全文获取类型
收费全文 | 180719篇 |
免费 | 807篇 |
国内免费 | 269篇 |
专业分类
化学 | 90442篇 |
晶体学 | 2639篇 |
力学 | 9403篇 |
综合类 | 7篇 |
数学 | 21038篇 |
物理学 | 58266篇 |
出版年
2020年 | 1874篇 |
2019年 | 2305篇 |
2018年 | 3411篇 |
2017年 | 3528篇 |
2016年 | 4184篇 |
2015年 | 1869篇 |
2014年 | 3601篇 |
2013年 | 7099篇 |
2012年 | 5602篇 |
2011年 | 6661篇 |
2010年 | 5547篇 |
2009年 | 5676篇 |
2008年 | 6415篇 |
2007年 | 6386篇 |
2006年 | 5682篇 |
2005年 | 5030篇 |
2004年 | 4863篇 |
2003年 | 4406篇 |
2002年 | 4554篇 |
2001年 | 5010篇 |
2000年 | 3703篇 |
1999年 | 2838篇 |
1998年 | 2613篇 |
1997年 | 2468篇 |
1996年 | 2261篇 |
1995年 | 2063篇 |
1994年 | 2018篇 |
1993年 | 2054篇 |
1992年 | 2085篇 |
1991年 | 2397篇 |
1990年 | 2322篇 |
1989年 | 2391篇 |
1988年 | 2269篇 |
1987年 | 2302篇 |
1986年 | 2129篇 |
1985年 | 2668篇 |
1984年 | 2681篇 |
1983年 | 2322篇 |
1982年 | 2377篇 |
1981年 | 2288篇 |
1980年 | 2084篇 |
1979年 | 2398篇 |
1978年 | 2553篇 |
1977年 | 2643篇 |
1976年 | 2738篇 |
1975年 | 2540篇 |
1974年 | 2474篇 |
1973年 | 2637篇 |
1972年 | 2152篇 |
1971年 | 1977篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
The glow curve structures for LiF:Mg,Cu,Na,Si TL detectors with various dopant concentrations and sintering temperatures were investigated for the improvement of the glow curve structure and sensitivity of the TL detector. The dopant concentrations were varied over the following ranges: Mg (0–0.25 mol%), Cu (0–0.07 mol%), Na and Si (0–1.5 mol%). With increasing Cu concentration, the intensity of the main peak was intensified and reached a maximum at a concentration of 0.05 mol%. The high-temperature peak was reduced. The dependency of the main peak intensity on the Mg concentration exhibits a sharp maximum at 0.2 mol%. The intensity of the high-temperature peak tends to rise slightly with increasing Mg concentration. It was found that the optimum concentrations of the dopants in the LiF:Mg,Cu,Na,Si TL material are Mg: 0.2 mol%, Cu: 0.05 mol%, Na and Si: 0.9 mol%. The dependency of the main peak intensity on sintering temperature exhibits a very sharp maximum at 830°C. The high-temperature peak was rapidly reduced after 825°C. 相似文献
132.
J. R. Lindle W. W. Bewley I. Vurgaftman J. R. Meyer J. L. Johnson M. L. Thomas W. E. Tennant 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):558
A self-referencing, optical modulation technique was used to measure the negative luminescence efficiencies of an array of mid-wave infrared HgCdTe photodiodes with cutoff wavelength 4.6 μm as a function of sample temperature. The internal efficiency at a wavelength of 4 μm was 93% at 295 K, and nearly independent of temperature in the 240–300 K range. This corresponds to an apparent temperature reduction >50 K at room temperature and >30 K at 240 K. Moreover, the reverse-bias saturation current density was only 0.13 A/cm2. The measured transmission and emission spectra were simulated using empirical HgCdTe absorption formulas from the literature. 相似文献
133.
134.
A. V. Turik A. I. Chernobabov G. S. Radchenko S. A. Turik 《Physics of the Solid State》2004,46(12):2213-2216
Effective complex piezoelectric and dielectric constants of disordered heterogeneous systems, such as statistical mixtures consisting of spheroidal particles of the same orientation but with random distribution in space, are studied. It is found for the first time that, in such systems, there exists giant piezoelectric enhancement accompanied by giant relaxation of piezoelectric coefficients and permittivity. The piezoelectric and dielectric spectra differ considerably from the Debye spectra and have a Cole-Cole character. The dependence of the effects considered on the aspect ratios of the spheroids is investigated. The physical mechanisms responsible for the anomalous behavior of the piezoelectric coefficients and permittivity are considered. 相似文献
135.
A. I. Grachev 《Physics of the Solid State》2004,46(3):442-444
The phenomenology of the photogalvanic effect permits prediction of a number of physical phenomena, the most interesting of which is the galvano-dipolar effect. This effect consists in the appearance of an electric dipole moment in a sample through which an electric current is passed. A possible microscopic mechanism of this phenomenon, which can be realized in centrosymmetric media as well, is considered. 相似文献
136.
It is found that, when a bismuth crystal is subjected simultaneously to concentrated loading and a dc magnetic field, the magnetoplastic effect manifests itself as an abrupt decrease in the average length of wedge twins on the (111) cleavage plane (and, hence, as a decrease in the total twinned volume of the crystal) as a threshold value of the magnetic field is reached. However, the magnetic field stimulates glide deformation, which is indicated by an increase in the size of dislocation rosettes. The microhardness of a crystal varies smoothly and tends to increase with increasing magnetic field. The last phenomenon is accounted for by hardening of the crystal under the indenter in the presence of a magnetic field, because several slip systems become operative. 相似文献
137.
In terms of two-dimensional dislocation-disclination dynamics, a theoretical model is developed to describe the decay of a low-angle tilt boundary in a deformed nanocrystalline material under the action of an externally applied elastic stress and of the elastic field of a neighboring decayed boundary. The critical external stresses are calculated at which the boundary decays and the dislocations making up this boundary either are trapped by the boundary that decayed earlier or break away from both boundaries. The decay of a low-angle tilt boundary is shown to result in a substantial decrease in the critical decay stresses for the neighboring boundaries, which can cause an avalanche-like chain decay of low-angle boundaries yielding high-density ensembles of mobile dislocations capable of carrying substantial plastic deformations and of forming shear bands in deformed nanocrystalline materials. 相似文献
138.
The exact solution of the problem of ion transport current in an electrolyte in the presence of a conjugate flow of solvent
is obtained in the framework of the one-dimensional Gurevich-Kharkats diffusion-migration model; the conditions for the existence
of the solution are analyzed. 相似文献
139.
V. L. Bychkov L. P. Grachev I. I. Esakov A. A. Ravaev K. V. Khodataev 《Technical Physics》2004,49(7):833-838
A longitudinal dc electric discharge in a submerged high-pressure supersonic air jet is described. Photographs of the discharge
are provided. The experimental voltage across the discharge gap and the discharge current are given for two resistances of
the resistor that limits the discharge current over a certain range of the discharge channel length along the air flow. The
current-voltage discharge characteristic is provided at a constant discharge length. The main discharge characteristics are
obtained from a comparison of the experimental and theoretical results calculated on the basis of the simplest model. 相似文献
140.
O. Yu. Borkovskaya N. L. Dmitruk I. B. Ermolovich R. V. Konakova V. V. Milenin 《Technical Physics》2004,49(3):325-329
The properties of nonrectifying AuGe/GaAs (Al0.4Ga0.6As) contacts exposed to heat treatment, 60Co γ radiation, and γ radiation combined with the application of an electrical bias are studied. A correlation between the
type of interfacial interaction in the contacts and their resistance is found. Results obtained are explained in terms of
a diffusion model with a movable boundary of the metal layer. 相似文献