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   433830篇
  免费   4234篇
  国内免费   1296篇
化学   219699篇
晶体学   6769篇
力学   20646篇
综合类   10篇
数学   58107篇
物理学   134129篇
  2018年   11063篇
  2017年   11990篇
  2016年   8277篇
  2015年   4247篇
  2014年   4690篇
  2013年   14654篇
  2012年   14742篇
  2011年   25376篇
  2010年   15706篇
  2009年   15810篇
  2008年   22455篇
  2007年   25913篇
  2006年   11902篇
  2005年   17927篇
  2004年   13427篇
  2003年   11906篇
  2002年   9756篇
  2001年   10676篇
  2000年   8356篇
  1999年   6365篇
  1998年   4930篇
  1997年   4950篇
  1996年   5022篇
  1995年   4500篇
  1994年   4307篇
  1993年   4086篇
  1992年   4792篇
  1991年   4641篇
  1990年   4329篇
  1989年   4371篇
  1988年   4326篇
  1987年   4294篇
  1986年   4019篇
  1985年   5667篇
  1984年   5677篇
  1983年   4666篇
  1982年   4985篇
  1981年   4823篇
  1980年   4701篇
  1979年   4817篇
  1978年   5099篇
  1977年   4849篇
  1976年   4760篇
  1975年   4591篇
  1974年   4418篇
  1973年   4603篇
  1972年   2822篇
  1968年   2595篇
  1967年   2768篇
  1966年   2406篇
排序方式: 共有10000条查询结果,搜索用时 23 毫秒
991.
A new approach to identify the independent amplitudes along with their partial wave multipole expansions, for photo-and electro-production is suggested, which is generally applicable to mesons with arbitrary spin-parity. These amplitudes facilitate direct identification of different resonance contributions.   相似文献   
992.
We present the results of a spectroscopic study of a nonequilibrium plasma in a Hall accelerator, in particular for such an important parameter as the electron temperature. For the studied conditions, we used the semicoronal equilibrium model, which relates the intensity ratios for two successive ionization steps for the same element. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 93–96, January–February, 2007.  相似文献   
993.
994.
995.
996.
Nanostructures formed during the reduction of ionic selenium in the selenite-ascorbate redox system in an aqueous solution of bovine serum albumin (BSA) were studied using static and dynamic light scattering and flow birefringence. It was established that this process results in the formation of stable aggregates of selenium nanoparticles that adsorb BSA molecules. It was found that highly-ordered superhigh-molecular-weight spherical nanostructures with high density and unique morphology are formed. Experiments with a cell culture of promyelocytic leukemia HL-60 showed that BSA adsorbed on selenium nanoparticles can inhibit the growth of tumor cells and deactivate free radicals with an efficiency comparable with that of sodium selenite.  相似文献   
997.
Let T be a bounded linear operator in a Banach space, with σ(T)={1}. In 1983, Esterle-Berkani' s conjecture was proposed for the decay of differences (I - T) T^n as follows: Eitheror lim inf (n→∞(n+1)||(I-T)T^n||≥1/e or T = I. We prove this claim and discuss some of its consequences.  相似文献   
998.
Seismic data is modeled in the high‐frequency approximation, using the techniques of microlocal analysis. We consider general, anisotropic elastic media. Our methods are designed to allow for the formation of caustics. The data is modeled in two ways. First, we give a microlocal treatment of the Kirchhoff approximation, where the medium is assumed to be piecewise smooth, and reflection and transmission occur at interfaces. Second, we give a refined view on the Born approximation based upon a linearization of the scattering process in the medium parameters around a smooth background medium. The joint formulation of Born and Kirchhoff scattering allows us to take into account general scatterers as well as the nonlinear dependence of reflection coefficients on the medium parameters. The latter allows the treatment of scattering up to grazing angles. The outcome of the analysis is a characterization of the singular part of seismic data. We obtain a set of pseudodifferential operators that annihilate the data. In the process we construct a Fourier integral operator and a reflectivity function such that the data can be represented by this operator acting on the reflectivity function. In our construction this Fourier integral operator becomes invertible. We give the conditions for invertibility for general acquisition geometry. The result is also of interest for inverse scattering in acoustic media. © 2002 John Wiley & Sons, Inc.  相似文献   
999.
Methods of silicon planar technology and pulsed laser deposition were applied to fabricate fully solid-state chemical sensors for determining ions of copper, lead, cadmium, thallium, and also sulfide and chloride ions on the basis of thin chalcogenide films as ion-sensitive membranes.  相似文献   
1000.
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