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   130258篇
  免费   8568篇
  国内免费   14797篇
化学   72082篇
晶体学   1196篇
力学   2693篇
综合类   904篇
数学   13064篇
物理学   25135篇
综合类   38549篇
  2024年   207篇
  2023年   962篇
  2022年   2405篇
  2021年   2518篇
  2020年   2882篇
  2019年   2841篇
  2018年   2516篇
  2017年   3595篇
  2016年   3892篇
  2015年   3753篇
  2014年   4942篇
  2013年   8090篇
  2012年   8588篇
  2011年   7427篇
  2010年   6011篇
  2009年   7619篇
  2008年   8020篇
  2007年   9317篇
  2006年   8698篇
  2005年   7477篇
  2004年   6971篇
  2003年   5716篇
  2002年   6601篇
  2001年   4253篇
  2000年   3945篇
  1999年   3623篇
  1998年   2973篇
  1997年   2496篇
  1996年   2151篇
  1995年   1960篇
  1994年   1790篇
  1993年   1526篇
  1992年   1418篇
  1991年   1103篇
  1990年   904篇
  1989年   858篇
  1988年   645篇
  1987年   485篇
  1986年   360篇
  1985年   249篇
  1984年   246篇
  1983年   140篇
  1982年   216篇
  1981年   177篇
  1980年   199篇
  1979年   193篇
  1978年   169篇
  1977年   125篇
  1976年   109篇
  1973年   68篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
本文首先提出逆(反)对策这一新问题,给出了数学模型;探讨了“奇门遁甲”预测理论(术)中的数学问题;通过系统分析“专门遁甲”预测过程,可知它的预测过程隐含着一个特殊的逆(反)对策问题;最后指出逆(反)对策问题的广泛存在并给出案例分析.  相似文献   
182.
Summary. We study a diffusion model of an interacting particles system with general drift and diffusion coefficients, and electrostatic inter-particles repulsion. More precisely, the finite particle system is shown to be well defined thanks to recent results on multivalued stochastic differential equations (see [2]), and then we consider the behaviour of this system when the number of particles goes to infinity (through the empirical measure process). In the particular case of affine drift and constant diffusion coefficient, we prove that a limiting measure-valued process exists and is the unique solution of a deterministic PDE. Our treatment of the convergence problem (as ) is partly similar to that of T. Chan [3] and L.C.G. Rogers - Z. Shi [5], except we consider here a more general case allowing collisions between particles, which leads to a second-order limiting PDE. Received: 5 August 1996 / In revised form: 17 October 1996  相似文献   
183.
Summary. We use the qualitative properties of the solution flow of the gradient equation to compute a local minimum of a real-valued function . Under the regularity assumption of all equilibria we show a convergence result for bounded trajectories of a consistent, strictly stable linear multistep method applied to the gradient equation. Moreover, we compare the asymptotic features of the numerical and the exact solutions as done by Humphries, Stuart (1994) and Schropp (1995) for one-step methods. In the case of -stable formulae this leads to an efficient solver for stiff minimization problems. Received July 10, 1995 / Revised version received June 27, 1996  相似文献   
184.
185.
186.
187.
188.
Unique crystallization and melting behavior in poly(aryl ether ketone ketone) containing alternated terephthalic and isophthalic moieties were studied by time-resolved synchrotron x-ray methods. Recently, this material has been shown to exhibit three polymorphs (forms I, II, and III). In this work, we further investigated their distinctive thermal properties and found that form I is the dominating and the most thermally stable phase while form II is favored by fast nucleation conditions and is the least stable phase. On the other hand, form III represents a minor intermediate phase that usually coexists with form I and can be transferred from form II and to form I. Structural and morphological changes in form I have been followed by simultaneous wide-angle x-ray diffraction (WAXD)/small-angle x-ray scattering (SAXS) measurements during cold- or melt-crystallization and subsequent melting. In all cases, a larger dimensional change was found in the crystallographic a-axis than the b-axis during heating and cooling. This may be due to the greater lateral stress variation with respect to temperature along the a direction of the primary lamellae which is induced by either the formation of secondary lamellae or the preferential chain-folding direction in poly(aryl ether ketone ketone)s. During the phase transitions of form II ← III in the cold-crystallized specimen and form III ← I in the melt-crystallized samples, lamellar variables (long period, lamellar thickness, and invariant) obtained from SAXS remain almost constant. This indicates that the density distribution in the long spacing is independent of the melting in form II or III. For melt-crystallization, the corresponding changes in unit-cell dimensions and lamellar morphology during the annealing-induced low endotherm are most consistent with the argument that these changes are due to the melting of thin lamellar population. © 1995 John Wiley & Sons, Inc.  相似文献   
189.
用中子活化法相对于54Fe(n,P)54Mn反应,在13.50—14.80MeV中子能区测量了Ba(n,x)134Cs,134Ba(n,2n)133Ba,140Ce(n,2n)139Ce,142Ce(n,2n)141Ce和23Na(n,2n)22Na的反应截面.并将所测的结果和其他作者的结果进行了比较,中子能量是用90Zr(n,2n)89m+gZr反应和93Nb(n,2n)92mNb反应截面比法测定的。  相似文献   
190.
选择了结晶性含氟树脂添加改性剂为树脂基体,与炭黑制居复合导电体系。通过这个对体系不同条件下PTC特性的研究,对其配方与加工工艺进行优化。并利用扫描电镜,X射线衍射,DSC等分析测试手段,对体系的各种开矿结构进行了研究,阐明了该导电复合体系的形态结构与性能的关系。  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