全文获取类型
收费全文 | 301348篇 |
免费 | 16600篇 |
国内免费 | 1062篇 |
专业分类
电工技术 | 5105篇 |
综合类 | 210篇 |
化学工业 | 57937篇 |
金属工艺 | 8649篇 |
机械仪表 | 8184篇 |
建筑科学 | 8886篇 |
矿业工程 | 558篇 |
能源动力 | 8415篇 |
轻工业 | 37817篇 |
水利工程 | 2483篇 |
石油天然气 | 1963篇 |
武器工业 | 5篇 |
无线电 | 40249篇 |
一般工业技术 | 58333篇 |
冶金工业 | 47792篇 |
原子能技术 | 3428篇 |
自动化技术 | 28996篇 |
出版年
2022年 | 1957篇 |
2021年 | 3020篇 |
2020年 | 3100篇 |
2019年 | 5061篇 |
2018年 | 5900篇 |
2017年 | 6202篇 |
2016年 | 7000篇 |
2015年 | 6252篇 |
2014年 | 7790篇 |
2013年 | 17454篇 |
2012年 | 10095篇 |
2011年 | 12837篇 |
2010年 | 10599篇 |
2009年 | 11449篇 |
2008年 | 11485篇 |
2007年 | 11181篇 |
2006年 | 10216篇 |
2005年 | 9031篇 |
2004年 | 8713篇 |
2003年 | 8545篇 |
2002年 | 7961篇 |
2001年 | 8144篇 |
2000年 | 7423篇 |
1999年 | 7406篇 |
1998年 | 16598篇 |
1997年 | 11555篇 |
1996年 | 8726篇 |
1995年 | 6643篇 |
1994年 | 5801篇 |
1993年 | 5648篇 |
1992年 | 4087篇 |
1991年 | 3841篇 |
1990年 | 3606篇 |
1989年 | 3416篇 |
1988年 | 3326篇 |
1987年 | 2632篇 |
1986年 | 2553篇 |
1985年 | 3212篇 |
1984年 | 2838篇 |
1983年 | 2594篇 |
1982年 | 2370篇 |
1981年 | 2414篇 |
1980年 | 2237篇 |
1979年 | 2077篇 |
1978年 | 1907篇 |
1977年 | 2202篇 |
1976年 | 2751篇 |
1975年 | 1598篇 |
1974年 | 1499篇 |
1973年 | 1568篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Heat transfer of highly consistent shear-thinning fluids flowing in a horizontal cylindrical channel has been investigated numerically and experimentally when the outer channel wall is subjected to a constant convective heat exchange. The case considered being cooling, a possible ice deposit must be taken into account. The variation of the rheological properties with temperature must be considered as well. 相似文献
102.
103.
Daniela M. Nevskaia Maria Luisa Rojas Cervantes Antonio Guerrero Ruíz Juan de Dios Lpez Gonzlez 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1995,63(3):249-256
Adsorption of Triton X-100 on various silica substrates has been investigated. A number of solids, including a natural quartz, this quartz washed with HCl acid and subsequently heated at 1273 K; two aerosils and one Kieselgel silicas were studied. These solids exhibit surface areas in the range of 5 to 430 m2 g?1. All the Triton adsorption isotherms display an S-shape at the adsorption temperatures studied (298 and 308 K). It has been found that the pretreatments of natural quartz (by water washing, impurities removed by acid and/or high temperature calcination) affect considerably the amounts of TX-100 adsorbed. Measurements of surface composition have been made by X-ray photoelectron spectroscopy (XPS) with particular emphasis on the presence of impurities and on the number of OH groups at the surface of the samples. The nature of the surface hydroxyl has also been studied by infrared spectroscopy. Furthermore, the specific number of hydroxyl groups on the surface of the silica samples has been determined by thermogravimetric analysis. Finally an attempt to correlate solid surface characteristics with adsorption isotherms has been developed. 相似文献
104.
Zhengmao Ye Campbell J.C. Zhonghui Chen Eui-Tae Kim Madhukar A. 《Quantum Electronics, IEEE Journal of》2002,38(9):1234-1237
An InAs/AlGaAs quantum-dot infrared photodetector based on bound-to-bound intraband transitions in undoped InAs quantum dots is reported. AlGaAs blocking layers were employed to achieve low dark current. The photoresponse peaked at 6.2 /spl mu/m. At 77 K and -0.7 V bias, the responsivity was 14 mA/W and the detectivity, D*, was 10/sup 10/ cm/spl middot/Hz/sup 1/2//W. 相似文献
105.
106.
The early history of the IEEE Microwave Theory and Techniques Society (IEEE MTT-S) is summarized since its founding in 1952, and all administrative committee members and presidents are listed. Some of the more recent changes resulting from growth and multinational participation are described. Publications are discussed with editors listed for this Transactions, the IEEE Microwave and Wireless Components Letters, the IEEE Microwave Newsletter, and IEEE Microwave Magazine. The chronological evolution of the IEEE MTT-S's awards is presented, including a listing of all award winners. Distinguished lecturers and microwave symposia sites and chairpersons are also discussed. Early technology trends are described 相似文献
107.
In antenna design there are some fundamental relationships based on reciprocity. The equivalence of antenna pattern in transmission and reception is well known. Less well known is the time-derivative relationship going from reception to transmission. These relationships are derived here and expressed in various useful forms. Electric and magnetic dipoles are given special consideration, and the combined form constructed as a terminated TEM transmission line (the BTW antenna) is discussed for its transmission and reception properties 相似文献
108.
Using AuGeNiCr multilayered metals as the wafer bonding medium, long-wavelength GaInAsP/InP vertical cavity surface emitting lasers employing Al-oxide/Si as the upper and lower distributed Bragg reflectors were fabricated on Si substrate with the bonding interface formed outside the vertical cavity surface emitting laser cavity. Laser emission at 1.545 μm was measured under pulsed operations near room temperature. The low-temperature metallic bonding process demonstrates a great potential in device fabrication 相似文献
109.
Depletion and hillock formation were examined in-situ in a scanning electron microscope (SEM) during electromigration of bamboo
Al interconnect segments. Hillocks formed directly at the anode ends of the segments by epitaxial addition of Al at the bottom
Al/TiN interface. Depletion occurred nonuniformly from the cathode end and stopped once the distance between the leading void
and the hillock reached the critical length for electromigration at the given current density. A modified equation for the
drift velocity is proposed, which includes the effect of nonuniform depletion and predicts that interconnects with nonuniform
depletion are more reliable than those with uniform depletion. 相似文献
110.
C. Ebert presents his views on the state of software engineering as a field, its roots and inherent conflicts, its relationship to other engineering disciplines, where it is headed, and what we can do to influence that direction. T. Matsubara, T. Webb, M. Pezze, and O.W. Bertelsen offer a spectrum of further insights 相似文献