全文获取类型
收费全文 | 576644篇 |
免费 | 94338篇 |
国内免费 | 59803篇 |
专业分类
电工技术 | 49439篇 |
技术理论 | 46篇 |
综合类 | 49255篇 |
化学工业 | 88526篇 |
金属工艺 | 44870篇 |
机械仪表 | 31280篇 |
建筑科学 | 42268篇 |
矿业工程 | 24546篇 |
能源动力 | 18871篇 |
轻工业 | 48143篇 |
水利工程 | 14820篇 |
石油天然气 | 34887篇 |
武器工业 | 6610篇 |
无线电 | 71386篇 |
一般工业技术 | 72234篇 |
冶金工业 | 27850篇 |
原子能技术 | 5499篇 |
自动化技术 | 100255篇 |
出版年
2024年 | 3990篇 |
2023年 | 9757篇 |
2022年 | 14930篇 |
2021年 | 19847篇 |
2020年 | 19148篇 |
2019年 | 26035篇 |
2018年 | 28706篇 |
2017年 | 31020篇 |
2016年 | 30056篇 |
2015年 | 33106篇 |
2014年 | 36196篇 |
2013年 | 39508篇 |
2012年 | 40925篇 |
2011年 | 40650篇 |
2010年 | 36289篇 |
2009年 | 32218篇 |
2008年 | 30327篇 |
2007年 | 28710篇 |
2006年 | 28061篇 |
2005年 | 24914篇 |
2004年 | 21270篇 |
2003年 | 18615篇 |
2002年 | 18087篇 |
2001年 | 15967篇 |
2000年 | 14683篇 |
1999年 | 14352篇 |
1998年 | 11551篇 |
1997年 | 9995篇 |
1996年 | 9393篇 |
1995年 | 8369篇 |
1994年 | 6772篇 |
1993年 | 5334篇 |
1992年 | 4661篇 |
1991年 | 3480篇 |
1990年 | 2769篇 |
1989年 | 2450篇 |
1988年 | 1954篇 |
1987年 | 906篇 |
1986年 | 731篇 |
1985年 | 558篇 |
1984年 | 430篇 |
1983年 | 343篇 |
1982年 | 347篇 |
1981年 | 279篇 |
1980年 | 263篇 |
1978年 | 169篇 |
1976年 | 337篇 |
1975年 | 262篇 |
1972年 | 260篇 |
1960年 | 210篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Supported metal catalysts, particularly noble metals supported on SiO2, have attracted considerable attention due to the importance of the silica–metal interface in heterogeneous catalysis and in electronic device fabrication. Several important issues, e.g., the stability of the metal–oxide interface at working temperatures and pressures, are not well-understood. In this review, the present status of our understanding of the metal–silica interface is reviewed. Recent results of model studies in our laboratories on Pd/SiO2/Mo(1 1 2) using LEED, AES and STM are reported. In this work, epitaxial, ultrathin, well-ordered SiO2 films were grown on a Mo(1 1 2) substrate to circumvent complications that frequently arise from the silica–silicon interface present in silica thin films grown on silicon. 相似文献
3.
World oil production and reserve additions heavily depend on giant oilfields. Currently, there are more than 4,000 producing oilfields in the world, producing around 68 million barrels of oil per day. Most oilfields in the world are minor ones, with oil production below 20,000 barrels per day; only 3% (about 120) oilfields in the world produce over 100,000 barrels per day with overall daily production exceeding 32 million barrels, which accounts for 47% of the total world oil supply . The scales of the oilfields heavily influence economic indices like investment, production and life spans of the oilfields. Therefore, giant oilfields have always been the dream of oil finders and targets of geologists' researches . 相似文献
4.
The catalytic activities of alumina prepared from an Al alkoxide-amine adduct monomer for the reaction of cyclopentene oxide with piperidine was determined after various pretreatments, including calcination and exposure to moisture. They were compared with the activity of alumina prepared by the conventional hydrolysis method. It was found that the as-prepared sample from the alkoxide-amine monomer preparation was five times more active than a conventional preparation, suggesting that it has a higher density of surface Lewis acid sites. However, its activity was much more severely suppressed by exposure to moisture. 相似文献
5.
H. L. Du S. R. Rose Z. D. Xiang P. K. Datta X. Y. Li 《Materialwissenschaft und Werkstofftechnik》2003,34(4):421-426
The oxidation/sulphidation behaviour of a Ti‐46.7Al‐1.9W‐0.5Si alloy with a TiAl3 diffusion coating was studied in an environment of H2/H2S/H2O at 850oC. The kinetic results demonstrate that the TiAl3 coating significantly increased the high temperature corrosion resistance of Ti‐46.7Al‐1.9W‐0.5Si. The SEM, EDX, XRD and TEM analysis reveals that the formation of an Al2O3 scale on the surface of the TiAl3‐coated sample was responsible for the enhancement of the corroison resistance. The Ti‐46.7Al‐1.9W‐0.5Si alloy was also modified by Nb ion implantation. The Nb ion implanted and as received sampels were subjected to cyclic oxidation in an open air at 800oC. The Nb ion implantation not only increased the oxidation resistance but also substantially improved the adhesion of scale to the substrate. 相似文献
6.
Marcia Cristina Kaezer Fran a Rosane Aguiar da Silva San Gil Jean-Guillaume Eon 《Catalysis Today》2003,78(1-4):105-115
γ-Al2O3 supported vanadium oxides were modified by tungsten and molybdenum oxides in order to improve dispersion and selectivity towards olefins in propane oxidative dehydrogenation (ODH). Both vanadium–tungsten and vanadium–molybdenum catalysts were obtained by adsorption of mixed isopolyanions (VW5O195−, V2W4O194−, VMo5O195− and V2Mo4O194−) from aqueous solutions. The isopolyanion solutions were characterized by UV-Vis and 51V NMR spectroscopy. Vanadium, vanadium–tungsten and vanadium–molybdenum precursors and catalysts were also characterized by UV-Vis (diffuse reflectance) and solid state 51V NMR spectroscopy. An improved selectivity to propene in the presence of tungsten and molybdenum in VOx/γ-Al2O3 was observed and attributed to dilution of vanadium by tungsten or molybdenum oxides on the γ-Al2O3 surface. 相似文献
7.
Kee S. Moon M. Levy Yong K. Hong H. Bakhru S. Bakhru 《Ferroelectrics Letters Section》2003,30(3):47-57
Advances in the fabrication of solid-solution single crystal relaxor ferroelectrics have made it possible to produce highly efficient piezoelectric crystals, and have attracted renewed interest in the use of these crystals for a new generation of piezoelectric transducers, actuators and sensors. Of particular interest is their incorporation into micro-electromechanical systems (MEMS). In this paper we report on the laser-induced wet chemical etching of lead zinc niobate-lead titanate (PZN-PT) in hydrochloric acid (HCl). Argon-ion laser radiation at power levels up to 4 W is focused to a spot diameter of about 15μm and results in the chemical etching of grooves at patterning speeds up to 5μm/sec. Crystal ion slicing, an ion-implant-based film separation technique, is used in combination with laser etching to form 5 to 10μm-thick patterned and freestanding films for incorporation into micro-electromechanical devices. 相似文献
8.
Shi-Jin Ding Hang Hu Lim H.F. Kim S.J. Yu X.F. Chunxiang Zhu Li M.F. Byung Jin Cho Chan D.S.H. Rustagi S.C. Yu M.B. Chin A. Dim-Lee Kwong 《Electron Device Letters, IEEE》2003,24(12):730-732
For the first time, we successfully fabricated and demonstrated high performance metal-insulator-metal (MIM) capacitors with HfO/sub 2/-Al/sub 2/O/sub 3/ laminate dielectric using atomic layer deposition (ALD) technique. Our data indicates that the laminate MIM capacitor can provide high capacitance density of 12.8 fF//spl mu/m/sup 2/ from 10 kHz up to 20 GHz, very low leakage current of 3.2 /spl times/ 10/sup -8/ A/cm/sup 2/ at 3.3 V, small linear voltage coefficient of capacitance of 240 ppm/V together with quadratic one of 1830 ppm/V/sup 2/, temperature coefficient of capacitance of 182 ppm//spl deg/C, and high breakdown field of /spl sim/6 MV/cm as well as promising reliability. As a result, the HfO/sub 2/-Al/sub 2/O/sub 3/ laminate is a very promising candidate for next generation MIM capacitor for radio frequency and mixed signal integrated circuit applications. 相似文献
9.
10.
分析了韩国、日本及国内运营商手机游戏业务的发展状况.探讨了手机游戏业务的模式.论述了该业务的战略定位和市场前景。从地区提供给移动通信市场对外部环境、产业链的准备是否充分以及运营商内部的资源和运营状况等三个方面阐明了手机游戏业务发展的关键因素。 相似文献