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   402363篇
  免费   4919篇
  国内免费   1472篇
化学   220832篇
晶体学   5852篇
力学   16601篇
综合类   12篇
数学   46444篇
物理学   119013篇
  2020年   2519篇
  2019年   2475篇
  2018年   2469篇
  2016年   4895篇
  2015年   4054篇
  2014年   5520篇
  2013年   17488篇
  2012年   13193篇
  2011年   16498篇
  2010年   10220篇
  2009年   10060篇
  2008年   15102篇
  2007年   15343篇
  2006年   14988篇
  2005年   13884篇
  2004年   12472篇
  2003年   11037篇
  2002年   10813篇
  2001年   12202篇
  2000年   9441篇
  1999年   7531篇
  1998年   6167篇
  1997年   5987篇
  1996年   6003篇
  1995年   5568篇
  1994年   5181篇
  1993年   4996篇
  1992年   5618篇
  1991年   5453篇
  1990年   5091篇
  1989年   4937篇
  1988年   5195篇
  1987年   4922篇
  1986年   4732篇
  1985年   6816篇
  1984年   6932篇
  1983年   5674篇
  1982年   6311篇
  1981年   6216篇
  1980年   5988篇
  1979年   6059篇
  1978年   6207篇
  1977年   6124篇
  1976年   6089篇
  1975年   5920篇
  1974年   5658篇
  1973年   5921篇
  1972年   3497篇
  1971年   2629篇
  1968年   2579篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Palladium(II) complexes with N,N‐bis(diphenylphosphino)aniline ligands catalyse the Heck reaction between styrene and aryl bromides, affording stilbenes in good yield. The structures of two of the complexes used as pre‐catalysts have been determined by single‐crystal X‐ray diffraction. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   
92.
Analysis of stochastic processes governed by the Langevin equation is discussed. The analysis is based on a general method for non-parametric estimation of deterministic and random terms of the Langevin equation directly from given data. Separate estimation of the terms corresponds to the decomposition of process dynamics into deterministic and random components. Part I of the paper presented several possibilities for qualitative and quantitative analysis of process dynamics based on such decomposition. In Part II, some of these analysis possibilities are applied to experimental datasets from metal cutting and laser-beam welding.  相似文献   
93.
It is shown that the construction of needle variations can be carried out for almost lower semicontinuous differential inclusions rather than for the case of ordinary single-valued continuously differentiable vector fields usually considered in the literature. The construction leads to needle variations whose flows are in general set-valued but still have good differentiability properties. The variations are constructed by using single-valued selections that are not necessarily continuous with respect to the state variable, but have instead a much weaker 'integral continuity' property, somewhat more general that the 'directional continuity' considered in previous work by A. Cambini and S. Querci, A. Pucci, and A. Bressan. The existence of many such selections is proved by slightly adapting an argument due to Bressan, extending it from the lower semicontinuous to the almost lower semicontinuous case, and strengthening it to yield not only directional continuity at all points but also full continuity at a specified point.  相似文献   
94.
95.
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   
96.
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   
97.
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   
98.
99.
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   
100.
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   
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