全文获取类型
收费全文 | 206691篇 |
免费 | 2642篇 |
国内免费 | 640篇 |
专业分类
化学 | 107203篇 |
晶体学 | 3206篇 |
力学 | 8160篇 |
综合类 | 8篇 |
数学 | 25764篇 |
物理学 | 65632篇 |
出版年
2021年 | 1506篇 |
2020年 | 1849篇 |
2019年 | 1883篇 |
2018年 | 2460篇 |
2017年 | 2532篇 |
2016年 | 4147篇 |
2015年 | 2632篇 |
2014年 | 3950篇 |
2013年 | 9406篇 |
2012年 | 7368篇 |
2011年 | 8594篇 |
2010年 | 6171篇 |
2009年 | 5949篇 |
2008年 | 8112篇 |
2007年 | 7914篇 |
2006年 | 7495篇 |
2005年 | 6764篇 |
2004年 | 6198篇 |
2003年 | 5468篇 |
2002年 | 5247篇 |
2001年 | 5890篇 |
2000年 | 4425篇 |
1999年 | 3404篇 |
1998年 | 2849篇 |
1997年 | 2743篇 |
1996年 | 2692篇 |
1995年 | 2535篇 |
1994年 | 2548篇 |
1993年 | 2472篇 |
1992年 | 2812篇 |
1991年 | 2582篇 |
1990年 | 2532篇 |
1989年 | 2429篇 |
1988年 | 2410篇 |
1987年 | 2435篇 |
1986年 | 2301篇 |
1985年 | 3078篇 |
1984年 | 3135篇 |
1983年 | 2728篇 |
1982年 | 2880篇 |
1981年 | 2670篇 |
1980年 | 2667篇 |
1979年 | 2789篇 |
1978年 | 2819篇 |
1977年 | 2770篇 |
1976年 | 2778篇 |
1975年 | 2658篇 |
1974年 | 2640篇 |
1973年 | 2755篇 |
1972年 | 1769篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
B.V. Raghavaiah 《Journal of Physics and Chemistry of Solids》2004,65(6):1153-1164
PbO-Sb2O3 glasses added with different concentrations of As2O3 (10-55 mol%) were prepared to understand their IR spectra, elastic properties (Young's modulus E, Shear modulus G, microhardness H), optical absorption and dielectric properties (constant ε, loss tan δ, ac conductivity σac over a moderately wide range of frequency and temperature and breakdown strength in air medium at room temperature). Results have indicated that the structure of the PbO-Sb2O3-As2O3 glass is more rigid when the concentration of As2O3 is around 40 mol%. 相似文献
92.
We examine several interesting relationships and expressions involving Fourier-Feynman transform, convolution product and
first variation for functionals in the Fresnel class F(B) of an abstract Wiener space B. We also prove a translation theorem and Parseval's identity for the analytic Feynman integral.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
93.
We present a practical polynomial-time algorithm for computing the
zeta function of a Kummer curve over a finite field of small
characteristic. Such algorithms have recently been obtained using a
method of Kedlaya based upon Monsky–Washnitzer cohomology, and are of
interest in cryptography. We take a different approach.
The problem is reduced to that of computing the L-function
of a multiplicative character sum. This latter task is achieved via a
cohomological formula based upon the work of Dwork and Reich. We show,
however, that our method and that of Kedlaya are very closely related.Dedicated to the memory of Gian-Carlo Rota 相似文献
94.
The concept and application of phase-space reconstructions are reviewed. Fractional derivatives are then proposed for the purpose of reconstructing dynamics from a single observed time history. A procedure is presented in which the fractional derivatives of time series data are obtained in the frequency domain. The method is applied to the Lorenz system. The ability of the method to unfold the data is assessed by the method of global false nearest neighbors. The reconstructed data is used to compute recurrences and correlation dimensions. The reconstruction is compared to the commonly used method of delays in order to assess the choice of reconstruction parameters, and also the quality of results. 相似文献
95.
This paper presents an evaluation of the capability of turbulence models available in the commercial CFD code FLUENT 6.0 for their application to hydrofoil turbulent boundary layer separation flow at high Reynolds numbers. Four widely applied two‐equation RANS turbulence models were assessed through comparison with experimental data at Reynolds numbers of 8.284×106 and 1.657×107. They were the standard k–εmodel, the realizable k–εmodel, the standard k–ωmodel and the shear‐stress‐transport (SST) k–ωmodel. It has found that the realizable k–εturbulence model used with enhanced wall functions and near‐wall modelling techniques, consistently provides superior performance in predicting the flow characteristics around the hydrofoil. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
96.
A new approach to the robust handling of non‐linear constraints for GAs (genetic algorithms) optimization is proposed. A specific feature of the approach consists of the change in the conventional search strategy by employing search paths which pass through both feasible and infeasible points (contrary to the traditional approach where only feasible points may be included in a path). The method (driven by full Navier–Stokes computations) was applied to the problem of multiobjective optimization of aerodynamic shapes subject to various geometrical and aerodynamic constraints. The results demonstrated that the method retains high robustness of conventional GAs while keeping CFD computational volume to an acceptable level, which allowed the algorithm to be used in a demanding engineering environment. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
97.
P. Murzyn C. R. Pidgeon P. J. Phillips J. -P. Wells N. T. Gordon T. Ashley J. H. Jefferson T. M. Burke J. Giess M. Merrick B. N. Murdin C. D. Maxey 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):220
We have made direct pump–probe measurements of spin lifetimes in long wavelength narrow-gap semiconductors at wavelengths between 4 and 10 μm and from 4 to 300 K. In particular, we measure remarkably long spin lifetimes, τs300 ps, even at 300 K for epilayers of degenerate n-type InSb. In this material the mobility is approximately constant between 77 and 300 K, and we find that τs is approximately constant in this temperature range. In order to determine the dominant spin relaxation mechanism we have investigated the temperature dependence of τs in non-degenerate lightly n-type Hg0.78Cd0.22Te of approximately the same band gap as InSb, and find that τs varies from 356 ps at 150 K to 24 ps at 300 K. Our results, both in magnitude and temperature dependence of τs, imply that the Elliott–Yafet model dominates in these materials. 相似文献
98.
The dependence of the strangeness saturation factor on the system size, centrality and energy is studied in relativistic heavy-ion collisions. 相似文献
99.
Spatial parameters of the X-ray radiation produced by a high-voltage nanosecond discharge evolving in air under atmospheric
pressure in the rod (cathode)-plane electrode system with a 10-cm electrode spacing are studied experimentally. A ∼170-ns
voltage pulse with an amplitude of ∼200 kV and 10-ns rise time is applied to the cathode. The photoelectronic method is used
to study, under the same conditions, the integrated (over the gap) characteristics of the radiation, in particular, the duration
of its generation. It is found that, when the size of the X-ray source is not smaller than that of the discharge region of
diffusive luminescence, radiation from the cathode region of the gap is primarily observed (i.e., from the region where the
electric field distribution is sharply inhomogeneous). The X-ray generation is usually observed after the bridging of the
discharge gap, the X-ray pulse having a rise time of ∼3 ns, a duration of ∼10 ns, and an effective radiation energy of ∼6
keV. 相似文献
100.
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