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   78293篇
  免费   3914篇
  国内免费   8790篇
林业   9198篇
农学   12283篇
基础科学   7088篇
  12571篇
综合类   24706篇
农作物   4131篇
水产渔业   2932篇
畜牧兽医   10228篇
园艺   2878篇
植物保护   4982篇
  2024年   206篇
  2023年   823篇
  2022年   2188篇
  2021年   3019篇
  2020年   2878篇
  2019年   2708篇
  2018年   1932篇
  2017年   2867篇
  2016年   2674篇
  2015年   3430篇
  2014年   3377篇
  2013年   4173篇
  2012年   5030篇
  2011年   5430篇
  2010年   5140篇
  2009年   4672篇
  2008年   4423篇
  2007年   4819篇
  2006年   4360篇
  2005年   3910篇
  2004年   1922篇
  2003年   1756篇
  2002年   1732篇
  2001年   1733篇
  2000年   1912篇
  1999年   1954篇
  1998年   1757篇
  1997年   1503篇
  1996年   1378篇
  1995年   1298篇
  1994年   1135篇
  1993年   1074篇
  1992年   889篇
  1991年   719篇
  1990年   625篇
  1989年   448篇
  1988年   390篇
  1987年   269篇
  1986年   144篇
  1985年   62篇
  1984年   51篇
  1983年   52篇
  1982年   36篇
  1981年   48篇
  1980年   22篇
  1979年   11篇
  1965年   4篇
  1964年   4篇
  1956年   5篇
  1955年   2篇
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
891.
Intelligent recognition system of gun code is designed , which achieves online recognition of gun code. We applied video camera to get image, and some special technique in this deformed character recognition. As well, we applied dynamic template matching to get a better result.  相似文献   
892.
In order to settle some problems involved in applying ANSYS into nonlinear Finite Element Analysis of RC structure,this paper discusses the nonlinear FEM method for staggered joint,incorporating its experimental result.The main solved problems are as follows:(1) The fundamental process of nonlinear FEM analysis;(2) How to model the behaviors of reinforcement and concrete respectively;(3) How to model the bond-slip relationship between reinforcement and concrete.  相似文献   
893.
894.
The adsorption quantities of methane on anthracite and its char at different tem-perature and time were measured by using volumetric niethod. The corresponding adsorption formula-is presented. The experimental results have shown that the diffusion acti-vation energies of methane in the anthracite and its char are 14.3 kJ/mol and 26. 3 kJ/mol.It issuggested that the diffusion process of methane could be the flow through the micropores in the an-thracite and its char.  相似文献   
895.
This paper presents the lately released frame work for Client / Server applica-tions software development, stressing on the characteristics of its OOP and Multi-DataBase supports.  相似文献   
896.
This paper studies the effects of ground stress and ground electrical field onmethane transpont in coal seam. A gas seepage equation is set up based on the principles of seepagetheory,which takes the ground stress and ground electrical field into considerationz  相似文献   
897.
In this paper,the electrical field distribution along the polluted cylindrical insu-lator before a nd after the local a re appea rs is calculated with the optim lzed pa rtially cha rge simula-tinn method and measured with the pockels device. Based on the calculating and measuring results,the in fluen ce of the electric field distri bu tion on the propagation of local a re in the flashover ofcyIlndrical insufator under various conditions is analyzed systematieally.  相似文献   
898.
This paper uses n nature numbers from 1 to n to form a numerical table of twofold maoic square' s necessary condition. It also proves that x>n(n-1) and the numerical table is the sufficient condition of the basic solution.  相似文献   
899.
In this paper, a new high - strength worm gearing, named'rolling cone enveloping hourglass worm gearing' is proposed. With such a new type of worm gearing, the motion form between meshing tooth surfaces is changed in nature. A systematic theoretical study. a lot of numerical calculations and parameter analyses have been done. Based on these analyses,the optimum design of worm gearing is obtained. It is shown that this worm gearing possesses the virtues of high efficiency, large load capacity, long life -span and easy meanufacture.  相似文献   
900.
The spraying codeposition process is used to produce metal matrix paniculate composites, whose technical procedure and main processing parameters are analyzed. The microstructure of the composites is examined and the properties are tested. The solidification characteristics in the spraying deposition and solidification process are discussed. The results indicate that several problems involved in conventional methods can be overcome with this technique to preduce metal matrix paniculate composites. The reinforce particles are dispersed in the matrix homogeneously without solidification segregation. Compared with the matrix alloy,the composite proves to be harder and has excellent wear resistance.  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