全文获取类型
收费全文 | 18891篇 |
免费 | 1899篇 |
国内免费 | 558篇 |
专业分类
电工技术 | 926篇 |
技术理论 | 1篇 |
综合类 | 772篇 |
化学工业 | 4094篇 |
金属工艺 | 903篇 |
机械仪表 | 1031篇 |
建筑科学 | 920篇 |
矿业工程 | 278篇 |
能源动力 | 811篇 |
轻工业 | 1649篇 |
水利工程 | 211篇 |
石油天然气 | 595篇 |
武器工业 | 112篇 |
无线电 | 2638篇 |
一般工业技术 | 3217篇 |
冶金工业 | 779篇 |
原子能技术 | 226篇 |
自动化技术 | 2185篇 |
出版年
2024年 | 34篇 |
2023年 | 240篇 |
2022年 | 449篇 |
2021年 | 730篇 |
2020年 | 573篇 |
2019年 | 573篇 |
2018年 | 601篇 |
2017年 | 644篇 |
2016年 | 677篇 |
2015年 | 711篇 |
2014年 | 1049篇 |
2013年 | 1249篇 |
2012年 | 1351篇 |
2011年 | 1537篇 |
2010年 | 1307篇 |
2009年 | 1207篇 |
2008年 | 1126篇 |
2007年 | 960篇 |
2006年 | 877篇 |
2005年 | 791篇 |
2004年 | 599篇 |
2003年 | 572篇 |
2002年 | 577篇 |
2001年 | 474篇 |
2000年 | 380篇 |
1999年 | 371篇 |
1998年 | 343篇 |
1997年 | 246篇 |
1996年 | 180篇 |
1995年 | 169篇 |
1994年 | 135篇 |
1993年 | 103篇 |
1992年 | 98篇 |
1991年 | 54篇 |
1990年 | 64篇 |
1989年 | 58篇 |
1988年 | 27篇 |
1987年 | 30篇 |
1986年 | 20篇 |
1985年 | 14篇 |
1984年 | 25篇 |
1983年 | 22篇 |
1982年 | 11篇 |
1981年 | 20篇 |
1980年 | 12篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1977年 | 12篇 |
1976年 | 14篇 |
1975年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
As IC devices scale down to the submicron level, the resistance-capacitance (RC) time delays are the limitation to circuit
speed. A solution is to use low dielectric constant materials and low resistivity materials. In this work, the influence of
underlying barrier Ta on the electromigration (EM) of Cu on hydrogen silsesquioxane (HSQ) and SiO2 substrates was investigated. The presence of a Ta barrier not only improves the adhesion between Cu and dielectrics, but
also enhances the crystallinity of Cu film and improves the Cu electromigration resistance. The activation energy obtained
suggests a grain boundary migration mechanism and the current exponent calculated indicates the Joule heating effect. 相似文献
72.
For multi-step heterogeneous consecutive reactions affected entirely by interphase diffusion under isothermal condition, the
equations for the effectiveness factors, the surface concentrations and the point yields were derived in terms of the Damkoehler
numbers or the measurables from the mass balances set up on the assumption that the mass-transfer rate balances the surface-reaction
rate at steady state.
From the analyses of the equations derived, the effectiveness factors for the intermediate steps and the surface concentrations
of intermediates were understood to be enhanced by the measurables inclusive of the concentrations and the mass-transfer coefficients.
Then the effect of the concentrations was concluded to be most significant. The effects of these measurables to the effectiveness
factors and the surface concentrations were qualitatively discussed for simple consecutive reactions and also for additive
consecutive reactions. Especially, as for two-step additive consecutive reactions, the effects of measurables η Da and the
concentrations to the effectiveness factors were examined with graphical presentations.
Finally, the brief discussion of the dependency of the Damkoehler number upon reaction time and the effect of the Renolds
number and diffusivity to the extent of the mass-transfer resistance were presented. 相似文献
73.
根据中原油田地层高温、高盐、易塌、易漏失及水平井的特点,优选了适用于水平井的强抑制强封堵聚合物钻井液体系,并进行了现场应用.室内实验结果表明,优选的强抑制强封堵聚合物钻井液具有良好的井眼净化、摩阻控制、井壁稳定及油层保护等性能.现场应用时能满足钻井、录井、测井的需要,钻井施工顺利,取得了良好的经济和社会效益. 相似文献
74.
沿江圩区排涝水文计算实例 总被引:2,自引:0,他引:2
设计排涝模数的计算是圩区排涝规划的主要内容之一,它的大小决定了排涝站的装机容量和涵闸尺寸.本文推求了安徽省马鞍山市大公圩地区的排涝模数,是沿江圩区排涝水文计算的一个应用实例. 相似文献
75.
The main purpose of this paper is to find the mixed-mode stress intensity factors of composite materials using the crack opening displacement (COD). First, a series solution of the composite material with a crack was used to evaluate COD values. Then, the least-squares method was used to calculate mixed-mode stress intensity factors. This algorithm can be applied to any method that generates or measures COD values. The major advantage of this method is that COD values very near the crack tip are not necessary. Both finite element simulations and laboratory experiments were applied to validate this least-squares method with acceptable accuracy if the even terms of the series solution are removed. 相似文献
76.
Single-crystalline 3C-SiC nanowires have been synthesized in large scale through a one-step autoclave route by the reaction of SiCl4, (C5H5)2Fe and metallic Na at 500 °C. Electron microscopy investigations show that the nanowires have typical diameters of 15-50 nm, lengths up to several tens of micrometers and grow along the [111] direction. The possible growth mechanism of the nanowires is discussed. 相似文献
77.
78.
Hyun-Chul Kim Author VitaeDaijin KimAuthor Vitae Sung Yang Bang Author Vitae 《Pattern recognition》2003,36(5):1095-1105
Linear discriminant analysis (LDA) is a data discrimination technique that seeks transformation to maximize the ratio of the between-class scatter and the within-class scatter. While it has been successfully applied to several applications, it has two limitations, both concerning the underfitting problem. First, it fails to discriminate data with complex distributions since all data in each class are assumed to be distributed in the Gaussian manner. Second, it can lose class-wise information, since it produces only one transformation over the entire range of classes. We propose three extensions of LDA to overcome the above problems. The first extension overcomes the first problem by modelling the within-class scatter using a PCA mixture model that can represent more complex distribution. The second extension overcomes the second problem by taking different transformation for each class in order to provide class-wise features. The third extension combines these two modifications by representing each class in terms of the PCA mixture model and taking different transformation for each mixture component. It is shown that all our proposed extensions of LDA outperform LDA concerning classification errors for synthetic data classification, hand-written digit recognition, and alphabet recognition. 相似文献
79.
Sanghyun Ju Jianye Li Pimparkar N. Alam M.A. Chang R.P.H. Janes D.B. 《Nanotechnology, IEEE Transactions on》2007,6(3):390-395
Nanorod field-effect transistors (FETs) that use multiple Mg-doped ZnO nanorods and a SiO2 gate insulator were fabricated and characterized. The use of multiple nanorods provides higher on-currents without significant degradation in threshold voltage shift and subthreshold slopes. It has been observed that the on-currents of the multiple ZnO nanorod FETs increase approximately linearly with the number of nanorods, with on-currents of ~1 muA per nanorod and little change in off-current (~4times10-12). The subthreshold slopes and on-off ratios typically improve as the number of nanorods within the device channel is increased, reflecting good uniformity of properties from nanorod to nanorod. It is expected that Mg dopants contribute to high n-type semiconductor characteristics during ZnO nanorod growth. For comparison, nonintentionally doped ZnO nanorod FETs are fabricated, and show low conductivity to compare with Mg-doped ZnO nanorods. In addition, temperature-dependent current-voltage characteristics of single ZnO nanorod FETs indicate that the activation energy of the drain current is very low (0.05-0.16 eV) at gate voltages both above and below threshold 相似文献
80.
Yi Kai Zhou Sung Woo Choi Shigeya Kimura Shuichi Emura Shigehiko Hasegawa Hajime Asahi 《Journal of Superconductivity and Novel Magnetism》2007,20(6):429-432
GaGdN layers were grown at temperatures below 300°C by radio-frequency plasma-assisted molecular beam epitaxy on sapphire
substrates. GaGdN samples with high Gd concentration as high as 12.5% were obtained by lowering the growth temperature. X-ray
diffraction results showed no obvious secondary phase, which means that the phase separation can be suppressed by the growth
at low temperatures. All samples, including those grown at room temperature, showed ferromagnetic characteristics. Photoluminescence
emission was observed, though spectra exhibit broad and sharp luminescence bands related to many kinds of defects. It is suggested
that electrons coming from defects, especially, nitrogen vacancy, stabilize ferromagnetism, and that the carrier-induced ferromagnetism
occurs in the low-temperature-growth GaGdN. 相似文献