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   2749篇
  免费   169篇
  国内免费   227篇
化学   580篇
晶体学   28篇
力学   162篇
综合类   18篇
数学   1476篇
物理学   881篇
  2024年   3篇
  2023年   29篇
  2022年   33篇
  2021年   68篇
  2020年   61篇
  2019年   60篇
  2018年   54篇
  2017年   83篇
  2016年   61篇
  2015年   74篇
  2014年   85篇
  2013年   217篇
  2012年   95篇
  2011年   142篇
  2010年   111篇
  2009年   158篇
  2008年   176篇
  2007年   219篇
  2006年   171篇
  2005年   150篇
  2004年   130篇
  2003年   132篇
  2002年   127篇
  2001年   90篇
  2000年   86篇
  1999年   111篇
  1998年   108篇
  1997年   79篇
  1996年   43篇
  1995年   31篇
  1994年   25篇
  1993年   17篇
  1992年   27篇
  1991年   16篇
  1990年   8篇
  1989年   12篇
  1988年   9篇
  1987年   7篇
  1986年   4篇
  1985年   5篇
  1984年   7篇
  1982年   5篇
  1981年   2篇
  1980年   2篇
  1979年   2篇
  1978年   2篇
  1975年   2篇
  1974年   1篇
  1973年   1篇
  1969年   2篇
排序方式: 共有3145条查询结果,搜索用时 218 毫秒
21.
This paper seeks to solve the difficult nonlinear problem in financial markets on the complex system theory and the nonlinear dynamics principle, with the data-model-concept-practice issue-oriented reconstruction of the phase space by the high frequency trade data. In theory, we have achieved the differentiable manifold geometry configuration, discovered the Yang-Mills functional in financial markets, obtained a meaningful conserved quantity through corresponding space-time non-Abel localization gauge symmetry transformation, and derived the financial solitons, which shows that there is a strict symmetry between manifold fiber bundle and guage field in financial markets. In practical applications of financial markets, we have repeatedly carried out experimental tests in a fluctuant evolvement, directly simulating and validating the existence of solitons by researching the price fluctuations (society phenomena) using the same methods and criterion as in natural science and in actual trade to test the stock Guangzhou Proprietary and the futures Fuel Oil in China. The results demonstrate that the financial solitons discovered indicates that there is a kind of new substance and form of energy existing in financial trade markets, which likely indicates a new science paradigm in the economy and society domains beyond physics.   相似文献   
22.
If M is an isoparametric hypersurface in a sphere S n with four distinct principal curvatures, then the principal curvatures κ1, . . . , κ4 can be ordered so that their multiplicities satisfy m 1 = m 2 and m 3 = m 4, and the cross-ratio r of the principal curvatures (the Lie curvature) equals −1. In this paper, we prove that if M is an irreducible connected proper Dupin hypersurface in R n (or S n ) with four distinct principal curvatures with multiplicities m 1 = m 2 ≥ 1 and m 3 = m 4 = 1, and constant Lie curvature r = −1, then M is equivalent by Lie sphere transformation to an isoparametric hypersurface in a sphere. This result remains true if the assumption of irreducibility is replaced by compactness and r is merely assumed to be constant.   相似文献   
23.
The Randers spaces RFn were introduced by R. S. Ingarden. They are considered as Finsler spaces Fn = (M, α + β) equipped with the Cartan nonlinear connection. In the present paper we define and study what we call the Ingarden spaces, I Fn, as Finsler spaces I Fn = (M, α + β) equipped with the Lorentz nonlinear connection. The spaces R Fn and I Fn are completely different. For I Fn we discuss: the variational problem, Lorentz nonlinear connection, canonical N-metrical connection and its structure equations, the Cartan 1-form ω, the electromagnetic 2-form tF and the almost symplectic 2-form 0. The formula = F+θ is established. It has as a consequence the generalized Maxwell equations. Finally, the almost Hermitian model of I Fn is constructed.  相似文献   
24.
25.
The aim of this article is to give a new dynamical proof of the Ferrand–Obata theorem when the manifold is compact. This will give us a generalisation of this theorem to transversally conformal foliations ofcodimension greater than three and constant basic functions.  相似文献   
26.
王秀兰  刘云 《数学杂志》2006,26(5):529-536
本文对几类B值小指标鞅空间建立了原子分解定理,利用原子分解讨论了它们之间的相互嵌入关系,其原子分解的存在性和它们之间的关系均与Banach空间的凸性和光滑性有密切联系.  相似文献   
27.
吕东辉  王朔中  庄天戈 《光学学报》2002,22(10):187-1194
研究了一种新的圆加垂直单弧段的锥顶轨迹的锥形束计算机层析(CT)的完全性条件和精确重建的Grangeat方法,提出了倒置结构锥形束计算机层析的便于实现的圆加垂直多弧段的成像结构及进行精确重建的完全性条件。利用倒置成像结构与现有成像结构之间的等价关系,给出了倒置结构锥形束计算机层析的重建算法。最后,对上述几方面进行了计算机模拟。  相似文献   
28.
A phenanthridinium salt was prepared in four steps, including an intramolecular CH-arylation and a hydride abstraction reaction. Treatment with sterically demanding bases does not lead to the corresponding carbene, but rather to addition products: the planar-constrained geometry significantly enhances the electrophilicity over the acidity of C-aryl iminium salts.  相似文献   
29.
利用密度泛函理论研究了Al12N和Al12B团簇的原子结构和电子性质,通过各种异构体的比较,发现两种掺杂团簇的最低能量结构都是完好的二十面体(Ih)结构,N(B)原子占据在二十面体的中心.高对称性团簇形成稀疏离散的电子态密度和大的电子能隙.在Al-N之间发生较大的电荷转移.因此我们建议把Al12N团簇看作是碱金属超原子,Al12B团簇看作是卤素超原子,用来构造团簇组装固体.  相似文献   
30.
It was proved in 1957 by Huber that any complete surface with integrable Gauss curvature is conformally equivalent to a compact surface with a finite number of points removed. Counterexamples show that the curvature assumption must necessarily be strengthened in order to get an analogous conclusion in higher dimensions. We show in this paper that any non compact Riemannian manifold with finite -norm of the Ricci curvature satisfies Huber-type conclusions if either it is a conformal domain with volume growth controlled from above in a compact Riemannian manifold or if it is conformally flat of dimension 4 and a natural Sobolev inequality together with a mild scalar curvature decay assumption hold. We also get partial results in other dimensions. Received: April 14, 2000; revised version: March 20, 2001  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