全文获取类型
收费全文 | 511篇 |
免费 | 60篇 |
国内免费 | 27篇 |
专业分类
化学 | 65篇 |
力学 | 140篇 |
综合类 | 8篇 |
数学 | 179篇 |
物理学 | 206篇 |
出版年
2023年 | 4篇 |
2022年 | 1篇 |
2021年 | 5篇 |
2020年 | 10篇 |
2019年 | 11篇 |
2018年 | 12篇 |
2017年 | 15篇 |
2016年 | 13篇 |
2015年 | 7篇 |
2014年 | 17篇 |
2013年 | 34篇 |
2012年 | 22篇 |
2011年 | 20篇 |
2010年 | 13篇 |
2009年 | 29篇 |
2008年 | 26篇 |
2007年 | 20篇 |
2006年 | 30篇 |
2005年 | 28篇 |
2004年 | 26篇 |
2003年 | 29篇 |
2002年 | 19篇 |
2001年 | 21篇 |
2000年 | 23篇 |
1999年 | 22篇 |
1998年 | 19篇 |
1997年 | 10篇 |
1996年 | 17篇 |
1995年 | 15篇 |
1994年 | 14篇 |
1993年 | 9篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1990年 | 7篇 |
1989年 | 8篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有598条查询结果,搜索用时 31 毫秒
71.
J. L. Consalvi Y. Pizzo A. Kaiss J. L. Torero B. Porterie 《Combustion Theory and Modelling》2013,17(3):451-475
The steady state burning rate of vertically oriented slabs of poly-methyl-methacrylate (PMMA) is numerically investigated. Model predictions are compared with measurements and results of the laminar boundary layer (LBL) theory. The numerical model provides a solution of the Favre-averaged Navier–Stokes equations coupled with sub-models for turbulence, combustion, soot production and radiation. The modelling of condensed phase processes is based on the one-dimensional heat transfer equation and pyrolysis is treated as a phase change using the latent heat approach. Results show that the pyrolysing region can be divided into three regions. In the laminar part of the flow (Gr x < 4.3 × 107), the predicted normalised burning rate, [mdot]″ p x/μ∞, is a power-law function of Gr x with an exponent close to that of the LBL theory, surface re-radiation being the primary source of discrepancies. From the LBL theory for free flow, it is demonstrated that the local burning rate is inversely proportional to the shear velocity gradient. This is globally confirmed by numerical model results. At Gr x = 4.3 × 107 the change in slope of the burning rate observed experimentally, which indicates the end of the laminar flow region, is reproduced numerically. From Gr x = 2.5 × 109 model results show that the surface mass flux of pyrolyzate increases with x, in agreement with experimental data in literature. 相似文献
72.
Time-reversal symmetry relation for nonequilibrium flows ruled by the fluctuating Boltzmann equation
A time-reversal symmetry relation is established for out-of-equilibrium dilute or rarefied gases described by the fluctuating Boltzmann equation. The relation is obtained from the associated coarse-grained master equation ruling the random numbers of particles in cells of given position and velocity in the one-particle phase space. The symmetry relation concerns the fluctuating particle and energy currents of the gas flowing between reservoirs or thermalizing surfaces at given particle densities or temperatures. 相似文献
73.
In chemical and biochemical processes, steady‐state models are widely used for process assessment, control and optimisation. In these models, parameter adjustment requires data collected under nearly steady‐state conditions. Several approaches have been developed for steady‐state identification (SSID) in continuous processes, but no attempt has been made to adapt them to the singularities of batch processes. The main aim of this paper is to propose an automated method based on batch‐wise unfolding of the three‐way batch process data followed by a principal component analysis (Unfold‐PCA) in combination with the methodology of Brown and Rhinehart 2 for SSID. A second goal of this paper is to illustrate how by using Unfold‐PCA, process understanding can be gained from the batch‐to‐batch start‐ups and transitions data analysis. The potential of the proposed methodology is illustrated using historical data from a laboratory‐scale sequencing batch reactor (SBR) operated for enhanced biological phosphorus removal (EBPR). The results demonstrate that the proposed approach can be efficiently used to detect when the batches reach the steady‐state condition, to interpret the overall batch‐to‐batch process evolution and also to isolate the causes of changes between batches using contribution plots. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
74.
Christian Maes 《Physica A》2008,387(12):2675-2689
We consider overdamped diffusion processes driven out of thermal equilibrium and we analyze their dynamical steady fluctuations. We discuss the thermodynamic interpretation of the joint fluctuations of occupation times and currents; they incorporate respectively the time-symmetric and the time-antisymmetric sector of the fluctuations. We highlight the canonical structure of the joint fluctuations. The novel concept of traffic complements the entropy production for the study of the occupation statistics. We explain how the occupation and current fluctuations get mutually coupled out of equilibrium. Their decoupling close-to-equilibrium explains the validity of entropy production principles. 相似文献
75.
Siddhartha Biswas 《Waves in Random and Complex Media》2020,30(4):759-775
ABSTRACT The article deals with the study of plane wave propagation in the thermoelastic medium in the presence of voids. The problem is considered in the context of three-phase-lag model of generalized thermoelasticity. There exists three longitudinal waves, namely elastic (E-mode), thermal (T-mode) and volume fraction (V-mode) in addition to transverse waves which get decoupled from the rest of motion and not affected by thermal and volume fraction fields. The fundamental solution of the system of differential equations in case of steady oscillations in terms of the elementary functions has been constructed. The phase velocity and attenuation coefficient of these waves are computed numerically and presented graphically. 相似文献
76.
This paper deals with a variable diffusion predator–prey model with additive Allee effect. A good understanding of the existence of steady states is gained for the case . The result shows that the reduce problem has multiple solutions. Moreover, by applying the singular perturbation method, we give a proof of existence of large amplitude solutions when is sufficiently small. 相似文献
77.
《Mathematical Methods in the Applied Sciences》2018,41(14):5691-5710
We consider a 2 time scale nonlinear system of ordinary differential equations. The small parameter of the system is the ratio ϵ of the time scales. We search for an approximation involving only the slow time unknowns and valid uniformly for all times at order O(ϵ2). A classical approach to study these problems is Tikhonov's singular perturbation theorem. We develop an approach leading to a higher order approximation using the renormalization group (RG) method. We apply it in 2 steps. In the first step, we show that the RG method allows for approximation of the fast time variables by their RG expansion taken at the slow time unknowns. Next, we study the slow time equations, where the fast time unknowns are replaced by their RG expansion. This allows to rigorously show the second order uniform error estimate. Our result is a higher order extension of Hoppensteadt's work on the Tikhonov singular perturbation theorem for infinite times. The proposed procedure is suitable for problems from applications, and it is computationally less demanding than the classical Vasil'eva‐O'Malley expansion. We apply the developed method to a mathematical model of stem cell dynamics. 相似文献
78.
Valerio Lucarini 《Journal of statistical physics》2009,134(2):381-400
Along the lines of the nonlinear response theory developed by Ruelle, in a previous paper we have proved under rather general
conditions that Kramers-Kronig dispersion relations and sum rules apply for a class of susceptibilities describing at any
order of perturbation the response of Axiom A non equilibrium steady state systems to weak monochromatic forcings. We present
here the first evidence of the validity of these integral relations for the linear and the second harmonic response for the
perturbed Lorenz 63 system, by showing that numerical simulations agree up to high degree of accuracy with the theoretical
predictions. Some new theoretical results, showing how to derive asymptotic behaviors and how to obtain recursively harmonic
generation susceptibilities for general observables, are also presented. Our findings confirm the conceptual validity of the
nonlinear response theory, suggest that the theory can be extended for more general non equilibrium steady state systems,
and shed new light on the applicability of very general tools, based only upon the principle of causality, for diagnosing
the behavior of perturbed chaotic systems and reconstructing their output signals, in situations where the fluctuation-dissipation
relation is not of great help. 相似文献
79.
动静叶栅优化改型及其性能分析 总被引:1,自引:0,他引:1
本文对动静叶栅分别进行优化改型,并对改型前后叶栅的气动性能进行数值分析。动静叶栅的优化改型基于正反问题相结合的流函数方法,性能分析一方面基于单排叶栅定常粘性流动的数值计算,另一方面基于动静叶栅相互干扰非定常粘性流动的数值计算。算例结果表明,经过优化改型后的动静叶栅的气动性能,无论在定常流动条件下还是在非定常流动条件下,相比改型前均有较大幅度的改善。 相似文献
80.