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   82524篇
  免费   422篇
  国内免费   383篇
化学   26527篇
晶体学   888篇
力学   6796篇
数学   32630篇
物理学   16488篇
  2022年   76篇
  2021年   86篇
  2020年   65篇
  2018年   10467篇
  2017年   10299篇
  2016年   6173篇
  2015年   947篇
  2014年   416篇
  2013年   562篇
  2012年   3969篇
  2011年   10716篇
  2010年   5783篇
  2009年   6177篇
  2008年   6679篇
  2007年   8847篇
  2006年   296篇
  2005年   1386篇
  2004年   1605篇
  2003年   2040篇
  2002年   1083篇
  2001年   302篇
  2000年   358篇
  1999年   227篇
  1998年   260篇
  1997年   213篇
  1996年   270篇
  1995年   181篇
  1994年   137篇
  1993年   163篇
  1992年   115篇
  1991年   123篇
  1990年   117篇
  1989年   122篇
  1988年   109篇
  1987年   128篇
  1986年   98篇
  1985年   108篇
  1984年   108篇
  1983年   101篇
  1982年   111篇
  1981年   103篇
  1980年   99篇
  1979年   112篇
  1978年   91篇
  1977年   63篇
  1976年   78篇
  1975年   79篇
  1974年   59篇
  1973年   65篇
  1966年   68篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
911.
Neutrino mixing lead to a non zero contribution to the dark energy of the universe. We assume that the neutrino masses and mixing arise through physics at a scale intermediate between Planck Scale and the electroweak scale. The mechanism of neutrino mixing is a possible candidate to contribute the cosmological dark energy. Quantum gravitational (Planck scale) effects lead to an effective SU(2) L ×U(1) invariant dimension-5 Lagrangian involving neutrino and Higgs fields, which gives rise to additional terms in neutrino mass matrix. There additional term can be considered to be perturbation of the GUT scale bi-maximal neutrino mass matrix. We assume that the gravitational interaction is flavor. In this paper, we discuss the three flavor neutrino mixing and cosmological dark energy contributes due to Planck scale effects.  相似文献   
912.
We consider Hermitian and symmetric random band matrices H in d ≥ 1 dimensions. The matrix elements H xy , indexed by \({x,y \in \Lambda \subset \mathbb{Z}^d}\), are independent, uniformly distributed random variables if \({\lvert{x-y}\rvert}\) is less than the band width W, and zero otherwise. We prove that the time evolution of a quantum particle subject to the Hamiltonian H is diffusive on time scales \({t\ll W^{d/3}}\). We also show that the localization length of the eigenvectors of H is larger than a factor W d/6 times the band width. All results are uniform in the size \({\lvert{\Lambda}\rvert}\) of the matrix.  相似文献   
913.
914.
Cosmological models with variable G in C-field cosmology for barotropic fluid distribution in FRW space-time are investigated. To get the deterministic model of the universe, we have assumed that G=R n where R is the scale factor and n the constant. To obtain the results in terms of cosmic time t, we have assumed n=−1. We find that for n=−1, Creation field (C) and spatial volume increase with time, G and ρ (matter density) decreases with time, the model represent accelerating universe. Thus inflationary scenario exists in the model. The model is also free from horizon. The results so obtained match with the astronomical observations.  相似文献   
915.
We prove that the maximum norm of the deformation tensor of velocity gradients controls the possible breakdown of smooth(strong) solutions for the 3-dimensional (3D) barotropic compressible Navier-Stokes equations. More precisely, if a solution of the 3D barotropic compressible Navier-Stokes equations is initially regular and loses its regularity at some later time, then the loss of regularity implies the growth without bound of the deformation tensor as the critical time approaches. Our result is the same as Ponce’s criterion for 3-dimensional incompressible Euler equations (Ponce in Commun Math Phys 98:349–353, 1985). In addition, initial vacuum states are allowed in our cases.  相似文献   
916.
We study the entanglement evolution between two atoms, which are initially entangled with a third atom and trapped in two separated cavities coupled by an optical fiber. We also investigate the temporal evolution in the entanglement between the atom and the local cavity mode. The influence of the state-selective measurement on the atom outside the cavities and the influence of cavity-fiber coupling coefficient on the entanglement are discussed. The results show that the entanglement can be strengthened through the state-selective measurement on the atom outside the cavities. We also find that, by increasing the cavity-fiber coupling coefficient, the atom-atom entanglement is strengthened, but the atom-cavity entanglement is weakened.  相似文献   
917.
The new coherent-entangled state |z,x;θ〉 is proposed in the two-mode Fock space, which exhibits both the properties of coherent and entangled states. The completeness relation of |z,x;θ〉 is proved by virtue of the technique of integral within an ordered product of operators. A generalized Hadamard-Fresnel complementary transformation derived by virtue of the coherent-entangled state |z,x;θ〉, which is unitary. The new unitary operator plays the role of both Hadamard transformation for ([^(a)]1sinq-[^(a)]2cosq)(\hat{a}_{1}\sin\theta -\hat{a}_{2}\cos\theta) and Fresnel transformation for ([^(a)]1cosq+[^(a)]2sinq)(\hat{a}_{1}\cos\theta +\hat{a}_{2}\sin\theta), respectively.  相似文献   
918.
Consider the classical XY model in a weak random external field pointing along the Y axis with strength ε. We study the behavior of this model as the range of the interaction is varied. We prove that in any dimension d≥2 and for all ε sufficiently small, there is a range L=L(ε) so that whenever the inverse temperature β is larger than some β(ε), there is strong residual ordering along the X direction.  相似文献   
919.
The reactive vacuum deposition of CeO2 on Cu(1 1 1) surface in oxygen atmosphere provides high quality epitaxial ceria overlayers. We report the growth characteristics of Ce oxide, the structures, and the temperature stability of the oxide phases as investigated by low-energy electron diffraction (LEED) and X-ray photoelectron spectroscopy. We find that Ce oxide on the Cu(1 1 1) grows initially in the form of islands giving sharp hexagonal LEED pattern of the CeO2(1 1 1) structure corresponding to the (1.5 × 1.5) structure. The CeO2-Cu(1 1 1) films exhibited mixed valence states and temperature dependent CeO2-Ce2O3 transition above 900 K due to the vacuum annealing. The transition progressed more rapidly at the surface, probably by formation of oxygen vacancies.  相似文献   
920.

Background  

The kelch repeat protein muskelin mediates cytoskeletal responses to the extracellular matrix protein thrombospondin 1, (TSP1), that is known to promote synaptogenesis in the central nervous system (CNS). Muskelin displays intracellular localization and affects cytoskeletal organization in adherent cells. Muskelin is expressed in adult brain and has been reported to bind the Cdk5 activator p39, which also facilitates the formation of functional synapses. Since little is known about muskelin in neuronal tissues, we here analysed the tissue distribution of muskelin in rodent brain and analysed its subcellular localization using cultured neurons from multiple life stages.  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