全文获取类型
收费全文 | 185414篇 |
免费 | 15270篇 |
国内免费 | 11494篇 |
专业分类
电工技术 | 11462篇 |
技术理论 | 6篇 |
综合类 | 16131篇 |
化学工业 | 32509篇 |
金属工艺 | 12391篇 |
机械仪表 | 12784篇 |
建筑科学 | 22282篇 |
矿业工程 | 5056篇 |
能源动力 | 5635篇 |
轻工业 | 11386篇 |
水利工程 | 2967篇 |
石油天然气 | 8671篇 |
武器工业 | 1750篇 |
无线电 | 17191篇 |
一般工业技术 | 20087篇 |
冶金工业 | 6045篇 |
原子能技术 | 1662篇 |
自动化技术 | 24163篇 |
出版年
2024年 | 635篇 |
2023年 | 2536篇 |
2022年 | 4592篇 |
2021年 | 5250篇 |
2020年 | 4953篇 |
2019年 | 4420篇 |
2018年 | 4195篇 |
2017年 | 5338篇 |
2016年 | 5740篇 |
2015年 | 6067篇 |
2014年 | 9881篇 |
2013年 | 9827篇 |
2012年 | 11606篇 |
2011年 | 13411篇 |
2010年 | 10774篇 |
2009年 | 12158篇 |
2008年 | 11432篇 |
2007年 | 12823篇 |
2006年 | 12088篇 |
2005年 | 10185篇 |
2004年 | 8653篇 |
2003年 | 8066篇 |
2002年 | 6768篇 |
2001年 | 5485篇 |
2000年 | 4767篇 |
1999年 | 3862篇 |
1998年 | 2922篇 |
1997年 | 2388篇 |
1996年 | 2016篇 |
1995年 | 1893篇 |
1994年 | 1717篇 |
1993年 | 1303篇 |
1992年 | 1067篇 |
1991年 | 732篇 |
1990年 | 528篇 |
1989年 | 444篇 |
1988年 | 319篇 |
1987年 | 194篇 |
1986年 | 173篇 |
1985年 | 155篇 |
1984年 | 124篇 |
1983年 | 101篇 |
1982年 | 112篇 |
1981年 | 76篇 |
1980年 | 91篇 |
1979年 | 36篇 |
1978年 | 33篇 |
1977年 | 25篇 |
1976年 | 35篇 |
1975年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Ying Chen HuiLi Zhang YuNing Liang YanHua Gao Yongchao Li 《Petroleum Science and Technology》2019,37(7):787-795
In this study, a simple hydrothermal synthesis method was adapted for the preparation of Co-doping Co2+/F-/TiO2 nanotubes photocatalyst, and the micro-nano structure of catalysts prepared by biomimetic technology which makes the catalyst have super-oleophilicity property. Co2+/F-/TiO2 revealed improved photocatalytic performance for denitrification of light oil compared to single TiO2 photocatalysts. The enhance of photocatalytic activity can be attributed to narrowing the band gap, increasing the light response wavelength and exposing more highly active crystal surfaces due to synergistic effects of Co2+ and F? in the photocatalyst. 相似文献
103.
Using a comprehensive set of drop weight impact test data (h50) newly compiled from literature for 308 materials, a recent approach to predict impact sensitivities of nitro compounds is generalized to most explosive substances of interest. Compared to previous ones, this procedure is more thoroughly validated and exhibits a good predictive value. Furthermore, it yields new insight into the physical mechanisms involved, explaining for instance the unexpected desensitization of some oxygen-deficient triazoles upon nitration. 相似文献
104.
Artificial bee colony (ABC) algorithm has several characteristics that make it more attractive than other bio-inspired methods. Particularly, it is simple, it uses fewer control parameters and its convergence is independent of the initial conditions. In this paper, a novel artificial bee colony based maximum power point tracking algorithm (MPPT) is proposed. The developed algorithm, does not allow only overcoming the common drawback of the conventional MPPT methods, but it gives a simple and a robust MPPT scheme. A co-simulation methodology, combining Matlab/Simulink™ and Cadence/Pspice™, is used to verify the effectiveness of the proposed method and compare its performance, under dynamic weather conditions, with that of the Particle Swarm Optimization (PSO) based MPPT algorithm. Moreover, a laboratory setup has been realized and used to experimentally validate the proposed ABC-based MPPT algorithm. Simulation and experimental results have shown the satisfactory performance of the proposed approach. 相似文献
105.
Traditional maximum power point tracking (MPPT) methods can hardly find global maximum power point (MPP) because output characteristics curve of photovoltaic (PV) array may have multi local maximum power points in irregular shadow, and thus easily fall into the local maximum power point. To address this drawback, Considering that sliding mode variable structure (SMVS) control strategy have such advantages as simple structure, fast response and strong robustness, and P&O method have the advantages of simple principle and convenient implementation, so a new algorithm combining SMVS control method and P&O method is proposed, besides, PI controller is applied to reduce system chattering caused by switching sliding surface. It is applied to MPPT control of PV array in irregular shadow to solve the problem of multi-peak optimization in partial shadow. In order to verity the rationality of the proposed algorithm, the experimental circuit is built, which achieves MPPT control by means of the proposed algorithm and P&O method. The experimental results show that compared with the traditional P&O algorithm, the proposed algorithm can fast track the global MPP, tracking speed increases by 60% and the relative error decreased by 20%. Moreover, the system becomes more stable near the MPP, the fluctuations of output power is greatly reduced, and thus make full use of solar energy. 相似文献
106.
Catalytic Hydrocracking of a Bitumen‐Derived Asphaltene over NiMo/γ‐Al2O3 at Various Temperatures
下载免费PDF全文
![点击此处可从《化学工程与技术》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Hydrocracking of a bitumen‐derived asphaltene over NiMo/γ‐Al2O3 was investigated in a microbatch reactor at varying temperatures. The molar kinetics of asphaltene cracking reaction was examined by fitting the experimental data. Below a defined temperature, the molar reaction showed the first‐order kinetic feature while at higher temperatures secondary reactions such as coke formation became significant, causing deviation of the reaction behavior from the proposed first‐order kinetic model. Selectivity analysis proved that dominant products varied from gases to liquids to gases with increasing temperature, shifting the dominant reaction from C–S bonds cleavage to C–C bonds cleavage. 相似文献
107.
The eutectic 80Au/20Sn solder alloy is widely used in high power electronics and optoelectronics packaging. In this study, low cycle fatigue behavior of a eutectic 80Au/20Sn solder alloy is reported. The 80Au/20Sn solder shows a quasi-static fracture characteristic at high strain rates, and then gradually transforms from a transgranular fracture (dominated by fatigue damage) to intergranular fracture (dominated by creep damage) at low strain rates with increasing temperature. Coffin-Manson and Morrow models are proposed to evaluate the low cycle fatigue behavior of the 80Au/20Sn solder. Besides, the 80Au/20Sn solder has enhanced fatigue resistance compared to the 63Sn/37Pb solder. 相似文献
108.
To improve the electrochemical properties of rare-earth–Mg–Ni-based hydrogen storage alloys, the effects of stoichiometry and Cu-substitution on the phase structure and thermodynamic properties of the ... 相似文献
109.
基于传统AI-EBG结构,提出了一种小尺寸的增强型电磁带隙结构,实现了从0.5~9.4 GHz的宽频带-40 dB噪声抑制深度,且下截止频率减少到数百MHz,可有效抑制多层PCB板间地弹噪声。文中同时研究了EBG结构在高速电路应用时的信号完整性问题,使用差分信号方案可改善信号完整性。 相似文献