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   105186篇
  免费   1013篇
  国内免费   604篇
化学   42890篇
晶体学   908篇
力学   7284篇
综合类   1篇
数学   36984篇
物理学   18736篇
  2022年   183篇
  2021年   276篇
  2020年   347篇
  2019年   314篇
  2018年   10617篇
  2017年   10458篇
  2016年   6602篇
  2015年   1440篇
  2014年   936篇
  2013年   1698篇
  2012年   5125篇
  2011年   12061篇
  2010年   6514篇
  2009年   6772篇
  2008年   7930篇
  2007年   10072篇
  2006年   1749篇
  2005年   2667篇
  2004年   2819篇
  2003年   3026篇
  2002年   2028篇
  2001年   691篇
  2000年   688篇
  1999年   544篇
  1998年   572篇
  1997年   574篇
  1996年   589篇
  1995年   473篇
  1994年   465篇
  1993年   435篇
  1992年   370篇
  1991年   385篇
  1990年   323篇
  1989年   337篇
  1988年   318篇
  1987年   276篇
  1986年   300篇
  1985年   407篇
  1984年   411篇
  1983年   348篇
  1982年   384篇
  1981年   349篇
  1980年   383篇
  1979年   313篇
  1978年   332篇
  1977年   297篇
  1976年   239篇
  1975年   205篇
  1974年   205篇
  1973年   188篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The magnitude of spectral change in blood glucose measurements with diffuse reflectance spectroscopy is investigated. Spectral change is estimated by simulation of light propagation in skin tissue and measurements of absorbance spectra of aqueous glucose solution. Required sensitivity of spectrophotometers for monitoring change in the blood glucose concentration as small as 10 mg/dL has been obtained using the estimated change in the absorbance spectrum and mean pathlength of light in tissue.  相似文献   
992.
Frank E. Harris 《Pramana》2003,61(4):C779-C780
Guseinov, Mamedov, Kara and Orbay (Pramana - J. Phys. 56, 691 (2001)) propose methods for evaluating the molecular auxiliary functionsA n(p) andB n(pt) for the range 17 ≤n ≤ 60 and 25 ≤pt ≤ 60. However, their procedure forA n(p) is not new, and that forB n(pt) is less efficient for their target range than another well-known method. Their approach does have merit for smaller non-zero values ofpt. Two minor errors in table 1 of their paper are also identified.  相似文献   
993.
A finite rank separable approximation for the quasiparticle random phase approximation with Skyrme interactions is applied to study the low-lying quadrupole and octupole states in some S isotopes and giant resonances in some spherical nuclei. It is shown that characteristics calculated within the suggested approach are in good agreement with available experimental data.  相似文献   
994.
 We study the half-space problem of the nonlinear Boltzmann equation, assigning the Dirichlet data for outgoing particles at the boundary and a Maxwellian as the far field. We will show that the solvability of the problem changes with the Mach number ℳ of the far Maxwellian. If ℳ<−1, there exists a unique smooth solution connecting the Dirichlet data and the far Maxwellian for any Dirichlet data sufficiently close to the far Maxwellian. Otherwise, such a solution exists only for the Dirichlet data satisfying certain admissible conditions. The set of admissible Dirichlet data forms a smooth manifold of codimension 1 for the case −1<ℳ<0, 4 for 0<ℳ<1 and 5 for ℳ>1, respectively. We also show that the same is true for the linearized problem at the far Maxwellian, and the manifold is, then, a hyperplane. The proof is essentially based on the macro-micro or hydrodynamics-kinetic decomposition of solutions combined with an artificial damping term and a spatially exponential decay weight. Received: 20 April 2002 / Accepted: 4 December 2002 Published online: 21 March 2003 Communicated by H.-T. Yau  相似文献   
995.
It is explicitly shown that if phase transition occurs at the core of a newborn neutron star with moderately strong magnetic field strength, which populates only the electron’s Landau levels, then in the β -equilibrium condition, the quark core is energetically much more unstable than the neutron matter of identical physical condition.  相似文献   
996.
We consider several statistical models defined on the Farey fractions. Two of these models may be regarded as spin chains, with long-range interactions, while another arises in the study of multifractals associated with chaotic maps exhibiting intermittency. We prove that these models all have the same free energy. Their thermodynamic behavior is determined by the spectrum of the transfer operator (Ruelle–Perron–Frobenius operator), which is defined using the maps (presentation functions) generating the Farey tree. The spectrum of this operator was completely determined by Prellberg. It follows that these models have a second-order phase transition with a specific heat divergence of the form C [ ln2 ]–1. The spin chain models are also rigorously known to have a discontinuity in the magnetization at the phase transition.  相似文献   
997.
Energy cascade rates and Kolmogorov’s constant for non-helical steady magnetohydrodynamic turbulence have been calculated by solving the flux equations to the first order in perturbation. For zero cross helicity and space dimensiond = 3, magnetic energy cascades from large length-scales to small length-scales (forward cascade). In addition, there are energy fluxes from large-scale magnetic field to small-scale velocity field, large-scale velocity field to small-scale magnetic field, and large-scale velocity field to large-scale magnetic field. Kolmogorov’s constant for magnetohydrodynamics is approximately equal to that for fluid turbulence (≈ 1.6) for Alfvén ratio 05 ≤r A ≤ ∞. For higher space-dimensions, the energy fluxes are qualitatively similar, and Kolmogorov’s constant varies asd 1/3. For the normalized cross helicity σc →1, the cascade rates are proportional to (1 − σc)/(1 + σc , and the Kolmogorov’s constants vary significantly with σcc.  相似文献   
998.
We have succeeded in the operation of rotating a fine particle which was held without mechanical contact by circularly polarized laser beams with opposite propagation directions. A polystyrene latex particle 11.9 μm in diameter deformed in a disk-like shape was dispersed in water, and was trapped using the anti-parallel collinear laser beams which were set up so that they had the circular polarization rotating in the same direction. It was observed that the trapped particle rotated in the same direction as the rotation of the circular polarization of light. Inversion of the rotational direction of the circular polarization of light reversed the direction of the rotation of the particle. Although the rotational speed of a particle varied significantly from particle to particle, it was found to be proportional to the laser beam intensity. A typical value for the rotational speed per beam intensity was 2.1 Hz/W.  相似文献   
999.
Using a general classification of dark enegy models in four classes, we discuss the complementarity of cosmological observations to tackle down the physics beyond the acceleration of our universe. We discuss the tests distinguishing the four classes and then focus on the dynamics of the perturbations in the Newtonian regime. We also exhibit explicitely models that have identical predictions for a subset of observations.  相似文献   
1000.
The word problem for an arbitrary associative Rota–Baxter algebra is solved. This leads to a noncommutative generalization of the classical Spitzer identities. Links to other combinatorial aspects are indicated.   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