全文获取类型
收费全文 | 91454篇 |
免费 | 6052篇 |
国内免费 | 2667篇 |
专业分类
电工技术 | 3413篇 |
综合类 | 3526篇 |
化学工业 | 15572篇 |
金属工艺 | 4382篇 |
机械仪表 | 5344篇 |
建筑科学 | 4099篇 |
矿业工程 | 1143篇 |
能源动力 | 3409篇 |
轻工业 | 6239篇 |
水利工程 | 997篇 |
石油天然气 | 1844篇 |
武器工业 | 373篇 |
无线电 | 14036篇 |
一般工业技术 | 14998篇 |
冶金工业 | 7462篇 |
原子能技术 | 1172篇 |
自动化技术 | 12164篇 |
出版年
2024年 | 213篇 |
2023年 | 960篇 |
2022年 | 1715篇 |
2021年 | 2649篇 |
2020年 | 1935篇 |
2019年 | 1859篇 |
2018年 | 2292篇 |
2017年 | 2335篇 |
2016年 | 2537篇 |
2015年 | 2574篇 |
2014年 | 3703篇 |
2013年 | 5286篇 |
2012年 | 5396篇 |
2011年 | 6163篇 |
2010年 | 5213篇 |
2009年 | 5234篇 |
2008年 | 4933篇 |
2007年 | 4404篇 |
2006年 | 4017篇 |
2005年 | 3345篇 |
2004年 | 3492篇 |
2003年 | 3836篇 |
2002年 | 4615篇 |
2001年 | 3833篇 |
2000年 | 2370篇 |
1999年 | 1887篇 |
1998年 | 2499篇 |
1997年 | 1675篇 |
1996年 | 1441篇 |
1995年 | 1124篇 |
1994年 | 846篇 |
1993年 | 777篇 |
1992年 | 573篇 |
1991年 | 554篇 |
1990年 | 463篇 |
1989年 | 446篇 |
1988年 | 352篇 |
1987年 | 294篇 |
1986年 | 270篇 |
1985年 | 243篇 |
1984年 | 213篇 |
1983年 | 160篇 |
1982年 | 166篇 |
1981年 | 134篇 |
1980年 | 142篇 |
1979年 | 106篇 |
1978年 | 95篇 |
1977年 | 126篇 |
1976年 | 159篇 |
1975年 | 80篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Choong Do Lee 《Metals and Materials International》2002,8(3):283-288
In the present study, the effect of microporosity on the tensile properties of as-cast AZ91D magnesium alloy was investigated through experimental observation and numerical prediction. The test specimens were fabricated by die-casting and gravity-casting. For gravity-casting, the inoculation and use of various metallic moulds were applied to obtain a wide range of microporosity. The deficiency of the interdendritic feeding of the liquid phase acted as a dominant mechanism on the formation of the micropores in the Mg?Al-alloys, rather than the evolution of hydrogen gas. Although tensile strength and elongation has a nonlinear and very intensive dependence upon microporosity, the yield strength appeared to have a linear relationship with microporosity. However, it was possible to quantitatively estimate the linear contribution of microporosity on the individual tensile property for a range of microporosity, which was below about 1%. The numerical prediction suggests that the effect of microporosity on fractured strength and elongation decreased as the strain hardening exponent increased. Furthermore, the shape and distribution of micropores may play a more dominant role than local plastic deformation on the tensile behavior of AZ91D alloy. 相似文献
52.
直线式电机在有杆抽油设备中的应用 总被引:4,自引:0,他引:4
通过对游梁式抽油机的效率、启动特性与直线式电机驱动的有杆抽油机特性的对比,论述了直线抽油机的优越性及应用前景。 相似文献
53.
超声波处理和染料结晶性能对粒度分布的影响 总被引:1,自引:0,他引:1
超声波是一种频率超越人类听觉范围的声波 ,主要分为动力超声波 ( 1 8kHz~ 1MHz)和用于诊断的超声波 ( 1MHz以上 )。多年以来 ,超声波作为一种辅助工具广泛应用于许多领域 ,从而引起了化学家的极大兴趣。研究表明 ,在纺织品染色过程中 ,超声波能提高反应速率可能归因于超声波的能量 ,有关超声波的应用潜力已有许多文献报道。超声波能提高染色效率主要归因于液体介质中的空化现象 ,这一点已被一致认可。所谓空化现象是指微气泡增长、崩溃、爆炸。Mason指出 ,经超声波辐射的固体粒度显著减小。Tomlisom和其他工作者也… 相似文献
54.
Smart TDI readout circuit for long-wavelength IR detector 总被引:3,自引:0,他引:3
Byunghyuk Kim Hee Chul Lee 《Electronics letters》2002,38(16):854-855
A smart time delay and integration (TDI) readout circuit is suggested which performs background suppression, cell-to-cell non-uniformity compensation, and dead pixel correction. Using the smart TDI readout circuit, the integration capacitor area occupying almost the whole area of a unit-cell can be reduced to one-fifth and transimpedance gain can increase by five times. From measurement results, it is found that the skimming current error for a few hundred nA background current is < 1.25 nA corresponding to LSB/2 of ADC and the non-uniformity introduced by cell-to-cell background current variation is reduced to 1.02 nA 相似文献
55.
Zhang Li Chun Jin Hai Yan Ye Hong Fei Gao Yu Zhi Ning Bao Jun Mo Bang Xian 《Electron Devices, IEEE Transactions on》2002,49(6):1075-1076
A polysilicon emitter RCA transistor (an ultra-thin interfacial oxide layer exists between polysilicon and silicon emitter) is presented which can operate at 77 K for the first time. An ultra-thin (1.5 nm) interfacial oxide layer is grown deliberately between polysilicon and silicon emitter using RCA oxidation and excellent device stability is obtained after rapid thermal annealing (RTA) treatment in nitrogen atmosphere. The RCA transistor exhibits good electrical performance at very low temperature for an emitter area of 3 × 8 μm2. The maximum toggle frequency of a 1:2 static divider is 1.2 GHz and 732 MHz at 300 K and 77 K, respectively 相似文献
56.
57.
比较了几种长距离传动方式的特点与适用场合,重点探讨了实现长距离精密传动的技术要点。结合实际工程,完成了长距离钢带精密传动的应用,并指出张紧机构的设计与应用是钢带实现长距离精密传动的关键。为此文中对钢带传动的典型张紧机构进行了比较,并分析了这几类张紧机构的应用情况,有参考和应用价值。 相似文献
58.
Rotating-bending uniaxial fatigue tests and micro-fatigue crack initiation tests were carried out using a permanent mold cast
(PMC) and semi-solid die cast (SDC) with Al−7%Si−0.35%Mg composition in order to examine the relationship between solidification
structures and fatigue behaviors. The crack length was measured using a replication method. Fatigue strength was improved
in SDC, which was almost consistent with the predicted fatigue strength using the size of Si particle cluster. Resistance
to fatigue crack initiation and fatigue strength were improved in SDC owing to the finer Si cluster and to higher ultimate
tensile strength. Fatigue crack in PMC was preferentially initiated at pores. For SDC, the fatigue crack was initiated at
the Si particle/matrix interface, and then sucessively grew along eutectic cell boundaries. 相似文献
59.
60.