全文获取类型
收费全文 | 2177篇 |
免费 | 71篇 |
国内免费 | 5篇 |
专业分类
化学 | 1354篇 |
晶体学 | 5篇 |
力学 | 63篇 |
数学 | 458篇 |
物理学 | 373篇 |
出版年
2024年 | 3篇 |
2023年 | 29篇 |
2022年 | 53篇 |
2021年 | 60篇 |
2020年 | 55篇 |
2019年 | 62篇 |
2018年 | 35篇 |
2017年 | 30篇 |
2016年 | 97篇 |
2015年 | 72篇 |
2014年 | 80篇 |
2013年 | 118篇 |
2012年 | 180篇 |
2011年 | 155篇 |
2010年 | 89篇 |
2009年 | 99篇 |
2008年 | 131篇 |
2007年 | 130篇 |
2006年 | 116篇 |
2005年 | 95篇 |
2004年 | 105篇 |
2003年 | 77篇 |
2002年 | 87篇 |
2001年 | 30篇 |
2000年 | 19篇 |
1999年 | 17篇 |
1998年 | 21篇 |
1997年 | 14篇 |
1996年 | 22篇 |
1995年 | 16篇 |
1994年 | 21篇 |
1993年 | 17篇 |
1992年 | 9篇 |
1991年 | 11篇 |
1990年 | 9篇 |
1989年 | 14篇 |
1988年 | 10篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1966年 | 2篇 |
1948年 | 1篇 |
1939年 | 1篇 |
1910年 | 1篇 |
排序方式: 共有2253条查询结果,搜索用时 15 毫秒
171.
We introduce a new mechanism for producing locally stable de Sitter or Minkowski vacua, with spontaneously broken N = 1 supersymmetry and no massless scalars, applicable to superstring and M-theory compactifications with fluxes. We illustrate the mechanism with a simple N = 1 supergravity model that provides parametric control on the sign and the size of the vacuum energy. The crucial ingredient is a gauged U(1) that involves both an axionic shift and an R symmetry, and severely constrains the F- and D-term contributions to the potential. 相似文献
172.
173.
174.
We consider a finite-range spin glass model in arbitrary dimension, where the strength of the two-body coupling decays to zero over some distance gamma(-1). We show that, under mild assumptions on the interaction potential, the infinite-volume free energy of the system converges to that of the Sherrington-Kirkpatrick one, in the Kac limit gamma-->0. This could be a first step toward an expansion around mean-field theory, for spin glass systems. 相似文献
175.
Benincasa C Maiuolo L Mazzotti F Perri E Sindona G Urso E 《Journal of mass spectrometry : JMS》2004,39(1):61-65
A method is presented which allows the identification and assay of a nucleoside in the presence of other analogues and homologues. The method is based on the conventional multiple reaction monitoring approach performed on the [M + H]+ ions of wild-type and modified nucleosides produced by the turbo ionspray ionization method on a triple-quadrupole mass spectrometer. The accuracy of the quantitative determination relies on the evaluation of a response factor rho, which takes into account the kinetics of dissociation of the parent ions into the protonated [B + 2H]+ nucleobase ions. The evaluation of the absolute concentration of each analyte in the examined mixture does not require any previous chromatographic separation. 相似文献
176.
Köhler R Tredicucci A Beltram F Beere HE Linfield EH Davies AG Ritchie DA 《Optics letters》2003,28(10):810-812
Chirped-superlattice quantum-cascade lasers are reported that emit at lambda approximately 85 microm (3.6 THz), which is to the authors' knowledge the longest wavelength demonstrated so far with this technology. Collected peak output powers of 1.5 mW per facet were measured at liquid-helium temperature, and a maximum operating temperature of 45 K was reached. Record low-threshold-current densities of 95 and 115 A cm(-2) were observed in pulsed and continuous-wave operation, respectively. For the latter, output powers of a few hundred microwatts are estimated at low temperatures. 相似文献
177.
We discuss boosts in a deformed Minkowski space, i.e., a four-dimensional spacetime with metric coefficients depending on nonmetric coordinates (in particular on the energy). The general form of a boost in an arbitrary direction is derived in the case of space anisotropy. Two maximal trivector velocities are mathematically possible, an isotropic and an anisotropic one. However, only the anisotropic velocity has physical meaning, being invariant indeed under deformed boosts. 相似文献
178.
179.
We report on the use of a single-polarization, 41 μm core-diameter, intrinsically single-mode photonic crystal fiber (PCF) to obtain high peak power (up to 800 kW), 1 ns-duration pulses in a 100:1 linearly polarized, intrinsically single-mode (M2 1.2) output. By transmitting the PCF output through nonlinear crystals, we also obtained efficient second, third, and fourth harmonic generation resulting in peak power >400 kW in the visible (green, 531 nm) and 200 kW in the UV (265.5 nm). To our knowledge these results represent the highest peak power obtained in a linearly polarized output from a fiber and the highest peak power in the visible and UV obtained through harmonic generation of the direct fiber output. 相似文献
180.
Sulphur-headgroup organic molecules have been chemisorbed on Cu(1 0 0) as self-assembled monolayers (SAMs) in highly-ordered two-fold symmetry structures, and the electronic states induced at the interface have been measured by photoemission: a close similarity of the main interface states for methane-thiolate and mercaptobenzoxazole on Cu(1 0 0) in the same p(2 × 2)-phase is observed. The bonding states for methane-thiolate/Cu(1 0 0) in the p(2 × 2) and c(2 × 2) structures have been compared to ab-initio calculation of the total density of states (DOS) for the S/Cu(1 0 0) system in the same phases. The major role of the S-Cu bonding to determine the density of state evolution at the interface is brought to light. The observed differences in the two phases depend mainly on the charge distribution associated to the different molecular packing, with a minor role of the radical group. 相似文献