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   172篇
  免费   3篇
  国内免费   2篇
化学   133篇
力学   6篇
数学   8篇
物理学   30篇
  2022年   1篇
  2021年   3篇
  2018年   2篇
  2017年   2篇
  2015年   6篇
  2013年   6篇
  2012年   8篇
  2011年   13篇
  2010年   7篇
  2009年   3篇
  2008年   15篇
  2007年   9篇
  2006年   8篇
  2005年   11篇
  2004年   7篇
  2003年   9篇
  2002年   8篇
  2001年   6篇
  2000年   4篇
  1999年   1篇
  1998年   4篇
  1997年   4篇
  1996年   4篇
  1995年   3篇
  1994年   3篇
  1993年   4篇
  1992年   4篇
  1991年   1篇
  1990年   4篇
  1989年   1篇
  1988年   1篇
  1985年   1篇
  1983年   1篇
  1981年   3篇
  1980年   1篇
  1978年   1篇
  1977年   1篇
  1975年   1篇
  1974年   1篇
  1973年   1篇
  1971年   1篇
  1943年   2篇
  1934年   1篇
排序方式: 共有177条查询结果,搜索用时 15 毫秒
91.
92.
A series of coordination compounds has been prepared comprising manganese, iron, nickel, and zinc bound by a hexaanionic cryptand where carboxamides are anionic N-donors. The metal complexes have been investigated by X-ray crystallography, and possess metal centers in trigonal monopyramidal geometries with intermetallic distances spanning d(Mn,avg) = 6.080 ? to d(Ni,avg) = 6.495 ?. All complexes featuring trigonal monopyramidal metal(II) ions crystallize in Cc, and feature extended three-dimensional networks composed of cryptate anions linked by bridging potassium countercations. We also report the first solid state structure of the free cryptand ligand, which features no guest in its cavity and which possesses an extended hydrogen-bonding network. SQuID magnetometry data of the metal complexes reveal weak antiferromagnetic coupling of the metal centers. Only the diiron(II) complex exhibits reversible electrochemistry, and correspondingly, its chemical oxidation yields a powder formulated as the diiron(III) congener. The insertion of cyanide into the intermetallic cleft of the diiron(II) complex has been achieved, and comparisons of its solid state structure to the recently reported dicobalt(II) analogue are made. The antiferromagnetic coupling between the diiron(II) and the dicobalt(II) centers when bridged by cyanide does not increase significantly relative to the unbridged congeners. A one-site model satisfactorily fits Mo?ssbauer spectra of unbridged diiron(II) and diiron(III) complexes whereas a two site fit was needed to model the iron(II) centers that are bridged by cyanide.  相似文献   
93.
Any single permanent magnet or electromagnet will always attract a magnetic fluid. For this reason it is difficult to precisely position and manipulate ferrofluid at a distance from magnets. We develop and experimentally demonstrate optimal (minimum electrical power) 2-dimensional manipulation of a single droplet of ferrofluid by feedback control of 4 external electromagnets. The control algorithm we have developed takes into account, and is explicitly designed for, the nonlinear (fast decay in space, quadratic in magnet strength) nature of how the magnets actuate the ferrofluid, and it also corrects for electromagnet charging time delays. With this control, we show that dynamic actuation of electromagnets held outside a domain can be used to position a droplet of ferrofluid to any desired location and steer it along any desired path within that domain—an example of precision control of a ferrofluid by magnets acting at a distance.  相似文献   
94.
In this article we consider nuclear magnetic resonance (NMR) as an example of a quantum technology; we consider in particular detail the implementation of quantum computers using NMR. We begin by outlining the physical principles underlying NMR, and give an introduction to the quantum mechanics involved. We next discuss the general characteristics of quantum technologies and the ways and extent to which these characteristics are expressed in NMR. We then give an introduction to the subject of quantum computation and its implementation using NMR. Finally, we describe some spectroscopy techniques which also exploit the quantum nature of NMR.  相似文献   
95.
96.
Here we describe a nuclear magnetic resonance (NMR) experiment that uses a three qubit NMR device to implement the one-to-two approximate quantum cloning network of Buzek et al. [Phys. Rev. A 56, 3446 (1997)]. As expected the experimental results indicate that the network clones all input states with similar fidelities, but as a result of decoherence and incoherent evolution arising from B(1) inhomogeneity the total fidelity achieved does not exceed the measurement bound.  相似文献   
97.
We calculate explicitly the -invariants of the elliptic curves corresponding to rational points on the modular curve by giving an expression defined over of the -function in terms of the function field generators and of the elliptic curve . As a result we exhibit infinitely many elliptic curves over with nonsplit mod representations.

  相似文献   

98.
99.
A new method is described for the preparation of cobalt(III) acetylides, in which monosubstituted alkynes are treated directly with cobalt(III) forms of quadridentate Schiff base compounds in methanol.  相似文献   
100.
High bit rate systems can be achieved by operating at the wavelength of zero second order dispersion in optical fibres. The bandwidth is then limited by higher order dispersion terms. We consider the propagation of high intensity pulses in such a system, where the Kerr effect cannot be ignored. It is shown that the bandwidth is further limited by the optical nonlinearity.  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