全文获取类型
收费全文 | 6127篇 |
免费 | 574篇 |
国内免费 | 346篇 |
专业分类
化学 | 1868篇 |
晶体学 | 84篇 |
力学 | 1057篇 |
综合类 | 50篇 |
数学 | 923篇 |
物理学 | 3065篇 |
出版年
2024年 | 5篇 |
2023年 | 45篇 |
2022年 | 114篇 |
2021年 | 158篇 |
2020年 | 169篇 |
2019年 | 129篇 |
2018年 | 143篇 |
2017年 | 158篇 |
2016年 | 122篇 |
2015年 | 140篇 |
2014年 | 175篇 |
2013年 | 522篇 |
2012年 | 306篇 |
2011年 | 382篇 |
2010年 | 279篇 |
2009年 | 330篇 |
2008年 | 324篇 |
2007年 | 345篇 |
2006年 | 344篇 |
2005年 | 305篇 |
2004年 | 304篇 |
2003年 | 281篇 |
2002年 | 256篇 |
2001年 | 186篇 |
2000年 | 201篇 |
1999年 | 135篇 |
1998年 | 183篇 |
1997年 | 158篇 |
1996年 | 116篇 |
1995年 | 97篇 |
1994年 | 87篇 |
1993年 | 75篇 |
1992年 | 84篇 |
1991年 | 39篇 |
1990年 | 53篇 |
1989年 | 32篇 |
1988年 | 36篇 |
1987年 | 23篇 |
1986年 | 29篇 |
1985年 | 36篇 |
1984年 | 23篇 |
1983年 | 9篇 |
1982年 | 27篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 11篇 |
1978年 | 13篇 |
1977年 | 5篇 |
1976年 | 9篇 |
1973年 | 7篇 |
排序方式: 共有7047条查询结果,搜索用时 671 毫秒
1.
In the present work, the use of cylindrical turbulators in a double pipe heat exchanger has been investigated. Cylindrical fin type of turbulators has been placed circumferentially separated by 90° on the outer side of an inner pipe at a regular pitch. Experimental studies were undertaken for different air flow rates in a turbulent regime whose Reynolds number range between 2500 and 10000. Heat transfer characteristics like Nu and friction factor have been experimentally determined. Parametric studies were conducted by changing the pitch and also the orientation of the turbulators. Nu and friction factor were found to increase as the pitch is reduced. A model with alternatively changed orientation outperformed others by exhibiting highest Nu and reduced friction factor. 相似文献
2.
3.
4.
B. Dubrulle F. Hersant 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):379-386
We generalize an analogy between rotating and stratified shear flows. This analogy is summarized in Table 1. We use this analogy
in the unstable case (centrifugally unstable flow vs. convection) to compute the torque in Taylor-Couette configuration, as a function of the Reynolds number. At low Reynolds
numbers, when most of the dissipation comes from the mean flow, we predict that the non-dimensional torque G = T/ν2
L, where L is the cylinder length, scales with Reynolds number R and gap width η, G = 1.46η3/2(1 - η)-7/4
R
3/2. At larger Reynolds number, velocity fluctuations become non-negligible in the dissipation. In these regimes, there is no
exact power law dependence the torque versus Reynolds. Instead, we obtain logarithmic corrections to the classical ultra-hard (exponent 2) regimes: G = 0.50
. These predictions are found to be in excellent agreement with avail-able experimental data. Predictions for scaling of velocity
fluctuations are also provided.
Received 7 June 2001 and Received in final form 7 December 2001 相似文献
5.
6.
新颖外燃式湿空气燃气轮机循环及性能研究 总被引:2,自引:0,他引:2
本文首先提出一种新型的高效燃煤燃气轮机循环一外燃式湿空气透平循环动力系统。由于外燃的特点,作功工质为洁净湿空气,从而可以实现水的回收,是对常规HAT循环的突破;另外洁净湿空气排放不受通常烟气露点限制,从而可回收利用湿空气降温时的低温凝结潜热,提高了加湿能力,从而提高系统性能。揭示了新型循环的基本规律;推导出具有湿化特点的约束方程和系统性能简明表达式,指明影响系统性能的关键因素。在透平初温为850℃的工况下,系统热效率高达48.11%。基于能量品位梯级利用原理和系统集成方法论,通过探索充分而合理利用中低温余热的有效途径,开拓洁净煤燃气轮机总能系统的新方向。 相似文献
7.
8.
Geng Sheng WANG 《数学学报(英文版)》2005,21(5):1005-1014
This work is concerned with Pontryagin's maximum principle of optimal control problems governed by some non-well-posed semilinear heat equations. A type of approach to the non-well-posed optimal control problem is given. 相似文献
9.
C. H. Hesse 《Statistical Inference for Stochastic Processes》2007,10(1):75-95
In this work the Cauchy problem for the one-dimensional heat equation is considered. In contrast to existing literature it
is assumed that the initial state f is unknown and that information regarding f is obtained by some process of measurement. To enhance realism, both measurement errors and missing data are allowed for.
Under assumptions on f in the Fourier-domain first an approximation to f is derived from the data by means of a novel uncertainty principle. Then, it is studied how this perturbation in the initial
state propagates with time.
相似文献
10.
V. I. Sakharov 《Fluid Dynamics》2007,42(6):1007-1016
The results of numerical simulation are presented for thermally and chemically nonequilibrium air plasma flows in a plasmatron discharge channel and underexpanded dissociated and partially ionized air jets flowing past a cylindrical model with a blunt leading edge and cooled copper surface under the experimental conditions realized in a VGU-4 100 kW induction plasmatron (Institute for Problems in Mechanics of the Russian Academy of Sciences) (see, for example, [1, 2]). The nonequilibrium excitation of the vibrational degrees of freedom of the molecules in the modal approximation and the difference between the electron and translational heavy-particle temperatures are taken into account in the calculations. The calculated data on the heat transfer and pressure at the stagnation point are compared with the results obtained within the framework of the thermally equilibrium model. Comparison with the experimental data obtained in the Institute for Problem in Mechanics of the Russian Academy of Sciences (Laboratory for interaction between plasma and radiation and materials) and kindly provided for comparison purposes gives satisfactory agreement. 相似文献