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   73篇
  免费   0篇
化学   30篇
晶体学   5篇
力学   2篇
数学   4篇
物理学   32篇
  2023年   1篇
  2021年   1篇
  2020年   1篇
  2018年   1篇
  2016年   2篇
  2015年   1篇
  2014年   1篇
  2013年   4篇
  2012年   2篇
  2011年   3篇
  2010年   9篇
  2009年   7篇
  2008年   3篇
  2007年   1篇
  2006年   4篇
  2005年   4篇
  2002年   1篇
  2001年   1篇
  2000年   3篇
  1998年   4篇
  1997年   3篇
  1994年   3篇
  1992年   2篇
  1988年   1篇
  1987年   1篇
  1986年   5篇
  1985年   1篇
  1982年   1篇
  1977年   1篇
  1973年   1篇
排序方式: 共有73条查询结果,搜索用时 31 毫秒
21.
Collinear laser spectroscopy experiments on the ScII transition 3d4s 3D2→3d4p 3F3 at λ ≈ 363.1 nm were performed on the 42–46Sc isotopic chain using an ion guide isotope separator with a cooler–buncher. Isotope and isomer shifts and hyperfine structures of five ground states and two isomers were measured. Preliminary results on the nuclear moments and charge radii changes deduced from these measurements are reported.  相似文献   
22.
23.
It is established that the hydrocarbon coverage (0<1) formed at T<400 K on the Ir surface is oxidized upon oxygen exposures to CO and H2O by an adsorption mechanism. Complete oxidation to CO2 and H2O is achieved at T350 K after C2H4 exposures of the oxygen coverage.
, (<1), T<400 K Ir, CO H2O . CO2 H2O T350 K C2H4 .
  相似文献   
24.
We report on fast beam collinear laser spectroscopy measurements that demonstrate the feasibility of accurate isotope shift measurements for short lived Ne isotopes including the proton halo candidate 17Ne. Ultra high sensitivity is achieved by the application of an efficient resonance detection scheme based on collisional ionization and ion counting via the β decay. A direct measurement of the kinetic energy of the atomic Ne beam provides the required high accuracy. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
25.
Organic–inorganic hybrid structure, assembled by Rh-doped Bi12TiO20 crystal and liquid crystal (LC) layer, operating at near-infrared range is proposed and demonstrated. Due to the photorefractive properties of inorganic substrate, light illumination caused a space charge field which acts as a driving force for LC molecules re-alignment and subsequent refractive index modulation. All optically controlled phase retardation ability has been demonstrated supporting possibilities for further infrared applications.  相似文献   
26.
Infrared spectra of K2Zn(SeO4)2·6H2O and (NH4)2Zn(SeO4)2·6H2O containing SO42? guest ions and those of K2Zn(SO4)2·6H2O and K2Zn(SeO4)2·6H2O containing NH4+ guest ions are presented and discussed in the region of the stretching modes ν3 and ν1 of the sulfate ions and in the region of asymmetric bending modes ν4 of the NH4+ ions, respectively. The SO42? ions matrix-isolated in the selenate matrices (approximately 2 mol%) exhibit three bands for ν3 and one band for ν1 in agreement with the low site symmetry C1 of the selenate host ions. The NH4+ guest ions included in the potassium sulfate matrix are characterized also with three site symmetry components of ν4. However, the ammonium ions in (NH4)2Zn(SeO4)2·6H2O as well as those included in K2Zn(SeO4)2·6H2O display four infrared bands corresponding to ν4 probably due to some kind of disorder of the ammonium ions. The extent of energetic distortion of the isomorphously included sulfate ions as deduced from the values of Δν3 (site-group splitting) and Δνmax (the difference between the highest and the lowest wavenumbered components of the stretching modes) are commented. The spectroscopic experiments reveal that the SO42? guest ions are weaker distorted in the potassium selenate matrix than the same ions in the neat potassium sulfate due to the larger unit-cell volumes of the selenate compounds. However, the SO42? guest ions are stronger distorted in the ammonium selenate matrix as compared to the same ions in the neat ammonium sulfate owing to the formation of hydrogen bonds between the SO42? guest ions and the NH4+ host ions. The analysis of the spectra shows that the band positions of the water librations in the host potassium compounds are affected by the included ammonium cations. The formation of the hydrogen bonds between the NH4+ guest ions and the XO42? host ions leads to a decrease in the proton acceptor capabilities of the anions (anti-cooperative or proton acceptor competitive effect) and as a result the hydrogen bonds formed by the water molecules weaken on going from the neat potassium compounds to the mixed crystals K1.8(NH4)0.2Zn(SO4)2·6H2O and K1.8(NH4)0.2Zn(SeO4)2·6H2O (the bands corresponding to water librations are broadened and shifted to lower frequencies).  相似文献   
27.
The hyperfine structure of the D2 optical line in 22Na and 23Na has been investigated using high resolution laser spectroscopy of a well-collimated atomic beam. The hyperfine splitting constants A and B for the excited 3p 2P3/2 level for both investigated sodium isotopes have been obtained. They are as follows: A(22) = 7.31(4) MHz, B(22) = 4.71(28) MHz, A(23) = 18.572(24) MHz, B(23) = 2.723(55) MHz. With this data, using the high precision MCHF calculations for the electric field gradient at the nucleus, the electric quadrupole moment of 22Na has been deduced: Qs(22) =+0.185(11) b. The sign of Qs(22), determined for the first time, indicates a prolate nuclear deformation. A precise value of the isotope shift 22,23Na in the D2 line has also been obtained. Received: 26 February 1998 / Revised version: 25 June 1998  相似文献   
28.
The thermal dehydration of the title compounds was studied by TG, DTA and DSC methods and the enthalpies of dehydration were calculated (87.6 kJ mol–1 and 167.5 kJ mol–1 for the sulfate and selenate compound, respectively). The larger value of ΔHdeh of K2Be(SeO4)2·2H2O is due to the stronger hydrogen bonds formed in the selenate as compared to those formed in the respective sulfate owing to the stronger proton acceptor capabilities of the SeO42– ions. The enthalpies of formation (ΔHf0) of the dihydrates are also calculated from the DSC measurements (– 4467.4 kJ mol–1 and – 3447.1 kJ mol–1 for the sulfate and selenate compound, respectively). The anhydrous double salt, K2Be(SO4)2, forms tetragonal crystals with lattice parameters: a = 7.232(2) Å; c = 14.168(2) Å; V = 741.0 Å3, while the anhydrous salt, K2Be(SeO4)2, forms monoclinic crystals with lattice parameters: a = 9.217(3) Å; b = 10.645(3) Å; c = 8.989(2) Å; β = 108.52(4)°; V = 836.2 Å3. Vibrational spectra (infrared and Raman) of both the dihydrates and the anhydrous compounds are also presented and discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   
29.
Dihydroxy naphthalenes have been applied in Betti-type solventless condensation between aldehydes and (S)-phenylethylamine as a chiral auxiliary. A series of chiral 1,3-aminonaphthols has been synthesized and isolated in diastereoisomerically pure form. The absolute configurations of the aminonaphthols synthesized have been determined by means of advanced NMR experiments and confirmed by X-ray crystallography. The new chiral aminonaphthols have been tested as pre-catalysts for the addition of diethyl zinc and alkynyl-Zn-reagents to aldehydes with enantioselectivities of up to 98% ee.  相似文献   
30.
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