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排序方式: 共有94条查询结果,搜索用时 15 毫秒
1.
2.
To investigate the solvation structure of the Cu(II) ion in liquid ammonia, ab initio quantum-mechanical/molecular-mechanical (QM/MM) molecular dynamics (MD) simulations were carried out at Hartree Fock (HF) and hybrid density functional theory (B3 LYP) levels. A sixfold-coordinated species was found to be predominant in the HF case whereas five- and sixfold-coordinated complexes were obtained in a ratio 2:1 from the B3 LYP simulation. In contrast to hydrated Cu(II), which exhibits a typical Jahn-Teller distortion, the geometrical arrangement of ligand molecules in the case of ammonia can be described as a [2 + 4] ([2 + 3]) configuration with 4 (3) elongated copper-nitrogen bonds. First shell solvent exchange reactions at picosecond rate took place in both HF and B3 LYP simulations, again in contrast to the more stable sixfold-coordinated hydrate. NH3 ligands apparently lead to strongly accelerated dynamics of the Cu(II) solvate due to the "inverse" [2 + 4] structure with its larger number of elongated copper-ligand bonds. Several dynamical properties, such as mean ligand residence times or ion-ligand stretching frequencies, prove the high lability of the solvated complex. 相似文献
3.
Ulrich Schwenk und Erhard Weber 《Fresenius' Journal of Analytical Chemistry》1958,164(1):159-164
Zusammenfassung An Stelle der Podbielniak-Analyse für Gasproben, die neben Inertgasen und leichten Kohlenwasserstoffen auch C5- und höhere Kohlenwasserstoffe enthalten, wird ein neues Verfahren vorgeschlagen. Die Inertgase und leichten Kohlenwasserstoffe werden wie üblich gaschromatographisch bestimmt. Zusätzlich trennt man aus einer zweiten Probe gaschromatographisch die leichten Anteile ab, spült durch Umkehr der Trägergasrichtung die Summe der schweren Kohlenwasserstoffe wieder aus der Säule und bestimmt ihre Menge durch Wägung. 相似文献
4.
Abstract We present the first study of convective director structures in nematic side group polymers. A thin liquid crystal cell (10–500 μm) was continuously rotated about an axis perpendicular to the field of a 7T NMR magnet. The director behaviour was followed by deuteron NMR as well as by polarization microscopy. While by optical studies the development of periodic director structures can be directly monitored, the analysis of the NMR lineshape gives detailed information about the director distribution in these structures. The development of the structures depends sensitively on the rotation frequency and is discussed in terms of non-linear amplification of long wavelength director fluctuations due to the coupling between director rotation and viscous flow of the nematic. 相似文献
5.
J. Kaufmann J. Kronenbitter A. Schwenk 《Zeitschrift für Physik A Hadrons and Nuclei》1975,274(2):87-90
The spin-lattice relaxation timesT 1 of the NMR signals of95Mo and97Mo in aqueous K2MoO4 solutions were determined by the inversion recovery technique. To separate the relaxation rates due to electric quadrupole interaction and due to magnetic dipole interaction, pure H2O and mixtures of H2O and D2O were used as solvent. No dependence of the ratio of the relaxation ratesT 1(95Mo)/T 1(97Mo) on the composition of the solvent was to be detected, i.e. the relaxation due to magnetic dipole interaction may be neglected. From the ratio of the relaxation rates the absolute value of the ratio of the quadrupole moments of the molybdenum isotopes was evaluated: ¦Q(97Mo)/Q(95Mo)¦ = 11.4 ±0.3. 相似文献
6.
S. Bacca A. Schwenk G. Hagen T. Papenbrock 《The European Physical Journal A - Hadrons and Nuclei》2009,42(3):553-558
We present ground-state energies of helium halo nuclei based on chiral low-momentum interactions, using the hyperspherical-harmonics
method for 6He and coupled-cluster theory for 8He , with correct asymptotics for the extended halo structure. 相似文献
7.
We calculate the modification of the effective interaction of particles on the Fermi surface due to polarization contributions, with particular attention to spin-dependent forces. In addition to the standard spin-spin, tensor, and spin-orbit forces, spin nonconserving effective interactions are induced by screening in the particle-hole channels. Furthermore, a novel long-wavelength tensor force is generated. We compute the polarization contributions to second order in the low-momentum interaction V(low k) and find that the medium-induced spin-orbit interaction leads to a reduction of the 3P2 pairing gap for neutrons in the interior of neutron stars. 相似文献
8.
A novel N.M.R. method is described in which very high values of the rotational viscosity in nematic liquid crystals are measured with an improved accuracy of several orders of magnitude as compared to conventional N.M.R. methods. It consists of monitoring the deuteron line splitting while rotating the sample in a magnetic field. The rotation speed of the sample container is chosen such that the director orientation follows the container orientation, albeit with a certain phase lag. By synchronizing the data acquisition with the container orientation the phase lag is monitored for several hours. A simple relation, derived from the Ericksen-Leslie-Parodi equations, holds between the rotational viscosity and the phase lag. Frequencies as low as 10-6 Hz can be measured precisely. 相似文献
9.
Stingeder G. Gara S. Pahlke S. Schwenk H. Guerrero E. Grasserbauer M. 《Analytical and bioanalytical chemistry》1989,333(4-5):576-582
Analytical and Bioanalytical Chemistry - VLSI devices are almost exclusively fabricated on Czochralski (CZ) silicon containing high concentrations of interstitially dissolved oxygen ([Oi] ∼... 相似文献
10.
Coordination and ligand exchange dynamics of solvated metal ions 总被引:2,自引:0,他引:2
B.M. Rode C.F. Schwenk T.S. Hofer B.R. Randolf 《Coordination chemistry reviews》2005,249(24):2993-3006
Recent developments in computer speed and capacity have opened the access to highly accurate molecular dynamics simulations based on quantum mechanically calculated forces for the chemically relevant region around ions in solution (QM/MM formalism). This accuracy, although still extremely consuming (30-300 days of CP time per simulation), is needed for reliable structural details and ligand exchange rates. A large number of main group and transition metal ions have been investigated by this approach, giving very detailed insight into the properties of these ions in solution and allowing to classify the ions by various characteristics. Most first-row transition metal ions have a very stable first hexa-coordinated solvation shell, whose vibrational distortions, however, strongly influence the dynamics of the second shell. The dynamical Jahn-Teller effect - shown to be a femto- and picosecond phenomenon - can strongly influence ligand coordination and exchange dynamics. A large number of ions with very labile solvation shell such as most main group ions, but also transition metal ions, e.g. Ag(I) and Hg(II), can change their coordination within the picosecond scale, leading to an almost simultaneous presence of several species hardly accessible by present experimental techniques. Among these ions, the structure breakers are of particular interest, and it could be shown that there are two types of them, one with a large and very labile first coordination shell such as Cs(I), the other characterised by a small first but an unusually large second solvation shell such as Au(I). Investigations of metal ions coordinated to ammonia ligands have shown that coordination to hetero-atoms can accelerate the ligand exchange reaction rates by several orders of magnitude, e.g. for Cu(II) and Ni(II). Simulations of ions in aqueous ammonia gave a very detailed picture of the complexity of species almost simultaneously present and illustrate the enormous difficulties encountered when trying to fit X-ray or neutron diffraction data for such systems. In general, ligand exchange rates situated in the picosecond range are far below the NMR scale, and as femtosecond laser pulse spectroscopy could not be applied so far to ionic solutions, accurate simulations have become a very important tool to access structure and dynamics of solvated ions. A number of VIDEO clips supplied on the Web as supporting material illustrates the processes occurring in solutions of the metal ions. 相似文献