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   434651篇
  免费   5527篇
  国内免费   1226篇
化学   233106篇
晶体学   6489篇
力学   18761篇
综合类   13篇
数学   49927篇
物理学   133108篇
  2021年   3742篇
  2020年   4184篇
  2019年   4517篇
  2018年   5853篇
  2017年   5743篇
  2016年   8831篇
  2015年   5561篇
  2014年   8542篇
  2013年   20183篇
  2012年   15647篇
  2011年   19261篇
  2010年   13497篇
  2009年   13351篇
  2008年   17647篇
  2007年   17541篇
  2006年   16252篇
  2005年   14551篇
  2004年   13523篇
  2003年   11892篇
  2002年   11728篇
  2001年   13429篇
  2000年   10085篇
  1999年   7916篇
  1998年   6569篇
  1997年   6314篇
  1996年   6080篇
  1995年   5470篇
  1994年   5392篇
  1993年   5197篇
  1992年   5828篇
  1991年   5924篇
  1990年   5664篇
  1989年   5472篇
  1988年   5493篇
  1987年   5374篇
  1986年   5091篇
  1985年   6560篇
  1984年   6694篇
  1983年   5299篇
  1982年   5387篇
  1981年   5367篇
  1980年   4955篇
  1979年   5352篇
  1978年   5491篇
  1977年   5385篇
  1976年   5328篇
  1975年   4914篇
  1974年   4885篇
  1973年   4880篇
  1972年   3455篇
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
871.
The relativistic four-quark equations are found in the framework of the dispersion relation technique. The behaviour of the low-energy four-particle amplitude is determined by its leading singularities in the pair invariant masses. The approximate solutions of these equations using the method based on the extraction of leading singularities of the amplitudes are obtained. The mass values of lowest exotic mesons are calculated.  相似文献   
872.
In this paper we investigate the effects of heavy Majorana neutrinos in the reaction e + e ?W + W ?. We consider neutrino masses in the 1–10 TeV region. We show that at LEP II and NLC energies it is possible to use this processes to verify indirect evidence of heavy neutral particles with mixing angles of the order sin2 α = 0.01. We discuss the unitarity restrictions that can be obtained for vector singlet and fermion-mirror-fermion models.  相似文献   
873.
It is shown that the potential perturbation that shifts a chosen standing wave in space is a block of potential barrier and well for every wave bump between neighbouring knots. The algorithms shifting the range of the primary localization of a chosen bound state in a potential well of finite width are as well applicable to the scattering functions if states of the continuous spectrum are considered as bound states normalized to unity but distributed on an infinite interval with vanishing density. The potential perturbations of the same type on the half-axis concentrate the scattering wave at the origin, thus creating a bound state embedded into the continuous spectrum (zero width resonance).  相似文献   
874.
A Lieb-Thirring-Sobolev type inequality for Pauli Hamiltonians with magnetic fields is derived. The bound is in terms of an effective field, whose energy is comparable to that of the magnetic field itself. An application to the stability of matter in magnetic fields is given. Received: 19 September 1996 / Accepted: 3 January 1997  相似文献   
875.
876.
The one-loop self-energy correction to the hyperfine splitting of the 1 s and 2 s states of hydrogenlike ions is calculated for both point and finite nuclei. The results of the calculation are combined with other corrections to find the ground state hyperfine splitting in lithiumlike 209Bi80+ and 165Ho64+. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 1, 19–22 (10 July 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.  相似文献   
877.
The effect of the replacement of MnO2 by Fe2O3 on the oxidation states of iron in some lithium borosilicate glasses were studied using Mössbauer spectroscopy. DTA and infrared measurements showed the presence of two glassy phases, one of them containing iron and the other manganese. The Mössbauer spectra were measured at room temperature for all the glass samples. The spectra revealed the presence of Fe ions only in ferric state in both tetrahedral and octahedral coordination. Also, it was observed that the ratio between the number of iron ions in both coordination states has not changed with the increase of MnO2 content.  相似文献   
878.
879.
Luminescence properties of porous anodic aluminum oxide films formed in a 0.6 M solution of citric acid and luminescence of paraterphenyl, perylene, coumarin 7, and rhodamine 6G dyes adsorbed by the films are investigated. The nature of emitting centers in anodic aluminum oxide is revealed. Intense photoluminescence of all tested dyes embedded into pores of anodic aluminum oxide has been found. A redshift of fluorescence spectra of dyes adsorbed by the matrix and emergence of an additional longwave band have been detected. Data obtained can be used in developing new thin-film luminescent coatings for future applications in optoelectronics and molecular electronics. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No 4, pp. 483–488, July–August, 1997.  相似文献   
880.
A laser system containing four CW Nd:YAG double-rod lasers, transforming optics and a fibre with input-output optics has been designed and investigated. It is shown that reduction of the beam parameter product of the non-Gaussian beams in the image space of the lens has made it possible to collect the emission of four lasers to the same fibre. Independent laser operation has provided the output power control in the range of 10–900 W with a stable light spot size on the input end of the fibre.  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