全文获取类型
收费全文 | 6470篇 |
免费 | 58篇 |
国内免费 | 11篇 |
专业分类
化学 | 3740篇 |
晶体学 | 75篇 |
力学 | 170篇 |
数学 | 653篇 |
物理学 | 1901篇 |
出版年
2016年 | 59篇 |
2015年 | 59篇 |
2014年 | 52篇 |
2013年 | 232篇 |
2012年 | 187篇 |
2011年 | 175篇 |
2010年 | 106篇 |
2009年 | 129篇 |
2008年 | 164篇 |
2007年 | 167篇 |
2006年 | 178篇 |
2005年 | 207篇 |
2004年 | 175篇 |
2003年 | 152篇 |
2002年 | 126篇 |
2001年 | 107篇 |
2000年 | 90篇 |
1999年 | 97篇 |
1998年 | 59篇 |
1997年 | 100篇 |
1996年 | 129篇 |
1995年 | 111篇 |
1994年 | 88篇 |
1993年 | 84篇 |
1992年 | 88篇 |
1991年 | 87篇 |
1990年 | 80篇 |
1989年 | 72篇 |
1988年 | 87篇 |
1987年 | 91篇 |
1986年 | 64篇 |
1985年 | 84篇 |
1984年 | 95篇 |
1983年 | 73篇 |
1982年 | 96篇 |
1981年 | 92篇 |
1980年 | 96篇 |
1979年 | 78篇 |
1978年 | 104篇 |
1977年 | 90篇 |
1976年 | 81篇 |
1975年 | 91篇 |
1974年 | 59篇 |
1973年 | 52篇 |
1970年 | 45篇 |
1969年 | 49篇 |
1968年 | 47篇 |
1967年 | 45篇 |
1955年 | 61篇 |
1934年 | 45篇 |
排序方式: 共有6539条查询结果,搜索用时 15 毫秒
21.
22.
Polymer lightguides of PMMA doped with the azo dyes methyl-red and N, N-dihexyl-4-amino-4'-nitro-azobenzene (DHANA) are investigated with respect to their opto-optical properties. The trans-cis photoisomerisation of the dyes leads to reversible polarization-dependent optically induced refractive index changes. The index changes are anisotropic. Birefringence is measured using index matched lightguides. The changes with respect to each polarization are determined by leaky mode spectroscopy and by using a half-integrated interferometer. These changes are intensity dependent and, with a suitable geometry, bistability at low intensities (3 mW/mm3) can be obtained. 相似文献
23.
24.
Near-infrared laser photoacoustic detection of methane: the impact of molecular relaxation 总被引:1,自引:0,他引:1
A photoacoustic sensor has been developed for trace-gas monitoring using a near-infrared semiconductor laser emitting in the
2ν3 band of methane at 1.65 μm. The apparatus was designed for on-line process control in the manufacturing of the novel low-water-peak
fibres developed for optical telecommunications. The importance of collisional relaxation processes in the generation of the
photoacoustic signal is reported in the particular case of CH4 detection in dry O2 and O2–N2 mixtures. The negative influence of these effects results in a strongly reduced and phase-shifted photoacoustic signal, induced
by a fast resonant coupling between the vibrational states of methane and oxygen, associated with the slow relaxation of the
excited oxygen molecules. An unusual parabolic response of the sensor with respect to the methane concentration has been observed
and is discussed. Finally, the beneficial effect of several species, including water vapour and helium, acting as a catalyst
to hasten the relaxation of the CH4–O2 system, is demonstrated.
PACS 42.62.Fi; 33.20.Ea; 34.50.Ez 相似文献
25.
The dependence of the formation of a p-n or p-p+ junction in semiconducting TiO2 as a function of various parameters is investigated through a computer model. The effect of the polarizing conditions on
the I–V characteristics is also discussed and related to experimental results.
Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Sept. 15–22, 1996 相似文献
26.
27.
28.
We present anO(p · n) algorithm for the problem of finding disjoint simple paths of minimum total length betweenp given pairs of terminals on oriented partial 2-trees withn nodes and positive or negative arc lengths. The algorithm is inO(n) if all terminals are distinct nodes. We characterize the convex hull of the feasible solution set for the casep=2.We gratefully acknowledge the referee's many helpful suggestions to improve the presentation of this paper. 相似文献
29.
Th. Mühge Yu. V. Goryunov K. Theis-Bröhl K. Westerholt H. Zabel I. A. Garifullin 《Applied magnetic resonance》1998,14(4):567-582
Magnetic and superconducting properties of Fe/Nb epitaxial bilayers have been studied. Single crystal Fe/Nb (110) bilayers with a Nb thicknessd Nb in the range from 250 to 650 Å and with a Fe thicknessd Fe in the range from 7 to 27 Å were prepared using molecular beam epitaxy techniques. Magnetization measurements showed the existence of a magnetically “dead” Fe-interface layer with a thicknessd NM varying strongly with minor modifications of the growth conditions. For bilayers with a small magnetic layer thicknessd M and a smalld NM the FMR measurements revealed an anomalous decrease of the effective magnetization 4πM eff of the ferromagnetic Fe layer below the superconducting transition temperatureT c. The absolute change of 4πM eff belowT c depends strongly on the actual values ofd M andd NM: upon decreasing bothd M andd NM the effect increases considerably. As a possible mechanism for the anomalous temperature dependence of 4πM eff belowT c we discuss a spatial modulation of ferromagnetic order due to a modification of the RKKY inter-action in the superconducting state. 相似文献
30.
Th. Brückel Y. Chernenkov B. Dorner V. P. Plakhty O. P. Smirnov 《Zeitschrift für Physik B Condensed Matter》1990,79(3):389-395
We have measured the spin wave spectrum for the garnet Ca3Cr2Ge3O12 by means of inelastic neutron scattering. The data can be well described in the framework of linear spin wave theory if we assume a Heisenberg model with two exchange parameters up to the next nearest neighbours (J
1 andJ
2) and a staggered anisotropy field (A). A least squares fit to the observed dispersion relations yield the following values for these parameters: J
1=–0.582(8)K,J
2=0.416(4)K,A=0.25(8)K. Although symmetry requires that two nearest neighbour exchange constantsJ
1 andJ
1
'
must be distinguished, only the average J
1=(J
1+3J
1
'
)/4 and the condition –0.35 K <J
1=J
1-J
1
'
<0.50 K could be deduced from the experiment. The most striking result is the positive value ofJ
2. We discuss the implications for an understanding of superexchange mediated by more than one oxygen atom. In an extension of the conventional analysis we have calculated the integrated intensities in order to check the eigenvectors directly. Good agreement between observed and calculated intensities was obtained. 相似文献