全文获取类型
收费全文 | 4107篇 |
免费 | 232篇 |
国内免费 | 450篇 |
专业分类
化学 | 1973篇 |
晶体学 | 37篇 |
力学 | 627篇 |
综合类 | 58篇 |
数学 | 919篇 |
物理学 | 1175篇 |
出版年
2023年 | 50篇 |
2022年 | 94篇 |
2021年 | 120篇 |
2020年 | 111篇 |
2019年 | 69篇 |
2018年 | 74篇 |
2017年 | 79篇 |
2016年 | 116篇 |
2015年 | 101篇 |
2014年 | 152篇 |
2013年 | 279篇 |
2012年 | 190篇 |
2011年 | 345篇 |
2010年 | 239篇 |
2009年 | 307篇 |
2008年 | 285篇 |
2007年 | 276篇 |
2006年 | 284篇 |
2005年 | 218篇 |
2004年 | 176篇 |
2003年 | 176篇 |
2002年 | 136篇 |
2001年 | 114篇 |
2000年 | 99篇 |
1999年 | 81篇 |
1998年 | 92篇 |
1997年 | 76篇 |
1996年 | 58篇 |
1995年 | 41篇 |
1994年 | 49篇 |
1993年 | 36篇 |
1992年 | 32篇 |
1991年 | 22篇 |
1990年 | 24篇 |
1989年 | 23篇 |
1988年 | 27篇 |
1987年 | 15篇 |
1986年 | 20篇 |
1985年 | 17篇 |
1984年 | 11篇 |
1982年 | 15篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 2篇 |
1976年 | 5篇 |
1975年 | 2篇 |
1973年 | 4篇 |
1972年 | 4篇 |
排序方式: 共有4789条查询结果,搜索用时 15 毫秒
1.
2.
3.
Turbulent forced convection in a corrugated tube with spring tape is investigated experimentally, for Reynolds numbers from 10,000 to 50,000. The working fluid is air. Experiments are performed for different pitch and spring ratios. Results show that Nusselt numbers can be increased considerably, depending on pitch and spring ratios. An overall assessment, considering the friction losses, is achieved using the thermo-hydraulic performance parameter. The latter is observed to take values larger than unity for all cases, where quite high values around 2.8 occur for cases with smallest pitch and spring ratios. Predictive Nusselt number and friction factor correlations are proposed. 相似文献
4.
The aim of this work is to derive an accurate model of two-dimensional switched control heating system from data generated by a Finite Element solver. The nonintrusive approach should be able to capture both temperature fields, dynamics and the underlying switching control rule. To achieve this goal, the algorithm proposed in this paper will make use of three main ingredients: proper orthogonal decomposition (POD), dynamic mode decomposition (DMD) and artificial neural networks (ANN). Some numerical results will be presented and compared to the high-fidelity numerical solutions to demonstrate the capability of the method to reproduce the dynamics. 相似文献
5.
《Physics letters. A》2019,383(18):2201-2206
This investigation presents the unsteady rheology of Maxwell nanomaterial induced to flow over an inclined surface. Simultaneous effects of stratification, thermal radiation, heat source/sink and magnetic field are taken into account. Viscous dissipation and mixed convection due to concentration and temperature differences are also analyzed. The governing partial differential equations for the Maxwell nanofluid which incorporate the effects of Brownian and thermophoresis effects are simplified by using appropriate similarity transformations, and solved analytically by using homotopy analysis method (HAM). The effects of involved physical parameters on the flow field are analyzed graphically and numerically. 相似文献
6.
7.
This study investigated the effects of different treatment of alkaline pH-shifting on milk protein concentrate (MPC), micellar casein concentrate (MCC) and whey protein isolate (WPI) assisted by the same ultrasound conditions, including changes in the physicochemical properties, solubility and foaming capacity. The solubility of milk proteins had a significant increase with gradual enhancement of ultrasound-assisted alkaline pH-shifting (p < 0.05), especially for MCC up to 99.50 %. Also, treatment made a significant decline in the particle size of MPC and MCC, as well as the turbidity of the proteins (p < 0.05). The foaming capacity of MPC, MCC, and WPI was all improved, especially at pH 11, and at this pH, the milk protein also showed the highest surface hydrophobicity. The best foaming capacity at pH 11 was the result of the combined effect of particle size, potential, protein conformation, solubility, and surface hydrophobicity. In conclusion, ultrasound-assisted pH-shifting treatment was found to be effective in improving the physicochemical properties and solubility and foaming capacity of milk proteins, especially MCC, with promising application prospect in food industry. 相似文献
8.
Mihir Samantaray Seshadev Sahoo Direndranath Thatoi 《Comptes Rendus Mecanique》2018,346(11):1043-1054
Direct Metal Laser Sintering (DMLS) is one of the leading additive manufacturing processes, which produces complex metallic parts directly from the powder. One of the major problems of this rapid manufacturing process is an inhomogeneous temperature distribution, which leads to residual stress in the build part. Thus, temperature analyses must be performed, to better understand the temperature distribution and sintering behavior of the powder bed with a different laser recipe. In this study, a comprehensive three-dimensional numerical model was developed to understand the temperature distribution during direct metal laser sintering of AlSi10Mg alloy powder. The computer simulation was carried out in ANSYS 17.0 platform. Further, the effect of process parameters such as laser power and scan speed on the temperature distribution and sintering behavior were studied. From the simulation results, it was found that, when the laser power increased from 70 W to 190 W, the maximum temperature of the molten pool increased from 731?°C to 2672?°C, and the molten pool length changed from 0.286 mm to 2.167 mm. A reverse phenomenon was observed with an increase in scan speed. The sintering depth of the powder layer increases significantly from 0.061 mm to 0.872 mm with increasing the applied laser power, but decreased from 0.973 mm to 0.209 mm as a higher scan speed was applied. The developed model helps to optimize the powder layer thickness and minimize the wastage of excess powders during the sintering process. 相似文献
9.
使用热侵蚀沉积粒子程序(HEDPIC)模拟了由小块沿环向表面倾斜的瓦片组成类 ITER 偏滤器的极向
缝隙附近瓦片表面的热流密度分布,研究了不同倾斜高度对热流密度分布的影响。研究结果表明,当瓦片设置成
合适的倾斜角度时,瓦片上表面靠近缝隙附近的电子热通量为零;离子热流密度小于上表面远离缝隙的热流密度,
棱边处热流密度过高的问题得到解决。 相似文献
10.
为提升组建效率,降低组建难度与成本,在分析区域小微企业及其群体特点的基础上,提出由小微企业构建产品制造模块,通过模块的组合,形成大规模客户化制造系统的模块化组建方法.同时,结合对产品制造模块及其构建方式,以及模块选择主要影响因素的分析,研究了基于模块选择系数的制造模块选择策略,为制造系统的模块化组建提供了必要条件. 相似文献