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   29554篇
  免费   980篇
  国内免费   170篇
化学   20012篇
晶体学   281篇
力学   1046篇
综合类   1篇
数学   2551篇
物理学   6813篇
  2023年   164篇
  2022年   438篇
  2021年   528篇
  2020年   471篇
  2019年   479篇
  2018年   364篇
  2017年   344篇
  2016年   809篇
  2015年   694篇
  2014年   889篇
  2013年   1642篇
  2012年   2141篇
  2011年   2309篇
  2010年   1444篇
  2009年   1255篇
  2008年   1905篇
  2007年   1809篇
  2006年   1674篇
  2005年   1554篇
  2004年   1374篇
  2003年   1065篇
  2002年   1058篇
  2001年   715篇
  2000年   613篇
  1999年   365篇
  1998年   276篇
  1997年   315篇
  1996年   362篇
  1995年   276篇
  1994年   292篇
  1993年   294篇
  1992年   280篇
  1991年   217篇
  1990年   168篇
  1989年   154篇
  1988年   148篇
  1987年   125篇
  1986年   98篇
  1985年   175篇
  1984年   116篇
  1983年   104篇
  1982年   129篇
  1981年   97篇
  1980年   87篇
  1978年   84篇
  1977年   92篇
  1976年   99篇
  1975年   103篇
  1974年   85篇
  1973年   103篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
We construct functions Mα which are piecewise homogeneous polynomials on the (d+1)-dimensional torus Ud+1. These functions possess complete symmetry with respect to the independent variables. The symmetry and homogeneous relations for these functions are exploited to obtain a recurrence relation and explicit representations. Furthermore, we show that , where ω=e12x/k, 0≤jt≤k−1, are linearly independent. By restricting Mα to Ud, we obtain the complex analogue of polynomial box splines on a (d+1)-direction mesh on Ud, which is a multivariate analogue of B-splines on the circle studied by I.J. Schoenberg[8].  相似文献   
112.
113.
We give the polarization density matrix ofZ andW for the decay processZ 0Wff' with generalZWW couplings. The matrix elements are expressed in terms of kinematical invariants so that they can be readily used in \(p\bar p \to Z^0 W\) as well. Using these formulas, we analyze the possibilities of probing theZWW couplings through the decay of polarizedZ 0.  相似文献   
114.
115.
116.
117.
118.
Three new polyoxygenated briarane-type diterpenoids, briaexcavatolides X-Z (1-3), have been isolated from the gorgonian coral Briareum excavatum. The structures, including the relative configurations of briaranes 1-3, were elucidated by spectroscopic methods, particularly in 1D and 2D NMR experiments. The configuration of briarane 1 was further supported by molecular mechanics calculations.  相似文献   
119.
The effect of CuO on the thermal behaviour of Zr/KClO4 primer mixtures was studied by thermoanalytical techniques, and the Bruceton method and its related calculation. It was found that the CuO catalytically promoted the decomposition of Zr/KClO4 primer mixtures and shifted the exothermic peak of DSC curves to lower temperatures. In addition, the Zr/KClO4 primer mixture containing CuO had a significant effect on the firing characteristics of electro-explosive devices.  相似文献   
120.
Methane conversion using an electric discharge has been studied for many years. Recently, many research groups have developed high-frequency pulsed plasma reaction for methane conversion to higher hydrocarbons and synthesis gas. CO2 reforming of methane to synthesis gas has also attracted considerable interest as a method of utilization of the greenhouse gases, CO2 and CH4, which occupy most of man-made greenhouse gases. In this study, the influence of pulse form of applied voltage on methane and carbon dioxide conversions and product selectivity has been investigated using a cylindrical type DBD reactor. For this purpose, two kinds of power supply were compared, that is, AC power supply which has a high-frequency sinusoidal wave form, and AC pulse power supply which has modified AC pulse wave form. The conversions of methane and carbon dioxide were enhanced using pulsed plasma. The lower pulse width was more profitable economically.  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