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   10481篇
  免费   344篇
  国内免费   60篇
化学   6955篇
晶体学   62篇
力学   306篇
数学   1795篇
物理学   1767篇
  2023年   69篇
  2022年   157篇
  2021年   189篇
  2020年   198篇
  2019年   204篇
  2018年   213篇
  2017年   196篇
  2016年   345篇
  2015年   336篇
  2014年   352篇
  2013年   676篇
  2012年   772篇
  2011年   800篇
  2010年   487篇
  2009年   418篇
  2008年   615篇
  2007年   585篇
  2006年   517篇
  2005年   483篇
  2004年   427篇
  2003年   357篇
  2002年   288篇
  2001年   159篇
  2000年   142篇
  1999年   112篇
  1998年   87篇
  1997年   71篇
  1996年   85篇
  1995年   64篇
  1994年   76篇
  1993年   62篇
  1992年   63篇
  1991年   76篇
  1990年   75篇
  1989年   65篇
  1988年   56篇
  1987年   51篇
  1985年   60篇
  1984年   80篇
  1983年   42篇
  1982年   60篇
  1981年   48篇
  1980年   57篇
  1979年   43篇
  1978年   43篇
  1977年   57篇
  1976年   42篇
  1975年   47篇
  1974年   37篇
  1973年   35篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
The degree of phase separation in several moisture‐cured poly(urethane urea)s (PUUs) was studied by FTIR spectroscopy, wide angle X‐ray diffraction (WAXD), and temperature‐modulated differential scanning calorimetry (TMDSC). This latter technique was shown to be particularly useful in analysing the degree of phase separation in PUU polymers. Both phase mixing and phase segregation coexisted in the PUUs and the degree of phase separation increased as the urea hard segment (HS) content in the PUU increased. The maximum solubility of urea HSs into the polyol soft segments (SSs) was achieved for 50 wt % urea HS content in diol‐based PUUs, whereas for triol‐based PUUs the highest solubility between HS and SS was reached for lower urea HS amount. Finally, the higher the urea HS content the higher the extent of phase separation in the PUU. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3034–3045, 2007  相似文献   
3.
Book rewiev     
Howard Anton and Robert C. Busby, John Wiley & Sons, Inc., 2002.  相似文献   
4.
In order to understand better the way in which radioactive contamination may be transferred from the atmosphere to other ecological compartments it is necessary to obtain information of the deposition mechanisms of radionuclides. Concentration and speciation of 137Cs and 7Be in the atmospheric aerosol and deposition were studied. The mixed deposition velocities of water-soluble and insoluble 137Cs and 7Be were determined. The relation between activity concentrations of insoluble 7Be in the atmosphere and its amount in deposition was observed. It is supposed that in the deposition process of radiocesium the precipitation plays an important role in scavenging of water-soluble radiocesium by falling raindrops, in contrast to insoluble 137Cs where the dry deposition becomes predominant.  相似文献   
5.
The control of piecewise-deterministic processes is studied where only local boundedness of the data is assumed. Moreover the discount rate may be zero. The value function is shown to be solution to the Bellman equation in a weak sense; however the solution concept is strong enough to generate optimal policies. Continuity and compactness conditions are given for the existence of nonrelaxed optimal feedback controls.  相似文献   
6.
The purpose of this paper is to give the Reid ``Roundabout Theorem' for quadratic functionals with general boundary conditions. In particular, we describe the so-called coupled point and regularity condition introduced in [16] in terms of Riccati equation solutions. Accepted 27 February 1996  相似文献   
7.
The article referenced above was first published online on 30 August 2007 with incorrect pagination; the pagination has now been corrected online and in print. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   
8.
Pentacyclic isoxazolines were obtained by the cycloaddition of benzonitrile oxide to norbornene-azetidinone-fused 3,1-oxazines. The constitutions of two of the isomers obtained, and the configurations and conformations of all products, were determined by means of 1H and 13C NMR spectroscopy and DNOE experiments.  相似文献   
9.
Chulsu Jo  Y.-R. Jang 《Surface science》2006,600(8):1592-1595
Magnetic properties of Co chain-coated carbon nanotube (CNT) were investigated using a first-principles calculation. Binding energy between Co chain and CNT increased with the coverage ratio, and the adsorption of Co chains on CNT enhanced the conductance channel. Total magnetic moment of Co chains coated on CNT increased with the coverage ratio, while the magnetic moment per Co atom decreased due to spin flip of majority spin states in Co atoms. Spin polarization at the Fermi level of the Co chains was calculated to converge to that of bulk fcc Co.  相似文献   
10.
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