全文获取类型
收费全文 | 7497篇 |
免费 | 225篇 |
国内免费 | 206篇 |
专业分类
化学 | 1293篇 |
晶体学 | 64篇 |
力学 | 40篇 |
综合类 | 34篇 |
数学 | 5881篇 |
物理学 | 616篇 |
出版年
2023年 | 41篇 |
2022年 | 80篇 |
2021年 | 80篇 |
2020年 | 45篇 |
2019年 | 191篇 |
2018年 | 174篇 |
2017年 | 108篇 |
2016年 | 83篇 |
2015年 | 128篇 |
2014年 | 238篇 |
2013年 | 416篇 |
2012年 | 291篇 |
2011年 | 481篇 |
2010年 | 374篇 |
2009年 | 483篇 |
2008年 | 510篇 |
2007年 | 480篇 |
2006年 | 398篇 |
2005年 | 277篇 |
2004年 | 226篇 |
2003年 | 203篇 |
2002年 | 157篇 |
2001年 | 152篇 |
2000年 | 133篇 |
1999年 | 209篇 |
1998年 | 143篇 |
1997年 | 119篇 |
1996年 | 94篇 |
1995年 | 128篇 |
1994年 | 124篇 |
1993年 | 123篇 |
1992年 | 86篇 |
1991年 | 67篇 |
1990年 | 143篇 |
1989年 | 160篇 |
1988年 | 92篇 |
1987年 | 97篇 |
1986年 | 119篇 |
1985年 | 112篇 |
1984年 | 81篇 |
1983年 | 36篇 |
1982年 | 32篇 |
1981年 | 32篇 |
1980年 | 36篇 |
1979年 | 29篇 |
1978年 | 28篇 |
1977年 | 30篇 |
1976年 | 20篇 |
1975年 | 10篇 |
1973年 | 11篇 |
排序方式: 共有7928条查询结果,搜索用时 31 毫秒
21.
Hypersonic longitudinal sound velocities in five silicate and alumino-silicate liquids have been measured between 293 and 2550 K by Brillouin spectroscopy. Together with previous observations for four other glasses and liquids of the system SiO2-Al2O3-CaO-MgO, these results are used to discuss changes in hypersonic velocities in three adjacent temperature domains, i.e., below, in, and above the glass transformation range. The temperature dependence of Brillouin velocities is consistent with the observed variations with temperature of viscosity, density, and mean heat capacity for the same three temperature domains. These variations of physical properties of alumino-silicate liquids are qualitatively in agreement with the Inherent Structure Theory for liquids. 相似文献
22.
A locally convex space is said to be a Gateaux differentiability space (GDS)provided every continuous convex function defined on a nonempty convex open subset D of the space is densely Gateaux differentiable in D.This paper shows that the product of a GDS and a family of separable Frechet spaces is a GDS,and that the product of a GDS and an arbitrary locally convex space endowed with the weak topology is a GDS. 相似文献
23.
We investigate some topological properties of a normal functorH introduced earlier by Radul which is some functorial compactification of the Hartman-Mycielski construction HM. We prove
that the pair (H X, HMY) is homeomorphic to the pair (Q, σ) for each nondegenerated metrizable compactumX and each denseσ-compact subsetY. 相似文献
24.
The ρ-T curves in our single phase HgBa2Ca2Cu3O8+δ superconductor were measured as a function of temperature and magnetic field, ρ=ρ0exp(−Ueff/κBT). It can be transformed to another form d(lnρ)/d(1/T)=−Ueff+TdUeff/dT, then this becomes a plot of the activation energy Ueff as a function of temperature. Our data plotted in these ways show a clear crossover from high-temperature two-dimensional vortex-liquid to a critical region associated with the low-temperature three-dimensional vortex-glass phase transition. The critical exponents v(z−1)=3.9±1.9 in this system are little different with previous measurements in BSCCO and YBCO systems. 相似文献
25.
26.
H. Tietze-Jaensch D. Sieger R. Geick W. Zulehner A. de Geyer 《Applied Physics A: Materials Science & Processing》1992,54(1):19-21
The formation of silicon oxide precipitates from Czochralski grown silicon depends on the time and temperature of the heat treatment as well as on the initial content of interstitially dissolved oxygen. Samples containing between 5×1017 Oi/cm3 and 13×1017 Oi/cm3 have been heated at 750° C for 96 h. SiO2 precipitates of various shape and size have been obtained and investigated by means of small angle neutron scattering (SANS) in the Q-range 0.05 Å–1<Q<0.2 Å–1. The obtained SANS patterns reveal a typical anisotropy of their intensity distribution, which splits into a central peak at Q<0.1 Å–1 due to the shape of the individual particles and a number of weak intensities for large Q-values, originating from a correlation between defects, possibly between the precipitates. While these correlation peaks in the SANS patterns are seen best for rather low values of about (5–7)×1017 Oi/cm3 oxygen content, the central peak anisotropy is most pronounced for higher values of ca 10×1017 Oi/cm3. The integrated intensity of the central peak increases with increasing initial oxygen content. For comparison, untreated samples of the same initial oxygen content do not reveal any anisotropic SAN scattering or a broadened central peak beam. 相似文献
27.
Properties of nonparametric estimators of autocovariance for stationary random fields 总被引:1,自引:0,他引:1
Summary We introduce nonparametric estimators of the autocovariance of a stationary random field. One of our estimators has the property that it is itself an autocovatiance. This feature enables the estimator to be used as the basis of simulation studies such as those which are necessary when constructing bootstrap confidence intervals for unknown parameters. Unlike estimators proposed recently by other authors, our own do not require assumptions such as isotropy or monotonicity. Indeed, like nonparametric function estimators considered more widely in the context of curve estimation, our approach demands only smoothness and tail conditions on the underlying curve or surface (here, the autocovariance), and moment and mixing conditions on the random field. We show that by imposing the condition that the estimator be a covariance function we actually reduce the numerical value of integrated squared error. 相似文献
28.
The problem of nonparametric stationary distribution function estimation by the observations of an ergodic diffusion process is considered. The local asymptotic minimax lower bound on the risk of all the estimators is found and it is proved that the empirical distribution function is asymptotically efficient in the sense of this bound. 相似文献
29.
Y.P. Venkata Subbaiah 《Applied Surface Science》2006,253(5):2409-2415
ZnS films have been deposited on glass substrates by close-spaced evaporation (CSE) technique. The films were grown at different temperatures in the range, 200-350 °C. The layers have been characterized with X-ray diffractometer (XRD), atomic force microscope (AFM), energy dispersive analysis of X-rays (EDAX) and optical spectrophotometer to evaluate the quality of the layers for photovoltaic applications. The studies showed that the optimum substrate temperature for the growth of ZnS layers was 300 °C. The films grown at these temperatures exhibited cubic structure with nearly stoichiometric composition. The AFM data revealed that the films had nano-sized grains with a grain size of ∼40 nm. The optical studies exhibited direct allowed transition with an energy band gap of 3.61 eV. The other structural and optical parameters such as lattice stress, dislocation density, refractive index and extinction coefficient were also evaluated. The temperature-dependent conductivity measured in the range, 303-523 K showed a change in the conduction mechanism at 120 °C. The activation energy values evaluated using the temperature dependence of electrical conductivity are 7 and 29 meV at low and high temperature regions, respectively. 相似文献
30.
Lévy processes in matrix Lie groups are studied. Subordination (random time change) is used to show that quasi-invariance of the Brownian motion in a Lie group induces absolute continuity of the laws of the corresponding pure jump processes. These results are applied to several examples which are discussed in detail. 相似文献