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   237078篇
  免费   2694篇
  国内免费   1188篇
化学   109431篇
晶体学   3673篇
力学   12530篇
综合类   46篇
数学   37794篇
物理学   77486篇
  2018年   10339篇
  2017年   11231篇
  2016年   5910篇
  2015年   2235篇
  2014年   1814篇
  2013年   5409篇
  2012年   8555篇
  2011年   18287篇
  2010年   10836篇
  2009年   10720篇
  2008年   15683篇
  2007年   19512篇
  2006年   4584篇
  2005年   11718篇
  2004年   7459篇
  2003年   6958篇
  2002年   4767篇
  2001年   3910篇
  2000年   3155篇
  1999年   2408篇
  1998年   2056篇
  1997年   2015篇
  1996年   2126篇
  1995年   1982篇
  1994年   1749篇
  1993年   1722篇
  1992年   1919篇
  1991年   1900篇
  1990年   1814篇
  1989年   1837篇
  1988年   1826篇
  1987年   1806篇
  1986年   1702篇
  1985年   2260篇
  1984年   2381篇
  1983年   1997篇
  1982年   2309篇
  1981年   2125篇
  1980年   2166篇
  1979年   2169篇
  1978年   2297篇
  1977年   2123篇
  1976年   2186篇
  1975年   2104篇
  1974年   1947篇
  1973年   2197篇
  1972年   1322篇
  1971年   1001篇
  1968年   1152篇
  1967年   1132篇
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
961.
Laser treatment of bone tissue has already been the subject of many studies to find substitutes for mechanical instruments that are nowadays used in implantology and orthopaedics. Mainly lasers with pulse durations in the μs region have been tested leaving surface features that are not always satisfactory. Therefore, in the present study laser osteotomy has been performed with a 330 fs Yb:glass laser, λ = 1040 nm, at a pulse repetition rate of 1 kHz. For bovine spongiosa, compacta, and cartilage, the ablation thresholds as well as the ablation rates for various pulse energies have been determined. Additionally, quadratic areas have been ablated in bone tissue. The remaining morphology has been analyzed via scanning electron microscopy. Laser ablation has also been performed with an Er, Cr:YSGG laser, λ = 2780 nm, PRR = 20 Hz, τ ~ 50 μs. The results of USPL and Erbium laser ablation are compared.  相似文献   
962.
A new long-lived isomeric state in the near proton dripline nucleus 125Ce has been identified with Schottky mass spectrometry at GSI. The excitation energy E * = 103(12)keV and the decay time of 193(1)s have been obtained from a single stored fully ionized 125m Ce58+ ion. The data implies an E3 transition and a 1/2+ assignment for the spin of the isomer.  相似文献   
963.
This work presents a formulation based on UPML for truncating conductive media by using a local and non-orthogonal coordinate system to solve Maxwell’s equations by the FDTD method. The detailed procedure for obtaining the UPML equations for this case is shown and the complete equation set is provided.  相似文献   
964.
An integrated study of diffusion, solubility, and electrical properties of scandium and praseodymium in silicon annealed in various media and temperature ranges (1100–1280 °C) was performed for the first time. The tracer technique, autoradiography, measurements of isothermic capacity and current relaxation, conductivity, and the Hall effect were used for the investigations. The diffusion parameters, solubility, and an acceptor character of scandium and praseodymium impurities in silicon were determined. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 75–77, January, 2007.  相似文献   
965.
966.
The equation of sound propagation in an unstable medium produced by the presence of supersaturated water vapor in it, which can appear in a hurricane area, is derived. This equation takes into account the effects of sound velocity dispersion, amplification, damping, and nonlinear effects. Some solutions to this equation are presented, illustrating the specific features of sound propagation in an unstable medium. Published in Akusticheskiĭ Zhurnal, 2007, Vol. 53, No. 3, pp. 477–480.  相似文献   
967.
We study the hyperon-nucleus potential with distorted-wave impulse wave approximation (DWIA) using the Green's function method. In order to include the nucleon and hyperon potential effects in Fermi averaging, we introduce the local optimal momentum approximation of target nucleons. We can describe the quasi-free Λ , Σ and Ξ production spectra in a better way than in the standard Fermi-averaged t -matrix treatments.  相似文献   
968.
In this paper we establish a sharp result concerning integral mean estimates for self-reciprocal polynomials.  相似文献   
969.
970.
We study the evolution of radiating and viscous fluid spheres assuming an additional homothetic symmetry on the spherically symmetric space-time. We match a very simple solution to the symmetry equations with the exterior one (Vaidya). We then obtain a system of two ordinary differential equations which rule the dynamics, and find a self-similar collapse which is shear-free and with a barotropic equation of state. Considering a huge set of initial self-similar dynamics states, we work out a model with an acceptable physical behavior.  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