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   94918篇
  免费   3581篇
  国内免费   2772篇
化学   36490篇
晶体学   979篇
力学   7933篇
综合类   165篇
数学   33670篇
物理学   22034篇
  2024年   63篇
  2023年   380篇
  2022年   648篇
  2021年   654篇
  2020年   756篇
  2019年   661篇
  2018年   10888篇
  2017年   10663篇
  2016年   6794篇
  2015年   1647篇
  2014年   1306篇
  2013年   1524篇
  2012年   5356篇
  2011年   12033篇
  2010年   6663篇
  2009年   7008篇
  2008年   7703篇
  2007年   9719篇
  2006年   1264篇
  2005年   2153篇
  2004年   2185篇
  2003年   2516篇
  2002年   1563篇
  2001年   716篇
  2000年   681篇
  1999年   605篇
  1998年   508篇
  1997年   439篇
  1996年   538篇
  1995年   407篇
  1994年   350篇
  1993年   295篇
  1992年   243篇
  1991年   218篇
  1990年   183篇
  1989年   173篇
  1988年   166篇
  1987年   123篇
  1986年   118篇
  1985年   91篇
  1984年   73篇
  1983年   63篇
  1982年   54篇
  1981年   56篇
  1980年   53篇
  1979年   47篇
  1914年   45篇
  1912年   40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
61.
In this paper we obtain a number of Maharam-type slice integral representations, with respect to scalar measures, for positive projections in Dedekind complete vector lattices and f-algebras. AMS Classification: 47B65, 46A40, 06F25  相似文献   
62.
We define analytic functions within Clifford Algebras CL, and study their trigonometric properties. We write the addition formulas when their arguments, A and B in CL, commute, this generalizes ordinary trigonometry. We examine in particular the case A2 = 1.   相似文献   
63.
In the present paper it is shown that if S1 and S2 are two Clifford topological semigroups satisfying certain conditions and T is an isometric isomorphism of LUC(S1*) onto LUC(S2*), then T maps S1 topologically isomorphically onto S2. Furthermore, T maps M l n(S1) (M(S1), respectively) isometrically isomorphically onto M l n(S2) (M(S2), respectively). Indeed, we have obtained a generalization of a well-known result of Ghahramani, Lau and Losert for locally compact groups to a more general setting of Clifford topological semigroups.  相似文献   
64.
The irreversibility field (Hirr) of Y-based superconductor is much higher than that of Bi-based superconductor. Y-based superconductor is capable of maintaining stable electrical currents in high magnetic field and electric field, so it is a better suited mate-rial for electric-current applications. Commonly, the Y-based tapes comprise a YBCO thick film deposited on a flexible substrate, typically with an intermediate buffer layer, and an overcoat of noble metal. In this process, the interm…  相似文献   
65.
In this paper, a very useful numerical technique has been developed for analyzing the transient characteristics of a planar-spiral inductor on-chip. A locally conformal technique and an alternating-direction implicit scheme are applied to the finite-difference time-domain method. A formulation for solving three dimensional Maxwell’s equations is proposed. Using the proposed method, various parameters of the planar-spiral inductors have been analyzed and an equivalent circuit, which includes frequency-independent circuit elements, has been introduced. Highly computational efficiency is implemented. Numerical results show excellent agreement with the measured data over a wide frequency range.  相似文献   
66.
This paper describes some work carried out in the Scientific Research and Development Branch (SRDB) of the Home Office, intended to contribute to an overall aim of building up internal expertise in the field of expert systems. This was done by carrying out a number of pilot and demonstrator projects, two of which are described in some detail. The plan, which proved successful, was to build as far as possible on the relevant skills already possessed by an OR group in the branch. The lessons learned from these are summarized in the hope that they will be of use to other groups who wish to become involved in this important area.  相似文献   
67.
68.
69.
What strategy should a football (soccer, in American parlance) club adopt when deciding whether to sack its manager? This paper introduces a simple model assuming that a club's objective is to maximize the number of league points that it scores per season. The club's strategy consists of three choices: the length of the honeymoon period during which it will not consider sacking a new manager, the level of the performance trapdoor below which the manager get the sack, and the weight that it will give to more recent games compared to earlier ones. Some data from the last six seasons of the English Premiership are used to calibrate the model. At this early stage of the research, the best strategy appears to have only a short honeymoon period of eight games (much less than the actual shortest period of 12 games), to set the trapdoor at 0.74 points per game, and to put 47% of the weight on the last five games. A club adopting this strategy would obtain on average 56.8 points per season, compared to a Premiership average of 51.8 points.  相似文献   
70.
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