全文获取类型
收费全文 | 742091篇 |
免费 | 9655篇 |
国内免费 | 2004篇 |
专业分类
电工技术 | 13866篇 |
综合类 | 1034篇 |
化学工业 | 111750篇 |
金属工艺 | 27084篇 |
机械仪表 | 21112篇 |
建筑科学 | 18424篇 |
矿业工程 | 2943篇 |
能源动力 | 20350篇 |
轻工业 | 67070篇 |
水利工程 | 6916篇 |
石油天然气 | 11572篇 |
武器工业 | 44篇 |
无线电 | 87174篇 |
一般工业技术 | 141439篇 |
冶金工业 | 145353篇 |
原子能技术 | 14032篇 |
自动化技术 | 63587篇 |
出版年
2021年 | 6343篇 |
2020年 | 4631篇 |
2019年 | 5937篇 |
2018年 | 10068篇 |
2017年 | 9788篇 |
2016年 | 10278篇 |
2015年 | 7214篇 |
2014年 | 12032篇 |
2013年 | 34129篇 |
2012年 | 19079篇 |
2011年 | 26619篇 |
2010年 | 20905篇 |
2009年 | 23665篇 |
2008年 | 24336篇 |
2007年 | 24028篇 |
2006年 | 21123篇 |
2005年 | 19434篇 |
2004年 | 18748篇 |
2003年 | 18422篇 |
2002年 | 17603篇 |
2001年 | 17741篇 |
2000年 | 16641篇 |
1999年 | 17678篇 |
1998年 | 44968篇 |
1997年 | 31746篇 |
1996年 | 24522篇 |
1995年 | 18545篇 |
1994年 | 16457篇 |
1993年 | 16012篇 |
1992年 | 11669篇 |
1991年 | 10978篇 |
1990年 | 10791篇 |
1989年 | 10486篇 |
1988年 | 9940篇 |
1987年 | 8658篇 |
1986年 | 8647篇 |
1985年 | 9871篇 |
1984年 | 9088篇 |
1983年 | 8248篇 |
1982年 | 7665篇 |
1981年 | 7853篇 |
1980年 | 7392篇 |
1979年 | 7238篇 |
1978年 | 6843篇 |
1977年 | 8346篇 |
1976年 | 10897篇 |
1975年 | 5986篇 |
1974年 | 5706篇 |
1973年 | 5790篇 |
1972年 | 4766篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
Effect of Thickness of the p-AlGaN Electron Blocking Layer on the Improvement of ESD Characteristics in GaN-Based LEDs 总被引:1,自引:0,他引:1
Chung-Hsun Jang Sheu J.K. Tsai C.M. Shei S.C. Lai W.C. Chang S.J. 《Photonics Technology Letters, IEEE》2008,20(13):1142-1144
The following letter presents a study regarding GaN-based light-emitting diodes (LEDs) with p-type AlGaN electron blocking layers (EBLs) of different thicknesses. The study revealed that the LEDs could endure higher electrostatic discharge (ESD) levels as the thickness of the AlGaN EBL increased. The observed improvement in the ESD endurance ability could be attributed to the fact that the thickened p-AlGaN EBL may partly fill the dislocation-related pits that occur on the surface of the InGaN-GaN multiple-quantum well (MQW) and that are due to the strain and the low-temperature-growth process. If these dislocation-related pits are not partly suppressed, they will eventually result in numerous surface pits associated with threading dislocations that intersect the InGaN-GaN (MQW), thereby reducing the ESD endurance ability. The results of the experiment show that the ESD endurance voltages could increase from 1500 to 6000 V when the thickness of the p-AlGaN EBL in the GaN LEDs is increased from 32.5 to 130 nm, while the forward voltages and light output powers remained almost the same. 相似文献
972.
Ann R Thryft 《电子设计技术》2008,15(7):78-78,80,82,84,86
数年来,具有10Gbps速度的下一代以太网一直处于即将成为主流的状况。一段时间以来,网络的某些区域已在使用光学技术,并且随着流量的增加,对10GbE数据速率的需求正在增长。但是,需要一种比上一代以太网复杂许多的技术,用于在100m长的铜缆上运行10GbE。这一要求导致了昂贵的MAC(媒体访问控制器)和交换芯片,以及昂贵而又不方便的PHY层接口芯片,由此限制了快速LAN用于那些覆盖数据中心内较短距离的高性能应用。 相似文献
973.
In this time of flat, team-based and technology-enabled organizations the effectiveness of communication and team leadership practices will be more important than ever before. Therefore, we believe that some of the earlier, time-tested classic works on group dynamics and leadership are worthy of re-reading. We are particularly impressed by how relevant one of the oldest classics, Benne and Sheats' (1948) article on functional roles of group members, remains to this day. 相似文献
974.
Porous carbon nanofibers are synthesized by CVD method from acetylene with use of iron-containing catalysts. Activation of the nanofibers in melted potassium hydroxide results in increasing surface area from initial 300–400 m2 g−1 to 1700 m2 g−1. As follows from XRD data, activated nanofibers do not contain regular packages of graphene layers, but retain high electric conductivity. Deposition of copper improves electrochemical hydrogen storing characteristics of carbon nanofibers. Carbon nanomaterials obtained can be used as hydrogen storing materials in batteries instead of hydride forming metals. 相似文献
975.
M Isabel Sánchez de Rojas Julián Rivera Moisés Frías Félix Marín 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(3):209-217
Copper slag is a by‐product generated during smelting to extract copper metal from the ore. The copper slag obtained may exhibit pozzolanic activity and may therefore be used in the manufacture of addition‐containing cements. In this paper the effect of the incorporation of the copper slag in cement is measured. Blends of copper slag with Portland cement generally possess properties equivalent to Portland cement containing fly ash, but very different to the silica fume incorporation. Copper slag and fly ash reduce the heat of hydration more effectively than silica fume in mortars. The replacement of 30% cement by copper slag reduces the flexural and compressive strength in a similar way to fly ash; however, after 28 days, the reduction is less than the percentage of substitution. Hydrated calcium aluminate phases were analysed using scanning electron microscopy (SEM) and X‐ray diffraction (XRD) techniques. The pozzolanic activity of copper slag is similar to that of fly ash and higher than silica fume. In the presence of low water/cement ratios, certain pozzolanic materials produce a very compact cement paste that limits the space available for hydration products, a determining factor in the formation of hydrated calcium aluminates. SEM was found to be a useful analytical technique when aluminates are formed and can be clearly detected by XRD. Copyright © 2008 Society of Chemical Industry 相似文献
976.
A membrane reactor containing different types of ZSM-5/porous SS membranes was used to perform the xylene isomerization reaction. The parent Na-ZSM-5 layer was synthesized by secondary growth on top of porous stainless steel tubes. The xylene isomerization reaction was carried out at different temperatures in the membrane reactor and in a fixed-bed reactor of identical geometry for comparison. Two different kinds of membranes were prepared by ion exchange: a Pt/H-ZSM-5 catalytic membrane and two Ba-ZSM-5 composites with different Ba2+ concentration. The p-xylene production using 100% exchanged Ba-membrane was about 28% higher than the fixed-bed reactor at 370 °C, when m-xylene was fed. 相似文献
977.
The photoelectric parameters of silicon solar cells degraded under the action of 60Co gamma-radiation can be partly restored using an ultrasonic treatment (UST). The growth of the maximum output power of solar cells after the UST is related to a redistribution of the radiation defects and an increase in the homogeneity of a semiconductor crystal structure. 相似文献
978.
Power distribution systems have been significantly affected by many outage-causing events. Good fault cause identification can help expedite the restoration procedure and improve the system reliability. However, the data imbalance issue in many real-world data sets often degrades the fault cause identification performance. In this paper, the E-algorithm, which is extended from the fuzzy classification algorithm by Ishibuchi to alleviate the effect of imbalanced data constitution, is applied to Duke Energy outage data for distribution fault cause identification. Three major outage causes (tree, animal, and lightning) are used as prototypes. The performance of E-algorithm on real-world imbalanced data is compared with artificial neural network. The results show that the E-algorithm can greatly improve the performance when the data are imbalanced 相似文献
979.
980.
R. A. Borzooei M. Bakhshi M. Mashinchi 《Soft Computing - A Fusion of Foundations, Methodologies and Applications》2008,12(8):739-749
In this paper, we study the lattice structure of some fuzzy algebraic systems such as (G-)fuzzy groups, some fuzzy ordered
algebras and fuzzy hyperstructures. We prove that under suitable conditions, these structures form a distributive or modular
lattice.
This research partially is supported by the “ Fuzzy Systems and its Applications Center of Excelence, Shahid Bahonar University
of Kerman, Iran”. 相似文献