全文获取类型
收费全文 | 249379篇 |
免费 | 17834篇 |
国内免费 | 9710篇 |
专业分类
电工技术 | 12845篇 |
技术理论 | 24篇 |
综合类 | 14186篇 |
化学工业 | 41027篇 |
金属工艺 | 14911篇 |
机械仪表 | 15353篇 |
建筑科学 | 17980篇 |
矿业工程 | 7539篇 |
能源动力 | 7209篇 |
轻工业 | 14450篇 |
水利工程 | 3712篇 |
石油天然气 | 16925篇 |
武器工业 | 1652篇 |
无线电 | 27592篇 |
一般工业技术 | 32989篇 |
冶金工业 | 16363篇 |
原子能技术 | 2508篇 |
自动化技术 | 29658篇 |
出版年
2024年 | 996篇 |
2023年 | 3838篇 |
2022年 | 6580篇 |
2021年 | 9245篇 |
2020年 | 7185篇 |
2019年 | 6210篇 |
2018年 | 7054篇 |
2017年 | 7848篇 |
2016年 | 7106篇 |
2015年 | 9140篇 |
2014年 | 11706篇 |
2013年 | 14586篇 |
2012年 | 14950篇 |
2011年 | 16633篇 |
2010年 | 14363篇 |
2009年 | 13751篇 |
2008年 | 13448篇 |
2007年 | 12957篇 |
2006年 | 13316篇 |
2005年 | 11649篇 |
2004年 | 7968篇 |
2003年 | 6902篇 |
2002年 | 6147篇 |
2001年 | 5535篇 |
2000年 | 6068篇 |
1999年 | 7104篇 |
1998年 | 6796篇 |
1997年 | 5421篇 |
1996年 | 5012篇 |
1995年 | 4018篇 |
1994年 | 3231篇 |
1993年 | 2316篇 |
1992年 | 1766篇 |
1991年 | 1458篇 |
1990年 | 1082篇 |
1989年 | 904篇 |
1988年 | 653篇 |
1987年 | 422篇 |
1986年 | 334篇 |
1985年 | 255篇 |
1984年 | 173篇 |
1983年 | 144篇 |
1982年 | 149篇 |
1981年 | 127篇 |
1980年 | 86篇 |
1979年 | 44篇 |
1978年 | 34篇 |
1977年 | 28篇 |
1976年 | 54篇 |
1973年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
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
22.
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
23.
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
24.
H. L. Du S. R. Rose Z. D. Xiang P. K. Datta X. Y. Li 《Materialwissenschaft und Werkstofftechnik》2003,34(4):421-426
The oxidation/sulphidation behaviour of a Ti‐46.7Al‐1.9W‐0.5Si alloy with a TiAl3 diffusion coating was studied in an environment of H2/H2S/H2O at 850oC. The kinetic results demonstrate that the TiAl3 coating significantly increased the high temperature corrosion resistance of Ti‐46.7Al‐1.9W‐0.5Si. The SEM, EDX, XRD and TEM analysis reveals that the formation of an Al2O3 scale on the surface of the TiAl3‐coated sample was responsible for the enhancement of the corroison resistance. The Ti‐46.7Al‐1.9W‐0.5Si alloy was also modified by Nb ion implantation. The Nb ion implanted and as received sampels were subjected to cyclic oxidation in an open air at 800oC. The Nb ion implantation not only increased the oxidation resistance but also substantially improved the adhesion of scale to the substrate. 相似文献
25.
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
26.
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
27.
28.
29.
Al-10Mg型固溶合金自然时效稳定性研究 总被引:3,自引:0,他引:3
测定了ZL30 5合金自然时效 33年的力学性能变化 ,观察了晶界的析出相 ,研究了组织和性能的关系 ,从而确定了ZL30 5合金具有长期自然时效稳定性。 相似文献
30.
Shi-Jin Ding Hang Hu Lim H.F. Kim S.J. Yu X.F. Chunxiang Zhu Li M.F. Byung Jin Cho Chan D.S.H. Rustagi S.C. Yu M.B. Chin A. Dim-Lee Kwong 《Electron Device Letters, IEEE》2003,24(12):730-732
For the first time, we successfully fabricated and demonstrated high performance metal-insulator-metal (MIM) capacitors with HfO/sub 2/-Al/sub 2/O/sub 3/ laminate dielectric using atomic layer deposition (ALD) technique. Our data indicates that the laminate MIM capacitor can provide high capacitance density of 12.8 fF//spl mu/m/sup 2/ from 10 kHz up to 20 GHz, very low leakage current of 3.2 /spl times/ 10/sup -8/ A/cm/sup 2/ at 3.3 V, small linear voltage coefficient of capacitance of 240 ppm/V together with quadratic one of 1830 ppm/V/sup 2/, temperature coefficient of capacitance of 182 ppm//spl deg/C, and high breakdown field of /spl sim/6 MV/cm as well as promising reliability. As a result, the HfO/sub 2/-Al/sub 2/O/sub 3/ laminate is a very promising candidate for next generation MIM capacitor for radio frequency and mixed signal integrated circuit applications. 相似文献