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   101895篇
  免费   2330篇
  国内免费   2080篇
化学   31870篇
晶体学   923篇
力学   7536篇
综合类   95篇
数学   33215篇
物理学   19411篇
无线电   13255篇
  2024年   51篇
  2023年   298篇
  2022年   341篇
  2021年   468篇
  2020年   492篇
  2019年   424篇
  2018年   12108篇
  2017年   11733篇
  2016年   7420篇
  2015年   1450篇
  2014年   1070篇
  2013年   1291篇
  2012年   5217篇
  2011年   12674篇
  2010年   7573篇
  2009年   7590篇
  2008年   8069篇
  2007年   10465篇
  2006年   1086篇
  2005年   2337篇
  2004年   2318篇
  2003年   2658篇
  2002年   1519篇
  2001年   663篇
  2000年   657篇
  1999年   566篇
  1998年   631篇
  1997年   507篇
  1996年   564篇
  1995年   434篇
  1994年   393篇
  1993年   305篇
  1992年   268篇
  1991年   230篇
  1990年   225篇
  1989年   158篇
  1988年   153篇
  1987年   160篇
  1986年   151篇
  1985年   125篇
  1984年   101篇
  1983年   74篇
  1982年   79篇
  1981年   69篇
  1980年   68篇
  1979年   61篇
  1978年   50篇
  1914年   45篇
  1909年   41篇
  1908年   40篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
In this paper we suggest a unique model for estimating the operating cost of each of three waste-collection systems. Under the traditional system, which is widely used, waste is typically collected in plastic bags and a three-man crew is needed on each vehicle. The other two systems require a one-man crew for vehicle collecting street containers. The side-loader system with fixed body automatically empties street containers into the vehicle body and empties the load at the disposal site. The side-loader system with demountable body allows the separation of the waste collection phase from transport to the disposal site, since the vehicle body can be demounted. We also present two case studies and show how the estimation of operating costs is a critical issue in decisions regarding the type of system to be used for waste collection.  相似文献   
82.
A nonlinear, compressible, non-isothermal gravity wave model that involves photochemistry is used to study the effects of gravity wave on atmospheric chemical species distributions in this paper. The changes in the distributions of oxygen compound and hydrogen compound density induced by gravity wave propagation are simulated. The results indicate that when a gravity wave propagates through a mesopause region, even if it does not break, it can influence the background distributions of chemical species. The effect of gravity wave on chemical species at night is larger than in daytime.  相似文献   
83.
Using the membrane model which is based on brick wall model, we calculated the free energy and entropy of Garfinkle-Horne dilatonic black hole due to arbitrary spin fields. The result shows that the entropy of scalar field and the entropy of Fermionic field have similar formulas. There is only a coefficient between them.  相似文献   
84.
关于广义函数δ(x)的讨论   总被引:1,自引:0,他引:1  
本文应用《电气子教学学报》之邀约而写,旨在针对一些读者对该韩过去刊出的有关广义函数δ(x)的文章中的质疑,从数学角度提供一些有助于正确认识、处理和运用广义函数的辅助材料。  相似文献   
85.
介绍了天线近场测量的基本原理和HD-1型平面近场测试系统,并对近场测量在实际天线测试中的应用情况、发展方向和应用前景等作了简单的描述。  相似文献   
86.
 Using elementary graded automorphisms of polytopal algebras (essentially the coordinate rings of projective toric varieties) polyhedral versions of the group of elementary matrices and the Steinberg and Milnor groups are defined. They coincide with the usual K-theoretic groups in the special case when the polytope is a unit simplex and can be thought of as compact/polytopal substitutes for the tame automorphism groups of polynomial algebras. Relative to the classical case, many new aspects have to be taken into account. We describe these groups explicitly when the underlying polytope is 2-dimensional. Already this low-dimensional case provides interesting classes of groups. Received: 13 December 2001 / Revised version: 24 June 2002 The second author was supported by the Deutsche Forschungsgemeinschaft, INTAS grant 99-00817 and TMR grant ERB FMRX CT-97-0107 Mathematics Subject Classification (2000): 14L27, 14M25, 19C09, 52B20  相似文献   
87.
This paper verifies the singularity conjecture for Jacobi forms with higher degree in some typical cases, and gives constructions for the Jacobi cusp forms whose Fourier coefficients can be expressed by some kind of Rankin-typeL-series.  相似文献   
88.
It is explicitly shown that if phase transition occurs at the core of a newborn neutron star with moderately strong magnetic field strength, which populates only the electron’s Landau levels, then in the β -equilibrium condition, the quark core is energetically much more unstable than the neutron matter of identical physical condition.  相似文献   
89.
90.
For more than 25 years production has helped to sharpen our understanding of QCD. In proton induced reaction some observations are rather well understood while others are still unclear. The current status of the theory of production will be sketched, paying special attention to the issues of formation time and re-interaction in a nuclear medium.  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