全文获取类型
收费全文 | 7925篇 |
免费 | 392篇 |
国内免费 | 24篇 |
专业分类
电工技术 | 125篇 |
综合类 | 7篇 |
化学工业 | 1382篇 |
金属工艺 | 242篇 |
机械仪表 | 389篇 |
建筑科学 | 118篇 |
矿业工程 | 3篇 |
能源动力 | 338篇 |
轻工业 | 516篇 |
水利工程 | 36篇 |
石油天然气 | 12篇 |
武器工业 | 2篇 |
无线电 | 944篇 |
一般工业技术 | 1447篇 |
冶金工业 | 2181篇 |
原子能技术 | 65篇 |
自动化技术 | 534篇 |
出版年
2024年 | 2篇 |
2023年 | 69篇 |
2022年 | 84篇 |
2021年 | 166篇 |
2020年 | 153篇 |
2019年 | 139篇 |
2018年 | 192篇 |
2017年 | 186篇 |
2016年 | 217篇 |
2015年 | 163篇 |
2014年 | 270篇 |
2013年 | 362篇 |
2012年 | 444篇 |
2011年 | 510篇 |
2010年 | 360篇 |
2009年 | 410篇 |
2008年 | 370篇 |
2007年 | 305篇 |
2006年 | 230篇 |
2005年 | 223篇 |
2004年 | 187篇 |
2003年 | 166篇 |
2002年 | 168篇 |
2001年 | 134篇 |
2000年 | 134篇 |
1999年 | 163篇 |
1998年 | 794篇 |
1997年 | 418篇 |
1996年 | 306篇 |
1995年 | 183篇 |
1994年 | 144篇 |
1993年 | 163篇 |
1992年 | 38篇 |
1991年 | 40篇 |
1990年 | 48篇 |
1989年 | 54篇 |
1988年 | 51篇 |
1987年 | 41篇 |
1986年 | 26篇 |
1985年 | 22篇 |
1984年 | 4篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 17篇 |
1980年 | 14篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 29篇 |
1976年 | 109篇 |
1975年 | 2篇 |
排序方式: 共有8341条查询结果,搜索用时 265 毫秒
81.
K- and Q-bands CMOS frequency sources with X-band quadrature VCO 总被引:1,自引:0,他引:1
Sangsoo Ko Jeong-Geun Kim Taeksang Song Euisik Yoon Songcheol Hong 《Microwave Theory and Techniques》2005,53(9):2789-2800
Fully integrated 10-, 20-, and 40-GHz frequency sources are presented, which are implemented with a 0.18-/spl mu/m CMOS process. A 10-GHz quadrature voltage-controlled oscillator (QVCO) is designed to have output with a low dc level, which can be effectively followed by a frequency multiplier. The proposed multipliers generate signals of 20 and 40 GHz using the harmonics of the QVCO. To have more harmonic power, a frequency doubler with pinchoff clipping is used without any buffers or dc-level shifters. The QVCO has a low phase noise of -118.67 dBc/Hz at a 1-MHz offset frequency with a 1.8-V power supply. The transistor size effect on phase noise is investigated. The frequency doubler has a low phase noise of -111.67 dBc/Hz at a 1-MHz offset frequency is measured, which is 7 dB higher than a phase noise of the QVCO. The doubler can be tuned between 19.8-22 GHz and the output is -6.83 dBm. A fourth-order frequency multiplier, which is used to obtain 40-GHz outputs, shows a phase noise of -102.0 dBc/Hz at 1-MHz offset frequency with the output power of -18.0 dBm. A large tuning range of 39.3-43.67 GHz (10%) is observed. 相似文献
82.
This paper deals with a stochastic version of the simple facility location problem where the demands of customers are random variables. Under the assumption of step function type distribution of demands, the problem is shown to be approximated by a mixed 0-1 linear programming problem. A heuristic procedure is developed to solve the problem, which successfully extends the well known dual-based approach by Bilde & Krarup, and Erlenkotter. Computational results with 20 test problems are presented to demonstrate the effectiveness of the proposed heuristic. 相似文献
83.
84.
Seok-Hyun Yoon Je-Hun Lee Doh-Yeon Kim Nong M. Hwang 《Journal of the American Ceramic Society》2003,86(1):88-92
Changes in the microstructure and dielectric properties with the variation of the donor/acceptor ratio in BaTiO3 ceramics were investigated. In donor-rich specimens, a liquid that appeared during sintering did not penetrate into grain boundaries. However, in the acceptor-rich specimens, the grains were separated by a liquid film during sintering. The much higher mobility of the liquid film than that of the grain boundaries was suggested to cause extensive grain growth in acceptor-rich BaTiO3 . The macroscopic homogenization of dopants because of grain growth in acceptor-rich specimens resulted in changes in the dielectric properties. 相似文献
85.
JaeHyunKim JounHoLee JiChulLim ChangHoonLee MooHyoungSong JuYeonYoon HeeDongChoi JeomJaeKim ChangHoOh SangDeogYeo 李路海 《现代显示》2004,31(5):31-33
薄膜晶体管液晶电视(TFT-LCD TV)因为具有薄、轻、紧凑和可随意放置的特点,已经占据了大部分电视机市场。除了这些物理特性以外,最重要的特性是已具有了良好像质的对比度。为了将对比度提高到1:600以上,对偏振片膜、背光源板、滤色片树脂、电极锥角和摩擦条件等都进行了研究。优化的背光板组合,光滑的电极锥角和摩擦方法的控制是提高对比度的主要控制因素。应用新开发的滤色片树脂,对获得高对比度最为有效。 相似文献
86.
87.
J.-M. Yoon M.-H. Cho J.-E. Park Y.-H. Kim T.-R. Hahn Y.-S. Paik 《Journal of food science》2003,68(3):839-843
ABSTRACT Three major yellow pigments were isolated from safflower petals ( Carthamus tinctorius ) and characterized as hydroxysafflor yellow A (1), safflor yellow B (2), and precarthamin (3) by 1 H-NMR, 1 H-1 H COSY, 13 C-NMR, HMQC, and HMBC spectral analysis. Thermal degradation reactions of 3 yellow pigments 1 to 3 at temperatures of 70 to 90 °C were carried out at different pH levels within the range of 3.0 to 10.0 by UV-vis spectral measurements. First-order reaction kinetics was observed for the degradation of safflower yellow pigments (1 to 3) at pH 3.0 and 5.0. Activation energies of thermal degradation of 1-3 at pH 5.0 were calculated as 17.0, 15.4, and 20.1 kcal/mol, respectively. At neutral and alkaline conditions, yellow pigments 1-3 did not follow simple first-order kinetics. 相似文献
88.
89.
RB Singh H Mori J Chen S Mendis M Moshiri S Zhu SH Kim RG Sy AM Faruqui 《Canadian Metallurgical Quarterly》1996,3(6):489-494
PURPOSE: Two types of glass wool were used to remove leukocytes in semen for evaluation of reactive oxygen species production by spermatozoa in oligozoospermic patients with leukocytospermia. METHODS: Semen samples were prepared using fine-structure glass wool (SpermFertil) and coarse-structure glass wool. In each treatment group, native semen was evaluated for sperm concentration, percentage motility, viability, leukocyte concentration, and production of reactive oxygen species. RESULTS: Electron microscopically, SpermFertil showed a higher number of leukocytes attached to the fibers compared to coarse-structure glass wool. Leukocytes in native semen and after glass wool filtration as determined by peroxidase cytochemistry confirmed this observation. Reactive oxygen species decreased from 45.303 counts/10(7) viable cells in native semen to 15.806 counts/10(7) cells in coarse structure wool and 7.465 counts/10(7) cells in Spermfertil, respectively. CONCLUSIONS: Removal of leukocytes from semen of oligozoospermic patients by means of glass wool filtration is a useful method to distinguish production of reactive oxygen species by leukocytes versus sperm cells. 相似文献
90.