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   656248篇
  免费   7642篇
  国内免费   2118篇
化学   353998篇
晶体学   9418篇
力学   28433篇
综合类   19篇
数学   79859篇
物理学   194281篇
  2021年   5004篇
  2020年   5628篇
  2019年   5955篇
  2018年   7263篇
  2017年   7070篇
  2016年   11567篇
  2015年   7852篇
  2014年   11595篇
  2013年   30209篇
  2012年   22960篇
  2011年   28437篇
  2010年   19235篇
  2009年   18916篇
  2008年   25838篇
  2007年   26013篇
  2006年   24428篇
  2005年   22068篇
  2004年   20268篇
  2003年   17981篇
  2002年   17584篇
  2001年   19535篇
  2000年   14908篇
  1999年   11864篇
  1998年   9785篇
  1997年   9439篇
  1996年   9366篇
  1995年   8411篇
  1994年   8190篇
  1993年   7884篇
  1992年   8871篇
  1991年   8789篇
  1990年   8361篇
  1989年   8136篇
  1988年   8255篇
  1987年   7991篇
  1986年   7657篇
  1985年   10304篇
  1984年   10506篇
  1983年   8487篇
  1982年   8880篇
  1981年   8874篇
  1980年   8381篇
  1979年   8840篇
  1978年   8974篇
  1977年   8940篇
  1976年   8792篇
  1975年   8348篇
  1974年   8197篇
  1973年   8355篇
  1972年   5539篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
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   
142.
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   
143.
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   
144.
145.
146.
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   
147.
Butyltins were analyzed in waters from California river and lake marinas and were detected at the part per trillion (ppt) level in most locations. The tributyltin:dibutyltin (TBT/DBT) ratios in the fresh waters were similar to those in their saline counterparts indicating like rates of degradation in the two salinity regimes.  相似文献   
148.
149.
An infinite row of periodically spaced, identical rigid circularcylinders is excited by an acoustic line source which is parallelto the generators of the cylinders. A method for calculatingthe scattered field accurately and efficiently is presented.When the cylinders are sufficiently close together, Rayleigh–Blochsurface waves that propagate energy to infinity along the arrayare excited. An expression is derived which enables the amplitudesof these surface waves to be computed without requiring thesolution to the full scattering problem.  相似文献   
150.
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   
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