全文获取类型
收费全文 | 255篇 |
免费 | 13篇 |
专业分类
化学 | 138篇 |
力学 | 11篇 |
数学 | 36篇 |
物理学 | 83篇 |
出版年
2021年 | 6篇 |
2020年 | 5篇 |
2019年 | 8篇 |
2018年 | 5篇 |
2017年 | 2篇 |
2016年 | 11篇 |
2015年 | 8篇 |
2014年 | 8篇 |
2013年 | 12篇 |
2012年 | 6篇 |
2011年 | 9篇 |
2010年 | 8篇 |
2009年 | 18篇 |
2008年 | 12篇 |
2007年 | 12篇 |
2006年 | 9篇 |
2005年 | 7篇 |
2004年 | 8篇 |
2003年 | 5篇 |
2002年 | 10篇 |
2001年 | 5篇 |
2000年 | 5篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1995年 | 2篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1991年 | 2篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1982年 | 3篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1977年 | 4篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1970年 | 2篇 |
1969年 | 4篇 |
1913年 | 1篇 |
1908年 | 1篇 |
1905年 | 1篇 |
1904年 | 1篇 |
1903年 | 1篇 |
1900年 | 1篇 |
1893年 | 1篇 |
1891年 | 3篇 |
1877年 | 1篇 |
1875年 | 1篇 |
排序方式: 共有268条查询结果,搜索用时 78 毫秒
61.
We formulate and solve the analog of the universal Conformal Ward Identity for the stress-energy tensor on a compact Riemann
surface of genus g > 1, and present a rigorous invariant formulation of the chiral sector in the induced two-dimensional gravity on higher genus
Riemann surfaces. Our construction of the action functional uses various double complexes naturally associated with a Riemann
surface, with computations that are quite similar to descent calculations in BRST cohomology theory. We also provide an interpretation
of the action functional in terms of the geometry of different fiber spaces over the Teichmüller space of compact Riemann
surfaces of genus g > 1.
Received: 12 September 1996 / Accepted: 6 January 1997 相似文献
62.
Mariateresa Giustiniano Sveva Pelliccia Ettore Novellino Gian Cesare Tron 《Tetrahedron letters》2018,59(13):1196-1199
N-Substituted α-amino acid amides can be easily obtained in two steps using the four-component Ugi reaction followed by chemoselective cleavage of the resulting tertiary amide. The use of the sacrificial acid, 2-hydroxymethylbenzoic acid is associated to shorter reaction times, higher yields, and safer and greener reaction conditions compared to strategies based on trifluoroacetic acid, a toxic and environmental hazardous reagent. The optimized procedure was easily scaled up to gram amounts. 相似文献
63.
We demonstrate a new technique for discovering the main mechanisms of energy transfer inside the active crystal of a solid-state laser. It consists of measuring the harmonic content of fluorescence when the pump has a sinusoidal modulation. In particular we discuss excited-state absorption and upconversion and present the equations for the fundamental and the second harmonic for both of these processes. We measured the fluorescence from the (4)S(3/2) multiplet of Er(3+) in three hosts, YLF, YAG, and CaSGG, with different doping. The results of the new method show that we are able to identify which multiplets transfer their energy to the observed one and through which process. 相似文献
64.
Antonello Santini Ettore Benedetti Carlo Pedone Giuseppe Caliendo Vincenzo Santagada Paolo Grieco Elisa Perissutti 《Structural chemistry》1996,7(3):173-181
The solid-state molecular conformations and crystal structures of three analogues of the CP-96,345 molecule, an important nonpeptidic SP antagonist, namely the (±)-2-(3-phenylbenzilidene)-3-(2-benzylamino) quinuclidine, theo-chloro- and theo-methoxy-derivatives, have been determined by X-ray diffusion analyses and refined to finalR values of 0.055, 0.045, and 0.056, respectively. All three molecules in the solid state show the same disposition of the substituents of the double bond and differences in the conformation mainly caused by the need of releasing intramolecular strains and/or nonbonded interactions. The observed molecular structures are compared to the reported solid-state structure of the CP-96,345 and correlated to the biological activity as NK antagonists. 相似文献
65.
A practical and efficient conversion of 4-bromomethyl-5-methyl-1, 3-dioxol-2-one 1 into the corresponding carbinol 2, a useful building block for the preparation of prodrugs, is reported. 相似文献
66.
A classical result in Lorentzian geometry states that a strongly causal spacetime is globally hyperbolic if and only if the Lorentzian distance is finite valued for every metric choice in the conformal class. It is proved here that a non-total imprisoning spacetime is globally hyperbolic if and only if for every metric choice in the conformal class the Lorentzian distance is continuous. Moreover, it is proved that a non-total imprisoning spacetime is causally simple if and only if for every metric choice in the conformal class the Lorentzian distance is continuous wherever it vanishes. Finally, a strongly causal spacetime is causally continuous if and only if there is at least one metric in the conformal class such that the Lorentzian distance is continuous wherever it vanishes. 相似文献
67.
Non-equilibrium vibrational kinetics as recently developed for adlayers is applied to experimental data on H-atom recombination and abstraction at solid surfaces. This model allows one to fit vibrational and translational energy distribution functions of the excited diatoms leaving the surface. Eley–Rideal and Langmuir–Hinshelwood mechanisms involving vibrationally excited adatoms are presented together with a criterion for establishing their relative contribution to the total reaction rate. Analogies of this multilevel ‘hot atom' (HA) model with recently employed two and three levels HA kinetic schemes are presented and discussed. 相似文献
68.
M. Amoruso I. Meccoli A. Minguzzi M. P. Tosi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,8(3):361-369
We discuss the ground state and the small-amplitude excitations of a degenerate vapour of fermionic atoms placed in two hyperfine states inside a spherical harmonic trap. An equations-of-motion approach is set up to discuss the hydrodynamic dissipation processes from the interactions between the two components of the fluid beyond mean-field theory and to emphasize analogies with spin dynamics and spin diffusion in a homogeneous Fermi liquid. The conditions for the establishment of a collisional regime via scattering against cold-atom impurities are analyzed. The equilibrium density profiles are then calculated for a two-component vapour of 40K atoms: they are little modified by the interactions for presently relevant values of the system parameters, but spatial separation of the two components will spontaneously arise as the number of atoms in the trap is increased. The eigenmodes of collective oscillation in both the total particle number density and the concentration density are evaluated analytically in the special case of a symmetric two-component vapour in the collisional regime. The dispersion relation of the surface modes for the total particle density reduces in this case to that of a one-component Fermi vapour, whereas the frequencies of all other modes are shifted by the interactions. 相似文献
69.
70.
Claudio Mele Sandra Rondinini Lucia D’Urzo Vincenzo Romanello Elisabetta Tondo Alessandro Minguzzi Alberto Vertova Benedetto Bozzini 《Journal of Solid State Electrochemistry》2009,13(10):1577-1584
Nucleation and growth of silver, electrodeposited from water–acetonitrile (CH3CN from 0 to 100% by volume) mixed solvents on glassy carbon electrodes, was studied by means of double-sweep voltammetry,
current–time transients (CTT) and scanning electron microscopy (SEM). The effects of the addition of the specifically interacting
tetrabuthylammonium cation were also investigated. From voltammetries, the formal potential, the nucleation potential and
the cathodic current efficiency have been evaluated as a function of the mixed solvent composition. The key role on nucleation
kinetics of transferring Ag+ from the bulk phase to the CH3CN-enriched electrode/solution interphase has been highlighted. CTT transients were described by a model combining instantaneous
and progressive nucleation mechanisms. SEM images highlighted the effects of the presence of the organic solvent, which yields
to a more regular growth, and of the quaternary ammonium salt, which exhibits grain-refining properties. 相似文献