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   12834篇
  免费   940篇
  国内免费   1600篇
化学   3467篇
晶体学   48篇
力学   412篇
综合类   174篇
数学   9000篇
物理学   2273篇
  2024年   16篇
  2023年   144篇
  2022年   190篇
  2021年   280篇
  2020年   313篇
  2019年   376篇
  2018年   367篇
  2017年   397篇
  2016年   293篇
  2015年   299篇
  2014年   471篇
  2013年   1451篇
  2012年   426篇
  2011年   575篇
  2010年   518篇
  2009年   716篇
  2008年   820篇
  2007年   954篇
  2006年   782篇
  2005年   718篇
  2004年   627篇
  2003年   670篇
  2002年   596篇
  2001年   474篇
  2000年   491篇
  1999年   415篇
  1998年   396篇
  1997年   353篇
  1996年   246篇
  1995年   141篇
  1994年   152篇
  1993年   99篇
  1992年   92篇
  1991年   64篇
  1990年   48篇
  1989年   49篇
  1988年   48篇
  1987年   44篇
  1986年   29篇
  1985年   56篇
  1984年   35篇
  1983年   22篇
  1982年   24篇
  1981年   21篇
  1980年   17篇
  1979年   12篇
  1978年   12篇
  1977年   12篇
  1976年   6篇
  1936年   5篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
赵小松  吕建钦 《中国物理 C》2009,33(Z2):125-127
Both the PIC (Particle-In-Cell) model and the Lie algebraic method can be used to simulate the transport of intense continuous beams. The PIC model is to calculate the space charge field, which is blended into the external field, and then simulate the trajectories of particles in the total field; the Lie algebraic method is to simulate the intense continuous beam transport with transport matrixes. Two simulation codes based on the two methods are developed respectively, and the simulated results of transport in a set of electrostatic lenses are compared. It is found that the results from the two codes are in agreement with each other, and both approaches have their own merits.  相似文献   
72.
In [A.L. Carey, J. Phillips, A. Rennie, Twisted cyclic theory and an index theory for the gauge invariant KMS state on Cuntz algebras. arXiv:0801.4605], we presented a K-theoretic approach to finding invariants of algebras with no non-trivial traces. This paper presents a new example that is more typical of the generic situation. This is the case of an algebra that admits only non-faithful traces, namely SUq(2) and also KMS states. Our main results are index theorems (which calculate spectral flow), one using ordinary cyclic cohomology and the other using twisted cyclic cohomology, where the twisting comes from the generator of the modular group of the Haar state. In contrast to the Cuntz algebras studied in [A.L. Carey, J. Phillips, A. Rennie, Twisted cyclic theory and an index theory for the gauge invariant KMS state on Cuntz algebras. arXiv:0801.4605], the computations are considerably more complex and interesting, because there are non-trivial ‘eta’ contributions to this index.  相似文献   
73.
近红外光谱分析中建模校正集的选择   总被引:5,自引:0,他引:5  
将极大线性无关组的概念及方法引入近红外光谱分析,探讨了在建立定量分析模型时代表性样品,即校正集样品的选择问题。以2 652个烟末样品为实验材料,随机选取1 001个样品构成预测集,其余1 651个样品为代表性样品备选集。用Matlab软件求出代表性样品备选集光谱矩阵的极大线性无关组,以此作为代表性样品,构成建模的校正集。用PLS回归法建立了烟末样品总糖含量定量分析的预测模型,并将模型用于预测集中1 001个烟末样品总糖含量的预测分析。实验结果表明,当选择的校正集包含的样品数量大于32时,所建各模型对预测集样品预测的平均相对误差均小于4%,平均相关系数大于0.96。其中选择32个代表性样品和146个代表性样品所建模型定量分析预测集中各样品的总糖含量,两个结果经统计检验没有显著性差异(α=0.05),说明求极大线性无关组的方法用于校正集样品的选择,可实现“少而精”选择样品的目的。此外,我们用求极大线性无关组选择校正集样品和随机方法选择校正集样品两种方法,选择了同样数目28,32,41,76,146,163个样品建模进行预测效果的对比实验,结果显示,求极大线性无关组法选择校正集建模的预测效果优于随机选择校正集建模的预测效果。  相似文献   
74.
75.
R. Tarumi  H. Nitta  H. Ogi  M. Hirao 《哲学杂志》2013,93(16):2140-2153
A complete set of elastic constants C ij and piezoelectric coefficients e ij of a La3Ga5SiO14 (langasite) single crystal was determined from 5.5 to 275.5?K by resonant ultrasound spectroscopy. Unlike a conventional crystal, the elastic constants C ij of the langasite crystal showed three types of temperature dependence: (i) monotonic elastic stiffening upon cooling (C 44 and C 14); (ii) monotonic elastic softening (C 66); and (iii) a stiffening-to-softening transition below 150?K (C 11, C 12, C 13 and C 33). In addition, a strong correlation between C 66 and the piezoelectric coefficient e 11 was confirmed. Group theoretical lattice dynamics analysis revealed that the novel phenomena of elastic softening and strong correlation are explained on the basis of two types of optical mode internal displacements which have the totally symmetric A 1 and doubly degenerated E symmetries in the point group D 3.  相似文献   
76.
77.
A supersymmetric integrable equation in (2+1) dimensions is constructed by means of the approach of the homogenous space of the super Lie algebra, where the super Lie algebra osp(3/2) is considered. For this (2+1) dimensional integrable equation, we also derive its Bäcklund transformation.  相似文献   
78.
In the context of massless quantum electrodynamics (QED) with a linear covariant gauge fixing, the connection between the counterterm and the Hopf-algebraic approach to renormalization is examined. The coproduct formula of Green’s functions contains two invariant charges, which give rise to different renormalization group functions. All formulas are tested by explicit computations to third loop order. The possibility of a finite electron self-energy by fixing a generalized linear covariant gauge is discussed. An analysis of subdivergences leads to the conclusion that such a gauge only exists in quenched QED.  相似文献   
79.
80.
The present paper, though inspired by the use of tensor hierarchies in theoretical physics, establishes their mathematical credentials, especially as genetically related to Lie algebra crossed modules. Gauging procedures in supergravity rely on a pairing – the embedding tensor – between a Leibniz algebra and a Lie algebra. Two such algebras, together with their embedding tensor, form a triple called a Lie-Leibniz triple, of which Lie algebra crossed modules are particular cases. This paper is devoted to showing that any Lie-Leibniz triple induces a differential graded Lie algebra – its associated tensor hierarchy – whose restriction to the category of Lie algebra crossed modules is the canonical assignment associating to any Lie algebra crossed module its corresponding unique 2-term differential graded Lie algebra. This shows that Lie-Leibniz triples form natural generalizations of Lie algebra crossed modules and that their associated tensor hierarchies can be considered as some kind of ‘lie-ization’ of the former. We deem the present construction of such tensor hierarchies clearer and more straightforward than previous derivations. We stress that such a construction suggests the existence of further well-defined Leibniz gauge theories.  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