全文获取类型
收费全文 | 76357篇 |
免费 | 5559篇 |
国内免费 | 3259篇 |
专业分类
电工技术 | 3913篇 |
技术理论 | 7篇 |
综合类 | 4240篇 |
化学工业 | 12334篇 |
金属工艺 | 4769篇 |
机械仪表 | 4423篇 |
建筑科学 | 5831篇 |
矿业工程 | 1853篇 |
能源动力 | 2384篇 |
轻工业 | 4632篇 |
水利工程 | 1242篇 |
石油天然气 | 4569篇 |
武器工业 | 451篇 |
无线电 | 8782篇 |
一般工业技术 | 11549篇 |
冶金工业 | 4684篇 |
原子能技术 | 895篇 |
自动化技术 | 8617篇 |
出版年
2024年 | 193篇 |
2023年 | 1022篇 |
2022年 | 1661篇 |
2021年 | 2522篇 |
2020年 | 1933篇 |
2019年 | 1742篇 |
2018年 | 2062篇 |
2017年 | 2294篇 |
2016年 | 2143篇 |
2015年 | 2557篇 |
2014年 | 3497篇 |
2013年 | 4509篇 |
2012年 | 4607篇 |
2011年 | 5193篇 |
2010年 | 4458篇 |
2009年 | 4476篇 |
2008年 | 4295篇 |
2007年 | 4214篇 |
2006年 | 4222篇 |
2005年 | 3563篇 |
2004年 | 2621篇 |
2003年 | 2276篇 |
2002年 | 2030篇 |
2001年 | 2001篇 |
2000年 | 2033篇 |
1999年 | 2127篇 |
1998年 | 2058篇 |
1997年 | 1635篇 |
1996年 | 1455篇 |
1995年 | 1219篇 |
1994年 | 983篇 |
1993年 | 719篇 |
1992年 | 558篇 |
1991年 | 472篇 |
1990年 | 420篇 |
1989年 | 318篇 |
1988年 | 245篇 |
1987年 | 152篇 |
1986年 | 151篇 |
1985年 | 93篇 |
1984年 | 84篇 |
1983年 | 57篇 |
1982年 | 59篇 |
1981年 | 40篇 |
1980年 | 33篇 |
1979年 | 21篇 |
1978年 | 21篇 |
1977年 | 17篇 |
1974年 | 13篇 |
1970年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
101.
用矩阵光学理论计算了由主振荡器和功率放大器组成的种子注入光腔。主振荡器光腔是由曲率半径R1=-250mm,R2=5000mm,相距L=2375mm的球面镜组成的正支非稳腔;功率非稳腔是由曲率半径R3=400mm,R4=5600mm,相距S=3000mm的球面镜构成的负支非稳腔。理论计算表明,该种子注入光腔可输出光束发散角约几十微弧的激光,可满足铜蒸气激光器主振荡器功率放大器(MOPA)的技术要求。 相似文献
102.
Chou Y.C. Leung D. Lai R. Grundbacher R. Barsky M. Kan Q. Tsai R. Wojtowicz M. Eng D. Tran L. Block T. Liu P.H. Nishimoto M. Oki A. 《Electron Device Letters, IEEE》2003,24(6):378-380
The authors have investigated the reliability performance of G-band (183 GHz) monolithic microwave integrated circuit (MMIC) amplifiers fabricated using 0.07-/spl mu/m T-gate InGaAs-InAlAs-InP HEMTs with pseudomorphic In/sub 0.75/Ga/sub 0.25/As channel on 3-in wafers. Life test was performed at two temperatures (T/sub 1/ = 200 /spl deg/C and T/sub 2/ = 215 /spl deg/C), and the amplifiers were stressed at V/sub ds/ of 1 V and I/sub ds/ of 250 mA/mm in a N/sub 2/ ambient. The activation energy is as high as 1.7 eV, achieving a projected median-time-to-failure (MTTF) /spl ap/ 2 /spl times/ 10/sup 6/ h at a junction temperature of 125 /spl deg/C. MTTF was determined by 2-temperature constant current stress using /spl Delta/G/sub mp/ = -20% as the failure criteria. The difference of reliability performance between 0.07-/spl mu/m InGaAs-InAlAs-InP HEMT MMICs with pseudomorphic In/sub 0.75/Ga/sub 0.25/As channel and 0.1-/spl mu/m InGaAs-InAlAs-InP HEMT MMICs with In/sub 0.6/Ga/sub 0.4/As channel is also discussed. The achieved high-reliability result demonstrates a robust 0.07-/spl mu/m pseudomorphic InGaAs-InAlAs-InP HEMT MMICs production technology for G-band applications. 相似文献
103.
104.
105.
106.
Finite element piezothermoelasticity analysis and the active control of FGM plates with integrated piezoelectric sensors and actuators 总被引:3,自引:0,他引:3
An efficient finite element model is presented for the static and dynamic piezothermoelastic analysis and control of FGM
plates under temperature gradient environments using integrated piezoelectric sensor/actuator layers. The properties of an FGM plate are functionally graded in the thickness
direction according to a volume fraction power law distribution. A constant displacement-cum-velocity feedback control algorithm that couples the direct and inverse piezoelectric effects is applied to provide active feedback
control of the integrated FGM plate in a closed loop system. Numerical results for the static and dynamic control are presented
for the FGM plate, which consists of zirconia and aluminum. The effects of the constituent volume fractions and the influence
of feedback control gain on the static and dynamic responses of the FGM plates are examined.
Received: 13 March 2002 / Accepted: 5 March 2003
The work described in this paper was supported by a grant awarded by the Research Grants Council of the Hong Kong Special
Administrative Region, China (Project No. CityU 1024/01E). 相似文献
107.
Properties of high reinforcement-content aluminum matrix composite for electronic packages 总被引:7,自引:0,他引:7
Gaohui Wu Qiang Zhang Guoqin Chen Longtao Jiang Ziyang Xiu 《Journal of Materials Science: Materials in Electronics》2003,14(1):9-12
Aluminum matrix composites reinforced by a high volume fraction of ceramic particles provide a novel solution to electronic packaging technology, because of their high thermal conductivity, compatible and tailorable coefficient of thermal expansion (CTE) with chips or substrates, low weight, enhanced specific stiffness, and low cost. In this paper, SiC-particle-reinforced aluminum matrix composites are fabricated by the cost-effective squeeze-casting technology, and their microstructure characteristics, thermo-physical, and mechanical properties are investigated. The reinforcement volume fraction is as high as 70% and composites with linear CTE of 6.9–9.7×10–6 °C–1 and thermal conductivity of 120–170 W m–1 °C–1 are produced. The composites can be electric-discharge machined, ground, and electric-spark drilled. An electroless nickel layer is plated on the composite by the conventional procedures. Finally, their potential applications in electronic packaging and thermal management are illustrated via prototype examples. 相似文献
108.
109.
110.
Fertuck Eric A.; Bucci Wilma; Blatt Sidney J.; Ford Richard Q. 《Canadian Metallurgical Quarterly》2004,41(1):13
This study examined the relation between changes in clinical functioning and changes in verbal expression in 81 seriously disturbed and treatment-resistant young adults seen in a comprehensive, psychoanalytically oriented inpatient treatment. Clinical functioning was evaluated with a battery of clinical and social measures. Verbal representations were assessed using computer-assisted scoring of Thematic Apperception Test responses. Changes in the frequency of verbal content and style in the narratives of these patients covaried with changes in clinical functioning. Significantly different covariations of verbal and clinical change, particularly differences in covariates of referential activity, were found for patients with anaclitic versus introjective personality configurations. The implications of these findings for understanding and treating severe psychopathology are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献