全文获取类型
收费全文 | 95494篇 |
免费 | 1353篇 |
国内免费 | 463篇 |
专业分类
电工技术 | 1009篇 |
综合类 | 2332篇 |
化学工业 | 13536篇 |
金属工艺 | 5109篇 |
机械仪表 | 3356篇 |
建筑科学 | 2362篇 |
矿业工程 | 630篇 |
能源动力 | 1803篇 |
轻工业 | 4706篇 |
水利工程 | 1418篇 |
石油天然气 | 422篇 |
无线电 | 10717篇 |
一般工业技术 | 18805篇 |
冶金工业 | 4100篇 |
原子能技术 | 441篇 |
自动化技术 | 26564篇 |
出版年
2023年 | 177篇 |
2022年 | 505篇 |
2021年 | 505篇 |
2020年 | 413篇 |
2019年 | 413篇 |
2018年 | 14817篇 |
2017年 | 13704篇 |
2016年 | 10352篇 |
2015年 | 878篇 |
2014年 | 665篇 |
2013年 | 1062篇 |
2012年 | 3615篇 |
2011年 | 9990篇 |
2010年 | 8729篇 |
2009年 | 6025篇 |
2008年 | 7193篇 |
2007年 | 8108篇 |
2006年 | 438篇 |
2005年 | 1449篇 |
2004年 | 1355篇 |
2003年 | 1375篇 |
2002年 | 708篇 |
2001年 | 237篇 |
2000年 | 321篇 |
1999年 | 210篇 |
1998年 | 404篇 |
1997年 | 257篇 |
1996年 | 294篇 |
1995年 | 227篇 |
1994年 | 193篇 |
1993年 | 179篇 |
1992年 | 154篇 |
1991年 | 173篇 |
1990年 | 115篇 |
1989年 | 108篇 |
1988年 | 139篇 |
1987年 | 109篇 |
1986年 | 89篇 |
1985年 | 115篇 |
1984年 | 94篇 |
1983年 | 107篇 |
1982年 | 99篇 |
1981年 | 88篇 |
1980年 | 78篇 |
1979年 | 54篇 |
1977年 | 56篇 |
1976年 | 76篇 |
1968年 | 51篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
112.
113.
114.
Understanding consumer behaviour is of vital importance to consumer-oriented e-business models today. In this paper, we study the relationships between consumer perceptions of risk and trust and the attitude towards purchasing at a consumer-to-consumer electronic marketplace (EM). Typical for EM settings is that consumer behaviour is subject to perceptions of the selling party as well as of the institutional structures of the intermediary that is operating the EM. Building upon the well-established literature of trust, we consider the concepts of intermediary trust and seller trust. We extend this categorisation by introducing the concepts of intermediary risk and seller risk. We developed measurement instruments for intermediary risk and seller risk. All measurement scales have acceptable alphas and are unidimensional. An empirical study is conducted to explore the relationships between the risk and trust types and consumer purchase attitude. The results reveal significant, direct effects of seller trust and seller risk. Second-order effects of intermediary trust and intermediary risk are investigated and reported. The paper concludes with general observations and recommendations for research and practice. 相似文献
115.
Yuan Y. Jambunathan R. Singh J. Bhattacharya P. 《Quantum Electronics, IEEE Journal of》1997,33(3):408-415
The performance characteristics of a coupled cavity InGaAsP-InP MQW laser/active waveguide made by one-step epitaxy and well-controlled reactive ion etching (RIE) have been theoretically analyzed and experimentally determined. A theoretical model based on a finite-difference time-domain (FDTD) technique was used to simulate the propagation of an optical wave launched in the coupled system and determine the reflectivity of the facets created by RIE. The calculated effective reflectivity of the coupling region consisting of two facets and an air gap is between 0.45 and 0.55, which is in good agreement with the experimentally measured value of 0.5. The reflectivity of a single etched mirror derived from this value is estimated to be 0.3. A 120-μm-long monolithically integrated active waveguide when biased as a modulator and excited by the laser shows a maximum extinction ratio of 8 dB and a modulation bandwidth ⩾14 GHz at a dc bias of -0.5 V with a bias swing of 2 V 相似文献
116.
R Singh 《Microelectronics Reliability》1998,38(9):1471-1483
This paper describes the role of single wafer processing in the development of sub-quarter micron silicon integrated circuits (ICs). The issues related to device processing, choice of materials, performance, reliability, and manufacturing are covered. Single wafer processing based rapid photothermal processing (dominant photons with wavelength less than about 800 nm) is an ideal answer to almost all the thermal processing requirements of current and future Si ICs. For process integration, a new model for process optimization based on minimization of thermal stress is proposed. For breaking the sub-100 nm manufacturing barriers, high throughput lithography based on direct writing is a proposed solution. 相似文献
117.
118.
119.
120.
Packaging engineers need to be able to accurately determine the forces present in the shipping environment in order to protect packaged goods. The purpose of this study was to determine the vertical vibration levels measured in three separate truck-trailer suspension systems; conventional leaf-spring, conventional air-ride and damaged air-ride. The main conclusion reached in this study is that the air-ride suspension when maintained gives lower power density (PD) levels on all road surfaces studied. A damaged air-ride suspension and leaf-spring suspension are very similar in response frequencies, although the damaged air-ride produces higher vibration levels at lower frequencies. 相似文献