全文获取类型
收费全文 | 1287篇 |
免费 | 150篇 |
国内免费 | 103篇 |
专业分类
电工技术 | 32篇 |
综合类 | 177篇 |
化学工业 | 304篇 |
金属工艺 | 42篇 |
机械仪表 | 100篇 |
建筑科学 | 42篇 |
矿业工程 | 47篇 |
能源动力 | 101篇 |
轻工业 | 18篇 |
水利工程 | 135篇 |
石油天然气 | 170篇 |
武器工业 | 102篇 |
无线电 | 34篇 |
一般工业技术 | 139篇 |
冶金工业 | 26篇 |
原子能技术 | 21篇 |
自动化技术 | 50篇 |
出版年
2024年 | 3篇 |
2023年 | 26篇 |
2022年 | 46篇 |
2021年 | 42篇 |
2020年 | 45篇 |
2019年 | 59篇 |
2018年 | 53篇 |
2017年 | 62篇 |
2016年 | 66篇 |
2015年 | 51篇 |
2014年 | 78篇 |
2013年 | 91篇 |
2012年 | 106篇 |
2011年 | 82篇 |
2010年 | 59篇 |
2009年 | 80篇 |
2008年 | 64篇 |
2007年 | 71篇 |
2006年 | 60篇 |
2005年 | 55篇 |
2004年 | 42篇 |
2003年 | 36篇 |
2002年 | 31篇 |
2001年 | 25篇 |
2000年 | 30篇 |
1999年 | 29篇 |
1998年 | 24篇 |
1997年 | 17篇 |
1996年 | 17篇 |
1995年 | 12篇 |
1994年 | 18篇 |
1993年 | 12篇 |
1992年 | 16篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1959年 | 1篇 |
排序方式: 共有1540条查询结果,搜索用时 15 毫秒
1.
Pengfei Chen Honggang Chang Tao Peng Yongfan Tang Youquan Liu Chao Xiang 《应用聚合物科学杂志》2021,138(30):50314
Hydraulic fracturing with slickwater is a field-proven stimulation technology used in tight reservoirs. Because of the high pumping rate associated with slickwater fracturing, drag reduction (DR) is critical in minimizing pressure drop and the success of oilfield operations. In this paper, a new type of drag reducer (SPR) was synthesized with acrylamide and 12-allyloxydodecyl acid sodium, and its drag reduction performance was evaluated. The results showed that the new drag reducer features low molecular weight, fast-dissolving rate and low interfacial tension. The algorithm of estimating the drag reduction rate of non-Newtonian fluid SPR was proposed and validated. Empirical or semianalytical models for estimating the friction ratio (σ) or friction factor (λ or f) were used to simulate the turbulence behavior of the SPR drag reducer under different Reynolds numbers (Re). The modified Virk's correlation could accurately model the turbulent behavior of the SPR drag reducer. A unified calculation formula was established in this study for different pipe diameters. 相似文献
2.
3.
The concept of moving surface boundary-layer control, as applied to a Joukowsky airfoil, is investigated through a planned
experimental programme complemented by numerical studies. The moving surface was provided by rotating cylinders located at
the leading edge and/or trailing edge as well as top surface of the airfoil. Results suggest that the concept is quite promising,
leading to a substantial increase in lift and a delay in stall. Depending on the performance desired, appropriate combinations
of cylinder geometry, location and speed can be selected to obtain favourable results over a wide range of angle of attack.
Next, effectiveness of the concept in reducing drag of bluff bodies such as a two-dimensional flat plate at large angles of
attack, rectangular prisms and three-dimensional models of trucks is assessed through an extensive wind tunnel test-programme.
Results show that injection of momentum through moving surfaces, achieved here by introduction of bearing-mounted, motordriven,
hollow cylinders, can significantly delay separation of the boundary-layer and reduce the pressure drag. The momentum injection
procedure also proved effective in arresting wind-induced vortex resonance and galloping type of instabilities. A flow visualization
study, conducted in a closed-circuit water tunnel using slit lighting and polyvinyl choride tracer particles, adds to the
wind-tunnel and numerical investigations. It shows, rather dramatically, the effectiveness of the moving surface boundary-layer
control (MSBC).
The Sabita Chaudhury Memorial Lecture
The models were fabricated in the Mechanical Engineering Workshop. The assistance of M/s E Abell, P Hurren and D Camp in the
design and construction of the models is gratefully acknowledged. The investigation was supported by the Natural Sciences
and Engineering Research Council of Canada, Grant No. A-2181. 相似文献
4.
多排数翅片管空冷器风阻特性的数值模拟 总被引:1,自引:0,他引:1
本文对多排数翅片管空冷器空气侧的风阻特性进行了数值模拟.利用商用软件Fluent进行数值计算,结合经验公式和已有的实验数据,分析了不同入口风速下,阻力的变化规律以及流动阻力和温度变化对模拟计算的影响. 相似文献
5.
6.
7.
一种新的位错运动理论及对材料动态力学行为的描述 总被引:3,自引:0,他引:3
通过对位错在晶格内运动的动力学过程的全面分析。本文提出了一种考虑到粘性阻尼效应和热激活的位错集体运动统一理论。其特点是可用一简单的方程对从低速到高速运动的大量位错的平均行为进行统一描述。对KCl晶体的典型实验怕拟合发现理论描述与实验结果相当一致。 相似文献
8.
本文重点介绍用于机床电力拖动系统中的电机脉冲调制(PWM)技术,在分析现有脉冲宽度调制技术的基础上,提出一种采用优化技术生成PWM调制波的方法,推导了优化PWM调制波的求解过程,给出了其计算公式。 相似文献
9.
新型螺杆挤出机熔体输送理论的研究 总被引:1,自引:0,他引:1
介绍了一种新型嵌套式螺杆挤出机。对熔体输送段进行了深入分析,把内螺杆的运动等效为螺杆轴的反向拖曳和螺棱的正向推力置换两部分作用,建立了对应的物理模型和数学模型,并得到了解析解。重点讨论了沿螺槽方向的流动和横向流动,并与普通单螺杆挤出机作对比,得到了螺杆和机筒同时旋转情况下的体积流率。结果表明,所建模型的解析解和文献中的实验数据较为吻合,当螺杆和机筒同时旋转时,熔体输送段的体积流率大大增加,横向流动和平行平板模型类似。 相似文献
10.
Experimental results are presented of wall effect for the slow motion of spheres in elastic, constant-viscosity liquids. The results are correlated in terms of diameter ratio for d/D < 0.3, and Weissenberg number We < 5. Weissenberg number is defined as We = 2θVm/d, with θ the Maxwellian relaxation time (θ = N1/2τγ). The wall effect is found to be adequately described by Newtonian expressions for small Weissenberg number, We < 0.01. For larger values of the Weissenberg number, We > 0.2, virtually no wall effect is discernible; the small effect observed is correlated by the wall factor expression The wall effect observed is ascribed to the influence of fluid elasticity alone, since all the fluids used were elastic to a greater or lesser extent, but showed no shear thinning. 相似文献