全文获取类型
收费全文 | 178371篇 |
免费 | 15989篇 |
国内免费 | 8993篇 |
专业分类
电工技术 | 12392篇 |
技术理论 | 10篇 |
综合类 | 12748篇 |
化学工业 | 28612篇 |
金属工艺 | 10073篇 |
机械仪表 | 11393篇 |
建筑科学 | 14817篇 |
矿业工程 | 5042篇 |
能源动力 | 5256篇 |
轻工业 | 12327篇 |
水利工程 | 3577篇 |
石油天然气 | 9847篇 |
武器工业 | 1561篇 |
无线电 | 20866篇 |
一般工业技术 | 20698篇 |
冶金工业 | 7592篇 |
原子能技术 | 2091篇 |
自动化技术 | 24451篇 |
出版年
2024年 | 912篇 |
2023年 | 3041篇 |
2022年 | 5573篇 |
2021年 | 7701篇 |
2020年 | 5849篇 |
2019年 | 4758篇 |
2018年 | 5051篇 |
2017年 | 5848篇 |
2016年 | 5139篇 |
2015年 | 7260篇 |
2014年 | 8898篇 |
2013年 | 10547篇 |
2012年 | 11946篇 |
2011年 | 12679篇 |
2010年 | 11201篇 |
2009年 | 10842篇 |
2008年 | 10682篇 |
2007年 | 9902篇 |
2006年 | 9929篇 |
2005年 | 8392篇 |
2004年 | 5842篇 |
2003年 | 5096篇 |
2002年 | 5186篇 |
2001年 | 4666篇 |
2000年 | 4329篇 |
1999年 | 4125篇 |
1998年 | 3286篇 |
1997年 | 2783篇 |
1996年 | 2510篇 |
1995年 | 2156篇 |
1994年 | 1734篇 |
1993年 | 1237篇 |
1992年 | 1025篇 |
1991年 | 795篇 |
1990年 | 568篇 |
1989年 | 514篇 |
1988年 | 407篇 |
1987年 | 288篇 |
1986年 | 188篇 |
1985年 | 120篇 |
1984年 | 80篇 |
1983年 | 57篇 |
1982年 | 75篇 |
1981年 | 48篇 |
1980年 | 49篇 |
1979年 | 16篇 |
1978年 | 3篇 |
1965年 | 3篇 |
1959年 | 9篇 |
1951年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
The solar photocatalytic degradation of methyl parathion was investigated using a circulating TiO2/solar light reactor. Under solar photocatalysis condition, parathion was more effectively degraded than solar photolysis and TiO2-only conditions. With solar photocatalysis, 20 mg/L of parathion was completely degraded within 60 min with a TOC decrease of 63% after 150 min. The main ionic byproducts during photocatalysis recovered from parathion degradation were mainly as NO3-, NO2- and NH4+, 80% of the sulphur as SO4(2-), and 5% of phosphorus as PO4(3-). The organic intermediates 4-nitrophenol and methyl paraoxon were also identified, and these were further degraded in solar photocatalytic condition. Two different bioassays (Vibrio fischeri and Daphnia magna) were used to test the acute toxicity of solutions treated by solar photocatalysis and photolysis. The Microtox test using V. fischeri showed that the toxicity expressed as EC50 (%) value increased from 5.5% to >82% in solar photocatalysis, indicating that the treated solution is non-toxic, but only increased from 4.9 to 20.5% after 150 min in solar photolysis. The acute toxicity test using D. magna showed that EC50 (%) increased from 0.05 to 1.08% under solar photocatalysis, but only increased to 0.12% after 150 min with solar photolysis, indicating the solution is still toxic. The pattern of toxicity reduction parallels the decrease in TOC and the parathion concentrations. 相似文献
62.
63.
It is demonstrated for the first time that long nanowires with radii as small as 30 nm can be manufactured with a conventional coupler fabrication rig. The temporal deterioration of nanowire optical properties has been studied and correlated with its mechanical behaviour. The original transmission properties have been restored by a post-fabrication treatment. 相似文献
64.
Ten-user truly asynchronous gigabit OCDMA transmission experiment with a 511-chip SSFBG en/decoder 总被引:8,自引:0,他引:8
Hamanaka T. Xu Wang Naoya Wada Nishiki A. Kitayama K. 《Lightwave Technology, Journal of》2006,24(1):95-102
A ten-user truly asynchronous gigabit coherent-optical-code-division-multiple-access (OCDMA) transmission was experimentally demonstrated without using any timing coordination. The enabling technologies are a record-length 511-chip superstructured-fiber-Bragg-grating (SSFBG) en/decoder and a supercontinuum (SC)-based optical-thresholding technique to significantly suppress the signal interference beat noise as well as the multiple-access-interference (MAI) noise. 相似文献
65.
The role of gas phase CH3 radicals in the oxidative coupling of CH4 over 1 wt% Sr/La2O3 is supported by the observations that (i) this is a very effective catalyst for the generation of CH3 · radicals and (ii) the concentration of CH3 · radicals increases with temperature over the range of 450 °C–800 °C. 相似文献
66.
67.
The tetrametallic ruthenium-oxo-hydroxo-hydride complex {[(PCy(3))(CO)RuH](4)(mu(4)-O)(mu(3)-OH)(mu(2)-OH)} (1) was synthesized in two steps from the monomeric complex (PCy(3))(CO)RuHCl (2). The tetrameric complex 1 was found to be a highly effective catalyst for the transfer dehydrogenation of alcohols. Complex 1 showed a different catalytic activity pattern towards primary and secondary benzyl alcohols, as indicated by the Hammett correlation for the oxidation reaction of p-X-C(6)H(4)CH(2)OH (rho = -0.45) and p-X-C(6)H(4)CH(OH)CH(3) (rho = +0.22) (X = OMe, CH(3), H, Cl, CF(3)). Both a sigmoidal curve from the plot of initial rate vs [PhCH(OH)CH(3)] (K(0.5) = 0.34 M; Hill coefficient, n = 4.2+/-0.1) and the phosphine inhibition kinetics revealed the highly cooperative nature of the complex for the oxidation of secondary alcohols. 相似文献
68.
Jiang-Li Chen Zhuo Xu Shao-Bo Qu Xiao-Yong Wei Xiao-Hui Liu 《Ceramics International》2008,34(4):803-807
The NiFe2O4 and Pb(Zr0.52Ti0.48)O3 ceramic composites are prepared by conventional solid state reaction method. The microstructural and morphological properties of the composites are studied by X-ray diffraction analysis and scanning electron microscopy. Results indicate that the ferrite and piezoelectric phases can co-exist in the composites. The relationship between the dielectric constant and frequency (40 Hz–40 MHz) as well as temperature is also investigated. It is noted that the transition temperature of the composites is about 380 °C. A double electric hysteresis loop is observed in our composites. The magnetic properties are relatively weak according to the magnetic hysteresis loop. With increase in the content of the ferrite phase, the permeability increases. The electromagnetic properties of the as-prepared composites are tunable according to the content of the NiFe2O4 phase. 相似文献
69.
70.