全文获取类型
收费全文 | 176篇 |
免费 | 8篇 |
专业分类
化学 | 126篇 |
力学 | 6篇 |
数学 | 22篇 |
物理学 | 30篇 |
出版年
2023年 | 6篇 |
2020年 | 6篇 |
2019年 | 2篇 |
2017年 | 1篇 |
2016年 | 3篇 |
2015年 | 8篇 |
2014年 | 7篇 |
2013年 | 10篇 |
2012年 | 5篇 |
2011年 | 4篇 |
2010年 | 4篇 |
2009年 | 2篇 |
2008年 | 7篇 |
2007年 | 4篇 |
2006年 | 12篇 |
2005年 | 15篇 |
2004年 | 8篇 |
2003年 | 5篇 |
2002年 | 5篇 |
2001年 | 8篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 4篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1979年 | 1篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1966年 | 1篇 |
1965年 | 2篇 |
1963年 | 2篇 |
1962年 | 3篇 |
1961年 | 3篇 |
1957年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有184条查询结果,搜索用时 15 毫秒
51.
52.
Christian Schnell 《Mathematische Zeitschrift》2011,268(3-4):1069-1089
Let X be a smooth complex projective variety of dimension d. We show that its primitive cohomology in degree d is generated by certain “tube classes,” constructed from the monodromy in the family of all hyperplane sections of X. The proof makes use of a result about the group cohomology of certain representations that may be of independent interest. 相似文献
53.
Schnell B Meyer H Fond C Wittmer JP Baschnagel J 《The European physical journal. E, Soft matter》2011,34(9):97
By means of molecular-dynamics simulation we study a flexible and a semiflexible bead-spring model for a polymer melt on cooling
through the glass transition. Results for the glass transition temperature T
g and for the elastic properties of the glassy state are presented. We find that T
g increases with chain length N and is for all N larger for the semiflexible model. The N dependence of T
g is compared to experimental results from the literature. Furthermore, we characterize the polymer glass below T
g via its elastic properties, i.e., via the Lamé coefficients λ and μ. The Lamé coefficients are determined from the fluctuation formalism which allows to split λ and μ into affine (Born term) and nonaffine (fluctuation term) contributions. We find that the fluctuation term represents a substantial
correction to the Born term. Since the Born terms for λ and μ are identical, the fluctuation terms are responsible for the different temperature dependence of the Lamé coefficients. While
λ decreases linearly on approaching T
g from below, the shear modulus μ displays a much stronger decrease near T
g. From the present simulation data it is not possible to decide whether μ takes a finite value at T
g, as would be expected from mode-coupling theory, or vanishes continuously, as suggested by recent work from replica theory. 相似文献
54.
By introducing dipolar recoupling methods to high-resolution magic-angle spinning (HRMAS) NMR spectroscopy, a class of experiments has been delevoped that allows the measurement of residual dipole-dipole couplings of approximately 1 Hz in weakly immobilized molecules. Using homonuclear 1H-1H recoupling, distances of up to approximately 8 A can be selectively determined, while heteronuclear 1H-13C recoupling provides access to dynamic order parameters of individual molecular segments on the order of approximately 10-3. The experiments are demonstrated on functionalized oligopeptides that are attached to polymer resins. 相似文献
55.
A model, predicting the release of potassium compounds and its effect on the deposition of superheaters, has been recently developed. The model has been implemented into the three-dimensional CFD program AIOLOS. Concerning the release of potassium compound, the vaporization of the potassium and its reactions in the gas phase are considered. The influence of turbulence on chemistry is considered by using the eddy dissipation concept. Two simulations, one for a coal with high content of chlorine and the other for a coal with low content of chlorine were performed on a small-scale entrained flow reactor. The modelling results are discussed and compared with measurements. Furthermore, the effect of the released potassium chloride on the deposition mechanisms has also been considered. In order to predict the deposition rate, two major deposition mechanisms i.e. condensation and inertial impaction are considered in the model. The sticking probability is modelled based on the melting behaviour of the species involved in the deposition process. Deposit formation in a 0.5 MW semi-industrial pulverized-fuel combustion test facility is predicted considering different operating conditions. Deposition rates on the deposition probe from two kinds of biomass are compared and discussed. 相似文献
56.
C Ochsenfeld S P Brown I Schnell J Gauss H W Spiess 《Journal of the American Chemical Society》2001,123(11):2597-2606
We present a quantum chemical ab initio study which demonstrates a new combined experimental and theoretical approach, whereby a comparison of calculated and experimental (1)H NMR chemical shifts allows the elucidation of structural arrangements in solid-state molecular ensembles, taking advantage of the marked sensitivity of the (1)H chemical shift to intermolecular interactions. Recently, Brown et al. have shown that, under fast magic-angle spinning (MAS) at 35 kHz, the resolution in a (1)H NMR spectrum of the solid phase of an alkyl-substituted hexabenzocoronene (HBC) derivative is sufficient to observe the hitherto unexpected resolution of three distinct aromatic resonances ( J. Am. Chem. Soc. 1999, 121, 6712). Exploiting the additional information about proton proximities provided by (1)H double-quantum (DQ) MAS NMR spectroscopy, it was shown that the results are qualitatively consistent with the aromatic cores packing in a manner similar to that in unsubstituted HBC. Using the HBC-C(12) molecule as an example, we show here that the new combined experimental and theoretical approach allows the observed (1)H chemical shifts to be related in a quantitative manner to the intermolecular structure. In the quantum chemical calculations, a series of model systems of stacked HBC oligomers are used. On account of the marked dependence of the (1)H chemical shift to ring currents arising from nearby aromatic rings, the calculated (1)H chemical shifts are found to be very sensitive to the stacking arrangement of the HBC molecules. Moreover, the ring current effect is found to be particularly long range, with a considerable influence of the second neighbor, at a distance of 700 pm, being observed. 相似文献
57.
Schnell M Gwinner G Badnell NR Bannister ME Böhm S Colgan J Kieslich S Loch SD Mitnik D Müller A Pindzola MS Schippers S Schwalm D Shi W Wolf A Zhou SG 《Physical review letters》2003,91(4):043001
Recombination involving the core excitation of two electrons, which may be termed trielectronic recombination, has been experimentally identified for the first time. Using Cl13+ ions circulating in the TSR heavy-ion storage ring, we have observed surprisingly strong low-energy trielectronic recombination resonances, comparable to the dielectronic process. At higher electron-ion collision energies, trielectronic recombination is suppressed due to the autoionization of the triply excited intermediate state into excited final states. The formation of the intermediate state depends sensitively on configuration mixing, making trielectronic recombination a challenge to atomic-structure calculations. 相似文献
58.
Rudzevich Y Rudzevich V Moon C Schnell I Fischer K Böhmer V 《Journal of the American Chemical Society》2005,127(41):14168-14169
Selective and independent dimerization of tri- and tetraurea derivatives was used to build up dendritic assemblies which are uniform in size and structure. Dendrimers with the total molecular masses of about 25 000 g/mol were obtained. The existence of uniform assemblies was proved by 1H and 1H DOSY NMR experiments and also by dynamic light scattering. 相似文献
59.
O.?Peschel I.?Schnell G.?CzychollEmail author 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,47(3):369-378
We propose and apply a combination of an ab initio
(band-structure) calculation with a many-body treatment including
screening effects.
We start from a linearized muffin-tin orbital (LMTO) calculation to
determine the Bloch functions for the Hartree one-particle
Hamiltonian, from which we calculate the static susceptibility
and dielectric function within the standard random
phase approximation (RPA). From the Bloch functions
we obtain maximally localized Wannier
functions, using a method proposed by Marzari and Vanderbilt.
Within this Wannier basis all relevant one-particle and unscreened and
screened Coulomb
matrix elements are calculated. This yields a
multi-band Hamiltonian in second quantization with ab initio parameters, for
which screening has been taken into account within the simplest standard
approximation. Then, established
methods of many-body theory are used.
We apply this concept to a simple metal, namely lithium (Li). Here the
maximally localized Wannier functions turn out to be of the sp3-orbital
kind. Furthermore, only the on-site contributions of the screened Coulomb
matrix elements are relevant, and a generalized, four-band Hubbard
model is justified. The screened
on-site Coulomb matrix elements are considerably smaller than the band width
because of which it is sufficient to calculate the selfenergy in
weak-coupling approximation. We compare results obtained within the screened
Hartree-Fock approximation (HFA) and within the second-order perturbation
theory (SOPT) in the Coulomb matrix elements for
Li and find that many-body effects are small but not negligible even for
this simple metal. 相似文献
60.
Zusammenfassung Es werden Darstellung und Eigenschaften der Verbindungen von Siliciumtetrarhodanid mit Pyridin, Chinolin und Isochinolin beschrieben. Das chemische Verhalten in Acetonitril und die elektrische Leitfähigkeit deuten auf die Zusammensetzung [Si(NCS)2B2](SCN)2, wobei B Pyridin, Chinolin oder Isochinolin sein kann. Röntgen-Pulverdiagramme und Infrarotspektren werden mitgetelt.Mit 8 Abbildungen 相似文献