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   5339篇
  免费   146篇
  国内免费   41篇
化学   3218篇
晶体学   26篇
力学   295篇
数学   878篇
物理学   1109篇
  2023年   33篇
  2022年   85篇
  2021年   101篇
  2020年   89篇
  2019年   86篇
  2018年   78篇
  2017年   70篇
  2016年   174篇
  2015年   138篇
  2014年   148篇
  2013年   300篇
  2012年   283篇
  2011年   301篇
  2010年   216篇
  2009年   180篇
  2008年   286篇
  2007年   285篇
  2006年   261篇
  2005年   235篇
  2004年   247篇
  2003年   208篇
  2002年   195篇
  2001年   98篇
  2000年   85篇
  1999年   81篇
  1998年   59篇
  1997年   66篇
  1996年   79篇
  1995年   65篇
  1994年   73篇
  1993年   59篇
  1992年   57篇
  1991年   47篇
  1990年   38篇
  1989年   35篇
  1988年   44篇
  1987年   38篇
  1986年   31篇
  1985年   63篇
  1984年   53篇
  1983年   42篇
  1982年   45篇
  1981年   39篇
  1980年   38篇
  1979年   39篇
  1978年   26篇
  1977年   23篇
  1976年   30篇
  1975年   26篇
  1974年   27篇
排序方式: 共有5526条查询结果,搜索用时 15 毫秒
51.
Let A 1,…,A N be complex self-adjoint matrices and let ρ be a density matrix. The Robertson uncertainty principle
gives a bound for the quantum generalized covariance in terms of the commutators [A h ,A j ]. The right side matrix is antisymmetric and therefore the bound is trivial (equal to zero) in the odd case N=2m+1. Let f be an arbitrary normalized symmetric operator monotone function and let 〈⋅,⋅〉 ρ,f be the associated quantum Fisher information. Based on previous results of several authors, we propose here as a conjecture the inequality
whose validity would give a non-trivial bound for any N∈ℕ using the commutators i[ρ,A h ].  相似文献   
52.
We introduce an order parameter for dynamical arrest. Dynamically available volume (unoccupied space that is available to the motion of particles) is expressed as holes for the simple lattice models we study. Near the arrest transition the system is dilute in holes, so we expand dynamical quantities in a series of hole density. Unlike the situation when presented in particle density, all cases of simple models that we examine have a quadratic dependence of the diffusion constant on hole density. This observation implies that in certain regimes ideal dynamical arrest transitions may possess a hitherto unnoticed degree of universality.  相似文献   
53.
It is shown that radiation pressure can be profitably used to entangle macroscopic oscillators like movable mirrors, using present technology. We prove a new sufficient criterion for entanglement and show that the achievable entanglement is robust against thermal noise. Its signature can be revealed using common optomechanical readout apparatus.  相似文献   
54.
55.
56.
Anatase/rutile mixed-phase titanium dioxide (TiO2) photocatalysts in the form of nanostructured powders with different primary particle size, specific surface area, and rutile content were produced from the gas-phase by flame spray pyrolysis (FSP) starting from an organic solution containing titanium (IV) isopropoxide as Ti precursor. Flame spray-produced TiO2 powders were characterized by means of X-ray diffraction, Raman spectroscopy, and BET measurements. As-prepared powders were mainly composed of anatase crystallites with size ranging from 7 to 15 nm according to the synthesis conditions. TiO2 powders were embedded in a multilayered fluoropolymeric matrix to immobilize the nanoparticles into freestanding photocatalytic membranes. The photocatalytic activity of the TiO2-embedded membranes toward the abatement of hydrosoluble organic pollutants was evaluated employing the photodegradation of rhodamine B in aqueous solution as test reaction. The photoabatement rate of best performing membranes significantly overcomes that of membranes produced by the same method and incorporating commercial P25-TiO2.  相似文献   
57.
We consider a general system of n noninteracting identical particles which evolve under a given dynamical law and whose initial microstates are a priori independent. The time evolution of the n-particle average of a bounded function on the particle microstates is then examined in the large-n limit. Using the theory of large deviations, we show that if the initial macroscopic average is constrained to be near a given value, y, then the macroscopic average at time t converges in probability as n to a value t(y) given explicitly in terms of a canonical expectation. Some general features of the graph of t(y) versus t are examined, particularly in regard to continuity, symmetry, and convergence.  相似文献   
58.
The purpose of the present work was to investigate the correlation between topographical changes in brain oscillatory activity and the blood oxygenation level-dependent (BOLD) signal during a motor imagery (MI) task using electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) coregistration.  相似文献   
59.
Mobile phones have become very commonly used worldwide within a short period of time. To date there is only limited knowledge about interaction between electromagnetic fields (EMFs) emitted by mobile phones and the auditory function. Moreover, there is widespread concern that there may be potential for harm. The aim of this study was to assess potential subtle changes in cochlear function by measuring the temporal and spectral fine structure of transiently evoked otoacoustic emissions (TEOAE) in normal hearing subjects after exposure to EMFs emitted by Global System for Mobile Communication (GSM) mobile phones. TEOAEs were recorded in 27 healthy young adults before and after 10 min of real or sham exposure in a double-blind design. TEOAE data were analyzed both globally (broadband analysis) and using the Wavelet Transform (analysis of the time-frequency fine structure). The broadband analysis revealed no significant effect on TEOAEs related to exposure, confirming results of previous studies; in addition, no significant change was detected in the analysis of the elementary wavelet components, suggesting that the temporal and spectral fine structure of TEOAEs is not affected by 10 min exposure to low-intensity EMFs emitted by GSM mobile phones.  相似文献   
60.
We present an analysis of suitable rotation curves (RCs) of eight galaxies, aimed at checking the consistency and universality of the gravitational suppression (GraS) hypothesis, a phenomenological model for a new interaction between dark matter and baryons. Motivated by the puzzle of the core versus cusp distribution of dark matter in the center of halos, this hypothesis claims to reconcile the predictions from N-body Lambda cold dark matter simulations with kinematic observations. The GraS model improves the kinematic fitting residuals, but the mass parameters are unphysical and put the theory in difficulty.  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