全文获取类型
收费全文 | 12795篇 |
免费 | 751篇 |
国内免费 | 43篇 |
专业分类
电工技术 | 171篇 |
综合类 | 15篇 |
化学工业 | 2691篇 |
金属工艺 | 456篇 |
机械仪表 | 940篇 |
建筑科学 | 233篇 |
矿业工程 | 3篇 |
能源动力 | 441篇 |
轻工业 | 1100篇 |
水利工程 | 83篇 |
石油天然气 | 13篇 |
无线电 | 2364篇 |
一般工业技术 | 2759篇 |
冶金工业 | 707篇 |
原子能技术 | 167篇 |
自动化技术 | 1446篇 |
出版年
2024年 | 13篇 |
2023年 | 165篇 |
2022年 | 233篇 |
2021年 | 440篇 |
2020年 | 284篇 |
2019年 | 329篇 |
2018年 | 375篇 |
2017年 | 422篇 |
2016年 | 460篇 |
2015年 | 383篇 |
2014年 | 557篇 |
2013年 | 828篇 |
2012年 | 835篇 |
2011年 | 1022篇 |
2010年 | 739篇 |
2009年 | 782篇 |
2008年 | 726篇 |
2007年 | 570篇 |
2006年 | 494篇 |
2005年 | 449篇 |
2004年 | 414篇 |
2003年 | 369篇 |
2002年 | 383篇 |
2001年 | 292篇 |
2000年 | 261篇 |
1999年 | 245篇 |
1998年 | 363篇 |
1997年 | 237篇 |
1996年 | 179篇 |
1995年 | 123篇 |
1994年 | 111篇 |
1993年 | 92篇 |
1992年 | 65篇 |
1991年 | 56篇 |
1990年 | 50篇 |
1989年 | 57篇 |
1988年 | 30篇 |
1987年 | 39篇 |
1986年 | 18篇 |
1985年 | 30篇 |
1984年 | 18篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1973年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
B Neppolian H C Choi S Sakthivel Banumathi Arabindoo V Murugesan 《Journal of hazardous materials》2002,89(2-3):303-317
The photocatalytic degradation of three commercial textile dyes with different structure has been investigated using TiO(2) (Degussa P25) photocatalyst in aqueous solution under solar irradiation. Experiments were conducted to optimise various parameters viz. amount of catalyst, concentration of dye, pH and solar light intensity. Degradation of all the dyes were examined by using chemical oxygen demand (COD) method. The degradation efficiency of the three dyes is as follows: Reactive Yellow 17(RY17) > Reactive Red 2(RR2) > Reactive Blue 4 (RB4), respectively. The experimental results indicate that TiO(2) (Degussa P25) is the best catalyst in comparison with other commercial photocatalysts such as, TiO(2) (Merck), ZnO, ZrO(2), WO(3) and CdS. Though the UV irradiation can efficiently degrade the dyes, naturally abundant solar irradiation is also very effective in the mineralisation of dyes. The comparison between thin-film coating and aqueous slurry method reveals that slurry method is more efficient than coating but the problems of leaching and the requirement of separation can be avoided by using coating technique. These observations indicate that all the three dyes could be degraded completely at different time intervals. Hence, it may be a viable technique for the safe disposal of textile wastewater into the water streams. 相似文献
52.
Young-Wan Choi O-Kyun Kwon El-Hang Lee 《Photonics Technology Letters, IEEE》1993,5(12):1406-1409
The authors report significantly improved performances of a symmetric self-electrooptic-effect device (S-SEED), with high on-off contrast ratio (>30:l) and large optical bistability loop widths (ΔP=44%) at an applied bias of Va=0 V, i.e., with no power supply. The S-SEED is made of extremely shallow quantum wells (ESQWs) in an asymmetric Fabry-Perot (AFP) cavity structure. At Va =5 V ΔP increased by up to 95%, preserving the high contrast ratio. The reflectivity changes at Va=0 and 5 V were about 15% and 30%, respectively. These are believed to be the largest values ever reported for such structures 相似文献
53.
A neural network-based power system stabilizer (neuro-PSS) is designed for a generator connected to a multi-machine power system utilizing the nonlinear power flow dynamics. The use of power flow dynamics provides a PSS for a wide range of operation with reduced size neural networks. The neuro-PSS consists of two neural networks: neuro-identifier and neuro-controller. The low-frequency oscillation is modeled by the neuro-identifier using the power flow dynamics, then a generalized backpropagation-through-time (GBTT) algorithm is developed to train the neuro-controller. The simulation results show that the neuro-PSS designed in this paper performs well with good damping in a wide operation range compared with the conventional PSS 相似文献
54.
55.
A compact dipole antenna for the terrestrial digital multimedia broadcasting (TDMB) application is presented. The length of the antenna is about 0.06λ at the TDMB resonance frequency of 190 MHz. Miniaturization of the antenna is achieved by using meander structures and lumped elements. The proposed antenna has two resonance frequencies and covers the TDMB band from 174 MHz to 216 MHz in Korea. The antenna has good impedance bandwidth and radiation characteristics for the TDMB. The experimental results of the designed dipole antenna are presented and analyzed. 相似文献
56.
Characterisation of a BioFET for detection of albumin in a mixture of human urine is presented. To avoid electrolyte effect of the urine, it was measured in PBS (phosphate buffer saline) at a fixed pH after albumin binding. The drain current was modulated by the albumin bound to the anti-albumin immobilised on the gate surface of the BioFET. The current variation ratio was likely to be proportional to the concentration of the albumin in the range 50-250 mg/1. The results show the feasibility of the BioFET as a urinary albumin sensor. 相似文献
57.
Effects of austenitizing treatment temperatures on aqueous corrosion properties of martensitic stainless steels were investigated by electrochemical tests (potentiodynamic test, potentiostatic test and electrochemical impedance spectroscopy), and surface analyses (optical microscopy and XRD). The results of potentiodynamic test revealed that the breakdown potential increased with the increased austenitizing temperature, indicating increased relative resistance to initiation of localized corrosion. EIS measurements showed that MSS3 (1030 °C) exhibits larger polarization resistance value than MSS1 (970 °C) and MSS2 (1000 °C) at passive and breakdown states. This was caused by decreasing the amount of Cr-rich M23C6 carbide which acts as preferential sites for pitting corrosion. 相似文献
58.
Yi Kai Zhou Sung Woo Choi Shigeya Kimura Shuichi Emura Shigehiko Hasegawa Hajime Asahi 《Journal of Superconductivity and Novel Magnetism》2007,20(6):429-432
GaGdN layers were grown at temperatures below 300°C by radio-frequency plasma-assisted molecular beam epitaxy on sapphire
substrates. GaGdN samples with high Gd concentration as high as 12.5% were obtained by lowering the growth temperature. X-ray
diffraction results showed no obvious secondary phase, which means that the phase separation can be suppressed by the growth
at low temperatures. All samples, including those grown at room temperature, showed ferromagnetic characteristics. Photoluminescence
emission was observed, though spectra exhibit broad and sharp luminescence bands related to many kinds of defects. It is suggested
that electrons coming from defects, especially, nitrogen vacancy, stabilize ferromagnetism, and that the carrier-induced ferromagnetism
occurs in the low-temperature-growth GaGdN. 相似文献
59.
Novel floating-patch micro-electro-mechanical system (MEMS) antennas are proposed for millimetre-wave applications. The floating-patch MEMS antennas are fabricated on a high resistivity silicon (HRS) substrate using surface micromachining technology. Simulation and experimental results for reflection coefficients and radiation patterns are presented. 相似文献
60.
Onishi K. Rino Choi Chang Seok Kang Hag-Ju Cho Young Hee Kim Nieh R.E. Jeong Han Krishnan S.A. Akbar M.S. Lee J.C. 《Electron Devices, IEEE Transactions on》2003,50(6):1517-1524
Bias-temperature instabilities (BTI) of HfO/sub 2/ metal oxide semiconductor field effect transistors (MOSFETs) have been systematically studied for the first time. NMOS positive BTI (PBTI) exhibited a more significant V/sub t/ instability than that of PMOS negative BTI (NBTI), and limited the lifetime of HfO/sub 2/ MOSFETs. Although high-temperature forming gas annealing (HT-FGA) improved the interface quality by passivating the interfacial states with hydrogen, BTI behaviors were not strongly affected by the technique. Charge pumping measurements were extensively used to investigate the nature of the BTI degradation, and it was found that V/sub t/ degradation of NMOS PBTI was primarily caused by charge trapping in bulk HfO/sub 2/ rather than interfacial degradation. Deuterium (D/sub 2/) annealing was found to be an excellent technique to improve BTI immunity as well as to enhance the mobility of HfO/sub 2/ MOSFETs. 相似文献