全文获取类型
收费全文 | 19751篇 |
免费 | 1918篇 |
国内免费 | 1213篇 |
专业分类
电工技术 | 449篇 |
综合类 | 1884篇 |
化学工业 | 1413篇 |
金属工艺 | 3994篇 |
机械仪表 | 2749篇 |
建筑科学 | 2222篇 |
矿业工程 | 312篇 |
能源动力 | 601篇 |
轻工业 | 454篇 |
水利工程 | 158篇 |
石油天然气 | 573篇 |
武器工业 | 181篇 |
无线电 | 574篇 |
一般工业技术 | 5491篇 |
冶金工业 | 1024篇 |
原子能技术 | 116篇 |
自动化技术 | 687篇 |
出版年
2024年 | 78篇 |
2023年 | 315篇 |
2022年 | 440篇 |
2021年 | 547篇 |
2020年 | 710篇 |
2019年 | 586篇 |
2018年 | 576篇 |
2017年 | 713篇 |
2016年 | 790篇 |
2015年 | 860篇 |
2014年 | 1105篇 |
2013年 | 1188篇 |
2012年 | 1225篇 |
2011年 | 1333篇 |
2010年 | 1003篇 |
2009年 | 1115篇 |
2008年 | 959篇 |
2007年 | 1156篇 |
2006年 | 1062篇 |
2005年 | 927篇 |
2004年 | 795篇 |
2003年 | 711篇 |
2002年 | 605篇 |
2001年 | 579篇 |
2000年 | 513篇 |
1999年 | 442篇 |
1998年 | 389篇 |
1997年 | 360篇 |
1996年 | 353篇 |
1995年 | 255篇 |
1994年 | 207篇 |
1993年 | 180篇 |
1992年 | 158篇 |
1991年 | 121篇 |
1990年 | 114篇 |
1989年 | 94篇 |
1988年 | 82篇 |
1987年 | 37篇 |
1986年 | 23篇 |
1985年 | 41篇 |
1984年 | 40篇 |
1983年 | 36篇 |
1982年 | 35篇 |
1981年 | 5篇 |
1980年 | 10篇 |
1979年 | 2篇 |
1974年 | 2篇 |
1956年 | 1篇 |
1955年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
G. G. Martin 《Journal of Failure Analysis and Prevention》2004,4(1):37-39
Piston failures are not a common occurrence, but they do occur, and failure is usually associated with fatigue crack growth.
Most failures initiate at the gudgeon pin hole or in the skirt of the piston. Occasionally they fail elsewhere. In the example
covered in this paper, failure initiated in the crown and progressed down to the gudgeon pin before final failure occurred.
This paper outlines the cause and mode of failure and shows that small metallurgical discontinuities can contribute to these
failures under the right circumstances. 相似文献
32.
R. A. SMITH 《Fatigue & Fracture of Engineering Materials & Structures》2003,26(10):901-907
The importance of the wheel–rail interface to the safe operation of railways is discussed. Some aspects of the history of rails and wheels are introduced. Several recent accidents involving the wheel–rail interface are described. The great importance of operating both vehicles and track as a system is emphasized, together with the necessity of maintaining both in good condition. 相似文献
33.
由于具有初曲率板弯曲问题的控制微分方程较复杂,直接求解原问题基本解推导边界积分方程较为困难。本文通过引入等效荷载,将此问题的控制微分方程化成与普通板弯曲基本方程形式相同的微分方程,利用一般求解板弯曲问题的边界元法迭代求解,建立了分析具有初曲率板弯曲问题的边界元法。算例表明本方法理论准确、精度良好。 相似文献
34.
This paper focuses on the microscopic damage and progressive failure of a composite reinforced by plain-weave glass cloth under tensile fatigue loading. The fatigue process was divided into three stages like that of multi-directional laminates. It was found that the internal damage at each stage (matrix cracks, debonds in the weft, successive debonds in the warp and ‘metadelaminations’ between warps and wefts) occurred near the cross-over point of the fabric. The modulus decay mechanism was explained by considering the progression of this internal damage. From the end of the first stage to the beginning of the middle stage, a characteristic damage state (CDS) (called a ‘meta-CDS’) was observed. It was found that woven composites have a unit area of damage accumulation (called a ‘unit cell’) and the damage of each unit cell and its distribution control the total fatigue damage of the material. 相似文献
35.
36.
Abstract— In response to the increasing structural applications in duplex steels for welded structures, fatigue behaviour of a SAF 2304 grade duplex stainless steel was investigated, considering both the base metal and GTAW welded joints. Fatigue curves and fatigue limits under rotary bending fatigue were obtained. The study focused attention on the microstructural features of fatigue crack propagation of the two series of experiments, thereby permitting an evaluation of the tortuous crack path of welded joints and the mechanisms related to threshold microstructural barriers. 相似文献
37.
C. M. Branco J. M. Ferreira M. O. W. Richardson P. Fael 《International Journal of Fatigue》1992,14(6):367-376
This paper presents results of a fatigue life investigations carried out in plate specimens of a fibre-glass-reinforced phenolic matrix composite. Tensile and Young's modulus data were obtained at four different testing temperatures (room temperature, 100, 150 and 200 °C). The fatigue S−N data were obtained at room temperature only and for two stress ratio values (R=0 and 0.4). Fatigue and tensile behaviour was assesesed in the composite with the fibres aligned in the longitudinal loading direction. The results were obtained for two values of volume fraction (0.28 and 0.42) and three different glass surface treatments. A detailed comparison of fatigue results is given taking into account several fatigue parameters and also the testing variables. Results of observations of SEM fracture surfaces are also presented. 相似文献
38.
This study provides experimental evidence for proton and hydrogen formation caused by the anodic electropolymerization of cyclohexyl benzene (CHB), which is a popular electrolyte additive for overcharge protection of lithium-ion batteries (LIBs). It is found that considerable H2 evolution is observed in overcharged LiCoO2/graphite cells, especially when CHB is included as an electrolyte additive. In order to confirm the proton generation during the CHB oxidation, Pt/Pt-rotating ring disc electrode (RRDE) measurements are performed in 1 M Li(C2F5SO2)2N ethylene carbonate/ethyl methyl carbonate (1/2, v/v) solutions with and without CHB. The cathodic ring current is intimately correlated to the anodic disc current, and the cathodic reaction at the ring is determined to be the reduction of the proton. The proton generation efficiency during the CHB oxidation is as high as 90%. Proton liberation is also observed during the anodic decomposition of the electrolyte solvents, although it occurs in a much less stoichiometric way compared with that during the CHB oxidation. 相似文献
39.
矿用圆环链弯曲点的角度分布 总被引:2,自引:1,他引:1
矿用圆环链弯曲点是应力集中点 ,肩部断裂发生于该点附近 .以 2 6× 92矿用圆环链为研究对象 ,应用方向数据统计导出该点的角度分布 ,并给出了批量检验矿用圆环链尺寸匹配状况的一种方法 相似文献
40.
In-phase(IP) and out-of-phase(OP)thermal-mechanical fatigue(TMF) behavior of cast Ni-base superalloy K417 was studied.All experiments were carried out under total strain control with temperature cycling between 400-850℃.Both in-phase and out-of-phase TMF specimens exhibited cyclic hardening followed by cyclic softening at the minimum temperature.Besides,they cyclically hardened in the early stage of life followed by cyclic softening at the minimum temperature.Besides,they cyclically hardened in the early stage of life followed by cyclic softening at the maximum temperature.OP TMF life was longer than of IP TMF.Various damage mechanisms operating in different controlled strain ranges and phasing were discussed.A few life prediction methods for isothermal fatigue were used to handle TMF fatigue and their applicability to superalloy K417 was evaluated.The SEM analysis of the fracture surface showed that transgranular fracture was the principal cracking mode for both IP and OP TMF.Oxidation was the main damage mechanism in causing shorter fatigue life for IP TMF compared with OP TMF. 相似文献