全文获取类型
收费全文 | 5201篇 |
免费 | 245篇 |
国内免费 | 164篇 |
专业分类
电工技术 | 64篇 |
综合类 | 119篇 |
化学工业 | 1094篇 |
金属工艺 | 730篇 |
机械仪表 | 133篇 |
建筑科学 | 130篇 |
矿业工程 | 597篇 |
能源动力 | 298篇 |
轻工业 | 96篇 |
水利工程 | 6篇 |
石油天然气 | 20篇 |
武器工业 | 10篇 |
无线电 | 726篇 |
一般工业技术 | 793篇 |
冶金工业 | 594篇 |
原子能技术 | 33篇 |
自动化技术 | 167篇 |
出版年
2024年 | 5篇 |
2023年 | 59篇 |
2022年 | 89篇 |
2021年 | 104篇 |
2020年 | 99篇 |
2019年 | 92篇 |
2018年 | 103篇 |
2017年 | 109篇 |
2016年 | 115篇 |
2015年 | 123篇 |
2014年 | 238篇 |
2013年 | 293篇 |
2012年 | 254篇 |
2011年 | 428篇 |
2010年 | 327篇 |
2009年 | 354篇 |
2008年 | 358篇 |
2007年 | 360篇 |
2006年 | 335篇 |
2005年 | 233篇 |
2004年 | 253篇 |
2003年 | 228篇 |
2002年 | 150篇 |
2001年 | 136篇 |
2000年 | 128篇 |
1999年 | 140篇 |
1998年 | 108篇 |
1997年 | 96篇 |
1996年 | 61篇 |
1995年 | 54篇 |
1994年 | 33篇 |
1993年 | 34篇 |
1992年 | 32篇 |
1991年 | 19篇 |
1990年 | 13篇 |
1989年 | 18篇 |
1988年 | 10篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1981年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有5610条查询结果,搜索用时 46 毫秒
21.
The partial oxidation of methanol to formaldehyde was studied over YBa2Cu3O7-x catalyst in a flow reactor. The structural change of YBa2Cu3O7-x before and after the reaction was measured by means of XRD and iodometric titration method. The catalytic characteristics
of YBa2Cu3O7-x for the partial oxidation of methanol to formaldehyde was due to copper ions. It was found that Cu+2 was responsible for the higher selectivity for formaldehyde. 相似文献
22.
Cu, In and Se have been codeposited in thin films by potentiostatic one-step electrodeposition. The as-deposited material has shown direct optical transitions attributable to the CuInSe2 semiconductor, but also additional absorption corresponding to another semimetallic phase. The secondary phases are selenium and copper selenide compounds which have been determined by composition measurements. In order to eliminate the semimetallic phases and to improve the semiconductor behaviour of the electrodeposited material, thermal and chemical treatments have been performed. After heat-treatment of the samples at 400°C in flowing argon, elemental selenium loss has been detected together with an enhancement of the allowed direct optical transition. The subsequent chemical etching of the layers in a KCN solution has showed to be successful in eliminating the copper selenide phases which were responsible of the remaining sub-bandgap absorption. 相似文献
23.
24.
Xueyuan ZhangWenle He Inger Odnevall Wallinder Jinshan PanChristofer Leygraf 《Corrosion Science》2002,44(9):2131-2151
Instantaneous corrosion rates of naturally patinated copper of varying age (16 months, 138 and 145 years) have been determined during continuous rain events in the laboratory with electrochemical impedance spectroscopy using a two-electrode cell. The two-electrode cell was found to yield the same information in bulk rainwater as a conventional three-electrode cell.Relatively constant corrosion rates, between 0.2 and 0.6 μm/y, were determined for samples having a two-layer structure with an inner brownish layer of cuprous oxide and an outer greenish layer of basic copper salts (138, 145 years). Samples with cuprous oxide as the dominating phase of the patina (16 months) showed higher and somewhat increasing corrosion rates during a rain event (from 0.6 to 1.2 μm/y). During a continuous rain event, corrosion rates were found to be approximately 10 (brownish patina) and 25 times (greenish patina) lower than corresponding instantaneous runoff rates. The first flush phenomena of the runoff process, with an increased concentration during first flush and a relatively constant concentration during steady state, was indirectly seen as an increase in solution conductivity during the first rain volume followed by relative constant value. The contribution of the concentration in the first flush to the total annual runoff rate was significant for panels having a greenish layer (138, 145 years) whereas it was negligible for panels having a brownish layer (16 months). 相似文献
25.
碘量法测铜中物质性质和分析操作 总被引:3,自引:0,他引:3
本文讨论了碘量法测定铜量中一些有关物质的特性,以及这些性质对分析条件和操作的要求。 相似文献
26.
Z. Gruba? 《Materials Letters》2007,61(3):794-798
The initial stage of copper electrodeposition on the electrochemically activated assembly of carbon microelectrodes from an acid solution of copper sulfate was investigated using cyclic voltammetry, potentiostatic pulse technique and electrochemical impedance spectroscopy. Analysis of the experimental current transients has been carried out using a non-linear fitting procedure according to the model that takes into account spherical diffusion towards a disc-shaped microelectrode. The higher values of diffusion coefficient in comparison with those observed on planar electrodes were explained with an increased diffusion caused by the electrode geometry. Impedance spectra showed two time constants, the high-frequency related to the charge transfer process and the low-frequency corresponded to the deposit morphology. 相似文献
27.
For the purpose of remediation of soils polluted by heavy metals, the use of some strong synthetic chelating agents such as ethylenediaminetetraacetic acid (EDTA) has been proposed. However, EDTA would not be considered as the preferential choice for the remediation of soil polluted with heavy metals like copper because of its nonbiodegradability and permanent residence in the natural environment. In the present work, some novel environmentally benign chelating agents, glucosamine hydrochloride, chito-oligosaccharide and
-asparaginic-N,N-diacetic acid (ASDA) were screened to find alternatives to EDTA by investigating the elution of copper from vermiculite with these reagents and comparing their effectiveness with EDTA. The effects of suspension contact time, reagent concentration and equilibrium pH of the solution on the removal of copper were examined. A stoichiometric amount of EDTA can quantitatively remove copper in both acidic and neutral conditions. Chito-oligosaccharide was a slightly less-effective reagent under acidic conditions compared to EDTA, and an amount well in excess of stoichiometry is required to achieve the maximum removal of copper from vermiculite. Glucosamine hydrochloride shows a relatively weak ability for the liberation of copper. The elution behavior of ASDA was equivalent to EDTA in acidic and neutral media. It was concluded that ASDA is the best substitute for EDTA because of its similar high complexing ability and superior biodegradability. 相似文献
28.
文章从提高铜加工产业国际竞争力角度,比较宏观地分析了浙江省铜加工产业国际竞争力提高的环境、积极与消极因素,针对性地提出了提升浙江省铜加工产业国际竞争力的应对思路。 相似文献
29.
Substituted uracils were tested as corrosion inhibitors of copper in 3% NaCl medium using electrochemical polarisation, impedance measurements and non-electrochemical techniques (weight loss, IR and UV-visible). This study permitted to follow the evolution of the inhibitory effect of the uracil derivatives, according to their substituents, on copper in 3% NaCl medium. Comparison of results showed that dithiouracil (DTUr) was the best inhibitor. The maximum inhibition efficiency reached 98% at 10−3 M. DTUr adsorbs on the copper surface according to the Frumkin isotherm model. 相似文献
30.
The successful use of palladium ion implantation into polyimide to seed an electroless plated film of copper on the polyimide surface is reported. Polyimide (Hitachi PIX 3400) was implanted with palladium ions to doses of 1.5 × 1015 − 1.2 × 1017 ions cm−2 using a MEVVA ion implanter. The implanted ions acted as sites for nucleation of copper film. A copper film was then deposited on implanted polyimide using a commercial electroless plating solution. The ion energy was kept low enough to facilitate a low critical ‘seed’ threshold dose that was measured to be 3.6× 1016 Pd ions cm−2. Test patterns were made using polyimide to study the adaptability of this technique to form thick structures. Plated films were studied with optical microscopy, Rutherford Backscattering Spectrometry (RBS) and Profilometry. The adhesion of films was qualitatively assessed by a ‘scotch tape test’. The film growth (thickness) was observed to be linear with plating time. A higher implantation dose led to greater plating rates. The adhesion was found to improve with increasing dose. 相似文献