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   84641篇
  免费   626篇
  国内免费   456篇
化学   28056篇
晶体学   1005篇
力学   6910篇
综合类   4篇
数学   32944篇
物理学   16804篇
  2022年   82篇
  2021年   78篇
  2020年   95篇
  2019年   146篇
  2018年   10503篇
  2017年   10335篇
  2016年   6181篇
  2015年   951篇
  2014年   469篇
  2013年   857篇
  2012年   4054篇
  2011年   10803篇
  2010年   5834篇
  2009年   6221篇
  2008年   6799篇
  2007年   8960篇
  2006年   415篇
  2005年   1456篇
  2004年   1677篇
  2003年   2149篇
  2002年   1168篇
  2001年   338篇
  2000年   377篇
  1999年   215篇
  1998年   238篇
  1997年   212篇
  1996年   273篇
  1995年   199篇
  1994年   156篇
  1993年   176篇
  1992年   150篇
  1991年   150篇
  1990年   123篇
  1989年   168篇
  1988年   134篇
  1987年   127篇
  1986年   138篇
  1985年   172篇
  1984年   160篇
  1983年   129篇
  1982年   139篇
  1981年   139篇
  1980年   131篇
  1979年   142篇
  1978年   108篇
  1977年   119篇
  1976年   95篇
  1975年   102篇
  1974年   103篇
  1973年   119篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
The Einstein–Podolsky–Rosen–Bohm (EPRB) experiment performed with random variable and spatially separated analyzers is a milestone test in the controversy between Objective Local Theories (OLT) and Quantum Mechanics (QM). Only a few OLT are still possible. Some of the surviving OLT (specifically, the so called non-ergodic theories) would be undetectable in the averaged statistical values, but they may leave their trace in the time dynamics. For, while QM predicts random processes, the OLT of this kind predict the existence of regularities that may be revealed as a low dimensional object in the phase space. We perform a numerical analysis of the time-resolved data recorded in that experiment to unveil any hypothetical low dimensional dynamics that may be present. We find no consistent indication of such dynamics except for one data file, the longest of all in the real time. The possible causes of these dynamics are discussed.   相似文献   
942.
The dependence of temperature on the fluorescence lifetime and fluorescence intensity ratio using Stark sublevels and thermally coupled (close lying) levels in triply ionized rare earth ions, doped into a variety of glasses and fibers, have been reviewed. Also, it is claimed that not only for the two closely lying levels of triply ionized rare earth ion of the same kind, but also for two different triply ionized rare earth ions, having their excited levels very close to each other, may be used to monitor the temperature. PACS 42.70.Ce  相似文献   
943.
Some polymer materials under tensile stress provide us interesting information. Internal structure changes of polymer materials must be observed by external stress. Birefringence shows the orientation characteristic in molecular orientation. A microscopic measurement system for birefringence distribution is proposed to analyze the relation between applied stress and birefringence distribution of an internal structure. Birefringence distributions of gelatin such as phase difference and azimuthal angle are shown in cases of loading and unloading stress as a demonstration. The phase difference increased nonlinearly with each process, and change of birefringence in the elastic domain was different from that in the plastic domain.  相似文献   
944.
Based on an α-particle model of 12C, an optical potential for intermediate-energy proton- 12C scattering is presented in the framework of the KMT theory. The parameterized proton- 4He amplitude, the required basic input for constructing the optical potential, is obtained by fitting the proton- 4He scattering data. The differential cross-sections and analyzing powers of the proton- 12C elastic scattering at incident energies ranging from 0.2 to 1.0GeV have been calculated by using the obtained optical potential. The main features of the measured angular distributions of the cross-section and the analyzing power can be satisfactorily described. The proton- 12C total cross-sections have also been calculated, and the results are in good agreement with the experimental data at energies below 0.6GeV but underestimate the data about 6% at higher energies.  相似文献   
945.
We consider a quantum system in contact with a heat bath consisting in an infinite chain of identical sub-systems at thermal equilibrium at inverse temperature β. The time evolution is discrete and such that over each time step of duration τ, the reference system is coupled to one new element of the chain only, by means of an interaction of strength λ. We consider three asymptotic regimes of the parameters λ and τ for which the effective evolution of observables on the small system becomes continuous over suitable macroscopic time scales T and whose generator can be computed: the weak coupling limit regime λ → 0, τ = 1, the regime τ → 0, λ2τ → 0 and the critical case λ2τ = 1, τ → 0. The first two regimes are perturbative in nature and the effective generators they determine is such that a non-trivial invariant sub-algebra of observables naturally emerges. The third asymptotic regime goes beyond the perturbative regime and provides an effective dynamics governed by a general Lindblad generator naturally constructed from the interaction Hamiltonian. Conversely, this result shows that one can attach to any Lindblad generator a repeated quantum interactions model whose asymptotic effective evolution is generated by this Lindblad operator.  相似文献   
946.
The effect of light noise on a Neurospora circadian clock system in the steady states is investigated. It is found that the circadian oscillations could be induced by light noise, leading to various resonance phenomena including internal signal stochastic resonance (ISSR) and ISSR without tuning in the system. The strength of ISSR could be significantly reinforced with the decrease of the distance of the control parameter to the Hopf bifurcation point of the system. The fundamental frequency of noise-induced circadian oscillations almost does not change with the increment of light noise intensity, which implies that the Neurospora system could sustain intrinsic circadian rhythms. In addition, the ISSR and ISSR without tuning could be both amplified, suppressed or destroyed by tuning the frequency or amplitude of external signal.  相似文献   
947.
We consider the question of the existence of stationary solutions for the Navier Stokes equations describing the flow of a incompressible fluid past a semi-infinite flat plate at zero incidence angle. By using ideas from the theory of dynamical systems we analyze the vorticity equation for this problem and show that a symmetry-breaking term fits naturally into the downstream asymptotic expansion of a solution. Finally, in order to check that our asymptotic expressions can be completed to a symmetry-breaking solution of the Navier–Stokes equations we solve the problem numerically by using our asymptotic results to prescribe artificial boundary conditions for a sequence of truncated domains. The results of these numerical computations a clearly compatible with the existence of such a solution. Mathematics Subject Classification (2000). 76D05, 76D25, 76M10, 41A60, 35Q35 Supported in part by the Fonds National Suisse.  相似文献   
948.
In this paper, we introduce a family of observables for the dimer model on a bi-periodic bipartite planar graph, called pattern density fields. We study the scaling limit of these objects for non-frozen Gibbs measures of the dimer model, and prove that they converge to a linear combination of a derivative of the Gaussian massless free field and an independent white noise.  相似文献   
949.
A specific research and development program has been carried out by BARC in India to develop the technology for large area silicon strip detectors for application in nuclear and high energy physics experiments. These strip detectors will be used as pre-shower detector in the CMS experiment at LHC, CERN for π 0/λ rejection. The fabrication technology to produce silicon strip detectors with very good uniformity over a large area of ∼40 cm2, low leakage currents of the order of 10 nA/cm2 per strip and high breakdown voltage of >500 V has been developed by BARC. The production of detectors is already under way to deliver 1000 detector modules for the CMS and 90% production is completed. In this paper, research and development work carried out to develop the detector fabrication technology is briefly described. The performance of the silicon strip detectors produced in India is presented. The present status of the detector technology is discussed.   相似文献   
950.
We study a continuous matrix-valued Anderson-type model. Both leading Lyapunov exponents of this model are proved to be positive and distinct for all energies in (2, +∞) except those in a discrete set, which leads to absence of absolutely continuous spectrum in (2, +∞). This result is an improvement of a previous result with Stolz. The methods, based upon a result by Breuillard and Gelander on dense subgroups in semisimple Lie groups, and a criterion by Goldsheid and Margulis, allow for singular Bernoulli distributions.   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