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   294346篇
  免费   3537篇
  国内免费   1071篇
化学   160851篇
晶体学   3861篇
力学   12818篇
综合类   10篇
数学   30215篇
物理学   91199篇
  2021年   1876篇
  2020年   2171篇
  2019年   2255篇
  2018年   2669篇
  2017年   2736篇
  2016年   4614篇
  2015年   3277篇
  2014年   4534篇
  2013年   13013篇
  2012年   10316篇
  2011年   12793篇
  2010年   8428篇
  2009年   8613篇
  2008年   12031篇
  2007年   11811篇
  2006年   11453篇
  2005年   10563篇
  2004年   9488篇
  2003年   8467篇
  2002年   8303篇
  2001年   10502篇
  2000年   7832篇
  1999年   6018篇
  1998年   4395篇
  1997年   4415篇
  1996年   3948篇
  1995年   3817篇
  1994年   3709篇
  1993年   3414篇
  1992年   4164篇
  1991年   4203篇
  1990年   3853篇
  1989年   3782篇
  1988年   3810篇
  1987年   3732篇
  1986年   3477篇
  1985年   4786篇
  1984年   4792篇
  1983年   3856篇
  1982年   4033篇
  1981年   3787篇
  1980年   3705篇
  1979年   3929篇
  1978年   4097篇
  1977年   4039篇
  1976年   3893篇
  1975年   3754篇
  1974年   3658篇
  1973年   3771篇
  1972年   2323篇
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
1.
Yang  T. L.  Kao  C. L.  Kuo  C. E.  Yeh  H. C.  Li  W. J.  Li  H. T.  Chen  C. Y. 《Chemistry of Natural Compounds》2022,58(5):825-827
Chemistry of Natural Compounds - A novel bibenzyl derivative, hydrangchinenin (1), was isolated from the stems of Hydrangea chinensis Maxim. (Hydrangeaceae). Its structure was determined on the...  相似文献   
2.
Chromatographia - We developed a simple, rapid, ecological RP-HPLC method for the estimation of Pitavastatin (PIT), Fenofibrate (FEN), and their impurities in a novel fixed dose combination. We...  相似文献   
3.
Fan  K.  Lu  R. S.  Liang  K. K.  Hou  Z. C. 《High Energy Chemistry》2022,56(4):264-269
High Energy Chemistry - Modification of Polyvinylidene fluoride (PVDF) by radiation grafting is a research hotspot in recent years. In this study, the monomer 2-Hydroxyethyl methacrylate (HEMA) was...  相似文献   
4.
Mechanics of Composite Materials - Carbon fiber (CF)/ polyamide (PA6) composites are one of the most promising thermoplastic materials for automobile applications. However, the interfacial...  相似文献   
5.
In the pursuit to enlarge the library of polyimide materials for energy applications, new polyimide/MWCNTs composite films have been developed by MWCNTs-assisted polycondensation reaction of a hydroxyl and triphenylmethane-containing diamine with benzophenone tetracarboxylic dianhydride targeting to highlight their electrical storage capability as flexible electrodes in micro-supercapacitors (mSCs). The Fourier-transform infrared spectroscopy, proton nuclear magnetic resonance, UV–vis, fluorescence, and Raman spectroscopies were used to demonstrate the evolution of interfacial interactions between MWCNTs and the precursors (diamine monomer and intermediate polyamidic acid) and polyimide matrix that proved to be the origin of MWCNTs homogeneous dispersion. Thus, composite films incorporating 1, 3, 5, and 10 w.t.% MWCNTs were obtained and thoroughly investigated with regard to their morphology, mechanical behavior, thermal stability, and electrical conductivity. The electrochemical performance of these composites was first analyzed in a classical three-electrode cell by cyclic voltammetry and galvanostatic charge-discharge in both aqueous and organic electrolyte systems. By far, the best electrical storage capacity was obtained with the composite polyimide film containing 10% MWCNTs that was further used as both active material and current collector in a flexible symmetric mSC realized by a straightforward and low-cost procedure. In the attempt to better exploit the advantages of this composite film, it was layered with a graphite-containing paint and tested as an electrode in a flexible mSC, which provided satisfactory results. To our knowledge, this is the first report on the electrical charge storage capability of a polyimide/MWCNTs free-standing film as a flexible electrode in mSCs, which do not require time- and resource-consuming processing steps.  相似文献   
6.
Journal of Structural Chemistry - A new polymorph of the [ReCl3(MeCN)(PPh3)2] complex is synthesized and characterized by single crystal X-ray diffraction (XRD). Its recrystallization from the...  相似文献   
7.
Journal of Structural Chemistry - Atomic and electronic structures of cyclic organosilicon compound 9,9,10,10-tetraethynyl-9,10-dihydrodisilaanthracene are studied by the density functional theory....  相似文献   
8.
Russian Journal of General Chemistry - The review article traces the main trends of the synthetic approach to the solution of the problem of overcoming the resistance of pathogenic bacterial...  相似文献   
9.
10.

A kinetic study of the effect of thermoheliox (inhalation of a helium and oxygen mixture, 70 °C) on the functional hemodynamics of the human brain by functional magnetic resonance imaging was carried out. The dynamic responses of the BOLD signal were found to be biphasic. An empirical equation describing the first phase of the hemodynamic response to visual stimulus was proposed. It was shown that preliminary inhalation of thermoheliox stimulates the hemodynamic responses by slowing down the vasoconstriction.

  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