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   399300篇
  免费   4744篇
  国内免费   1454篇
化学   218425篇
晶体学   5823篇
力学   16558篇
综合类   12篇
数学   46218篇
物理学   118462篇
  2020年   2463篇
  2019年   2406篇
  2018年   2424篇
  2016年   4759篇
  2015年   3955篇
  2014年   5377篇
  2013年   17284篇
  2012年   12929篇
  2011年   16220篇
  2010年   10062篇
  2009年   9907篇
  2008年   14897篇
  2007年   15156篇
  2006年   14835篇
  2005年   13736篇
  2004年   12310篇
  2003年   10930篇
  2002年   10689篇
  2001年   12168篇
  2000年   9376篇
  1999年   7504篇
  1998年   6153篇
  1997年   5975篇
  1996年   5986篇
  1995年   5554篇
  1994年   5165篇
  1993年   4981篇
  1992年   5593篇
  1991年   5439篇
  1990年   5088篇
  1989年   4933篇
  1988年   5193篇
  1987年   4917篇
  1986年   4730篇
  1985年   6801篇
  1984年   6927篇
  1983年   5671篇
  1982年   6305篇
  1981年   6205篇
  1980年   5980篇
  1979年   6053篇
  1978年   6201篇
  1977年   6115篇
  1976年   6084篇
  1975年   5913篇
  1974年   5648篇
  1973年   5918篇
  1972年   3496篇
  1971年   2627篇
  1968年   2577篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
91.
92.
A cosmological model is presented that produces He, C, O, D, Li, Be, and B in their observed abundances without a Big Bang. The elements are produced during the 1.5-Gy formation period of a galaxy, with C, O, and other heavy elements produced by stars of M>12 M3 , He by stars of 6 Ms<M<12 Ms, and D, Li, Be, and B by cosmic-ray reactions in a nearly pure H plasma halo. Thus, the model shows that the major elements used in astrophysical studies can be produced during galactic formation by exactly the same processes known to function today at much lower rates  相似文献   
93.
Self broadened widths of seven lines of ozone between 75 and 120 GHz have been measured at room temperature. The variation with temperature of the self-broadening parameter for three of these lines has been studied in the range 245–292°K.  相似文献   
94.
We discuss some variant superfield representations which can arise by the replacement of some of the usual fields in a multiplet with p-form gauge fields.  相似文献   
95.
96.
In recent years there has emerged significant interest in low pressure radio frequency (rf) glow discharges which are used widely particulary in IC fabrication. Various parameters of the rf glow discharge have been found to be useful for its electrical characterization; however, there is no uniformity and agreement. Extensive experimental investigations on various discharge systems have shown, that the self-bias on the rf driven electrode, the complex conductivity and the breakdown characteristic are preferable parameters of rf discharges. Advantageously the self-bias and the complex conductivity should be presented in dependence on the pressure and the applied rf voltage. The discharge current cannot be measured quite accurately due to currents via leaky capacitors and the deviations from a sinusoidal form of the current due to nonlinearities.  相似文献   
97.
The purpose of this note is to describe a procedure for transferring familiar estimates for transition probabilities on RN to transition probabilities on compact manifolds.  相似文献   
98.
In this paper, we study the consistency of a variant of fractionalstep Runge–Kutta methods. These methods are designed tointegrate efficiently semi-linear multidimensional parabolicproblems by means of linearly implicit time integration processes.Such time discretization procedures are also related to a splittingof the space differential operator (or the spatial discretizationof it) as a sum of ‘simpler’ linear differentialoperators and a nonlinear term.  相似文献   
99.
The electro-optic response of ferroelectric smectic C* liquid crystals has been studied. Anomalous switching behaviour of such materials which possess a negative dielectric anisotropy has been reported. These materials show a minimum in response time at a sufficiently high field. We present results showing the dependency of this minimum upon spontaneous polarisation and the effect of AC bias. Calculations based upon the equation of motion of the director around the cone are presented which describe this effect and its dependence on the relative magnitudes of the spontaneous polarization and dielectric anisotropy of the material. Good agreement with the experimental results is found.  相似文献   
100.
For fairly high concentrations, the effective arsenic diffusioncoefficient is known to grow linearly with the concentration.In this paper, we consider the strongly enhanced diffusion ofarsenic by asymptotic methods, and extend the results of a previouspaper (King & Please, 1987) in three ways: we characterizean additional (low-concentration) region; we consider the influenceof the initial data; and we consider the case of constant surfaceconcentration.  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