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   4207篇
  免费   118篇
  国内免费   22篇
化学   2849篇
晶体学   33篇
力学   87篇
数学   640篇
物理学   738篇
  2023年   23篇
  2021年   26篇
  2020年   42篇
  2019年   60篇
  2018年   40篇
  2017年   34篇
  2016年   84篇
  2015年   72篇
  2014年   101篇
  2013年   203篇
  2012年   182篇
  2011年   212篇
  2010年   134篇
  2009年   127篇
  2008年   190篇
  2007年   192篇
  2006年   176篇
  2005年   172篇
  2004年   136篇
  2003年   131篇
  2002年   123篇
  2001年   73篇
  2000年   87篇
  1999年   57篇
  1998年   63篇
  1997年   58篇
  1996年   67篇
  1995年   64篇
  1994年   55篇
  1993年   60篇
  1992年   61篇
  1991年   73篇
  1990年   47篇
  1989年   58篇
  1988年   60篇
  1987年   52篇
  1986年   72篇
  1985年   62篇
  1984年   69篇
  1983年   47篇
  1982年   44篇
  1981年   59篇
  1980年   64篇
  1979年   52篇
  1978年   43篇
  1977年   42篇
  1976年   40篇
  1975年   30篇
  1974年   27篇
  1973年   24篇
排序方式: 共有4347条查询结果,搜索用时 9 毫秒
971.
972.
Correction for ‘SuFEx-enabled, chemoselective synthesis of triflates, triflamides and triflimidates’ by Bing-Yu Li et al., Chem. Sci., 2022, 13, 2270–2279, DOI: 10.1039/D1SC06267K.

The authors would like to correct the second sentence in the Acknowledgements section, which should read “For HPLC analyses, we kindly acknowledge Marcus Frings and the support from RWTH Aachen University.”The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.  相似文献   
973.
974.
975.
The selectivity in the hydrogenation of acrolein over Fe3O4‐supported Pd nanoparticles has been investigated as a function of nanoparticle size in the 220–270 K temperature range. While Pd(111) shows nearly 100 % selectivity towards the desired hydrogenation of the C=O bond to produce propenol, Pd nanoparticles were found to be much less selective towards this product. In situ detection of surface species by using IR‐reflection absorption spectroscopy shows that the selectivity towards propenol critically depends on the formation of an oxopropyl spectator species. While an overlayer of oxopropyl species is effectively formed on Pd(111) turning the surface highly selective for propenol formation, this process is strongly hindered on Pd nanoparticles by acrolein decomposition resulting in CO formation. We show that the extent of acrolein decomposition can be tuned by varying the particle size and the reaction temperature. As a result, significant production of propenol is observed over 12 nm Pd nanoparticles at 250 K, while smaller (4 and 7 nm) nanoparticles did not produce propenol at any of the temperatures investigated. The possible origin of particle‐size dependence of propenol formation is discussed. This work demonstrates that the selectivity in the hydrogenation of acrolein is controlled by the relative rates of acrolein partial hydrogenation to oxopropyl surface species and of acrolein decomposition, which has significant implications for rational catalyst design.  相似文献   
976.
977.
Peracetylated glycals were treated with terminal alkyne derivatives under Lewis acid catalysis to result in the formation of the pure α- or β- anomerically substituted hex-2-enopyranosides carrying 2(E)-halogenated olefins.  相似文献   
978.
The luminescence of the inorganic–organic hybrid nanoparticles ZrO(MFP) (MFP=methylfluorescein phosphate) and ZrO(RP) (RP=resorufin phosphate) was modified by addition of different rare earth halides LnCl3. The resulting composite materials form dispersible nanoparticles that exhibit modified nanoparticle fluorescence depending on the rare earth ion. The resulting chromaticity of the luminescence is further variable by the employment of different solvents for ZrO(MFP)-based composite systems. The strong solvatochromic effect of the MFP chromophore leads to different luminescence chromaticities of the composite materials between green, yellow, and blue in THF, toluene, and dichloromethane, respectively. The luminescence of ZrO(RP)-based composite particles can be modified between the red and blue spectral regions in dependence on the applied reaction temperature. Beside a luminescence shift that is derived from nanoparticle modification by LnCl3, a strong turn-on effect of ZrO(RP) particles results after contact with different Brønsted acids and bases in combination with a respective chromaticity shift. Both effects enable the potential employment of such particles as highly sensitive optical pH sensors.  相似文献   
979.
Abstract

Glycal derivatives of N-acetylneuraminic acid were prepared and their N-iodosuccinimide-mediated glycosylation shown to proceed only with most reactive alcohols, Their reduced enol ether reactivity is attributed to the α unsaturated ester reature. Thus several reduced glycal derivatives were synthesized. These couid be glycosyiatec with simple alcohols as well as otner saccnarides as aglycones in averaae to modest yields with the trans-diaxiai additions compounas prevailing. A number or selective and specific prepparation led to both the anomeric phenylthioglycosides or N dcety Ineuraminic acid. These could be used in phenylmercurl triflate-promoted glycosylations to afford several derivatives.  相似文献   
980.
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