全文获取类型
收费全文 | 20566篇 |
免费 | 2016篇 |
国内免费 | 821篇 |
专业分类
化学 | 4622篇 |
晶体学 | 192篇 |
力学 | 7644篇 |
综合类 | 151篇 |
数学 | 3501篇 |
物理学 | 7293篇 |
出版年
2024年 | 13篇 |
2023年 | 182篇 |
2022年 | 285篇 |
2021年 | 448篇 |
2020年 | 543篇 |
2019年 | 423篇 |
2018年 | 477篇 |
2017年 | 533篇 |
2016年 | 542篇 |
2015年 | 583篇 |
2014年 | 754篇 |
2013年 | 1556篇 |
2012年 | 1046篇 |
2011年 | 1300篇 |
2010年 | 943篇 |
2009年 | 1197篇 |
2008年 | 1163篇 |
2007年 | 1182篇 |
2006年 | 1080篇 |
2005年 | 930篇 |
2004年 | 957篇 |
2003年 | 838篇 |
2002年 | 759篇 |
2001年 | 581篇 |
2000年 | 593篇 |
1999年 | 477篇 |
1998年 | 526篇 |
1997年 | 475篇 |
1996年 | 430篇 |
1995年 | 358篇 |
1994年 | 323篇 |
1993年 | 278篇 |
1992年 | 288篇 |
1991年 | 188篇 |
1990年 | 192篇 |
1989年 | 146篇 |
1988年 | 135篇 |
1987年 | 91篇 |
1986年 | 97篇 |
1985年 | 105篇 |
1984年 | 90篇 |
1983年 | 45篇 |
1982年 | 98篇 |
1981年 | 34篇 |
1980年 | 21篇 |
1979年 | 15篇 |
1978年 | 19篇 |
1976年 | 14篇 |
1973年 | 12篇 |
1957年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
David K Bisset 《国际流体数值方法杂志》2002,39(10):961-977
Turbulent flow simulation methods based on finite differences are attractive for their simplicity, flexibility and efficiency, but not always for accuracy or stability. This paper demonstrates that a good compromise is possible with the advected grid explicit (AGE) method. Starting from the same initial field as a previous spectral DNS, AGE method simulations of a planar turbulent wake were carried out as DNS, and then at three levels of reduced resolution. The latter cases were in a sense large‐eddy simulations (LES), although no specific sub‐grid‐scale model was used. Results for the two DNS methods, including variances and power spectra, were very similar, but the AGE simulation required much less computational effort. Small‐scale information was lost in the reduced resolution runs, but large‐scale mean and instantaneous properties were reproduced quite well, with further large reductions in computational effort. Quality of results becomes more sensitive to the value chosen for one of the AGE method parameters as resolution is reduced, from which it is inferred that the numerical stability procedure controlled by the parameter is acting in part as a sub‐grid‐scale model. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
22.
A. B. Mazo 《Fluid Dynamics》2002,37(6):913-918
Plane ideal incompressible flow in a rectangular channel partitioned by a thin permeable barrier (lattice) is considered. In flowing through the lattice the stream suddenly (jumpwise) changes direction and loses energy. The flow is assumed to be vortical; the vorticity is discontinuous on the lattice. A mathematical formulation of the problem for the stream function is proposed in the form of a nonlinear elliptic equation with coefficients discontinuous on the lattice line. A numerical solution is constructed using the finite-element iteration method. The results of the numerical simulation show how the flow velocity profile in the channel can be controlled by means of permeable barriers. 相似文献
23.
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
24.
The molding processes of polymer melts involve geometrically complex dies. Such dies are usually tapered or streamlined to achieve a maximum output rate under conditions of laminar flow. The model of a generalized second-grade fluid of power-law type is used and the results obtained are illustrated by examples of convergent flows in conical and wedge-shaped dies. 相似文献
25.
26.
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
27.
采用甚高频等离子体增强化学气相沉积技术制备了系列微晶硅薄膜太阳电池,指出了气体总流量和背反射电极的类型对电池性能参数的影响.电池的I-V测试结果表明:随反应气体总流量的增加,对应电池的短路电流密度、开路电压和填充因子都有很大程度的提高,结果使得电池的光电转换效率得以提高.另外,ZnO/Ag/Al背反射电极能明显提高电池的短路电流密度,进而也提高了电池的光电转换效率.对气体总流量和背反射电极类型影响电池效率的原因进行了分析.
关键词:
微晶硅薄膜太阳电池
气体流量
ZnO/Ag/Al背反射电极 相似文献
28.
29.
30.