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   3102篇
  免费   335篇
  国内免费   157篇
化学   209篇
晶体学   10篇
力学   91篇
综合类   41篇
数学   1760篇
物理学   724篇
无线电   759篇
  2025年   8篇
  2024年   40篇
  2023年   54篇
  2022年   66篇
  2021年   105篇
  2020年   103篇
  2019年   93篇
  2018年   110篇
  2017年   114篇
  2016年   139篇
  2015年   110篇
  2014年   172篇
  2013年   249篇
  2012年   139篇
  2011年   137篇
  2010年   106篇
  2009年   163篇
  2008年   186篇
  2007年   172篇
  2006年   148篇
  2005年   149篇
  2004年   102篇
  2003年   117篇
  2002年   116篇
  2001年   98篇
  2000年   98篇
  1999年   68篇
  1998年   69篇
  1997年   66篇
  1996年   46篇
  1995年   36篇
  1994年   26篇
  1993年   20篇
  1992年   21篇
  1991年   14篇
  1990年   15篇
  1989年   6篇
  1988年   13篇
  1987年   10篇
  1986年   7篇
  1985年   11篇
  1984年   9篇
  1983年   9篇
  1982年   12篇
  1980年   10篇
  1979年   5篇
  1978年   6篇
  1977年   5篇
  1976年   4篇
  1974年   3篇
排序方式: 共有3594条查询结果,搜索用时 15 毫秒
11.
由D3群一维表示,得到了正三角形上满足Dirichlet边界条件拉普拉斯算子的本征值和本征函数,并讨论了本征函数的对称性.  相似文献   
12.
Adiabatic potential energy, spectroscopic constants, dipole moments, and vibrational levels of the lowest electronic states of the alkali dimer LiNa molecule dissociating into Na (3s, 3p, 4s, 3d, and 4p) + Li (2s, 2p, 3s, and 3p) in 1,3Σ, 1,3Π, and 1,3Δ symmetries are presented. Adiabatic results are also reported for 2Σ, 2Π, and 2Δ electronic states of the molecular ion LiNa+ dissociating into Li (2s, 2p, 3s, and 3p) + Na+ and Li+  + Na(3s, 3p, 4s, 3d, and 4p). We use an ab initio approach involving a non-empirical pseudopotential for the Li (1s2) and Na (1s22s22p6) cores and core valence correlation correction. A very good agreement is obtained for some lowest states of the LiNa and LiNa+ molecules for spectroscopic constants with the available theoretical works. The existence of numerous avoided crossings between electronic states of 2Σ and 2Π symmetries is related to the charge transfer process between the two ionic systems Li+Na and LiNa+.  相似文献   
13.
14.
In this paper, we consider the problem of automatic face recognition with limited manually labeled training data. We propose a new semi-supervised self-training approach which is used to automatically augment the manually labeled training set with new unlabeled data. Semi-supervised Discriminant Analysis is used in each iteration of self-training for discriminative dimensionality reduction by making use of both labeled and unlabeled training data. Sparse representation is applied for classification. Experimental results on four independent databases show that our algorithm outperforms other face recognition methods under 3 different configurations, namely transductive, semi-supervised and single training image.  相似文献   
15.
In similar to the derivation of phase angle operator conjugate to the number operator by Arroyo Carrasco- Moya Cessay we deduce the Hermitian phase operators that are conjugate to the two-mode number-difference operator and the three-mode number combination operator. It is shown that these operators are on the same footing in the entangled state representation as the one of Turski in the coherent state representation.  相似文献   
16.
In this paper we present systematic differential representations for the dynamical group SO(4). These representations include the left and the right differential representations and the left and the right adjoint differential representations in both the group parameter space and its coset spaces. They are the generalization of the differential representations of the SO(3) rotation group in the Euler angles. These representations may find their applications in the study of the physical systems with SO(4) dynamical symmetry.  相似文献   
17.
18.
19.
Bézier曲线近似合并算法在几何数据压缩方面有着重要的应用.研究了两条相邻Bézier曲线近似合并的问题,用矩阵的形式给出了相邻Bézier曲线可精确合并的条件,并在此基础上通过广义逆矩阵的方法求解合并逼近后的Bézier曲线.同时,对保端点插值条件的近似合并也给出了结果.最后用实例说明了算法的有效性,得到了很好的逼近效果.  相似文献   
20.
S K Soni 《Pramana》1979,13(1):55-80
In view of an excellent agreement between the recently determinedv μ-hadron couplings and predictions of the standard model, the basic question discussed is how far its neutral current predictions can be mimiced in going either from the isodoublet to an isotriplet (or an even higher isospin) left-handed representation or from SU L (2) × U(1) toG × U(1), whereG is a simple group of rank two. This question is addressed with reference to a sufficiently broad class of schemes. Their most distinctive properties are: in the higher isospin scheme, neutrino couplings are precisely in the form obtainable with standard l.h. representation; the higher g.g. scheme isL+R type in which, to each light fermion of evenRU parity, a superheavy fermion of the same charge and oddRU parity is associated, parity conservation forbidding their mixing. Reasons for excluding theL-type andG 2 higher g.g. schemes are given. Their neutral current predictions are compared with those of the standard model. A higher isospin representation can mimic the predictions of the standard model in inclusive and semi-inclusivev μ-hadron reactions but is conclusively discriminated from the isodoublet representation by elasticv μ (− p scattering. TheG × U(1) scheme can mimic standard model neutrino sector but is conclusively discriminated from minimal scheme by parity violating effects.  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