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   298篇
  免费   4篇
  国内免费   1篇
化学   153篇
晶体学   9篇
力学   2篇
数学   14篇
物理学   125篇
  2021年   3篇
  2020年   2篇
  2019年   3篇
  2018年   4篇
  2017年   3篇
  2016年   3篇
  2015年   14篇
  2014年   5篇
  2013年   10篇
  2012年   9篇
  2011年   11篇
  2010年   12篇
  2009年   15篇
  2008年   14篇
  2007年   17篇
  2006年   6篇
  2005年   13篇
  2004年   7篇
  2003年   18篇
  2002年   7篇
  2001年   6篇
  2000年   10篇
  1999年   9篇
  1998年   11篇
  1997年   7篇
  1996年   6篇
  1995年   3篇
  1994年   9篇
  1993年   4篇
  1992年   6篇
  1991年   7篇
  1988年   5篇
  1987年   3篇
  1986年   6篇
  1985年   1篇
  1984年   2篇
  1983年   2篇
  1982年   3篇
  1981年   2篇
  1979年   2篇
  1978年   1篇
  1977年   1篇
  1976年   1篇
  1975年   1篇
  1974年   4篇
  1973年   4篇
  1972年   2篇
  1971年   4篇
  1969年   1篇
  1964年   1篇
排序方式: 共有303条查询结果,搜索用时 15 毫秒
61.
The coherent quantum transport properties through the spin-polarized polyphenoxyl radical molecule have been investigated, using the density-functional-derived tight-binding model and the Green's functions method. The majority and minority spin components exhibit considerably different transmission spectra in the vicinity of the Fermi level. Namely, each spin component carries a different amount of current when the bias voltage is applied between the two electrodes that sandwich the polyradical molecule. Therefore, if the magnetization axis of the polyradical is fixed by the external magnetic field, and if the spin flip does not occur during the transmission, the assumed molecular bridge is expected to work as a spin filter or a spin valve. Furthermore, as long as the bias voltage is weak, the total spin current is observed to be larger than the current through its reduced molecular form. It indicates that the adsorption of some chemical species on the radical sites can be sensed by the change in conductance of the molecular bridge.  相似文献   
62.
A residual oil sample prepared from a crude oil is chromatographed on a column having a molecular-weight exclusion limit at about 5000. Three-dimensional chromatograms (absorbance/wavelength/time) are recorded with a u.v.-visible rapid-scanning detector. The elution profiles of vanadium- or nickel-containing species are obtained by applying atomic absorption spectrophotometry to fractions of the column effluents. Both vanadium- and nickel-containing species are detected over the whole molecular-weight range available with the column. The elution profiles of vanadium and nickel differ; the major elution peak for vanadium appears at a slightly lower molecular-weight region of the chromatogram than that for nickel. By reference to the real-time recorded absorption spectra of the effluents, it is suggested that at least some of the metals are present as metalloporphyrins.  相似文献   
63.
Journal of Radioanalytical and Nuclear Chemistry - We have studied extraction behavior of group-6 elements Mo and W to search for suitable conditions for an on-line extraction experiment of their...  相似文献   
64.
65.
66.
The possibility of preparing bicrystalline Josephson junctions and bolometers based on superconducting MgB2 on specially prepared bicrystalline MgO substrates is investigated. Microbridges 0.85–6.00 μm in width, intersecting the bicrystalline interface, are formed in epitaxial bicrystalline MgB2 films grown on these substrates. It is found that annealing of bicrystalline samples in oxygen leads to a systematic decrease in the critical current, an increase in the temperature width of the superconducting transition region, and to an improvement of the current-voltage (IV) characteristic, which becomes close in shape to the IV characteristic of a Josephson junction. The response of such a junction to radiation at a frequency of 110 GHz with an amplitude attaining 0.5 mV is measured.  相似文献   
67.
The characteristics of electron transmission through C70 molecule bridge in which two atomic chain leads are connected to long-axis carbon atoms are investigated theoretically by using tight-binding approach based on the Green’s function with only one π orbital electron per carbon atom. Electron transmission through C70 molecule from the input to the output terminal is obtained. From the spectrum, the switching feature of the electron transmission through C70 is found, and the oscillation property based on the quantized level is explained. The quantum current distributions inside C70 molecule bridge are calculated and simulated by the quantum current density theory based on Fisher-Lee formula at the energy point E = −0.2 eV, where the transmission spectrum shows a peak. The maximum and the minimum bond quantum currents are presented, and the reason why the currents are distributed nonuniformly is explained by the phase difference of the atomic orbits. The result shows that the currents at each atomic site agree with Kirchhoff quantum current conservation law. Supported by the National Key Basic Research Development Project (Grant No. 2003CB716204), the International Corporation Project of the Education Department of China (Grant No. 20050360563), the Key Laboratory of Advanced Photonic and Electronic Materials of Jiangsu (Grant No. BM2003202) and the State Key Laboratory of Solid State Microstructures of Nanjing University  相似文献   
68.
Martensitic transformation is the phase transformation accompanying orderly shear deformation without atomic diffusion. The structures made by martensitic transformation are classified as thin plate, lens or lath in steels. The mechanism by which the hierarchic microstructure in the lath martensite phase forms has heretofore not been understood. We have made clear the mechanism by considering, independently, two plastic deformations using the slip deformation model proposed by Khachaturyan, and present herein a deformation matrix for each of the six crystallographic variants in a packet of the hierarchic structure. Our results are quantitatively consistent with experimental results for the Kurdjumov–Sachs (K-S) crystal orientation relationship and habit plane. Furthermore, the important points of our study are as follows: the origin of the sub-block structure and the specific combination of the sub-block structure are clarified; the laths existing in a block can be explained; and deviations between the directional parallel and plane parallel are obtained quantitatively, without any adjustable parameters.  相似文献   
69.
A significant effect of clay host was observed on the photocatalytic activity of TiO2; TiO2-pillared fluorine mica exhibited two orders of magnitude higher activity than TiO2 and TiO2-pillared montmorillonite for the photocatalytic degradation of gamma-HCH.  相似文献   
70.
Rapid chemical separation of berkelium is essential in order to measure the unknown isotope 252Bk. An anion exchange system of mineral acid and methanol was examined. An elution curve of Bk was obtained using 250Bk produced by the 248Cm+18O system and the 251Bk activity could be measured in the preliminary experiments. The whole chemical separation was completed within 30 minutes.  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