全文获取类型
收费全文 | 272802篇 |
免费 | 21385篇 |
国内免费 | 11879篇 |
专业分类
电工技术 | 15700篇 |
技术理论 | 28篇 |
综合类 | 18670篇 |
化学工业 | 45425篇 |
金属工艺 | 16178篇 |
机械仪表 | 17550篇 |
建筑科学 | 20548篇 |
矿业工程 | 8899篇 |
能源动力 | 7511篇 |
轻工业 | 17625篇 |
水利工程 | 4743篇 |
石油天然气 | 18688篇 |
武器工业 | 2148篇 |
无线电 | 29551篇 |
一般工业技术 | 31312篇 |
冶金工业 | 14779篇 |
原子能技术 | 2803篇 |
自动化技术 | 33908篇 |
出版年
2024年 | 1133篇 |
2023年 | 4210篇 |
2022年 | 7465篇 |
2021年 | 10405篇 |
2020年 | 8048篇 |
2019年 | 6866篇 |
2018年 | 7696篇 |
2017年 | 8616篇 |
2016年 | 7782篇 |
2015年 | 10486篇 |
2014年 | 13324篇 |
2013年 | 15916篇 |
2012年 | 17440篇 |
2011年 | 18877篇 |
2010年 | 16784篇 |
2009年 | 15993篇 |
2008年 | 15888篇 |
2007年 | 15361篇 |
2006年 | 15600篇 |
2005年 | 13442篇 |
2004年 | 9298篇 |
2003年 | 7701篇 |
2002年 | 6844篇 |
2001年 | 6102篇 |
2000年 | 6421篇 |
1999年 | 7118篇 |
1998年 | 5895篇 |
1997年 | 4844篇 |
1996年 | 4516篇 |
1995年 | 3778篇 |
1994年 | 3072篇 |
1993年 | 2124篇 |
1992年 | 1674篇 |
1991年 | 1314篇 |
1990年 | 989篇 |
1989年 | 811篇 |
1988年 | 583篇 |
1987年 | 370篇 |
1986年 | 299篇 |
1985年 | 200篇 |
1984年 | 145篇 |
1983年 | 119篇 |
1982年 | 129篇 |
1981年 | 105篇 |
1980年 | 75篇 |
1979年 | 38篇 |
1978年 | 27篇 |
1977年 | 21篇 |
1976年 | 36篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
In this paper, we propose a routing algorithm called minimum fusion Steiner tree (MFST) for energy efficient data gathering with aggregation (fusion) in wireless sensor networks. Different from existing schemes, MFST not only optimizes over the data transmission cost, but also incorporates the cost for data fusion, which can be significant for emerging sensor networks with vectorial data and/or security requirements. By employing a randomized algorithm that allows fusion points to be chosen according to the nodes' data amounts, MFST achieves an approximation ratio of 5/4log(k + 1), where k denotes the number of source nodes, to the optimal solution for extremely general system setups, provided that fusion cost and data aggregation are nondecreasing against the total input data. Consequently, in contrast to algorithms that only excel in full or nonaggregation scenarios without considering fusion cost, MFST can thrive in a wide range of applications 相似文献
23.
Commercial purity aluminum (99.5%) was fabricated by equal channel angular pressing (ECAP) up to total accumulated strains of approx. 10. The annealing behavior of material deformed to total strains of approx. 1 and 10 was investigated, using heat treatments of 2 h at various temperatures from 100 to 500 °C. The microstructure of the annealed materials was characterized using the electron back-scatter pattern technique. A number of parameters were determined including the distribution and average values of both the boundary spacings and misorientations. For samples deformed to a total strain of 1, annealing resulted in discontinuous recrystallization. For samples deformed to a total strain of 10, annealing resulted in microstructures exhibiting characteristics of both uniform coarsening and, in a number of places, of discontinuous recrystallization. An attempt was made, based on the boundary spacing distributions, to separate these two components. The grain size after annealing was still however small, being just 6.4 μm after 2 h at 300 °C. 相似文献
24.
农村通信如何"突围" 总被引:2,自引:0,他引:2
农村通信作为农村地区信息化的基础,对于全面建设小康具有特殊的重要地位。介绍了我国农村通信的发展现状,分析了农村通信发展的困难压其原因,最后对农村压边远、欠发达地区通信的均衡震展提出了一些建议。 相似文献
25.
26.
量子密码技术被认为是绝对安全的加密技术。近年来,在美国、德国、日本和中国,相关研究都取得了明显进展。2004年6月,世界上第一个量子密码通信网络在美国马萨诸塞州剑桥城正式投入运行,标志着这一技术迈上了新台阶。据相关机构估算,量子保密通信系统一旦商用,将形成高达10亿美元的市场。 相似文献
27.
Chun-Tsen Lu Kun-Wei Lin Huey-Ing Chen Hung-Ming Chuang Chun-Yuan Chen Wen-Chau Liu 《Electron Device Letters, IEEE》2003,24(6):390-392
A new and interesting Pd-oxide-Al/sub 0.3/Ga/sub 0.7/As MOS hydrogen sensor has been fabricated and studied. The steady-state and transient responses with different hydrogen concentrations has been measured at various temperatures. Based on the large Schottky barrier height and presence of oxide layer, the studied device exhibits a high hydrogen detection sensitivity and wide temperature operating regime. The studied device exhibits the low-leakage current and obvious current changes when exposed to hydrogen-contained gas. Even at room temperature, a very high hydrogen detection sensitivity of 155.9 is obtained when a 9090 ppm H/sub 2//air gas is introduced. Furthermore, when exposed to hydrogen-contained gas at 95/spl deg/C, both the forward and reverse currents are substantially increased with increased hydrogen concentration. In other words, the studied device can be used as a hydrogen sensor under the applied bidirectional bias. Under the applied voltage of 0.35 V and 9090 ppm H/sub 2//air hydrogen ambient, a fast adsorption response time about 10 s is found. The transient and steady-state characteristics of hydrogen adsorption are also investigated. 相似文献
28.
A simple template‐free high‐temperature evaporation method was developed for the growth of crystalline Si microtubes for the first time. As‐grown Si microtubes were characterized using X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, and room‐temperature photoluminescence. The lengths of the Si tubes can reach several hundreds of micrometers; some of them have lengths on the order of millimeters. Each tube has a uniform outer diameter along its entire length, and the typical outer diameter is ≈ 2–3 μm. Most of the tubes have a wall thickness of ≈ 400–500 nm, though a considerable number of them exhibit a very thin wall thickness of ≈ 50 nm. Room‐temperature photoluminescence measurement shows the as‐synthesized Si microtubes have two strong emission peaks centered at ≈ 589 nm and ≈ 617 nm and a weak emission peak centered at ≈ 455 nm. A possible mechanism for the formation of these Si tubes is proposed. We believe that the present discovery of the crystalline Si microtubes will promote further experimental studies on their physical properties and smart applications. 相似文献
29.
30.