全文获取类型
收费全文 | 8027篇 |
免费 | 878篇 |
国内免费 | 693篇 |
专业分类
电工技术 | 674篇 |
综合类 | 590篇 |
化学工业 | 2021篇 |
金属工艺 | 2281篇 |
机械仪表 | 273篇 |
建筑科学 | 140篇 |
矿业工程 | 170篇 |
能源动力 | 224篇 |
轻工业 | 293篇 |
水利工程 | 23篇 |
石油天然气 | 129篇 |
武器工业 | 33篇 |
无线电 | 613篇 |
一般工业技术 | 1599篇 |
冶金工业 | 319篇 |
原子能技术 | 64篇 |
自动化技术 | 152篇 |
出版年
2024年 | 47篇 |
2023年 | 272篇 |
2022年 | 250篇 |
2021年 | 349篇 |
2020年 | 407篇 |
2019年 | 351篇 |
2018年 | 309篇 |
2017年 | 396篇 |
2016年 | 385篇 |
2015年 | 382篇 |
2014年 | 435篇 |
2013年 | 491篇 |
2012年 | 600篇 |
2011年 | 613篇 |
2010年 | 422篇 |
2009年 | 479篇 |
2008年 | 365篇 |
2007年 | 482篇 |
2006年 | 460篇 |
2005年 | 374篇 |
2004年 | 353篇 |
2003年 | 288篇 |
2002年 | 221篇 |
2001年 | 187篇 |
2000年 | 148篇 |
1999年 | 112篇 |
1998年 | 99篇 |
1997年 | 76篇 |
1996年 | 48篇 |
1995年 | 42篇 |
1994年 | 28篇 |
1993年 | 25篇 |
1992年 | 21篇 |
1991年 | 13篇 |
1990年 | 14篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1980年 | 2篇 |
1959年 | 1篇 |
1951年 | 5篇 |
排序方式: 共有9598条查询结果,搜索用时 31 毫秒
11.
12.
Chloride doped polyaniline conducting polymer films have been prepared in a protic acid medium (HCl) by potentiodynamic method
in an electrochemical cell and studied by cyclic voltammetry and FTIR techniques. The FTIR spectra confirmed Cl- ion doping in the polymers. The polymerization rate was found to increase with increasing concentration of aniline monomer.
But the films obtained at high monomer concentration were rough having a nonuniform flaky polyaniline distribution. Results
showed that the polymerization rate did not increase beyond a critical HCl concentration. Cyclic voltammetry suggested that,
the oxidation-reduction current increased with an increase in scan rate and that the undoped polyaniline films were not hygroscopic
whereas chloride doped polyaniline films were found to be highly hygroscopic. 相似文献
13.
14.
LiFePO4 is a potential candidate for the cathode material of the lithium secondary batteries. A co-precipitation method was adopted to prepare LiFePO4 because it is simple and cheap. Nitrogen gas was needed to prevent oxidation of Fe2+ in the aqueous solution. The co-precipitated precursor shows the high reactivity with the reductive gas, and the single phase of LiFePO4 is successfully synthesized with the aid of carbon under less reductive conditions. LiFePO4 fine powder prepared by co-precipitation method shows high rate capability, impressive specific capacity and cycle property. 相似文献
15.
M.G. Pujar N. Parvathavarthini Sidhartha S. Jena B.V.R. Tata R.K. Dayal H.S. Khatak 《Journal of Materials Engineering and Performance》2008,17(6):793-801
In the present work 316LN as well as 316 stainless steel (SS) coupons each of dimensions (0.025 × 0.018 × 0.006 m3) in well-polished condition were used as two nominal electrodes which were immersed in the aerated solution of 0.5 M NaCl.
Correlated current and potential electrochemical noise (EN) signals were collected at 1 Hz sampling frequency for 1 h daily
over a period of 30 days. The detrended EN data were used to calculate the noise resistance (R
N) as well as the spectral noise resistance at zero frequency (R
SNo) values and other statistical parameters. To study the nature of pits and distribution of their diameters as well as depths,
extensive observations of the pitted and the blank specimens were carried out using Confocal Laser Scanning Microscopy (CLSM).
The current and the potential records of the two alloys showed distinct differences in their corrosion behavior. It was observed
that within less than 4 h of immersion, 316SS showed signals indicative of unstable pitting and onset of stable pitting was
noticed after 48 h of exposure. However, until about 24 h, 316LN showed just the random signals and unstable pitting was observed
after 28 h. The signals clearly indicated continuous growth of the stable pits in 316SS as against the repassivation of the
unstable pits in 316LN after 7 days exposure. It was observed that R
N values showed a continuous decrease in the case of 316SS, but were quite stable in the case of 316LN over the exposure period.
Concurrent to these observations it was observed that 316SS specimen was extensively pitted. The frequency distributions of
pit diameters as well pit depths were observed to be highest at 10-20 μm and 5-10 μm, respectively. However, pits with as
large as 70-80 μm diameter and as deep as 20-25 μm too were observed. No pits were observed in case of 316LN even after 30 days
of exposure, an observation that corroborates well with the stable R
N values. Thus, in the present investigation, the long-term tests using EN technique coupled with CLSM studies conclusively
prove that many unstable pits initiated in 316SS turn into stable ones resulting in insidious localized corrosion attack whereas
the unstable pits initiated in 316LN get passivated in the simulated coastal environment. 相似文献
16.
镍氢电池负极用低成本储氢合金的研究 总被引:1,自引:0,他引:1
研究了ABS型储氢合金在低Co含量条件下,随B组元替代元素Co,Al,Si等含量的变化对合金电化学性能的影响规律,同时研究了A组元中不同La/Ce比对合金电化学性能的影响情况。结果表明,随合金中Co含量的降低,合金的活化性能和放电容量得以改善,但合金的循环寿命下降也比较明显;在试验范围内,随Al元素的加入,合金的循环寿命得以改善,但材料的放电容量和活化性能均有所下降;随合金La/Ce比的降低,合金的放电容量略有下降,但其循环寿命和放电电压平台有较大提高。 相似文献
17.
18.
用电化学方法测定砂浆试件中钢筋的极化电阻,并测定了砂浆的孔隙率,结果发现:砂浆的孔隙率、孔径分布与钢筋极化电阻大小有良好的对应关系。电化学方法能可靠、快速测定砂浆配合比、添加剂对钢筋腐蚀速度的影响。 相似文献
19.
20.
P. Cañizares J. García-Gómez C. Sáez M.A. Rodrigo 《Journal of Applied Electrochemistry》2003,33(10):917-927
The electrochemical oxidation of 4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol aqueous wastes using boron-doped diamond electrodes was studied. This treatment led to complete mineralization of the wastes regardless of the operating conditions. A simple mechanistic model is consistent with the voltammetric and electrolysis results. According to this model, the electrochemical treatment of chlorophenol aqueous wastes involves the anodic and cathodic release of chlorine followed by the formation of non-chlorinated aromatic intermediates. Subsequent cleavage of the aromatic ring gives rise to non-chlorinated carboxylic acids. Chlorine atoms arising from the hydrodehalogenation of the chlorophenols are converted into more oxidized molecules at the anode. These molecules react with unsaturated C4 carboxylic acid to finally yield trichloroacetic acid through a haloform reaction. The non-chlorinated organic acids are ultimately oxidized to carbon dioxide and the trichloroacetic acid into carbon dioxide and volatile organo-chlorinated molecules. Both direct and mediated electrochemical oxidation processes are involved in the electrochemical treatment of chlorophenols. 相似文献