全文获取类型
收费全文 | 3999篇 |
免费 | 429篇 |
国内免费 | 160篇 |
专业分类
化学 | 290篇 |
晶体学 | 11篇 |
力学 | 1104篇 |
综合类 | 63篇 |
数学 | 1313篇 |
物理学 | 1807篇 |
出版年
2024年 | 5篇 |
2023年 | 42篇 |
2022年 | 76篇 |
2021年 | 71篇 |
2020年 | 84篇 |
2019年 | 81篇 |
2018年 | 100篇 |
2017年 | 146篇 |
2016年 | 156篇 |
2015年 | 114篇 |
2014年 | 247篇 |
2013年 | 344篇 |
2012年 | 179篇 |
2011年 | 220篇 |
2010年 | 185篇 |
2009年 | 211篇 |
2008年 | 223篇 |
2007年 | 214篇 |
2006年 | 188篇 |
2005年 | 205篇 |
2004年 | 143篇 |
2003年 | 140篇 |
2002年 | 153篇 |
2001年 | 125篇 |
2000年 | 148篇 |
1999年 | 113篇 |
1998年 | 97篇 |
1997年 | 86篇 |
1996年 | 71篇 |
1995年 | 53篇 |
1994年 | 55篇 |
1993年 | 79篇 |
1992年 | 27篇 |
1991年 | 44篇 |
1990年 | 21篇 |
1989年 | 23篇 |
1988年 | 13篇 |
1987年 | 14篇 |
1986年 | 10篇 |
1985年 | 24篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 16篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1976年 | 4篇 |
1972年 | 2篇 |
1957年 | 4篇 |
1936年 | 1篇 |
排序方式: 共有4588条查询结果,搜索用时 468 毫秒
11.
12.
For three‐dimensional flows with one inhomogeneous spatial coordinate and two periodic directions, the Karhunen–Loeve procedure is typically formulated as a spatial eigenvalue problem. This is normally referred to as the direct method (DM). Here we derive an equivalent formulation in which the eigenvalue problem is formulated in the temporal coordinate. It is shown that this so‐called method of snapshots (MOS) has some numerical advantages when compared to the DM. In particular, the MOS can be formulated purely as a matrix composed of scalars, thus avoiding the need to construct a matrix of matrices as in the DM. In addition, the MOS avoids the need for so‐called weight functions, which emerge in the DM as a result of the non‐uniform grid typically employed in the inhomogeneous direction. The avoidance of such weight functions, which may exhibit singular behaviour, guarantees satisfaction of the boundary conditions. The MOS is applied to data sets recently obtained from the direct simulation of turbulence in a channel in which viscoelasticity is imparted to the fluid using a Giesekus model. The analysis reveals a steep drop in the dimensionality of the turbulence as viscoelasticity is increased. This is consistent with the results that have been obtained with other viscoelastic models, thus revealing an essential generic feature of polymer‐induced drag reduced turbulent flows. Published in 2006 by John Wiley & Sons, Ltd. 相似文献
13.
We consider the isothermal flow through a cylindrical flat chamber, a model of some particular heat exchanger, for which LDV measurements and a numerical simulation have been performed. Experimental results show the establishment of an important vortex zone, the secondary flow extending all along the chamber radius. This observation leads to an expected significant increase of the fluid mixing. Results issued from the numerical simulation appear to be in close agreement with experimental data. Nevertheless, the k–ε model used here must be improved to obtain a better approach near the vortex centre. To cite this article: S. Petitot et al., C. R. Mecanique 330 (2002) 593–599. 相似文献
14.
Hui Ping Zhang 《数学学报(英文版)》2006,22(3):945-950
In this paper, we first define a kind of pseudo–distance function and annulus domain on Riemann surfaces, then prove the Hadamard
Theorem and the Borel–Carathéodory Theorem on any Riemann surfaces.
Supported by NSFC 10501052 相似文献
15.
J. J. EGOZCUE J. L. DIAZ-BARRERO V. PAWLOWSKY-GLAHN 《数学学报(英文版)》2006,22(4):1175-1182
The set of probability functions is a convex subset of L1 and it does not have a linear space structure when using ordinary sum and multiplication by real constants. Moreover, difficulties arise when dealing with distances between densities. The crucial point is that usual distances are not invariant under relevant transformations of densities. To overcome these limitations, Aitchison's ideas on compositional data analysis are used, generalizing perturbation and power transformation, as well as the Aitchison inner product, to operations on probability density functions with support on a finite interval. With these operations at hand, it is shown that the set of bounded probability density functions on finite intervals is a pre-Hilbert space. A Hilbert space of densities, whose logarithm is square-integrable, is obtained as the natural completion of the pre-Hilbert space. 相似文献
16.
Pearson-χ~2距离的若干性质 总被引:18,自引:0,他引:18
李开灿 《数学的实践与认识》2003,33(1):49-53
本文对数理统计中常用的 Pearson- χ2距离的分析特性进行了讨论 ,得到了这一距离的一些解析性质 ,最后我们还给出了几个常用距离的关系 . 相似文献
17.
E.V. Jansson 《Applied Acoustics》2004,65(12):1197-1205
Good violins have a broad hill in the 2-3 kHz range of their frequency response. This hill has previously been attributed to the first in-plane resonance of the violin bridge. Experiments prove, however, that the hill is the result of two forces acting in opposite directions at the bridge feet. The experiments reported here show that the hill can be “tuned” by altering the distance between the bridge feet. It can be tuned both in terms of frequency and level but the properties of the violin cannot be neglected. 相似文献
18.
A boundary element method for the calculation of noise barrier insertion loss in the presence of atmospheric turbulence 总被引:1,自引:0,他引:1
Yiu Wai Lam 《Applied Acoustics》2004,65(6):583-603
Atmospheric turbulence is an important factor that limits the amount of attenuation a barrier can provide in the outdoor environment. It is therefore important to develop a reliable method to predict its effect on barrier performance. The boundary element method (BEM) has been shown to be a very effective technique for predicting barrier insertion loss in the absence of turbulence. This paper develops a simple and efficient modification of the BEM formulation to predict the insertion loss of a barrier in the presence of atmospheric turbulence. The modification is based on two alternative methods: (1) random realisations of log-amplitude and phase fluctuations of boundary sources and (2) de-correlation of source coherence using the mutual coherence function (MCF). An investigation into the behaviours of these two methods is carried out and simplified forms of the methods developed. Some systematic differences between the predictions from the methods are found. When incorporated into the BEM formulation, the method of random realisations and the method of MCF de-correlation provide predictions that agree well with predictions by the parabolic equation method and by the scattering cross-section method on a variety of thin barrier configurations. 相似文献
19.
After carefull analysis in a turbulent zero-pressure gradient flow, various simple algebraic turbulence models were applied to the almost separated flow on the upperside of an airfoil at incidence. The Johnson-King and Horton non-equilibrium (or rate equation) models give clearly improved results. 相似文献
20.
1引言分离流动经常出现在许多实际流动中,对流体机械和飞行器产生重大影响。但由于这种流动具有方向性,变化快,给测量带来了困难。到目前为止,主要有以下三种测量方法:山激光多普勒测速治(*D川;(2)飞行热线(F坊In含*。卜w让e);O)脉冲热线技术(PulsedAVire。‘脉冲热线”比“激光多普勒测速仪”价格低一个数量级,操作简单,是一种比较理想的测量技术。其原理最初由Baner山提出,随后经过BradburyP],Eaton问,Castro*和Fernholz问等人不断发展与完善,目前国外正推广应用在分离流动的研究中。但在国内,尚不多见其… 相似文献