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   12630篇
  免费   1773篇
  国内免费   1932篇
化学   10354篇
晶体学   258篇
力学   458篇
综合类   152篇
数学   1350篇
物理学   3763篇
  2024年   21篇
  2023年   153篇
  2022年   315篇
  2021年   392篇
  2020年   434篇
  2019年   497篇
  2018年   373篇
  2017年   416篇
  2016年   561篇
  2015年   633篇
  2014年   790篇
  2013年   965篇
  2012年   1145篇
  2011年   1199篇
  2010年   911篇
  2009年   869篇
  2008年   1045篇
  2007年   851篇
  2006年   815篇
  2005年   681篇
  2004年   554篇
  2003年   452篇
  2002年   540篇
  2001年   354篇
  2000年   260篇
  1999年   204篇
  1998年   157篇
  1997年   99篇
  1996年   101篇
  1995年   76篇
  1994年   62篇
  1993年   64篇
  1992年   50篇
  1991年   67篇
  1990年   33篇
  1989年   42篇
  1988年   17篇
  1987年   26篇
  1986年   17篇
  1985年   23篇
  1984年   12篇
  1983年   9篇
  1982年   6篇
  1981年   6篇
  1980年   5篇
  1979年   4篇
  1978年   5篇
  1977年   4篇
  1976年   5篇
  1955年   3篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
For the Na I2 collision system, theoretical study is performed on the QCISD(T) level by using ab initio method. The ab initio potential energy surfaces are got and on them the long-lived complexes are found and optimized. These results verify the crossed molecule beam experimental phenomenon and the detailed geometry structures are given for the first time. The role of the complexes in the reaction path is also described in detail.  相似文献   
22.
2,5-Disubstituted oxazoles were prepared conveniently by treatment of aromatic α-methyl ketones and nitriles with poly[styrene(iodosodiacetate)] in one-pot process.  相似文献   
23.
A Glaser coupling reaction of terminal alkynes in the presence of nickel chloride withoutany organics and bases in hot water has been developed, which produces the correspondinghomo-coupling products in good yields.  相似文献   
24.
A mono-funtionalised tetraphenylporphyrin (TPP) bearing valine moiety at the phenyl ring was synthesized for photocytotoxicity examination in four steps, starting from regiospecific mono-nitration of TPP at the phenyl ring. The in vitro photocytotoxicitic effect against SPC-Al adenocarcinona cell line was tested.  相似文献   
25.
The distributions of limit cycles of cubic vector fields (P2, Q3) are considered in this paper, where P2 and Q3 are polynomials of x and y of order two and three, respectively. It is possibly seven different distributions of limit cycles given in [1]. We now prove that in which three kinds of distributions are impossible and other four kinds all can be realized by concrete vector fields of (P2,Q3). Some related results are also given.  相似文献   
26.
介绍用Josephson结电子模拟器在政党温度下,模拟测量磁通量子2e/h,用模拟器来研究Josephosn结的特性。该实验可作为普通物理实验中课题设计实验的一个内容。  相似文献   
27.
Outline imaging by THz time domain spectroscopy is proposed. Spectroscopic splitting at interface is reported, The principle of outline imaging is put forward. Experimental results demonstrate the feasibility of outline imaging by spectroscopic splitting, It is shown that clear out:line image of sample interface could be achieved easily by this technique. The spatial resolution is about 0.6mm. The THz-beam focus, the scanning step and the THz pulse width are the critical foctors affecting the imaging resolution. The signal-to-noise ratio of this technique could be improved greatly compared to the conventional transsion imaging.  相似文献   
28.
29.
New photocrosslinkable maleimide copolymers have been synthesized by the attachment of a tricyanopyrrolidene‐based chromophore. The 2‐(3‐cyano‐4‐(2‐{4‐[hexyl‐(6‐hydroxy‐hexyl)‐amino]‐phenyl}‐vinyl)‐5‐oxo‐1‐{4‐[4‐(3‐oxo‐3‐phenyl‐propenyl)‐ phenoxy]‐butyl}‐1,5‐dihydro‐pyrrol‐2‐ylidene)‐malononitrile chromophore exhibits nonlinear optical activity and contains a chalcone moiety that is sensitive to UV light (λ = 330–360 nm) for crosslink formation. The maleimide monomers have also been functionalized with chalcone moieties. The resultant copolymers exhibit great processability, and one of them shows a maximum electrooptic coefficient of 90 pm/V at 1300 nm. We could control the thermal stability of the electrooptic coefficient with the newly synthesized photoreactive copolymers successfully. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 531–542, 2007  相似文献   
30.
IntroductionClassical swine fever(CSF), included in the listA of the Office International des Epizooties(OIE), is ahighly contagious disease of domestic pigs and is con-sidered as the mostharmful disease occurring in pigs allover the world[1]. Outbreaks o…  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