214篇
植物保护   637篇
  2024年   72篇
  2023年   170篇
  2022年   254篇
  2021年   286篇
  2020年   312篇
  2019年   380篇
  2018年   218篇
  2017年   352篇
  2016年   441篇
  2015年   422篇
  2014年   505篇
  2013年   525篇
  2012年   745篇
  2011年   773篇
  2010年   505篇
  2009年   528篇
  2008年   465篇
  2007年   468篇
  2006年   417篇
  2005年   337篇
  2004年   282篇
  2003年   247篇
  2002年   148篇
  2001年   177篇
  2000年   117篇
  1999年   126篇
  1998年   122篇
  1997年   88篇
  1996年   103篇
  1995年   89篇
  1994年   85篇
  1993年   75篇
  1992年   52篇
  1991年   55篇
  1990年   41篇
  1989年   31篇
  1988年   17篇
  1987年   13篇
  1986年   6篇
  1985年   1篇
  1981年   1篇
  1977年   1篇
  1955年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
陆地棉品种间杂种苏杂16棉铃发育动态研究   总被引:5,自引:6,他引:5  
棉铃发育过程中,苏杂16单铃子棉主的提高表现为二个方面:一是纤维干重的增加,1991~1992两年平均增加10.0%;二是种子重量的提高,两年平均单铃种仁重增加9.4%。单铃纤维干重的增长与棉铃对位叶大小呈正相关关系,与棉铃对位叶中全N含量呈负相关关系.该杂文组合在棉铃发育过程中表现了较强的“源”“库”生理优势,光合产物积累多,营养物质运转快是该组合获得高产的重要生理基础。  相似文献   
72.
The angular frequency and decaying constant of each copmonect for the transient waveform in power systems were obtained by using the discrete Fourier transform; the amplitude and phase angle were calculated in the linear curve fitting method. And all of the parameters obtained above were treated in an unified optimization by using the curve fitting optimization of the least square method of general nonlinear funcrion so as to get the results of waveform analysis. Two examples are included.  相似文献   
73.
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   
74.
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   
75.
This paper presents a new method by using mass and acceleration parameters for balancing inertial force of mechanism. Compared with other balance methods, this one is simple, clear and superior in regularity when the balancing equation of complex mechanism is established, and its solving procedure is also easy. The new methcd is convenient to learn and use as well as convenient to program.  相似文献   
76.
By analyzing the process of enterprise information engineering construction and intra relationship among information system requirement, business process modeling, application system constructing and project management, one of 4 meta model composed of requirement engineering, process engineering, application system engineering and support engineering is proposed for enterprise information engineering. The developments and applications of the business processes and its application systems are integrated into the same development space and application space. Basing on this, a prototype system composed of requirement modeling environment, business process modeling environment, application system modeling environment, and support engineering environment has been designed and built, which is used for supporting enterprise information engineering constructing. It is valued for the enterprise information engineering construction in our country.  相似文献   
77.
In this paper the test results of mixed mode fracture of three kinds of brittle rock under two kinds of stress paths are reported. The fracture mechanism and failure patterns of brittle lock under different stress paths are discussed. Theory analysis and test results show that the Compression- Shear fracture criterion of brittle rock can be expressed:  相似文献   
78.
Bomsster is a key load-bearing part of railway lorry bogie.Because of its inherent defects casting-steel bomsster could not meet the demands of the heavy load,acceleration and security for lorry.So forging process is proposed to form it.The forming performance of forging-steel bomsster is analyzed.A forging technology is presented which realizes two forging-steel bomsster parts formed in one die.With the plastic forming simulation software DEFORM-3D,the simulation and optimization of the forming process of forging bomsster has been taken based on 3D rigid visco-plastic FEM theory.Optimized scheme has been used to direct the pilot product.The results of product's testing and application suggest that the new forging technology is feasible and the performance of the product is credibility and stabilization.The factory has realized large scale production of a series of forging-steel bomsster.Remarkable benefits of both economy and society have been achieved.  相似文献   
79.
The dynamic characteristic of active isolation atuator on flexible foundations was studied under the installation of parallel structure and foundation cancellation.The influencing relationships between active isolation force of the different installation ways and passive isolation system and flexible foundation were analyzed and compared.Scientific basis for selecting installation ways of active isolator is provided in this paper.  相似文献   
80.
In view of the complication of compreliensive evaluation to development projectplanning alternatives,an AHP model for comprehensive evaluation to the alternatives is advanced,the way of determinating the weight of each index affecting the aIternatives' quality is expounded,and the general methods of evaluating the alternatives with the indexes are given.  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