全文获取类型
收费全文 | 191191篇 |
免费 | 26495篇 |
国内免费 | 7669篇 |
专业分类
电工技术 | 11831篇 |
技术理论 | 10篇 |
综合类 | 10803篇 |
化学工业 | 39292篇 |
金属工艺 | 9187篇 |
机械仪表 | 10059篇 |
建筑科学 | 13753篇 |
矿业工程 | 4158篇 |
能源动力 | 5384篇 |
轻工业 | 17899篇 |
水利工程 | 3660篇 |
石油天然气 | 7153篇 |
武器工业 | 1454篇 |
无线电 | 25814篇 |
一般工业技术 | 28737篇 |
冶金工业 | 7854篇 |
原子能技术 | 1902篇 |
自动化技术 | 26405篇 |
出版年
2024年 | 732篇 |
2023年 | 2619篇 |
2022年 | 5239篇 |
2021年 | 7236篇 |
2020年 | 6417篇 |
2019年 | 6917篇 |
2018年 | 7418篇 |
2017年 | 8394篇 |
2016年 | 8265篇 |
2015年 | 10233篇 |
2014年 | 11861篇 |
2013年 | 14694篇 |
2012年 | 13570篇 |
2011年 | 14217篇 |
2010年 | 12834篇 |
2009年 | 12230篇 |
2008年 | 11578篇 |
2007年 | 10868篇 |
2006年 | 10173篇 |
2005年 | 8354篇 |
2004年 | 6039篇 |
2003年 | 4997篇 |
2002年 | 4851篇 |
2001年 | 4088篇 |
2000年 | 3879篇 |
1999年 | 3247篇 |
1998年 | 2513篇 |
1997年 | 2136篇 |
1996年 | 1966篇 |
1995年 | 1579篇 |
1994年 | 1265篇 |
1993年 | 1010篇 |
1992年 | 817篇 |
1991年 | 590篇 |
1990年 | 495篇 |
1989年 | 378篇 |
1988年 | 328篇 |
1987年 | 228篇 |
1986年 | 189篇 |
1985年 | 170篇 |
1984年 | 115篇 |
1983年 | 89篇 |
1982年 | 82篇 |
1981年 | 70篇 |
1980年 | 62篇 |
1979年 | 43篇 |
1978年 | 33篇 |
1977年 | 37篇 |
1976年 | 62篇 |
1973年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
Polyaryloxydiphenylsilanes were prepared from phosphorus‐containing diols and diphenydichlorolsilane through solution polymerization. With a stoichiometric imbalance in feed monomers, the resulting polymers exhibited moderate melting points and good processing properties. The polymers prepared showed initial decomposition temperatures above 340 °C, excellent thermal stability, high char yields at 850 °C and very high limited oxygen index values of 56–59. The polymers' char yields and their (P + Si) contents showed linear relationships. © 2003 Society of Chemical Industry 相似文献
33.
L. Sheeney‐Haj‐Ichia S. Pogorelova Y. Gofer I. Willner 《Advanced functional materials》2004,14(5):416-424
Three different configurations of Au‐nanoparticle/CdS‐nanoparticle arrays are organized on Au/quartz electrodes for enhanced photocurrent generation. In one configuration, Au‐nanoparticles are covalently linked to the electrode and the CdS‐nanoparticles are covalently linked to the bare Au‐nanoparticle assembly. The resulting photocurrent, φ = 7.5 %, is ca. 9‐fold higher than the photocurrent originating from a CdS‐nanoparticle layer that lacks the Au‐nanoparticles, φ = 0.8 %. The enhanced photocurrent in the Au/CdS nanoparticle array is attributed to effective charge separation of the electron–hole pair by the injection of conduction‐band electrons from the CdS‐ to the Au‐nanoparticles. Two other configurations involving electrostatically stabilized bipyridinium‐crosslinked Au/CdS or CdS/Au nanoparticle arrays were assembled on the Au/quartz crystal. The photocurrent quantum yields in the two systems are φ = 10 % and φ = 5 %, respectively. The photocurrents in control systems that include electrostatically bridged Au/CdS or CdS/Au nanoparticles by oligocationic units that lack electron‐acceptor units are substantially lower than the values observed in the analogous bipyridinium‐bridged systems. The enhanced photocurrents in the bipyridinium‐crosslinked systems is attributed to the stepwise electron transfer of conduction‐band electrons to the Au‐nanoparticles by the bipyridinium relay bridge, a process that stabilizes the electron–hole pair against recombination and leads to effective charge separation. 相似文献
34.
Yang C.W. Fang Y.K. Lin C.S. Tsair Y.S. Chen S.M. Wang W.D. Wang M.F. Cheng J.Y. Chen C.H. Yao L.G. Chen S.C. Liang M.S. 《Electronics letters》2003,39(21):1499-1501
A novel technique to form high-K dielectric of HfSiON by doping base oxide with Hf and nitridation with NH/sub 3/, sequentially, is proposed. The HfSiON gate dielectric demonstrates excellent device performances such as only 10% degradation of saturation drain current and almost 45 times of magnitude reduction in gate leakage compared with conventional SiO/sub 2/ gate at the approximately same equivalent oxide thickness. Additionally, negligible flatband voltage shift is achieved with this technique. Time-dependent dielectric breakdown tests indicate that the lifetime of HfSiON is longer than 10 years at V/sub dd/=2 V. 相似文献
35.
基于子波变换的涡街流量传感器信号分析 总被引:6,自引:0,他引:6
长期以来 ,如何提取潜在噪声下的涡街流量信号一直是个问题。流体流速脉动 ,局部阻力 ,随机振动———所有这些因素都给解决这一问题带来难度。文章应用子波变换消噪理论 ,从软件滤波的角度分析了强噪声干扰下的涡街流量信号 ,并提出了单支重构计数方法。分析结果表明 ,这种方法对低流速流量计量效果很好 ,能够有效地扩展量程下限 相似文献
36.
N. Jongen M. Donnet P. Bowen J. Lemaître H. Hofmann R. Schenk C. Hofmann M. Aoun‐Habbache S. Guillemet‐Fritsch J. Sarrias A. Rousset M. Viviani M.T. Buscaglia V. Buscaglia P. Nanni A. Testino J.R. Herguijuela 《化学工程与技术》2003,26(3):303-305
The synthesis of powders with controlled shape and narrow particle size distributions is still a major challenge for many industries. A continuous Segmented Flow Tubular Reactor (SFTR) has been developed to overcome homogeneity and scale‐up problems encountered when using batch reactors. Supersaturation is created by mixing the co‐reactants in a micromixer inducing precipitation; the suspension is then segmented into identical micro‐volumes by a non‐miscible fluid and sent through a tube. These micro‐volumes are more homogeneous when compared to large batch reactors leading to narrower size distributions, better particle morphology, polymorph selectivity and stoichiometry. All these features have been demonstrated on single tube SFTR for different chemical systems. To increase productivity for commercial application the SFTR is being “scaled‐out” by multiplying the number of tubes running in parallel instead of scaling‐up by increasing their size. The versatility of the multi‐tube unit will allow changes in type of precipitate with a minimum of new investment as new chemistry can be researched, developed and optimised in a single tube SFTR and then transferred to the multi‐tube unit for powder production. 相似文献
37.
Y.K. Su H.C. Wang C.L. Lin W.B. Chen S.M. Chen 《Photonics Technology Letters, IEEE》2003,15(10):1345-1347
The brightness of AlGaInP light emitting diodes (LEDs) has been raised by a factor of 1.12 at 20 mA by sulfide passivation. Meanwhile, the sulfide also can decrease leakage current of AlGaInP LEDs at -2 V to nearly one thousandth of that in the as-fabricated device. The possible causes for the brightness increase of AlGaInP LEDs after sulfide treatment including surface roughness, reduction of Fresnel loss, and effective injection of carriers were demonstrated. 相似文献
38.
M. Ganschow C. Hellriegel E. Kneuper M. Wark C. Thiel G. Schulz‐Ekloff C. Bruchle D. Whrle 《Advanced functional materials》2004,14(3):269-276
Dye‐loaded AlPO4‐5 single crystals were prepared by microwave‐assisted hydrothermal synthesis from a batch, containing a mixture of three chromophores (Coumarin 40, Rhodamine BE50, and Oxazine 1) differing in their absorption range, molecular dimensions, and solubilities. Confocal fluorescence images reveal a spatial separation effect of the dye molecules, where the slimmer, more‐soluble dye molecule (Coumarin 40) is uniformly distributed in the body of the single crystal, and the bulky and/or less‐soluble ones (Rhodamine BE50, Oxazine 1) are situated in distinct domains. Visible spectra show good panchromatic absorption of visible light. Fluorescence lifetime measurements indicate the presence of an energy transfer cascade of the entirely fixed dye molecules from Coumarin 40 to Oxazine 1. The transfer mechanism is predominantly radiative. 相似文献
39.
40.