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   901篇
  免费   34篇
  国内免费   5篇
化学   651篇
晶体学   4篇
力学   10篇
数学   158篇
物理学   117篇
  2023年   11篇
  2022年   27篇
  2021年   26篇
  2020年   32篇
  2019年   30篇
  2018年   13篇
  2017年   14篇
  2016年   28篇
  2015年   28篇
  2014年   29篇
  2013年   51篇
  2012年   71篇
  2011年   57篇
  2010年   34篇
  2009年   38篇
  2008年   45篇
  2007年   49篇
  2006年   47篇
  2005年   46篇
  2004年   39篇
  2003年   35篇
  2002年   24篇
  2001年   9篇
  2000年   8篇
  1998年   5篇
  1997年   12篇
  1996年   8篇
  1995年   5篇
  1994年   8篇
  1993年   5篇
  1991年   4篇
  1990年   6篇
  1989年   5篇
  1987年   5篇
  1986年   3篇
  1985年   5篇
  1983年   4篇
  1982年   7篇
  1981年   4篇
  1980年   3篇
  1978年   4篇
  1977年   3篇
  1973年   3篇
  1933年   2篇
  1931年   2篇
  1925年   2篇
  1923年   2篇
  1918年   3篇
  1917年   2篇
  1915年   2篇
排序方式: 共有940条查询结果,搜索用时 15 毫秒
71.
72.
73.
74.
The compounds diethyl-N-carbazolylmethylphosphonate 1 and diethyl-2-oxymethylphosphonate carbazole 2 have been synthesised and characterized by a range of techniques including NMR, absorption and emission spectroscopy, infrared, and mass spectroscopy. Compound 1 forms a 2:1 complex 3 with calcium nitrate and the single crystal X-ray diffraction structure of 3 is described. Titrations of 1 with Zn2+ and Ca2+ in ethanol reveal that the intrinsic fluorescence is only slightly perturbed in the presence of these metal ions in micromolar ethanol solutions. Compounds 1 and 2 are readily taken up and visualized in L929 fibrosarcoma and DRG (Dorsal root ganglia) cell lines.  相似文献   
75.
76.

In order to separate and pre-concentrate uranium from aqueous phase, a novel silica-based adsorbent was prepared by impregnating nalidixic acid (HNA) into a macroreticular silica/polymer composite support (SiO2-P) with a mean diameter of 60 μm. Adsorption behavior of uranium from aqueous solution onto the adsorbent was studied. Experimental results indicated that HNA/SiO2-P showed strong adsorption for uranium in a wide range of pH from 3.5 to 10.0, and the maximum adsorption capacity was 35.4 mg g−1. In addition, HNA/SiO2-P exhibited good selectivity for U(VI) and showed weak or bare adsorption affinity to foreign ions. Kinetic and isotherm of uranium adsorption were in accordance with the pseudo-second-order kinetic model and Langmuir isotherm adsorption model, respectively. Moreover, U(VI) sorption was found to be an endothermic reaction and spontaneous under experimental state. The synthesized adsorbent showed an admirable stability at lower pH values in aqueous solution.

  相似文献   
77.
Transition‐metal‐catalyzed C? H activation has recently emerged as a powerful tool for the functionalization of organic molecules. While many efforts have focused on the functionalization of arenes and heteroarenes by this strategy in the past two decades, much less research has been devoted to the activation of non‐acidic C? H bonds of alkyl groups. This Minireview highlights recent work in this area, with a particular emphasis on synthetically useful methods.  相似文献   
78.
79.
Most democratic countries use apportionment methods to transform election results into whole numbers, which usually give the number of seats in a legislative body that the parties obtained. Which apportionment method does this best can be specified by measuring the error between the allocated result and the ideal proportion. We show how to find an apportionment method which is best suited to a given error function. We also discuss several properties of apportionment methods that have been labelled paradoxa. In particular we explain the highly publicised “Alabama” Paradox for the Hare/Hamilton method and show that other popular apportionment methods come with their very own paradoxa.  相似文献   
80.
An s-geodesic in a graph Γ is a path connecting two vertices at distance s. Being locally transitive on s-geodesics is not a monotone property: if an automorphism group G of a graph Γ is locally transitive on s-geodesics, it does not follow that G is locally transitive on shorter geodesics. In this paper, we characterise all graphs that are locally transitive on 2-geodesics, but not locally transitive on 1-geodesics.  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