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   1428624篇
  免费   25927篇
  国内免费   7801篇
化学   720402篇
晶体学   21016篇
力学   76727篇
综合类   117篇
数学   248730篇
物理学   395360篇
  2021年   13611篇
  2020年   15996篇
  2019年   16110篇
  2018年   16402篇
  2017年   15115篇
  2016年   29599篇
  2015年   21207篇
  2014年   30559篇
  2013年   74504篇
  2012年   42524篇
  2011年   43623篇
  2010年   40615篇
  2009年   42369篇
  2008年   41704篇
  2007年   38717篇
  2006年   40179篇
  2005年   35339篇
  2004年   34640篇
  2003年   31806篇
  2002年   31918篇
  2001年   31893篇
  2000年   26885篇
  1999年   23488篇
  1998年   21410篇
  1997年   21292篇
  1996年   21319篇
  1995年   19307篇
  1994年   18812篇
  1993年   18321篇
  1992年   18771篇
  1991年   18959篇
  1990年   18200篇
  1989年   18206篇
  1988年   17878篇
  1987年   17752篇
  1986年   16676篇
  1985年   23032篇
  1984年   24166篇
  1983年   20267篇
  1982年   21798篇
  1981年   21024篇
  1980年   20358篇
  1979年   20773篇
  1978年   21940篇
  1977年   21633篇
  1976年   21297篇
  1975年   20038篇
  1974年   19666篇
  1973年   20112篇
  1972年   14590篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
231.
232.
233.
Components C1 and C2 form a series system. Suppose we can allocate the spare R1 in parallel with C1 and the spare R2 in parallel with C2, or otherwise, allocate R1 with C2 and R2 with C1. In this paper, we compare these two options using hazard rate ordering.  相似文献   
234.
The concepts of quasi-Chebyshev and weakly-Chebyshev and σ-Chebyshev were defined [3 - 7], andas a counterpart to best approximation in normed linear spaces, best coapprozimation was introduced by Franchetti and Furi^[1]. In this research, we shall define τ-Chebyshev subspaces and τ-cochebyshev subspaces of a Banach space, in which the property τ is compact or weakly-compact, respectively. A set of necessary and sufficient theorems under which a subspace is τ-Chebyshev is defined.  相似文献   
235.
236.
We establish soliton-like asymptotics for finite energy solutions to the Schrödinger equation coupled to a nonrelativistic classical particle. Any solution with initial state close to the solitary manifold converges to a sum of a travelling wave and an outgoing free wave. The convergence holds in global energy norm. The proof uses spectral theory and the symplectic projection onto the solitary manifold in the Hilbert phase space.  相似文献   
237.
J. H. Eberly 《Laser Physics》2006,16(6):921-926
We examine the application of Schmidt mode analysis to pure-state entanglement. Several examples permitting exact analytic calculation of Schmidt eigenvalues and eigenfunctions are included, as well as evaluation of the associated degree of entanglement.  相似文献   
238.
We demonstrate a method that permits to obtain generalized solutions for some quasilinear equations and systems of hyperbolic type. The corresponding variational principle is constructed using the theory of equilibrium of a potential in an external field. Dedicated to the memory of B. M. Levitan Supported by RFBR grants Nos. 05-01-00522 and NSh-1551.2003.1, by Program No. 1 of the Branch of Mathematics, Russian Academy of Sciences, and by INTAS project No. 03-51-6637.  相似文献   
239.
Thomson scattering of high-power laser and electron beams is a good test of electrodynamics in the high-field region. We demonstrated production of high-intensity X-rays in the head-on collision of a CO2 laser and 60-MeV electron beams at Brookhaven National Laboratory, Accelerator Test Facility. The energy of an X-ray photon was limited at 6.5 keV in the linear (lowest order) Thomson scattering, but the nonlinear (higher order) process produces higher energy X-rays. We measured the angular distribution of the high-energy X-rays and confirmed that it agrees with theoretical predictions.  相似文献   
240.
The tape stripping technique is an experimental method frequently used for reconstruction of the in-depth distribution of various topically administered substances within the horny layer of human skin, e.g., compounds contained in sunscreens. Titanium dioxide (TiO2) nanoparticles (25–200 nm in diameter) are one such compound. Optical techniques which apply blue light are found to be suitable for reconstruction. However, the presence of particles affects the light propagation within the skin and therefore causes incorrect determination of strip thickness, leading to an improper reconstructed distribution of nanoparticle concentration revealed from the experimental data. This study evaluates the errors emerging from the use of blue (400 nm) and NIR (800 nm) radiation and finds the use of longer wavelength light more advantageous. Particles of different diameters are considered, and it is revealed that the application of small particles (25–60 nm) results in the lowest rate of error.  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