全文获取类型
收费全文 | 32806篇 |
免费 | 2150篇 |
国内免费 | 943篇 |
学科分类
工业技术 | 35899篇 |
出版年
2024年 | 50篇 |
2023年 | 283篇 |
2022年 | 467篇 |
2021年 | 673篇 |
2020年 | 896篇 |
2019年 | 580篇 |
2018年 | 536篇 |
2017年 | 829篇 |
2016年 | 987篇 |
2015年 | 1046篇 |
2014年 | 2172篇 |
2013年 | 2017篇 |
2012年 | 2247篇 |
2011年 | 2468篇 |
2010年 | 1898篇 |
2009年 | 1921篇 |
2008年 | 1819篇 |
2007年 | 2191篇 |
2006年 | 2158篇 |
2005年 | 2236篇 |
2004年 | 1899篇 |
2003年 | 1350篇 |
2002年 | 926篇 |
2001年 | 760篇 |
2000年 | 635篇 |
1999年 | 545篇 |
1998年 | 471篇 |
1997年 | 326篇 |
1996年 | 332篇 |
1995年 | 275篇 |
1994年 | 221篇 |
1993年 | 192篇 |
1992年 | 136篇 |
1991年 | 89篇 |
1990年 | 53篇 |
1989年 | 49篇 |
1988年 | 48篇 |
1987年 | 17篇 |
1986年 | 12篇 |
1985年 | 19篇 |
1984年 | 24篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 5篇 |
1980年 | 9篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1972年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
大功率CO2激光器脉冲电源研究 总被引:1,自引:0,他引:1
本文论述了直流高压与高频脉冲电源相叠加,构成高频、高压脉冲电源,并使其对CO2激光器进行放电实验,研究了同条件下的放电参数与功率。 相似文献
53.
乡镇供水作为水利开发建设中的一个新领域,设计工作是龙头,有许多技术问题需要研究和探索,阐述了乡镇供水工程设计应注意的若干问题,并对设计中存在的一些具体问题进行了分析和探讨。 相似文献
54.
本文叙述了反应堆保护系统停棒与汽轮机降功率子系统的系统功能、保护参数和秦山核电站控制棒组插入监测器的设计与参数选择,确定了控制棒提升上极限值和在不同工况下棒插入低位、低-低位整定值,并在热态零功率条件下加以验证。试验证明参数选择是合理的,为功率运行阶段提供了数据。 相似文献
55.
Characteristics of hydrostatic bearing/seal parts for water hydraulic pumps and motors. Part 1: Experiment and theory 总被引:2,自引:0,他引:2
In this paper, the load-carrying capacity, power losses and stiffness of disk-type hydrostatic thrust bearings including the case of eccentric loading are discussed theoretically. The numerical analysis method is established based on a two-dimensional elastohydrostatic problem with an elastic deformation model, which is extended to adapt it for a non-axisymmetric load acting on the thrust bearing. The bearing is made of a combination of stainless steel/stainless steel and stainless steel/plastics. For the elastic materials, the maximum stiffness derived from, i.e., minimum film thickness is, larger than that of the rigid material in the range of a large ratio of pocket pressure and a hydrostatic balance ratio of over unity, which is defined as the ratio of the load to the maximum hydrostatic load-carrying capacity. The maximum load-carrying capacity and minimum power loss can exist in the domain of the hydrostatic balance ratio over unity for the case of the bearing consisting of elastic/rigid materials, in comparison with that composed of the same rigid materials. For the case of water, the power loss due to leakage flow is slightly larger but that due to frictional torque is much smaller than that in the case of hydraulic oil. Then, the total power loss is much smaller than that of hydraulic oil. 相似文献
56.
57.
58.
The failure of the conductor of the 460 kV overhead transmission line located along the crossing of the Paraná River was investigated. As a result of this failure, a blackout took place in the southern states of Brazil in January of 2002, reaching approximately 67 million inhabitants. Investigation of the external aluminium layer of the ACSR conductor near the fracture showed typical static deformation marks and dynamic fretting wear tangential marks, both associated with the presence of Al2O3 debris. Additionally, encrusted silicon particles were observed on the external surface of the strands. The internal Al layer showed elliptical deformation marks also associated with Al2O3 debris. Both Al2O3 and Si particles are efficient abrasive material, which associated with slight relative motion of metallic surfaces (clamp/strand and strand/strand) can promote fretting wear. Two types of fracture surface of the Al strands were identified: 45° and quasi-normal surfaces, the former being the predominant type. Delamination and particle detachment were the mechanisms of superficial degradation observed on the Al strands, indicating that the rupture of the strands occurred under a gross slip fretting regime induced by sub-conductor oscillation. Inspection of the internal surface of as-cast Al–10%Si spacer clamps revealed different stages of intense circumferential wear caused by the preferential cracking and particle detachment of the eutectic constituent of the as-cast microstructure. This intense wear reduces the clamping contact pressure, which allows higher displacement amplitude and leads to the critical fretting regime. Finally, a few suggestions are discussed to minimise the occurrence of future failures. 相似文献
59.
60.