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   53497篇
  免费   3290篇
  国内免费   3550篇
化学   21024篇
晶体学   447篇
力学   4320篇
综合类   525篇
数学   12664篇
物理学   21357篇
  2024年   76篇
  2023年   459篇
  2022年   1151篇
  2021年   1157篇
  2020年   1190篇
  2019年   1199篇
  2018年   1044篇
  2017年   1218篇
  2016年   1380篇
  2015年   1094篇
  2014年   1775篇
  2013年   3378篇
  2012年   2058篇
  2011年   2321篇
  2010年   1893篇
  2009年   3065篇
  2008年   3281篇
  2007年   3683篇
  2006年   3113篇
  2005年   2441篇
  2004年   2064篇
  2003年   2348篇
  2002年   2730篇
  2001年   2044篇
  2000年   1984篇
  1999年   1648篇
  1998年   1674篇
  1997年   961篇
  1996年   915篇
  1995年   794篇
  1994年   817篇
  1993年   618篇
  1992年   705篇
  1991年   462篇
  1990年   432篇
  1989年   337篇
  1988年   319篇
  1987年   312篇
  1986年   277篇
  1985年   279篇
  1984年   269篇
  1983年   151篇
  1982年   209篇
  1981年   193篇
  1980年   125篇
  1979年   162篇
  1978年   131篇
  1977年   125篇
  1976年   82篇
  1973年   63篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
本文利用自制云雾室把微观粒子的运动转化为宏观现象,从而供实验观察和研究。  相似文献   
42.
It is shown that the potential perturbation that shifts a chosen standing wave in space is a block of potential barrier and well for every wave bump between neighbouring knots. The algorithms shifting the range of the primary localization of a chosen bound state in a potential well of finite width are as well applicable to the scattering functions if states of the continuous spectrum are considered as bound states normalized to unity but distributed on an infinite interval with vanishing density. The potential perturbations of the same type on the half-axis concentrate the scattering wave at the origin, thus creating a bound state embedded into the continuous spectrum (zero width resonance).  相似文献   
43.
SomeNotesaboutTanaka'sEquationYanZhibin(严质彬)(DepartmentofMathematics,HarbinInstituteofTechnology,Harbin,150001)AbstractLet{Wt...  相似文献   
44.
A special family of partitions occurs in two apparently unrelated contexts: the evaluation of one-dimensional configuration sums of certain RSOS models, and the modular representation theory of symmetric groups or their Hecke algebras Hm. We provide an explanation of this coincidence by showing how the irreducible Hm-modules which remain irreducible under restriction to Hm_1 (Jantzen–Seitz modules) can be determined from the decomposition of a tensor product of representations sln.  相似文献   
45.
本文是[1,12]的继续,研究描述架中概念的结构;本文讨论后半部分,内容涉及概念内涵与外延的转换,清晰关系的内投影与内变换,概念的结构*以及有关问题的注记。  相似文献   
46.
In this paper we show that the Boltzmann weights of the three-dimensional Baxter-Bazhanov model give representations of the braid group if some suitable spectral limits are taken. In the trigonometric case we classify all possible spectral limits which produce braid group representations. Furthermore, we prove that for some of them we get cyclotomic invariants of links and for others we obtain tangle invariants generalizing the cyclotomic ones.  相似文献   
47.
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   
48.
We consider an optimal growth (multi-sector) model with nonconvex technology. Using the Clarke results on generalized gradients, we prove that the value function has left and right derivatives with respect to the initial capital stock, without requiring supermodularity assumptions.  相似文献   
49.
We have observed a remarkable two-armed spiral in the collapse process of a floating monolayer at the air-water interface by phase contrast microscopy. This demonstrates that the floating monolayer as a form of soft condensed matter reorganizes itself due to a certain kind of macroscopic or collective behavior of molecules as it collapses. This pattern formation is caused by the breakdown of a critical dynamical balance between the deformation of solid domain and the applied surface pressure. The fragility as well as the flexibility of the floating monolayer can be associated with the observed pattern growth. There are also observed interesting, periodically arranged collections of molecules in numerous collapsed regions. Received: 8 July 1997 / Accepted: 4 November 1997  相似文献   
50.
A numerical study of confined jets in a cylindrical duct is carried out to examine the performance of two recently proposed turbulence models: an RNG-based K-? model and a realizable Reynolds stress algebraic equation model. The former is of the same form as the standard K-? model but has different model coefficients. The latter uses an explicit quadratic stress-strain relationship to model the turbulent stresses and is capable of ensuring the positivity of each turbulent normal stress. The flow considered involves recirculation with unfixed separation and reatachment points and severe adverse pressure gradients, thereby providing a valuable test of the predictive capability of the models for complex flows. Calculations are performed with a finite volume procedure. Numerical credibility of the solutions is ensured by using second-order-accurate differencing schemes and sufficiently fine grids. Calculations with the standard K-? model are also made for comparison. Detailed comparisons with experiments show that the realizable Reynolds stress algebraic equation model consistently works better than does the standard K-? model in capturing the essential flow features, while the RNG-based K-? model does not seem to give improvements over the standard K-? model under the flow conditions considered.  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