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   1313322篇
  免费   25645篇
  国内免费   7772篇
化学   647957篇
晶体学   20433篇
力学   74425篇
综合类   107篇
数学   239953篇
物理学   363864篇
  2021年   13480篇
  2020年   15906篇
  2019年   16024篇
  2018年   13033篇
  2016年   27897篇
  2015年   20775篇
  2014年   30360篇
  2013年   74186篇
  2012年   36282篇
  2011年   32513篇
  2010年   36774篇
  2009年   39480篇
  2008年   32241篇
  2007年   27801篇
  2006年   33350篇
  2005年   26545篇
  2004年   27918篇
  2003年   26559篇
  2002年   27623篇
  2001年   25954篇
  2000年   23161篇
  1999年   21750篇
  1998年   20727篇
  1997年   20763篇
  1996年   20974篇
  1995年   19095篇
  1994年   18526篇
  1993年   18048篇
  1992年   17770篇
  1991年   18065篇
  1990年   17304篇
  1989年   17386篇
  1988年   16954篇
  1987年   16984篇
  1986年   15868篇
  1985年   22331篇
  1984年   23643篇
  1983年   19866篇
  1982年   21581篇
  1981年   20816篇
  1980年   20167篇
  1979年   20238篇
  1978年   21606篇
  1977年   21185篇
  1976年   20843篇
  1975年   19514篇
  1974年   19168篇
  1973年   19637篇
  1972年   14122篇
  1967年   12371篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Employing radical bridges between anisotropic metal ions has been a viable route to achieve high-performance single-molecule magnets (SMMs). While the bridges have been mainly considered for their ability to promote exchange interactions, the crystal-field effect arising from them has not been taken into account explicitly. This lack of consideration may distort the understanding and limit the development of the entire family. To shed light on this aspect, herein we report a theoretical investigation of a series of N -radical-bridged diterbium complexes. It is found that while promoting strong exchange coupling between the terbium ions, the N -radical induces a crystal field that interferes destructively with that of the outer ligands, and thus reduces the overall SMM behavior. Based on the theoretical results, we conclude that the SMM behavior in this series could be further maximized if the crystal field of the outer ligands is designed to be collinear with that of the radical bridge. This conclusion can be generalized to all exchange-coupled SMMs.  相似文献   
2.
3.
4.
A liquid dewetting method for the determination of the viscoelastic properties of ultrathin polymer films has been extended to study thickness effects on the properties of ultrathin polycarbonate (PC) films. PC films with film thicknesses ranging from 4 to 299 nm were placed on glycerol at temperatures from below the macroscopic glass transition temperature (Tg) to above it with the dewetting responses being monitored. It is found that the isothermal creep results for films of the same thickness, but dewetted at different temperatures can be superposed into one master curve, which is consistent with the fact of PC being a thermorheologically simple material. Furthermore, the results show that the Tg of PC thin films is thickness dependent, but the dependence is weaker than the results for freely standing films and similar to literature data for PC films supported on rigid substrates. It was also found that the rubbery plateau region for the PC films stiffens dramatically, but still less than what has been observed for freely standing polycarbonate films. The rubbery stiffening is discussed in terms of a recently reported model that relates macroscopic segmental dynamics with the stiffening. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1559–1566  相似文献   
5.
6.
7.
8.
9.
10.
The development of high‐surface‐area carbon electrodes with a defined pore size distribution and the incorporation of pseudo‐active materials to optimize the overall capacitance and conductivity without destroying the stability are at present important research areas. Composite electrodes of carbon nano‐onions (CNOs) and polypyrrole (Ppy) were fabricated to improve the specific capacitance of a supercapacitor. The carbon nanostructures were uniformly coated with Ppy by chemical polymerization or by electrochemical potentiostatic deposition to form homogenous composites or bilayers. The materials were characterized by transmission‐ and scanning electron microscopy, differential thermogravimetric analyses, FTIR spectroscopy, piezoelectric microgravimetry, and cyclic voltammetry. The composites show higher mechanical and electrochemical stabilities, with high specific capacitances of up to about 800 F g?1 for the CNOs/SDS/Ppy composites (chemical synthesis) and about 1300 F g?1 for the CNOs/Ppy bilayer (electrochemical deposition).  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