全文获取类型
收费全文 | 35376篇 |
免费 | 3722篇 |
国内免费 | 1985篇 |
专业分类
电工技术 | 2371篇 |
技术理论 | 4篇 |
综合类 | 2678篇 |
化学工业 | 5463篇 |
金属工艺 | 2111篇 |
机械仪表 | 2211篇 |
建筑科学 | 2807篇 |
矿业工程 | 1114篇 |
能源动力 | 1039篇 |
轻工业 | 2423篇 |
水利工程 | 750篇 |
石油天然气 | 1891篇 |
武器工业 | 330篇 |
无线电 | 4457篇 |
一般工业技术 | 4442篇 |
冶金工业 | 1470篇 |
原子能技术 | 448篇 |
自动化技术 | 5074篇 |
出版年
2024年 | 201篇 |
2023年 | 653篇 |
2022年 | 1222篇 |
2021年 | 1836篇 |
2020年 | 1280篇 |
2019年 | 1042篇 |
2018年 | 1194篇 |
2017年 | 1249篇 |
2016年 | 1091篇 |
2015年 | 1551篇 |
2014年 | 2059篇 |
2013年 | 2219篇 |
2012年 | 2534篇 |
2011年 | 2666篇 |
2010年 | 2297篇 |
2009年 | 2174篇 |
2008年 | 2213篇 |
2007年 | 2035篇 |
2006年 | 1938篇 |
2005年 | 1627篇 |
2004年 | 1084篇 |
2003年 | 906篇 |
2002年 | 814篇 |
2001年 | 695篇 |
2000年 | 667篇 |
1999年 | 629篇 |
1998年 | 536篇 |
1997年 | 486篇 |
1996年 | 431篇 |
1995年 | 403篇 |
1994年 | 311篇 |
1993年 | 248篇 |
1992年 | 180篇 |
1991年 | 105篇 |
1990年 | 114篇 |
1989年 | 112篇 |
1988年 | 72篇 |
1987年 | 49篇 |
1986年 | 34篇 |
1985年 | 26篇 |
1984年 | 18篇 |
1983年 | 14篇 |
1982年 | 17篇 |
1981年 | 9篇 |
1980年 | 18篇 |
1979年 | 4篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1970年 | 2篇 |
1959年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
62.
63.
64.
Enhanced light output in nitride-based light-emitting diodes by roughening the mesa sidewall 总被引:1,自引:0,他引:1
Chia-Feng Lin Zhong-Jie Yang Jing-Hui Zheng Jing-Jie Dai 《Photonics Technology Letters, IEEE》2005,17(10):2038-2040
In this letter, we will report on a nitride-based light emitting diode with a mesa sidewall roughening process that increases light output power. The fabricated GaN-based light-emitting diode (LED) wafers were first treated through a photoelectrochemical (PEC) process. The Ga/sub 2/O/sub 3/ layers then formed around the GaN : Si n-type mesa sidewalls and the bottoms mesa etching regions. Selective wet oxidation occurred at the mesa sidewall between the p- and the n-type GaN interface. The light output power of the PEC treated LED was seen to increase by about 82% which was caused by a reduced index reflectance of GaN-Ga/sub 2/O/sub 3/-air layers, by a rough Ga/sub 2/O/sub 3/ surface, by a microroughening of the GaN sidewall surface, and by a selective oxidation step profile of the mesa sidewall that increases the light-extraction efficiency from the mesa sidewall direction. Consequently, this wet PEC treated process is suitable for high powered nitride-based LEDs lighting applications. 相似文献
65.
On effective offloading services for resource-constrained mobile devices running heavier mobile internet applications 总被引:1,自引:0,他引:1
Kun Yang Shumao Ou Hsiao-Hwa Chen 《Communications Magazine, IEEE》2008,46(1):56-63
Rapid advances in wireless mobile network technologies and mobile handsets (MHs) facilitate ubiquitous infrastructure that can support a range of mobile services and applications in addition to conventional mobile Internet access. One recent trend is to effectively run desktop PC-oriented heavier applications on MHs. However, due to their miniature, portable size, MHs are resource-constrained and therefore, running these applications directly on an MH is not satisfactory given a user's expectations. To cope with this problem, this article proposes a novel offloading service that can seamlessly offload some of the tasks of a mobile application from an MH to nearby, resource-rich PCs (called surrogates). The system architecture and key components of the proposed offloading service are presented, prototyped, and evaluated. The results of experiments and simulations have demonstrated the effectiveness and efficiency of this offloading service for mobile applications. 相似文献
66.
A high‐melt‐strength polypropylene (HMSPP) was prepared using a twin‐screw reactive extruder from a commercial isotactic polypropylene through two stages, first, maleic anhydride is grafted to polypropylene to obtain a maleic anhydride‐grafted polypropylene (PP‐g‐MA), and then the grafted polymer is reacted with epoxy to extend the branched chain. Fourier transformed infrared spectroscopy indicated that maleic anhydride was grafted on polypropylene and reacted with epoxy. Melt flow rate and sag resistance test showed that the melt strength of the HMSPP improved considerably. Differential scanning calorimetry test showed that the long chain branches (LCBs) act as a nucleating agent in the crystallization of the HMSPP, which leads to a high crystallization temperature and crystallinity. Furthermore, the LCB efficiency of the HMSPP can also be calculated by analyzing its rheological property. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers 相似文献
67.
湖南省水库与城市水资源供求评价 总被引:1,自引:0,他引:1
对湖南省29个城市及靠近这些城市的67座大中型水库,采用模糊数学多级多因子综合评价方法,按水库人均供水量、水质类别、水库向城市可供水率等8个评价指标及其隶属度,评价得到2020年湖南省水库向城市可供水资源的程度.分析结果表明:至2020年,近城水库供水资源完全满足城市需水量的有7个城市,基本满足需水的城市有10座,说明在当前与将来城市供水资源紧缺的形势下,开发现有水库水资源,向城市供水意义重大. 相似文献
68.
嵌入式Web服务器在中小水电信息采集系统中的应用 总被引:1,自引:1,他引:0
中小水电站大多数建在偏远山区,并网管理难度非常大,解决中小水电站的信息传输是主要的技术难点之一。随着计算机技术的发展,嵌入式Web服务器技术在远程监控和实时通信系统中的应用越来越广泛。将Web技术引入中小水电站信息采集系统中,可以实现对中小水电站基于浏览器方式的远程监控。文中结合中小水电站通信结构,介绍了嵌入式Web服务器技术在中小水电站信息采集系统中的应用。 相似文献
69.
Guo Haitao Qiao Weihong Ba Yan Li Zongshi Jin Kun Peng Qinji 《Petroleum Science and Technology》2006,24(1):51-60
The GC/MS and NMR analysis of the reaction products of naphthalene with 1-bromohexane were reported. The products obtained were suggested to have six isomers of linear hexylnaphthalene and the structure of each isomer was determined by GC/MS and NMR spectra. For the first time, the unique chemical shift data were obtained. The content of each isomer calculated by 1H NMR and 13C NMR spectra was consistent with that by GC/MS spectra, which confirmed the accuracy of NMR data. 相似文献
70.
The catalysts of CeO2 and the mixture of CeO2 and CuO were prepared, and the activities of these catalysts for completely oxidizing benzene were studied.The results show that the optimal proportion of CeO2/CuO is 6: 4.The highest temperature at which benzene was completely oxidized on these catalysts at different airspeed was measured.Compared these catalysts with the noble metal used, our catalysts had superiority in the resources and the industrial cost besides good activities. 相似文献