全文获取类型
收费全文 | 44855篇 |
免费 | 5999篇 |
国内免费 | 3428篇 |
专业分类
电工技术 | 1927篇 |
技术理论 | 1篇 |
综合类 | 5285篇 |
化学工业 | 4421篇 |
金属工艺 | 3710篇 |
机械仪表 | 3350篇 |
建筑科学 | 5301篇 |
矿业工程 | 3101篇 |
能源动力 | 3508篇 |
轻工业 | 774篇 |
水利工程 | 3301篇 |
石油天然气 | 2741篇 |
武器工业 | 1373篇 |
无线电 | 1604篇 |
一般工业技术 | 4697篇 |
冶金工业 | 3139篇 |
原子能技术 | 648篇 |
自动化技术 | 5401篇 |
出版年
2024年 | 93篇 |
2023年 | 672篇 |
2022年 | 1306篇 |
2021年 | 1487篇 |
2020年 | 1614篇 |
2019年 | 1312篇 |
2018年 | 1290篇 |
2017年 | 1700篇 |
2016年 | 1984篇 |
2015年 | 2021篇 |
2014年 | 2731篇 |
2013年 | 3102篇 |
2012年 | 3537篇 |
2011年 | 3786篇 |
2010年 | 2769篇 |
2009年 | 2958篇 |
2008年 | 2648篇 |
2007年 | 3263篇 |
2006年 | 2845篇 |
2005年 | 2365篇 |
2004年 | 1913篇 |
2003年 | 1551篇 |
2002年 | 1225篇 |
2001年 | 1027篇 |
2000年 | 769篇 |
1999年 | 652篇 |
1998年 | 677篇 |
1997年 | 480篇 |
1996年 | 392篇 |
1995年 | 312篇 |
1994年 | 310篇 |
1993年 | 229篇 |
1992年 | 220篇 |
1991年 | 174篇 |
1990年 | 166篇 |
1989年 | 88篇 |
1988年 | 76篇 |
1987年 | 71篇 |
1986年 | 78篇 |
1985年 | 78篇 |
1984年 | 58篇 |
1983年 | 52篇 |
1982年 | 44篇 |
1981年 | 20篇 |
1980年 | 23篇 |
1979年 | 23篇 |
1978年 | 18篇 |
1977年 | 14篇 |
1959年 | 12篇 |
1951年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 215 毫秒
991.
992.
Numerical and physical requirements to simulations of sub-sonic release and dispersion of light gas in an enclosure with one vent are described and discussed. Six validation experiments performed at CEA in a fuel cell-like enclosure of sizes H × W × L = 126 × 93 × 93 cm with one vent, either W × H = 90 × 18 cm (vent A) or 18 × 18 cm (B) or 1 cm in diameter (C), with a vertical upward helium release from a pipe of internal diameter either 5 mm or 20 mm located 21 cm above the floor centre, were used in a parametric study comprising 17 numerical simulations. Three CFD models were applied, i.e. laminar, standard k-?, and dynamic LES Smagorinsky–Lilly, to clarify a range of their applicability and performance. The LES model consistently demonstrated the best performance in reproduction of measured concentrations throughout the whole range of experimental conditions, including laminar, transitional and turbulent releases even with large CFL numbers. The laminar and the standard k-? models were under performing in the reproduction of turbulent and laminar releases respectively, as expected, as well as in simulation of transitional flows. The laminar model demonstrated high sensitivity to the CFL (Courant–Friedrichs–Lewy) number even below the best practices limit of 40. Three different computational domains and grids were used in order to clarify the influence of mesh quality on the capability of simulations to reproduce the experimental data. It is concluded that physically substantiated choice of CFD model, the control of the CFL number (and released gas mass balance where appropriate), and the mesh quality can have a strong effect on the capability of simulations to reproduce experiments and, in general, on the reliability of CFD tools for application in hydrogen safety engineering. 相似文献
993.
Tina Marolt Cebasek Jakob Likar 《土木工程与建筑:英文版》2014,(11):1457-1466
The design procedure is made for a mine shaft where permanent underground facilities are interconnected. The highly faulted grounds were identified using empirical and semi-empirical theories. Furthermore, the behavior types are presented. This paper presents excavation and support methods in such ground conditions and the calculations results show that the installation of the yielding elements have an effect on support elements and prevent shotcrete damage during the curing stage. Different numerical analyses carried out showed that, with the yielding elements installed, the total displacements increase but the final axial force reduces, and therefore, the characteristic compressive strength of shotcrete is not exceeded. The calculation results of ground loads and displacements on the designed support system are presented with a 3D numerical geo-mechanical model adopted for highly faulted ground surrounding deeper complex underground structures. 相似文献
994.
Adam J. Hall Michael J. Chappell John A.D. Aston Stephen A. Ward 《Computer methods and programs in biomedicine》2014
A four compartment mechanistic mathematical model is developed for the pharmacokinetics of the commonly used anti-malarial drug artesunate and its principle metabolite dihydroartemisinin following oral administration of artesunate. The model is structurally unidentifiable unless additional constraints are imposed. Combinations of mechanistically derived constraints are considered to assess their effects on structural identifiability and on model fits. Certain combinations of the constraints give rise to locally or globally identifiable model structures. 相似文献
995.
为了解决传统箱形截面柱法兰连接节点对结构空间占用的问题,提出了一种箱形截面柱剪力键式全螺栓连接节点,并对2个全螺栓连接箱形截面柱和1个整体式箱形截面柱进行拟静力试验研究。观察了全螺栓连接箱形截面柱的破坏现象,分析了全螺栓连接箱形柱的滞回性能、承载力、刚度退化、延性以及耗能能力等受力特性。结果表明:整体式箱形截面柱和剪力键式全螺栓连接箱形截面柱均发生塑性铰破坏;滞回曲线饱满,具有良好耗能能力;剪力键和水平单向螺栓的设置可使全螺栓连接箱形截面柱承载力提高24.64%,竖向高强螺栓拉力降低29.44%;节点处钢连接件的设置约束了箱形截面柱的屈曲变形,与整体式箱形截面柱相比,全螺栓连接箱形截面柱的位移延性系数提高了26.47%;钢连接件间无滑移,剪力键式全螺栓连接节点连接可靠。通过剪力键式全螺栓连接节点与刚接节点有限元分析结果对比,表明在工程应用中箱形截面柱剪力键式全螺栓连接节点可等效刚接。采用GB 50011—2010《建筑抗震设计规范》对箱形截面柱剪力键式全螺栓连接节点进行承载力验算,计算结果与试验结果吻合。 相似文献
996.
浅埋暗挖隧道的开挖及支护方式对其周围地层的影响是三维空间问题,文中通过采用拉格朗日有限差分软件数值模拟管棚预支护对地层沉降的影响,对不同施工阶段下的地层位移、地表变形及管棚、初期支护的受力进行分析。结果表明,使用管棚预支护有效减少了地层在施工过程中的变形,将沉降值控制在允许范围。 相似文献
997.
《Journal of Nuclear Science and Technology》2013,50(12):1118-1123
A supercritical-water-cooled reactor (SCWR) is a high-temperature, high-pressure water cooled reactor that operates above the critical pressure of water. In order to perform efficiently the thermal design of the SCWR, it is important to assess the thermal hydraulics in rod bundles of the core. Experimental conditions of mockup tests, however, may be limited because of technical and financial reasons. Therefore, it is required to establish an analytical design technique that can extrapolate experimental data to various design conditions of the reactor. Japan Atomic Energy Agency (JAEA) has improved the three-dimensional two-fluid model analysis code ACE-3D, which was originally developed for the two-phase flow thermal hydraulics of light water reactors, to handle the thermal hydraulic properties of water in the supercritical region. In the present study, heat transfer experiments of supercritical water flowing in a vertical annular channel around a heater pin, which were performed at JAEA, were analyzed with the improved ACE-3D to assess the prediction performance of the code. As a result, it was implied that the ACE-3D code is applicable to the prediction of wall temperatures of a single rod that simulates the fuel bundle geometry of the SCWR core. 相似文献
998.
999.
In this paper we study a re-entrant line with unreliable asynchronous exponential machines and finite buffers. First, an approximation method is presented to estimate the throughput of the re-entrant line. The idea of the approximation is to transform an M-machine re-entrant line into a 2M-machine serial line. Then, a system approach to identify a c-bottleneck based on blockage and starvation information is proposed, where a c-bottleneck machine is the machine whose improvement in machine capacity leads to the largest improvement in system throughput compared with improving all other machines. It is shown that the approximation method results in acceptable accuracy, and the bottleneck identification method can correctly detect the bottlenecks in most cases. 相似文献
1000.