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   470篇
  免费   47篇
  国内免费   43篇
化学   61篇
晶体学   2篇
力学   51篇
综合类   11篇
数学   306篇
物理学   129篇
  2022年   5篇
  2021年   12篇
  2020年   16篇
  2019年   8篇
  2018年   13篇
  2017年   16篇
  2016年   17篇
  2015年   18篇
  2014年   25篇
  2013年   26篇
  2012年   23篇
  2011年   19篇
  2010年   21篇
  2009年   23篇
  2008年   39篇
  2007年   26篇
  2006年   37篇
  2005年   29篇
  2004年   25篇
  2003年   26篇
  2002年   29篇
  2001年   14篇
  2000年   10篇
  1999年   10篇
  1998年   21篇
  1997年   11篇
  1996年   11篇
  1995年   1篇
  1994年   5篇
  1993年   1篇
  1992年   2篇
  1991年   3篇
  1990年   3篇
  1988年   6篇
  1987年   3篇
  1986年   3篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
排序方式: 共有560条查询结果,搜索用时 50 毫秒
21.
This paper improves an old theorem about a rectangular hyperbola : its centre lies on the pedal circle of any point on with respect to any triangle inscribed in . We also prove that an analogous result holds for Cevian circles. These results are used to obtain new characterisations of the Feuerbach, Jarabek, and Kiepert hyperbolas of a triangle.  相似文献   
22.
We study a two-level atom interacting with an electromagnetic wave of circle polarization, and work out the wave functions, the energy values and momentum values of the atom. PACS: 32.80.-t, 03.65.Ge  相似文献   
23.
微小型光栅光谱仪光学系统的特点与光谱分辨率的提高   总被引:3,自引:0,他引:3  
微小型光谱仪的设计制作可以采用多种方法,其结构特点和光谱分辨率也各不相同,目前实用高光谱分辨率微小型光谱仪采用的是光栅色散型光学系统.简要回顾了微小型光谱仪的发展过程,分析了典型的光栅色散型微小型光谱仪采用的光学系统,如基于罗兰圆的光学系统,基于Czerny-Turner的光学系统的特点,总结了提高微小型光栅光谱仪光谱分辨率采用的方法和技术,特别是解决光谱仪的微小型化和光谱分辨率之间的矛盾以及测量光谱范围和光谱分辨率之间的矛盾的方法,从而为新型微小型光谱仪的研制提供经验和借鉴.  相似文献   
24.
In this work, we establish Weyl-Titchmarsh theory for symplectic difference systems. This paper extends classical Weyl-Titchmarsh theory and provides a foundation for studying spectral theory of symplectic difference systems.  相似文献   
25.
A simple dynamical condition is given for line fields within a contact structure, which is satisfied exactly by those line fields which are common kernels of contact circles. Some convexity properties are established which are useful in the study of contact circles up to homotopy. A necessary condition for extending a contact form to a contact circle is given. Based on work of Lisca–Matić and Honda, concrete examples are given which show that the condition is not just homotopic but a geometric one. The paper ends with an open question. Dedicated to Fernando Varela, for many reasons.  相似文献   
26.
Circle numbers are defined to reflect the Euclidean area-content and, for p ≠ 2, suitably defined non-Euclidean circumference properties of the l 2,p -circles, p ∈ [1, ∞]. The resulting function is continuous, increasing, and takes all values from [2, 4]. The actually chosen dual l 2,p -geometry for measuring the arc-length is closely connected with a generalization of the method of indivisibles of Cavalieri and Torricelli in the sense that integrating such arc-lengths means measuring area content. Moreover, this approach enables one to look in a new way into the co-area formula of measure theory which says that integrating Euclidean arc-lengths does not yield area content except for p = 2. The new circle numbers play a natural role, e.g., as norming constants in geometric measure representation formulae for p-generalized uniform probability distributions on l 2,p -circles.  相似文献   
27.
曹志刚  柴春红 《大学数学》2008,24(3):117-120
针对圆形工件合格性检验问题建立了两个优化模型,运用Matlab软件进行编程求解,确定了圆心的位置,据此判断出工件一为正品,工件二为次品.接下来为判断能否将次品经过再加工使其成为正品,建立了模型三,并指出了对工件二的简单再加工方法.  相似文献   
28.
This paper presents a new interpretation of a digital circle in terms of the distribution of square numbers in discrete intervals. The number-theoretic analysis that leads to many important properties of a digital circle succinctly captures the original perspectives of digital calculus and digital geometry for its visualization and characterization. To demonstrate the capability and efficacy of the proposed method, two simple algorithms for the construction of digital circles, based on simple number-theoretic concepts, have been reported. Both the algorithms require only a few primitive operations and are completely devoid of any floating-point computation. To speed up the computation, especially for circular arcs of high radii, a hybridized version of these two algorithms has been given. Experimental results have been furnished to elucidate the analytical power and algorithmic efficiency of the proposed approach. It has been also shown, how and why, for sufficiently high radius, the number-theoretic technique can expedite a circle construction algorithm.  相似文献   
29.
谢莉  李纯红  李进东 《数学杂志》2006,26(2):197-202
本文研究了圆内零级亚纯函数的充满圆序列,获得了在关于型函数的Borel点附近存在充满圆序列,从而得到了Hayman点的存在性.  相似文献   
30.
Branch length similarity (BLS) entropy is defined in a network consisting of a single node and branches. In this study, we mapped the binary time-series signal to the circumference of the time circle so that the BLS entropy can be calculated for the binary time-series. We obtained the BLS entropy values for “1” signals on the time circle. The set of values are the BLS entropy profile. We selected the local maximum (minimum) point, slope, and inflection point of the entropy profile as the characteristic features of the binary time-series and investigated and explored their significance. The local maximum (minimum) point indicates the time at which the rate of change in the signal density becomes zero. The slope and inflection points correspond to the degree of change in the signal density and the time at which the signal density changes occur, respectively. Moreover, we show that the characteristic features can be widely used in binary time-series analysis by characterizing the movement trajectory of Caenorhabditis elegans. We also mention the problems that need to be explored mathematically in relation to the features and propose candidates for additional features based on the BLS entropy profile.  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