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   204298篇
  免费   1971篇
  国内免费   591篇
化学   102567篇
晶体学   3348篇
力学   9299篇
综合类   5篇
数学   22517篇
物理学   69124篇
  2021年   1662篇
  2020年   1806篇
  2019年   2005篇
  2018年   2709篇
  2017年   2614篇
  2016年   3780篇
  2015年   2314篇
  2014年   3625篇
  2013年   9115篇
  2012年   7262篇
  2011年   8765篇
  2010年   6051篇
  2009年   5929篇
  2008年   7942篇
  2007年   8104篇
  2006年   7739篇
  2005年   6906篇
  2004年   6437篇
  2003年   5661篇
  2002年   5510篇
  2001年   6433篇
  2000年   4945篇
  1999年   3801篇
  1998年   3041篇
  1997年   3054篇
  1996年   2795篇
  1995年   2613篇
  1994年   2467篇
  1993年   2338篇
  1992年   2692篇
  1991年   2672篇
  1990年   2602篇
  1989年   2397篇
  1988年   2450篇
  1987年   2448篇
  1986年   2279篇
  1985年   2961篇
  1984年   3215篇
  1983年   2634篇
  1982年   2802篇
  1981年   2777篇
  1980年   2640篇
  1979年   2727篇
  1978年   2822篇
  1977年   2820篇
  1976年   2887篇
  1975年   2672篇
  1974年   2650篇
  1973年   2778篇
  1972年   1764篇
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
131.
Although coupled liquid chromatographygas chromatography (LC-GC) was first demonstrated ten years ago, only in the last few years has there been a sudden surge of interest in the technique. Approximately 70% of the total number of LC-GC applications have been published in the last two years (1987–88) alone. This review categorizes LC-GC publications into four main application areas: fossil fuels, foods, environmental samples, biologiical/pharmaceutical samples, and miscellaneous samples. Multidimensional separations carried out using other coupled-column chromatographic techniques (such as supercritical fluid chromatography (SFC) with GC, and on-line trace enrichment-GC) have also been included in this review.  相似文献   
132.
133.
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   
134.
An algorithm is proposed which allows one to construct higher symmetries of arbitrary order for some special classes of hyperbolic systems possessing integrals. The Pohlmeyer-Lund-Regge system and the open two-dimensional Toda lattices are shown to belong to the class of systems where our algorithm is applicable. __________ Translated from Fundamental’naya i Prikladnaya Matematika (Fundamental and Applied Mathematics), Vol. 10, No. 1, Geometry of Integrable Models, 2004.  相似文献   
135.
D.T. Son 《Annals of Physics》2006,321(1):197-224
We show that the Lagrangian for interacting nonrelativistic particles can be coupled to an external gauge field and metric tensor in a way that exhibits a nonrelativistic version of general coordinate invariance. We explore the consequences of this invariance on the example of the degenerate Fermi gas at infinite scattering length, where conformal invariance also plays an important role. We find the most general effective Lagrangian consistent with both general coordinate and conformal invariance to leading and next-to-leading orders in the momentum expansion. At the leading order the Lagrangian contains one phenomenological constant and reproduces the results of the Thomas-Fermi theory and superfluid hydrodynamics. At the next-to-leading order there are two additional constants. We express various physical quantities through these constants.  相似文献   
136.
The spatial structure of Bragg angles and the transfer functions of an acousto-optic cell are calculated for the cases of isotropic and anisotropic light diffraction in a uniaxial crystal. Their change with ultrasound frequency is traced. The possibility of image processing by acousto-optic filtration of the spatial spectrum of an image is considered. The results of experimental visualization of the transfer functions of a calcium molybdate crystal cell are presented.  相似文献   
137.
In this work we investigate the diffusion and precipitation of supersaturated substitutional carbon in 200-nm-thick SiGeC layers buried under a silicon cap layer of 40 nm. The samples were annealed in either inert (N2) or oxidizing (O2) ambient at 850 °C for times ranging from 2 to 10 h. The silicon self-interstitial (I) flux coming from the surface under oxidation enhances the C diffusion with respect to the N2-annealed samples. In the early stages of the oxidation process, the loss of C from the SiGeC layer by diffusion across the layer/cap interface dominates. This phenomenon saturates after an initial period (2–4 h), which depends on the C concentration. This saturation is due to the formation and growth of C-containing precipitates that are promoted by the I injection and act as a sink for mobile C atoms. The influence of carbon concentration on the competition between precipitation and diffusion is discussed. Received: 19 October 2001 / Accepted: 19 December 2001 / Published online: 20 March 2002 / Published online: 20 March 2002  相似文献   
138.
139.
140.
We have studied ultra-fast carrier dynamics of photo-excited carriers in hydrogenated microcrystalline silicon prepared by a very high frequency glow-discharge technique. We report on direct observation of two types of dynamics using selective photo-excitation in picosecond pump and probe measurements. One type of the observed dynamics has been found to be independent of the sample preparation, while the other reflects the relative weights of crystalline and amorphous fractions. We propose a simple rate-equation model that describes the carrier dynamics in microcrystalline silicon in terms of the composition of those in Si microcrystallites and in the a-Si:H tissue which surrounds the microcrystallites. The model without any fitting parameters reproduces the experimental data very well when the dynamics are scaled with relative volume fractions as obtained from Raman spectra. Received: 23 November 2000 / Accepted: 17 March 2001 / Published online: 23 May 2001  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