全文获取类型
收费全文 | 4932篇 |
免费 | 476篇 |
国内免费 | 52篇 |
专业分类
电工技术 | 96篇 |
技术理论 | 1篇 |
综合类 | 50篇 |
化学工业 | 1021篇 |
金属工艺 | 217篇 |
机械仪表 | 358篇 |
建筑科学 | 89篇 |
矿业工程 | 26篇 |
能源动力 | 209篇 |
轻工业 | 416篇 |
水利工程 | 37篇 |
石油天然气 | 70篇 |
武器工业 | 6篇 |
无线电 | 942篇 |
一般工业技术 | 1151篇 |
冶金工业 | 194篇 |
原子能技术 | 51篇 |
自动化技术 | 526篇 |
出版年
2024年 | 18篇 |
2023年 | 100篇 |
2022年 | 148篇 |
2021年 | 226篇 |
2020年 | 152篇 |
2019年 | 149篇 |
2018年 | 164篇 |
2017年 | 195篇 |
2016年 | 211篇 |
2015年 | 181篇 |
2014年 | 239篇 |
2013年 | 343篇 |
2012年 | 343篇 |
2011年 | 414篇 |
2010年 | 315篇 |
2009年 | 286篇 |
2008年 | 258篇 |
2007年 | 219篇 |
2006年 | 194篇 |
2005年 | 172篇 |
2004年 | 117篇 |
2003年 | 127篇 |
2002年 | 113篇 |
2001年 | 109篇 |
2000年 | 98篇 |
1999年 | 95篇 |
1998年 | 106篇 |
1997年 | 77篇 |
1996年 | 65篇 |
1995年 | 41篇 |
1994年 | 30篇 |
1993年 | 27篇 |
1992年 | 25篇 |
1991年 | 18篇 |
1990年 | 20篇 |
1989年 | 23篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1975年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有5460条查询结果,搜索用时 0 毫秒
1.
T. Choi J.‐H. Jang C.K. Ullal M.C. LeMieux V.V. Tsukruk E.L. Thomas 《Advanced functional materials》2006,16(10)
The probing of the micromechanical properties within a two‐dimensional polymer structure with sixfold symmetry fabricated via interference lithography reveals a nonuniform spatial distribution in the elastic modulus “imprinted” with an interference pattern in work reported by Tsukruk, Thomas, and co‐workers on p. 1324. The image prepared by M. Lemieux and T. Gorishnyy shows how the interference pattern is formed by three laser beams and is transferred to the solid polymer structure. The elastic and plastic properties within a two‐dimensional polymer (SU8) structure with sixfold symmetry fabricated via interference lithography are presented. There is a nonuniform spatial distribution in the elastic modulus, with a higher elastic modulus obtained for nodes (brightest regions in the laser interference pattern) and a lower elastic modulus for beams (darkest regions in the laser interference pattern) of the photopatterned films. We suggest that such a nonuniformity and unusual plastic behavior are related to the variable material properties “imprinted” by the interference pattern. 相似文献
2.
Transmission performance of 10-Gb/s 1550-nm transmitters using semiconductor optical amplifiers as booster amplifiers 总被引:1,自引:0,他引:1
Yonggyoo Kim Hodeok Jang Yonghoon Kim Jeongsuk Lee Donghoon Jang Jichai Jeong 《Lightwave Technology, Journal of》2003,21(2):476-481
We have demonstrated the transmission performance of 10-Gb/s transmitters based on LiNbO/sub 3/ modulator using semiconductor optical amplifiers (SOAs) as booster amplifiers. Utilizing the negative chirp converted in SOAs and self-phase modulation induced by high optical power, we can successfully transmit 10-Gb/s optical signals over 80 km through the standard single-mode fiber with the transmitter using SOAs as booster amplifiers. SOAs can be used for booster amplifiers with a careful adjustment of the operating conditions. In order to further understand an SOA's characteristics as a booster amplifier, we model SOAs and other subsystems to verify the experimental results. Based on the good agreement between the experimental and simulation results, we can find the appropriate parameters of input signals for SOAs, such as extinction ratio, rising/falling time, and chirp parameter to maximize output dynamic range and available maximum output power (P/sub o,max/). 相似文献
3.
An accurate printer model that is efficient enough to be used by halftoning algorithms is proposed. The proposed signal processing model (SPM) utilizes a physical model to train adaptive linear combiners (ALCs), after which the average exposure of each subpixel for any input pattern can be calculated using the optimized weight vector. The SPM can be used to model multi-level halftoning and resolution enhancement, as well as traditional halftoning. The SPM is comprised of a single ALC layer followed by a peak-to-average ratio (PAR) correction layer, which serves to produce a PAR of less than 1.5 in the modeled exposure. The PCN (PAR correction network) employs one ALC/pixel and exploits the physics governing the characteristics of exposure in small regions. A relatively small number of training patterns suffices to train the SPM. 相似文献
4.
低渗透率地层渗透率的确定方法 总被引:3,自引:0,他引:3
结合大庆油田外围低渗透率地层的地质特点,根椐渗流理论和岩心分析资料,分析了地层渗透率与孔隙度、组成地层的各种矿物含量以及泥质含量之间的关系,建立了不同矿物组合地层的渗透率计算方程。用本方法计算的和岩心分析的渗透率进行了对比,二者之间具有较好的一致性。 相似文献
5.
An experimental investigation was carried out to examine the tribological behavior of NAO (non-asbestos organic) type brake linings containing different volume ratios of graphite and antimony trisulfide (Sb2S3). A scale dynamometer was used for friction tests and particular emphases were given to the effect of applied pressure, sliding speed, and temperature on the coefficient of friction according to the relative amounts of the two solid lubricants. Results showed that the brake linings with both solid lubricants exhibited better friction stability and less speed sensitivity than the friction materials containing a single solid lubricant. In particular, the brake lining containing higher concentrations of graphite showed better fade resistance than others during high-temperature friction test. 相似文献
6.
Effect of Thickness of the p-AlGaN Electron Blocking Layer on the Improvement of ESD Characteristics in GaN-Based LEDs 总被引:1,自引:0,他引:1
Chung-Hsun Jang Sheu J.K. Tsai C.M. Shei S.C. Lai W.C. Chang S.J. 《Photonics Technology Letters, IEEE》2008,20(13):1142-1144
The following letter presents a study regarding GaN-based light-emitting diodes (LEDs) with p-type AlGaN electron blocking layers (EBLs) of different thicknesses. The study revealed that the LEDs could endure higher electrostatic discharge (ESD) levels as the thickness of the AlGaN EBL increased. The observed improvement in the ESD endurance ability could be attributed to the fact that the thickened p-AlGaN EBL may partly fill the dislocation-related pits that occur on the surface of the InGaN-GaN multiple-quantum well (MQW) and that are due to the strain and the low-temperature-growth process. If these dislocation-related pits are not partly suppressed, they will eventually result in numerous surface pits associated with threading dislocations that intersect the InGaN-GaN (MQW), thereby reducing the ESD endurance ability. The results of the experiment show that the ESD endurance voltages could increase from 1500 to 6000 V when the thickness of the p-AlGaN EBL in the GaN LEDs is increased from 32.5 to 130 nm, while the forward voltages and light output powers remained almost the same. 相似文献
7.
Jau-Jiun Chen Soohwan Jang F. Ren Yuanjie Li Hyun-Sik Kim D. P. Norton S. J. Pearton A. Osinsky S. N. G. Chu J. F. Weaver 《Journal of Electronic Materials》2006,35(4):516-519
Wet etch rates at 25°C for Zn0.9Mg0.1O grown on sapphire substrates by pulsed laser deposition (PLD) were in the range 300–1100 nm · min−1 with HCl/H2O (5×10−3−2×10−2 M) and 120–300 nm · min−1 with H3PO4/H2O (5×10−3−2×10−2 M). Both of these dilute mixtures exhibited diffusion-limited etching, with thermal activation energies of 2–3 kCal · mol−1. By sharp contrast, the etch rates for ZnO also grown on sapphire by PLD were much slower in similar solutions, with rates
of 1.2–50 nm · min−1 in HCl/H2O (0.01–1.2 M) and 12–54 nm · min−1 in H3PO4/H2O (0.02–0.15 M). The etching was reaction limited over the temperature range 25–75°C, with activation energies close to 6
kCal · mol−1. The resulting selectivity of Zn0.9Mg0.1O over ZnO can be a high as ∼400 with HCl and ∼30 with H3PO4. 相似文献
8.
Coating of 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 (PMN–PT) relaxor ferroelectrics by a sol–gel method is followed by growth of epitaxial SrRuO3 (SRO) metallic oxide electrodes on SrTiO3 (STO) single-crystal substrate by pulsed laser deposition. High-quality PMN–PT films on SRO with preferred growth orientation were successfully fabricated by controlling the operation parameters. Structural properties of relaxor ferroelectric PMN–PT thin films on SRO/STO substrates have been studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and atomic force microscopy (AFM). In-plane and out-of-plane alignments of the heterostructure are confirmed and the structural twinning of the materials are also revealed. 相似文献
9.
Steel dowel bar is used to transfer loads in concrete pavement slab. However, once the steel dowel bar corrodes, it may cause faults, such as joint freezing in concrete pavement, level differences resulting from spalling or decreased efficiency of load transfer, etc., which are the same problems experienced by typical reinforcing steel. This study evaluated the applicability of glass fiber-reinforced polymer (GFRP) dowel bar as a substitute for steel dowel bar. A microstructural analysis was conducted to examine the decrease in durability of GFRP dowel bar exposed to deterioration environments. To analyze the deterioration mechanism of GFRP dowel bar, scanning electron microscopy was employed and the porosity was measured by the gas absorption method. It was concluded that the longer the GFRP dowel bar was exposed to deterioration environments, the more the interlaminar shear stress decreased. This result was validated by the microstructural analysis. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
10.