全文获取类型
收费全文 | 23790篇 |
免费 | 863篇 |
国内免费 | 506篇 |
专业分类
化学 | 3493篇 |
晶体学 | 125篇 |
力学 | 663篇 |
综合类 | 73篇 |
数学 | 15556篇 |
物理学 | 5249篇 |
出版年
2024年 | 21篇 |
2023年 | 163篇 |
2022年 | 232篇 |
2021年 | 258篇 |
2020年 | 409篇 |
2019年 | 638篇 |
2018年 | 672篇 |
2017年 | 458篇 |
2016年 | 418篇 |
2015年 | 452篇 |
2014年 | 914篇 |
2013年 | 1340篇 |
2012年 | 760篇 |
2011年 | 1877篇 |
2010年 | 1378篇 |
2009年 | 1711篇 |
2008年 | 1881篇 |
2007年 | 1733篇 |
2006年 | 1338篇 |
2005年 | 984篇 |
2004年 | 845篇 |
2003年 | 733篇 |
2002年 | 666篇 |
2001年 | 434篇 |
2000年 | 428篇 |
1999年 | 469篇 |
1998年 | 377篇 |
1997年 | 338篇 |
1996年 | 395篇 |
1995年 | 390篇 |
1994年 | 393篇 |
1993年 | 311篇 |
1992年 | 243篇 |
1991年 | 166篇 |
1990年 | 131篇 |
1989年 | 149篇 |
1988年 | 95篇 |
1987年 | 88篇 |
1986年 | 86篇 |
1985年 | 136篇 |
1984年 | 109篇 |
1983年 | 76篇 |
1982年 | 124篇 |
1981年 | 88篇 |
1980年 | 73篇 |
1979年 | 27篇 |
1978年 | 50篇 |
1977年 | 36篇 |
1976年 | 37篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
A solution to the phase problem in optics is considered within the context of registration and analysis of two-dimensional stationary optical fields transformed by the object under study or fields forming an image. To obtain information on amplitude and phase distributions of the light field analyzed, a method of registration of two intensity distributions is used. The first distribution corresponds directly to the amplitude distribution. The other is formed for the sum of the initial field and the field shifted along a certain direction. The intensity distributions obtained allow one to calculate the two-dimensional structure of the field under study. It is noteworthy that the method requires no iteration procedures in solving the problem. This leads to speeding up of the processing and analysis of the information. Two variants of optical schemes for the analysis of light fields are considered. The first one corresponds to registration of the image of the analyzed plane and the second to registration of the spectrum of the spatial frequencies. 相似文献
162.
163.
Franc Forstnerič 《Mathematische Annalen》1992,292(1):163-180
164.
本文采用高分辨率格式和多块多网格方法求解雷诺平均Navier-Stokes方程,数值模拟多排叶片内的三维粘性流动;使用数值激盘模拟叶片排的存在,研究叶片排与非轴对称排气部件之间的相互作用以及复杂的内部流动。文中描述了数值方法,给出了NASA透平导叶和单级透平内部流场的数值结果及其与相应实验结果的对比,也给出了多级透平内部流场的数值结果,以及透平与排气部件之间的耦合流场的结果。 相似文献
165.
A robust and efficient adaptive reweighted estimator of multivariate location and scatter 总被引:1,自引:0,他引:1
Daniel Gervini 《Journal of multivariate analysis》2003,84(1):116-144
This article proposes a reweighted estimator of multivariate location and scatter, with weights adaptively computed from the data. Its breakdown point and asymptotic behavior under elliptical distributions are established. This adaptive estimator is able to attain simultaneously the maximum possible breakdown point for affine equivariant estimators and full asymptotic efficiency at the multivariate normal distribution. For the special case of hard-rejection weights and the MCD as initial estimator, it is shown to be more efficient than its non-adaptive counterpart for a broad range of heavy-tailed elliptical distributions. A Monte Carlo study shows that the adaptive estimator is as robust as its non-adaptive relative for several types of bias-inducing contaminations, while it is remarkably more efficient under normality for sample sizes as small as 200. 相似文献
166.
Yong Joon Park Min Gyu KimYoung-Sik Hong Xianglan WuKwang Sun Ryu Soon Ho Chang 《Solid State Communications》2003,127(7):509-514
Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2 (X=0.17, 0.25, 0.33, 0.5) compounds are prepared by a simple combustion method. The Rietvelt analysis shows that these compounds could be classified as having the α-NaFeO2 structure. The initial charge-discharge and irreversible capacity increases with the decrease of x in Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2. Indeed, Li[Ni0.50Mn0.50]O2 compound shows relatively low initial discharge capacity of 200 mAh/g and large capacity loss during cycling, with Li[Ni0.17Li0.22Mn0.61]O2 and Li[Ni0.25Li0.17Mn0.58]O2 compounds exhibit high initial discharge capacity over 245 mAh/g and stable cycle performance in the voltage range of 4.8 -2.0 V. On the other hand, XANES analysis shows that the oxidation state of Ni ion reversibly changes between Ni2+ and about Ni3+, while the oxidation state of Mn ion sustains Mn4+ during charge-discharge process. This result does not agree with the previously reported ‘electrochemistry model’ of Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2, in which Ni ion changes between Ni2+ and NI4+. Based on these results, we modified oxidation-state change of Mn and Ni ion during charge-discharge process. 相似文献
167.
Gunhild U. von Oertzen 《Journal of Physics and Chemistry of Solids》2007,68(3):324-330
Ab initio density functional calculations (plane wave GGA, CASTEP) were performed to determine the effect of O deficiency on the electronic structure of rutile, TiO2. O deficiency was introduced through either the removal of O or the insertion of interstitial Ti atoms. At physically realistic concentrations of O vacancies in the rutile lattice (i.e. 25% and less) O deficiency results in the population of the bottom of the conduction band, the location of the Ti 3d orbitals in the pure structure, increasingly with increasing vacancy concentration. We propose that this could be confused with the formation and population of gap states especially where O vacancies occur in isolated positions in the lattice. In contrast, Ti interstitials introduce a defect state into the energy gap, without an overall reduction in the size of the energy gap. O vacancies result in a spin polarized solution, whereas Ti interstitials do not. 相似文献
168.
We generalize several results on bounded analytic interpolation of Fitzgerald and Horn, which work by majorization by positive
definite kernels, to the cases of several complex variables and operator-valued interpolation. Using a lemma of Kolmogorov,
we complement a simplification due to Szafraniec in the proofs of the theorems.
Received: November 21, 2006. Accepted: August 03, 2007. 相似文献
169.
Sans résumé
相似文献
相似文献
170.
Joseph Majdalani Sjoerd W. Rienstra 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2007,58(2):289-308
The bidirectional vortex refers to the bipolar, coaxial swirling motion that can be triggered, for example, in cyclone separators
and some liquid rocket engines with tangential aft-end injectors. In this study, we present an exact solution to describe
the corresponding bulk motion in spherical coordinates. To do so, we examine both linear and nonlinear solutions of the momentum
and vorticity transport equations in spherical coordinates. The assumption will be that of steady, incompressible, inviscid,
rotational, and axisymmetric flow. We further relate the vorticity to some power of the stream function. At the outset, three
possible types of similarity solutions are shown to fulfill the momentum equation. While the first type is incapable of satisfying
the conditions for the bidirectional vortex, it can be used to accommodate other physical settings such as Hill’s vortex.
This case is illustrated in the context of inviscid flow over a sphere. The second leads to a closed-form analytical expression
that satisfies the boundary conditions for the bidirectional vortex in a straight cylinder. The third type is more general
and provides multiple solutions. The spherical bidirectional vortex is derived using separation of variables and the method
of variation of parameters. The three-pronged analysis presented here increases our repertoire of general mean flow solutions
that rarely appear in spherical geometry. It is hoped that these special forms will permit extending the current approach
to other complex fluid motions that are easier to capture using spherical coordinates. 相似文献