全文获取类型
收费全文 | 1372篇 |
免费 | 29篇 |
国内免费 | 6篇 |
专业分类
化学 | 875篇 |
晶体学 | 12篇 |
力学 | 30篇 |
数学 | 196篇 |
物理学 | 294篇 |
出版年
2021年 | 8篇 |
2019年 | 8篇 |
2018年 | 12篇 |
2017年 | 6篇 |
2016年 | 17篇 |
2015年 | 20篇 |
2014年 | 24篇 |
2013年 | 52篇 |
2012年 | 45篇 |
2011年 | 75篇 |
2010年 | 53篇 |
2009年 | 51篇 |
2008年 | 73篇 |
2007年 | 74篇 |
2006年 | 57篇 |
2005年 | 79篇 |
2004年 | 65篇 |
2003年 | 59篇 |
2002年 | 50篇 |
2001年 | 18篇 |
2000年 | 24篇 |
1999年 | 13篇 |
1998年 | 20篇 |
1997年 | 15篇 |
1996年 | 21篇 |
1995年 | 18篇 |
1994年 | 20篇 |
1993年 | 11篇 |
1992年 | 11篇 |
1991年 | 14篇 |
1990年 | 10篇 |
1989年 | 20篇 |
1988年 | 6篇 |
1987年 | 10篇 |
1986年 | 10篇 |
1985年 | 20篇 |
1984年 | 19篇 |
1983年 | 12篇 |
1982年 | 23篇 |
1981年 | 26篇 |
1980年 | 24篇 |
1979年 | 20篇 |
1978年 | 22篇 |
1977年 | 24篇 |
1976年 | 14篇 |
1975年 | 13篇 |
1974年 | 11篇 |
1973年 | 15篇 |
1972年 | 6篇 |
1971年 | 5篇 |
排序方式: 共有1407条查询结果,搜索用时 343 毫秒
91.
The utilization of tetrahedral pre-formed coordination compounds {M(C2O4)4}4- (M = Zr(IV), U(IV); C2O4(2-) = oxalate) permitted the efficient construction of rare examples of heteronuclear supramolecular nano-porous architectures. A series of metal-organic coordination frameworks prepared by association of these building units with either Mn2+, Cd2+, or Mg2+ have been structurally characterized and are described. Their 3-D chemical scaffold is based on the primary tetrahedral building unit but their pore sizes and topologies could be varied through the M2+ metal ion involved in the assembling process, and the anionic tetrahedral moiety. These structures display channels with apertures up to 12 Angstrom x 8 Angstrom which are emptied of solvates at mild temperatures without affecting the chemical scaffold, the integrity of which is maintained up to 250-300 degrees C. A certain degree of flexibility of the coordination polymers upon guest release is suggested by the temperature dependence of the powder X-ray patterns and N2 sorption experiments, but reversible and selective sorption of small molecules has been observed substantiating that these open-frameworks behave like sponges. 相似文献
92.
The Wigner's Theorem states that a bijective transformation of the set of all one-dimensional linear subspaces of a complex
Hilbert space which preserves orthogonality is induced by either a unitary or an anti-unitary operator. There exist many Wigner-type
theorems, in particular in indefinite metric spaces, von Neumanns algebras and Banach spaces and we try to find a common origin
of all these results by using properties of the lattice subspaces of certain topological vector spaces. We prove a Wigner-type
theorem for a pair of dual spaces which allows us to obtain, as particular cases, the usual Wigner's Theorem and some of its
generalizations.
PACS: 02.40.Dr, 03.65.Fd,03.65.Ta
AMS Subject Classification (1991): 06C15, 46A20, 81P10. 相似文献
93.
A theory of the metal-insulator transition in vanadium dioxide from the high- temperature rutile to the low- temperature monoclinic phase is proposed on the basis of cluster dynamical mean-field theory, in conjunction with the density functional scheme. The interplay of strong electronic Coulomb interactions and structural distortions, in particular, the dimerization of vanadium atoms in the low-temperature phase, plays a crucial role. We find that VO2 is not a conventional Mott insulator, but that the formation of dynamical V-V singlet pairs due to strong Coulomb correlations is necessary to trigger the opening of a Peierls gap. 相似文献
94.
We report a wide-field fluorescence lifetime imaging microscope based on a low-repetition-rate (3.7-MHz) passively mode-locked diode-pumped laser source. This inexpensive and compact laser source operating in the visible and UV range can excite a wide range of fluorophores of biological interest. We demonstrate that the power of this laser source is highly sufficient for studying biological systems with low quantum yields (autofluorescence of tissues and stained living cells). The maximum measurable lifetime is also strongly increased with this laser source, as fluorescence intensity measurement can occur 250 ns after the excitation pulse. 相似文献
95.
In a Hilbert space, there exists a natural correspondence between continuous projections and particular pairs of closed subspaces.
In this paper, we generalize this situation and associate to a symmetric lattice L a subset P(L) of L× L, called its projection poset. If L is the lattice of closed subspaces of a topological vector space then elements of P(L) correspond to continuous projections and we prove that automorphisms of P(L) are determined by automorphisms of the lattice L when this lattice satisfies some basic properties of lattices of closed subspaces.
Primary: 06C15, Secondary: 03G12 81P10. 相似文献
96.
Pavarini E Biermann S Poteryaev A Lichtenstein AI Georges A Andersen OK 《Physical review letters》2004,92(17):176403
Using t(2g) Wannier functions, a low-energy Hamiltonian is derived for orthorhombic 3d(1) transition-metal oxides. Electronic correlations are treated with a new implementation of dynamical mean-field theory for noncubic systems. Good agreement with photoemission data is obtained. The interplay of correlation effects and cation covalency (GdFeO3-type distortions) is found to suppress orbital fluctuations in LaTiO3 and even more in YTiO3, and to favor the transition to the insulating state. 相似文献
97.
Georges Y Allenbach Y Ariza X Campagne JM Garcia J 《The Journal of organic chemistry》2004,69(21):7387-7390
Enantioenriched 4-hydroxyalk-2-ynyl carbonates (or benzoates) have been prepared by stereoselective zinc-mediated addition of alkyl 2-propynyl carbonates (or their benzoate analogues) to aldehydes. Their partial reduction to Z-olefins followed by cyclization under mild Pd-catalyzed conditions allowed a straightforward access to enantioenriched syn-1,2-diols protected as cyclic carbonates. 相似文献
98.
Rajendra J Baxendale M Dit Rap LG Rodger A 《Journal of the American Chemical Society》2004,126(36):11182-11188
Structures of carbon nanotube/ligand complexes were studied by flow linear dichroism (the differential absorption of light polarized parallel and perpendicular to the flow orientation direction) with the aim of establishing linear dichroism as a technique to study such systems. Anthracene, naphthalene, and DNA were chosen as ligands, and the potential for flow linear dichroism to probe ligands noncovalently (as well as covalently) bound to single-walled nanotubes is reported. Linear dichroism enables the determination of approximate orientations of the ligands on the carbon nanotubes. 相似文献
99.
We use multispeckle diffusive wave spectroscopy to probe the micron-scale dynamics of a water-saturated granular pile submitted to discrete gentle taps. The typical time scale between plastic events is found to increase dramatically with the number of applied taps. Furthermore, this microscopic dynamics weakly depends on the solid fraction of the sample. This process is largely analogous to the aging phenomenon observed in thermal glassy systems. We propose a heuristic model where this slowing-down mechanism is associated with a slow evolution of the distribution of the contact forces between particles. This model accounts for the main features of the observed dynamics. 相似文献
100.
Lucca A Debourg G Jacquemet M Druon F Balembois F Georges P Camy P Doualan JL Moncorgé R 《Optics letters》2004,29(23):2767-2769
We report what is believed to be the first demonstration of a high-power passively mode-locked diode-pumped femtosecond laser based on an Yb3+:CaF2 single crystal, directly pumped by a 15-W fiber-coupled laser diode. With a 5-at. % Yb3+ -doped sample and prisms for dispersion compensation we obtained pulses as short as 150 fs, with 880 mW of average power and up to 1.4-W average output power, with a pulse duration of 220 fs, centered at 1049 nm. The laser wavelength could be tuned from 1040 to 1053 nm in the femtosecond regime. Using chirped mirrors for dispersion compensation, the oscillator provided up to 1.74 W of average power, with a pulse duration of 230 fs, corresponding to a pulse energy of 20 nJ and a peak power of 85 kW. 相似文献