全文获取类型
收费全文 | 4978篇 |
免费 | 181篇 |
国内免费 | 26篇 |
专业分类
电工技术 | 75篇 |
综合类 | 8篇 |
化学工业 | 966篇 |
金属工艺 | 156篇 |
机械仪表 | 117篇 |
建筑科学 | 50篇 |
矿业工程 | 16篇 |
能源动力 | 311篇 |
轻工业 | 226篇 |
水利工程 | 36篇 |
石油天然气 | 20篇 |
无线电 | 654篇 |
一般工业技术 | 1160篇 |
冶金工业 | 726篇 |
原子能技术 | 34篇 |
自动化技术 | 630篇 |
出版年
2023年 | 72篇 |
2022年 | 100篇 |
2021年 | 174篇 |
2020年 | 146篇 |
2019年 | 126篇 |
2018年 | 169篇 |
2017年 | 159篇 |
2016年 | 187篇 |
2015年 | 110篇 |
2014年 | 186篇 |
2013年 | 412篇 |
2012年 | 217篇 |
2011年 | 232篇 |
2010年 | 198篇 |
2009年 | 267篇 |
2008年 | 178篇 |
2007年 | 130篇 |
2006年 | 129篇 |
2005年 | 111篇 |
2004年 | 99篇 |
2003年 | 101篇 |
2002年 | 88篇 |
2001年 | 69篇 |
2000年 | 66篇 |
1999年 | 71篇 |
1998年 | 146篇 |
1997年 | 108篇 |
1996年 | 121篇 |
1995年 | 83篇 |
1994年 | 83篇 |
1993年 | 80篇 |
1992年 | 59篇 |
1991年 | 69篇 |
1990年 | 68篇 |
1989年 | 47篇 |
1988年 | 46篇 |
1987年 | 45篇 |
1986年 | 42篇 |
1985年 | 47篇 |
1984年 | 31篇 |
1983年 | 25篇 |
1982年 | 26篇 |
1981年 | 35篇 |
1980年 | 20篇 |
1979年 | 30篇 |
1978年 | 30篇 |
1977年 | 27篇 |
1976年 | 33篇 |
1975年 | 15篇 |
1973年 | 13篇 |
排序方式: 共有5185条查询结果,搜索用时 31 毫秒
21.
We report on the use of pulsed plasma-enhanced chemical vapor deposition (P-PECVD) technique and show that “state-of-the-art” amorphous silicon (a-Si:H) materials and solar cells can be produced at a deposition rate of up to 15 Å/s using a modulation frequency in the range 1–100 kHz. The approach has also been developed to deposit materials and devices onto large area, 30 cm×40 cm, substrates with thickness uniformity (<5%), and gas utilization rate (>25%). We have developed a new “hot wire” chemical vapor deposition (HWCVD) method and report that our new filament material, graphite, has so far shown no appreciable degradation even after deposition of 500 μm of amorphous silicon. We report that this technique can produce “state-of-the-art” a-Si:H and that a solar cell of p/i/n configuration exhibited an initial efficiency approaching 9%. The use of microcrystalline silicon (μc-Si) materials to produce low-cost stable solar cells is gaining considerable attention. We show that both of these techniques can produce thin film μc-Si, dependent on process conditions, with 1 1 1 and/or 2 2 0 orientations and with a grain size of approx. 500 A. Inclusion of these types of materials into a solar cell configuration will be discussed. 相似文献
22.
The aim of the present paper is to review the recent progress in the synthesis of in situ particle reinforced aluminum composites
using thermal, mechanical and combined mechanical-thermal activation of aluminothermic reduction reactions. The combination
of combustion synthesis (CS) and mechanosynthesis (MS) is the most recent development in the processing of advanced materials
like micro and nano aluminum based composites. The combined mechanical thermal synthesis (MTS) has widened the possibilities
for both CS and MS. MTS holds great potential for commercial viability and offers exciting processing route for the synthesis
of advanced materials. Enhanced reaction kinetics and extended concentration limits in MTS are demonstrated by illustrating
the synthesis of aluminum based nanocomposite involving Al–CeO2. 相似文献
23.
24.
Sirisha Nerella Debendra K. Das Godwin A. Chukwu Abhijit Y. Dandekar Santanu Khataniar Shirish L. Patil 《Petroleum Science and Technology》2003,21(7):1275-1294
Gas-to-liquids (GTL) technology involves the conversion of natural gas to liquid hydrocarbons. In this article, theoretical studies have been presented to determine the feasibility of transporting GTL products through the Trans-Alaska Pipeline System (TAPS). To successfully transport GTL through TAPS, heat loss along the route must be carefully determined. This study presents heat transfer and fluid dynamic calculations to evaluate this feasibility. Because of heat loss, the fluid temperature decreases in the direction of flow and this affects the fluid properties, which in turn influence convection coefficient and pumping power requirements. The temperature and heat loss distribution along the pipeline at different locations have been calculated. Fairly good agreement with measured oil temperatures is observed. The powers required to pump crude oil and GTL individually, against various losses have been calculated. Two GTL transportation modes have been considered; one as a pure stream of GTL and the second as a commingled mixture with crude oil. These results show that the pumping power and heat loss for GTL are less than that of the crude oil for the same volumetric flow rate. Therefore, GTL can be transported through TAPS using existing equipment at pump stations. 相似文献
25.
Finite sample properties of estimators of spatial autoregressive models with autoregressive disturbances 总被引:1,自引:0,他引:1
The article investigates the finite sample properties of estimators for spatial autoregressive models where the disturbance
terms may follow a spatial autoregressive process. In particular we investigate the finite sample behavior of the feasible
generalized spatial two-stage least squares (FGS2SLS) estimator introduced by Kelejian and Prucha (1998), the maximum likelihood
(ML) estimator, as well as that of several other estimators. We find that the FGS2SLS estimator is virtually as efficient
as the ML estimator. This is important because the ML estimator is computationally burdensome, and may even be forbidding
in large samples, while the FGS2SLS estimator remains computationally feasible in large samples.
Received: 20 January 2001 / Accepted: 31 August 2001 相似文献
26.
Cooperative cache-based data access in ad hoc networks 总被引:1,自引:0,他引:1
Cooperative caching, in which multiple nodes share and coordinate cached data, is widely used to improve Web performance in wired networks. However, resource constraints and node mobility have limited the application of these techniques in ad hoc networks. We propose caching techniques that use the underlying routing protocols to overcome these constraints and further improve performance. 相似文献
27.
Perceptual Temporal Quality Metric for Compressed Video 总被引:2,自引:0,他引:2
Kai-Chieh Yang Guest C.C. El-Maleh K. Das P.K. 《Multimedia, IEEE Transactions on》2007,9(7):1528-1535
This paper presents a metric to quantify frame loss according to the impact on perceived temporal quality. This metric particularly aims at measuring the temporal quality degradation caused by both regular and irregular frame loss. Experimental results with subjective viewing demonstrate high performance on prediction of perceptual temporal quality. 相似文献
28.
29.