全文获取类型
收费全文 | 2920篇 |
免费 | 325篇 |
国内免费 | 142篇 |
专业分类
电工技术 | 52篇 |
综合类 | 219篇 |
化学工业 | 570篇 |
金属工艺 | 107篇 |
机械仪表 | 55篇 |
建筑科学 | 145篇 |
矿业工程 | 17篇 |
能源动力 | 1380篇 |
轻工业 | 60篇 |
水利工程 | 76篇 |
石油天然气 | 58篇 |
武器工业 | 4篇 |
无线电 | 61篇 |
一般工业技术 | 304篇 |
冶金工业 | 49篇 |
原子能技术 | 138篇 |
自动化技术 | 92篇 |
出版年
2024年 | 15篇 |
2023年 | 61篇 |
2022年 | 62篇 |
2021年 | 138篇 |
2020年 | 104篇 |
2019年 | 113篇 |
2018年 | 71篇 |
2017年 | 92篇 |
2016年 | 88篇 |
2015年 | 89篇 |
2014年 | 118篇 |
2013年 | 247篇 |
2012年 | 177篇 |
2011年 | 197篇 |
2010年 | 145篇 |
2009年 | 171篇 |
2008年 | 145篇 |
2007年 | 162篇 |
2006年 | 125篇 |
2005年 | 135篇 |
2004年 | 126篇 |
2003年 | 130篇 |
2002年 | 110篇 |
2001年 | 81篇 |
2000年 | 64篇 |
1999年 | 75篇 |
1998年 | 58篇 |
1997年 | 43篇 |
1996年 | 49篇 |
1995年 | 31篇 |
1994年 | 26篇 |
1993年 | 23篇 |
1992年 | 28篇 |
1991年 | 13篇 |
1990年 | 11篇 |
1989年 | 19篇 |
1988年 | 15篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1975年 | 1篇 |
1951年 | 2篇 |
排序方式: 共有3387条查询结果,搜索用时 15 毫秒
11.
G. Scalabrin L. Piazza M. Condosta 《International Journal of Heat and Mass Transfer》2003,46(23):4413-4425
In a previous work, convective heating of carbon dioxide was studied with neural networks (NN), obtaining a totally heuristical heat transfer equation from the direct regression of experimental data. In the present work, the analysis focuses on the cooling process, which has a technical relevance in various applications, as for example in transcritical refrigeration cycles. Heat transfer around the critical zone presents a marked enhancement, that follows the peaks in thermophysical properties like thermal conductivity and heat capacity. Similarly, other properties like density and enthalpy, present a strong variation in narrow temperature intervals around the critical point.This constitutes then a highly non-linear phenomenon, for which it is advisable to use a very flexible function approximator like the NNs. NN models were applied both in terms of dimensionless numbers and of physical quantities, obtaining the two corresponding NN architectures. The choice of the optimal number of neurons in the NN hidden layer is discussed. The NN models are then compared with a recent correlation from literature, for which the validation results present an AAD of 27% and a bias of −26% with an evident prediction shifting. On the other hand the NN models in terms of dimensionless numbers and of physical quantities have AAD and bias of 14% and −4%, and of 7% and −2%, respectively, showing a largely better performance. 相似文献
12.
An expenmental and theoretical study of heat and mass transfer analogy and a comparison of that to a binary liquid mixture evaporation is presented. Common organic solvents, ethanol and n-heptane, were used to form an alcohol - hydrocarbon mixture. Studies were carried out in a horizontal rectangular channel having air flow velocities of 0.2 - 0.9 m/s. Heat transfer coefficients were measured with a copper plate resistor and mass transfer coefficients with a square pool. The heat and mass transfer analogy is presented for a system having two evaporating compounds with a fixed value of air flow and verified by measuring and comparing mass transfer coefficients for distilled water with air flow velocities of 0.2 - 0.9 mls. An illustrative example of the use of the theory for industrial ventilation is presented. 相似文献
13.
Basant Kumar Jha 《国际能源研究杂志》1992,16(1):85-88
An analytical study is performed to examine the thermal diffusion characteristics of free convection and mass transfer flow in a non-Newtonian fluid (Walters, 1962: liquid B') past a uniformly accelerated infinite vertical plate in the presence of thermal diffusion. The expression for the velocity field is obtained by the Laplace transform technique. The influence of the Soret number (a thermal diffusion parameter) on the velocity field is extensively discussed with the help of graphs. 相似文献
14.
Influence of thermal boundary conditions on natural convection in a square enclosure partially heated from below 总被引:1,自引:0,他引:1
Nader Ben Cheikh Brahim Ben BeyaTaieb Lili 《International Communications in Heat and Mass Transfer》2007
Natural convection in air-filled 2D square enclosure heated with a constant source from below and cooled from above is studied numerically for a variety of thermal boundary conditions at the top and sidewalls. Simulations are performed for two kinds of lengths of the heated source, i.e., a small and a large source corresponding to 20% and 80% of the total length of the bottom wall, respectively. The Rayleigh number varied from 103 to 107. Results are presented in the form of streamline and isotherm plots as well as the variation of the Nusselt number and maximum temperature at the heat source surface. Comparisons among the different thermal configurations considered are reported. 相似文献
15.
Steady laminar binary mixed convection flow along a vertical circular cone under the combined buoyancy effects of thermal and species diffusion is studied analytically. The analysis is confined to mass diffusion processes with low concentration levels. In the analysis the surface of the cone is assumed to be at a uniform temperature and uniform concentration. Numerical results for the local Sherwood number, local Nusselt number and local friction factor are presented. Representative temperature, concentration and velocity profiles are also shown. The analysis covers the diffusion of common gases and vapours into air. Considerations are given to the situations where the buoyancy forces assist and oppose the forced convection flow for various possible combinations of the thermal and species diffusion processes. 相似文献
16.
Asymmetric horizontal thermal profiles can change the flow field structure in the physical vapor transport (PVT)of Hg2Cl2. It is found that for the ratios of horizontal to vertical thermal Rayleigh numbers RaH/Ra ≥ 1·5, the convetive flow structure changes from multicellular to unicellular for the base parametric state of Ra = 2·79 × 104, Pr = 0·91, Le=l·01. Pe = 4·60, Ar= 0·2 and Cr = 1·01. The unicellular flow structure obtained by increasing ∇*H(RaH) is not likely to support the conjecture of the presence of unicellular convective mode in the laser Doppler velocimetry (LDV) experiments for PVT process of Hg2Cl2 (Kim el al., 1996). When the six parameters of Ra, Pr, Le, Pe, Ar and Cr are fixed, the dimensional maximum magnitude of the velocity vector |U|max is proportional to √∇T*H. 相似文献
17.
The inverse problem approach by conjugate gradient with adjoint equations is adapted to the context of a non-isothermal bioprocess, controlled by internal heat generation from microbial oxidation, as could be found in a composting reactor for instance, to determine the heat source from internal temperature measurements. The volumetric heat source is assumed proportional to the rate of consumption of a substrate by a biomass, as described by a Monod model. Computations are performed for Rayleigh numbers equal to 0.25 and 25, for a representative biochemical reaction under typical boundary conditions, for constant and temperature-dependent model parameters. The influence of noisy input data is also considered. It is found that good solutions can be obtained when heat release and diffusion occur over very different time scales. The variation of the model parameters with temperature must be taken into account, but single sensor solutions are possible at relatively small Rayleigh numbers when convection is present. 相似文献
18.
Boundary layer equations for free convection heat transfer along a semi-infinite horizontal plate are derived by giving more importance to the energy equation. The equations are obtained for low Prandtl number and two separate polynomials are used to approximate the temperature and velocity profiles in these regions. The rate of heat transfer is compared with the available analytical and numerical results based on conventional boundary layer equations. 相似文献
19.
20.
Wei-Mon Yan 《加拿大化工杂志》1993,71(1):54-62
Numerical results are presented for effects of latent heat transport associated with film vaporization on laminar mixed convection heat and mass transfer in a vertical channel with a half channel width b = 0.01 m. The influences of the inlet liquid mass flowrate and wall temperature on the film vaporization and the associated heat and mass transfer characteristics are examined for air-water and air-ethanol systems with gas Reynolds number Reg = 2000. Predicted results obtained by including transport in the liquid film are contrasted with those where liquid film transport is neglected, showing that the assumption of an extremely thin film made in Lin et al. (1988) and Yan and Lin (1989) is only valid for systems having small liquid mass flow rates. Additionally, it is found that the interfacial heat flux is predominantly determined by latent heat transfer connected with film evaporation. 相似文献