全文获取类型
收费全文 | 20593篇 |
免费 | 1833篇 |
国内免费 | 1143篇 |
专业分类
电工技术 | 270篇 |
技术理论 | 1篇 |
综合类 | 2279篇 |
化学工业 | 849篇 |
金属工艺 | 1422篇 |
机械仪表 | 1425篇 |
建筑科学 | 6043篇 |
矿业工程 | 438篇 |
能源动力 | 247篇 |
轻工业 | 249篇 |
水利工程 | 349篇 |
石油天然气 | 329篇 |
武器工业 | 138篇 |
无线电 | 3937篇 |
一般工业技术 | 3259篇 |
冶金工业 | 562篇 |
原子能技术 | 1094篇 |
自动化技术 | 678篇 |
出版年
2024年 | 66篇 |
2023年 | 184篇 |
2022年 | 316篇 |
2021年 | 402篇 |
2020年 | 508篇 |
2019年 | 448篇 |
2018年 | 444篇 |
2017年 | 560篇 |
2016年 | 562篇 |
2015年 | 638篇 |
2014年 | 1129篇 |
2013年 | 1149篇 |
2012年 | 1420篇 |
2011年 | 1651篇 |
2010年 | 1224篇 |
2009年 | 1385篇 |
2008年 | 1295篇 |
2007年 | 1499篇 |
2006年 | 1306篇 |
2005年 | 1112篇 |
2004年 | 920篇 |
2003年 | 819篇 |
2002年 | 702篇 |
2001年 | 620篇 |
2000年 | 538篇 |
1999年 | 461篇 |
1998年 | 397篇 |
1997年 | 333篇 |
1996年 | 280篇 |
1995年 | 232篇 |
1994年 | 212篇 |
1993年 | 144篇 |
1992年 | 116篇 |
1991年 | 104篇 |
1990年 | 87篇 |
1989年 | 63篇 |
1988年 | 61篇 |
1987年 | 46篇 |
1986年 | 43篇 |
1985年 | 16篇 |
1984年 | 23篇 |
1983年 | 10篇 |
1982年 | 13篇 |
1981年 | 5篇 |
1980年 | 10篇 |
1979年 | 3篇 |
1959年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Detection of multiple cracks using frequency measurements 总被引:2,自引:0,他引:2
D.P. Patil 《Engineering Fracture Mechanics》2003,70(12):1553-1572
A method for detection of multiple open cracks in a slender Euler-Bernoulli beams is presented based on frequency measurements. The method is based on the approach given by Hu and Liang [J. Franklin Inst. 330 (5) (1993) 841], transverse vibration modelling through transfer matrix method and representation of a crack by rotational spring. The beam is virtually divided into a number of segments, which can be decided by the analyst, and each of them is considered to be associated with a damage parameter. The procedure gives a linear relationship explicitly between the changes in natural frequencies of the beam and the damage parameters. These parameters are determined from the knowledge of changes in the natural frequencies. After obtaining them, each is treated in turn to exactly pinpoint the crack location in the segment and determine its size. The forward, or natural frequency determination, problems are examined in the passing. The method is approximate, but it can handle segmented beams, any boundary conditions, intermediate spring or rigid supports, etc. It eliminates the need for any symbolic computation which is envisaged by Hu and Liang [J. Franklin Inst. 330 (5) (1993) 841] to obtain mode shapes of the corresponding uncracked beams. The proposed method gives a clear insight into the whole analysis. Case studies (numerical) are presented to demonstrate the method effectiveness for two simultaneous cracks of size 10% and more of section depth. The differences between the actual and predicted crack locations and sizes are less than 10% and 15% respectively. The numbers of segments into which the beam is virtually divided limits the maximum number of cracks that can be handled. The difference in the forward problem is less than 5%. 相似文献
52.
53.
Javier Lara-Romero Rafael Maya-Yescas José Luis Rico-Cerda José Luis Rivera-Rojas Fernando Chiñas Castillo Matey Kaltchev 《Thin solid films》2006,496(2):463-468
The thermal decomposition of model extreme-pressure lubricant additives on clean iron was studied in ultrahigh vacuum conditions using molecular beam strategies. Methylene chloride and chloroform react to deposit a solid film consisting of FeCl2 and carbon, and evolve only hydrogen into the gas phase. No gas-phase products and less carbon on the surface are detected in the case of carbon tetrachloride. Dimethyl and diethyl disulfide react on clean iron to deposit a saturated sulfur plus carbon layer at low temperatures (∼600 K) and an iron sulfide film onto a Fe + C underlayer at higher temperatures (∼950 K). Methane is the only gas-phase product when dimethyl disulfide reacts with iron. Ethylene and hydrogen are detected when diethyl disulfide is used. 相似文献
54.
55.
对国内引进的、用于粉末冶金的步进梁式炉的运动,以图解法和解析法进行了分析,并对运动参数进行了理论推导和计算。本研究结果,对解决步进粱式炉的运动故障以及进行新型设计提供了有效的理论分析和计算依据。 相似文献
56.
为确保在T梁预制时 ,其内、外的质量和安全施工 ,介绍了四个需特别注意的问题。指出在T梁预制时 ,应把质量放在首位 ,进行具体、综合的分析和计算 相似文献
57.
Abstract The whole DNA of soybean was implanted into four varieties of wheat of Zhongyu5, Huaiyin 9628, Wenyou 1, Jimai 5 respectively via ion-beam mediation. There were 5 plantsobtained whose protein content was higher than 18.5%, the highest one was 21.44%. There were 3plants obtained whose protein content was lower than 11.5%, the lowest one was 10.96%. We cansee that the whole DNA of soybean transformed into wheat via ion beam implantation can inducethe increase in wheat protein content dramatically. The result also shows that the transformationefficiency of different gene types of wheat receptor varies greatly that the implanting time has acertain effect on the efficiency of transformation. 相似文献
58.
59.
给出平凹谐振腔和凹平凹谐振腔失调时光轴确定方法。在二维轴对称折迭-组合腔 激光器小角度失调运行时,对非相干并和和相干并和后的输出光束的近场强度分布做了分析和模拟。结果表明:小角度失调对4cm以内的近场影响不大,光强分布仍具有高斯状分布;对4cm以外的近场影响较大,光强分布发生相应的形变,且随着失调角度变大而变大。 相似文献
60.