全文获取类型
收费全文 | 4226篇 |
免费 | 285篇 |
国内免费 | 1426篇 |
专业分类
化学 | 4447篇 |
晶体学 | 33篇 |
力学 | 307篇 |
综合类 | 63篇 |
数学 | 77篇 |
物理学 | 1010篇 |
出版年
2024年 | 7篇 |
2023年 | 44篇 |
2022年 | 71篇 |
2021年 | 125篇 |
2020年 | 173篇 |
2019年 | 212篇 |
2018年 | 132篇 |
2017年 | 182篇 |
2016年 | 221篇 |
2015年 | 178篇 |
2014年 | 194篇 |
2013年 | 408篇 |
2012年 | 265篇 |
2011年 | 275篇 |
2010年 | 187篇 |
2009年 | 258篇 |
2008年 | 224篇 |
2007年 | 307篇 |
2006年 | 257篇 |
2005年 | 316篇 |
2004年 | 286篇 |
2003年 | 252篇 |
2002年 | 194篇 |
2001年 | 184篇 |
2000年 | 165篇 |
1999年 | 133篇 |
1998年 | 111篇 |
1997年 | 103篇 |
1996年 | 104篇 |
1995年 | 81篇 |
1994年 | 84篇 |
1993年 | 50篇 |
1992年 | 39篇 |
1991年 | 25篇 |
1990年 | 28篇 |
1989年 | 17篇 |
1988年 | 11篇 |
1987年 | 14篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
排序方式: 共有5937条查询结果,搜索用时 31 毫秒
81.
数值计算表明,逆向多环形分布射流可造成颗粒能直接进入,并能进行强烈的动量、能量交換的理想的迴流区结构。多环形结构可在大范围內造成所需尺寸的迴流区。逆向射流和主流速度比、环直径、射流直径和孔数、环的结构形式及离燃烧室进口的距离是影响迴流特性的主要参数。 相似文献
82.
本文讨论了激波后可燃颗粒点火、燃烧的机制和波后流场的松弛结构,结果表明,点火阶段颗粒外层浓度梯度极大,燃烧速率由非均相化学反应速率决定,而在燃烧阶段,外层的浓度梯度极大,燃烧速率由气体的扩散速率所决定。在考虑管壁效应时,对守恒方程中的能量耗散项作了说明。 相似文献
83.
84.
A. Brandl M. Pfitzner J. D. Mooney B. Durst W. Kern 《Flow, Turbulence and Combustion》2005,75(1-4):335-350
In order to simulate the turbulent combustion process occurring in spark-ignition (IC) engines, it is necessary to provide
suitable and numerically economical models, the latter being particularly important in the application to industrial problems.
Moreover, these models must deliver sufficiently accurate results for the unsteady operation of spark combustion engines,
concerning variable geometries, temperatures, pressures and charge development in different configurations. In this work different
turbulent combustion models for premixed hydrocarbon combustion are compared with respect to their ability to accurately predict
the propagation of turbulent perfectly premixed flames.
As a first configuration a cylinder of constant volume was studied. Transient calculations were used to simulate the propagation
of the turbulent flame and to evaluate the resulting turbulent burning velocity. These calculations were performed for a perfect
mixture of air and hydrocarbons at stoichiometric mixture and different initial conditions concerning pressure, temperature
and turbulence intensity. As a second configuration a stationary turbulent bunsen-type flame with methane fuel was used to
validate the turbulent combustion model of [Lindstedt and Vaos, Combust. Flame 116 (1999) 461] at different pressures. Calculated results were then compared to experimental data of [Kobayashi, Tamura,
Maruta and Niioka. In: Proceedings of the 26th Symposium on Combustion, 1996, p. 389] and show excellent agreement for the turbulent burning velocity at several pressure levels using only a single
set of model parameters. 相似文献
85.
To allow for a reliable examination of the interaction between velocity fluctuations, acoustics and combustion, a novel numerical procedure is discussed in which a spectral solution of the Navier–Stokes equations is directly associated to a high-order finite difference fully compressible DNS solver (sixth order PADE). Using this combination of high-order solvers with accurate boundary conditions, simulations have been performed where a turbulent premixed V-shape flame develops in grid turbulence. In the light of the DNS results, a sub-model for premixed turbulent combustion is analyzed. To cite this article: R. Hauguel et al., C. R. Mecanique 333 (2005). 相似文献
86.
We study the temporal evolution of the combustion flowfield established by the interaction of ram accelerator-type projectiles
with an explosive gas mixture accelerated to hypersonic speeds in an expansion tube. The Navier-Stokes equations for a chemically
reacting gas mixture are solved in a fully coupled manner using an implicit, time accurate algorithm. The solution procedure
is based on a spatially second order, total variation diminishing scheme and a temporally second order, variable-step, backward
differentiation formula method. The hydrogen-oxygen-argon chemistry is modeled with a 9-species, 19-step mechanism. The accuracy
of the solution method is first demonstrated by several benchmark calculations. Numerical simulations of expansion tube flowfields
are then presented for two different geometries: an axisymmetric projectile and a ram accelerator configuration. The development
of the shock-induced combustion process is followed. The temporal variations of the calculated thrust and drag forces on the
ram accelerator projectile are also presented. In the axisymmetric projectile case, which was designed to ensure combustion
only in the boundary layer, the radial extent of the flame front during the initial transient phase was surprisingly large.
In the ram accelerator configuration the flame propagated upstream along both the projectile and tube wall boundary layers,
resulting in unstart.
Received 25 September 1996 / Accepted 15 January 1997 相似文献
87.
Turbulence-intensity measurements were made in a Taylor-Couette flow reactor consisting of two counter-rotating concentric cylinders designed for the purpose of studying turbulent premixed-flame propagation. In the annulus separating the two cylinders, a nearly homogeneous turbulent flow is generated. The intensities of turbulent velocity fluctuations in the annulus in both axial and circumferential directions were measured by using laser-Doppler velocimetry for a wide range of cylinder rotation rates, corresponding to low through high (120 cm/s) intensities relative to typical laminar flame speeds for lean methane-air mixtures. The experimental measurements indicate a linear relation between turbulence intensities and average cylinder surface speed and demonstrate the usefulness of the Taylor-Couette apparatus for studies of premixed-flame propagation in high-intensity turbulent flow. 相似文献
88.
B. Peters 《Flow, Turbulence and Combustion》2005,73(3-4):217-229
The objective of this contribution is to investigate whether the mechanism of the thermal diffusion instability in gaseous
flames causing cellular flame structures also occurs during the combustion of porous solid fuel. Based on conservation for
mass and energy, the relevant set of differential equations was derived. Assuming thermal equilibrium between fuel and oxidiser,
a global energy equation was valid for both solid and gaseous phase. The resulting set of differential equations was discretised
by the Collocation method to arrive at a system of algebraic equations. In order to investigate into cellular flame structures,
an infinitesimal disturbance was superimposed onto the plane conversion front. Carrying out a linear instability analysis,
yielded eigenvalues dependent on the wave number of the disturbance. A critical wave number exists below which the real part
of the eigenvalues is positive, thus, indicating a regime of instability. Within this region, eigenvalues with a not-vanishing
imaginary part of the eigen value existed causing cellular flame structures. However, the growth rate of disturbances was
found to be small, which may explain the difficulty to investigate this phenomena experimentally. 相似文献
89.
90.
The development of mathematical models for the design of controlstrategies for spark ignition automotive engines is described. The objectiveof the models, used for both simulation and optimization analysis, is theprediction of the effects of control strategies on fuel consumption andemissions of a vehicle over arbitrary driving cycles. In order to achievethe best compromise between precision, experimental costs, computationaltime and flexibility, a mixed modelling approach is used, withphenomenological and input-output models integrated within a hierarchicalsystem.Mean value models have been used to describe the most significant dynamiceffects: (i) air flow. (ii) two phases fuel flow in the intake manifold, and(iii) thermal flow in the cylinder walls. Stochastic effects due to sensorsand actuators can be also predicted.Two-zone and multizone thermodynamic models for the prediction ofpressure cycle sub-models for engine emissions (HC, CO, andNO
x
and mechanical losses have been developed. Experimentaldesign techniques are also under development to optimize the interactionsbetween experimental analysis and models. Most of the models have beenintegrated in a computer code, used by a major automotive supplier. 相似文献