全文获取类型
收费全文 | 64837篇 |
免费 | 5416篇 |
国内免费 | 2845篇 |
专业分类
电工技术 | 3666篇 |
技术理论 | 7篇 |
综合类 | 4275篇 |
化学工业 | 11099篇 |
金属工艺 | 3612篇 |
机械仪表 | 3976篇 |
建筑科学 | 5500篇 |
矿业工程 | 1893篇 |
能源动力 | 1887篇 |
轻工业 | 4145篇 |
水利工程 | 1196篇 |
石油天然气 | 4543篇 |
武器工业 | 456篇 |
无线电 | 7144篇 |
一般工业技术 | 8087篇 |
冶金工业 | 3132篇 |
原子能技术 | 725篇 |
自动化技术 | 7755篇 |
出版年
2024年 | 230篇 |
2023年 | 1058篇 |
2022年 | 1749篇 |
2021年 | 2470篇 |
2020年 | 1920篇 |
2019年 | 1665篇 |
2018年 | 1887篇 |
2017年 | 2125篇 |
2016年 | 1933篇 |
2015年 | 2392篇 |
2014年 | 3261篇 |
2013年 | 3718篇 |
2012年 | 4139篇 |
2011年 | 4468篇 |
2010年 | 3925篇 |
2009年 | 3725篇 |
2008年 | 3637篇 |
2007年 | 3545篇 |
2006年 | 3603篇 |
2005年 | 3110篇 |
2004年 | 2108篇 |
2003年 | 1890篇 |
2002年 | 1669篇 |
2001年 | 1621篇 |
2000年 | 1667篇 |
1999年 | 1782篇 |
1998年 | 1392篇 |
1997年 | 1174篇 |
1996年 | 1061篇 |
1995年 | 941篇 |
1994年 | 776篇 |
1993年 | 557篇 |
1992年 | 435篇 |
1991年 | 338篇 |
1990年 | 312篇 |
1989年 | 226篇 |
1988年 | 174篇 |
1987年 | 107篇 |
1986年 | 104篇 |
1985年 | 60篇 |
1984年 | 42篇 |
1983年 | 27篇 |
1982年 | 33篇 |
1981年 | 22篇 |
1980年 | 13篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
Yuansheng Jiang Yihan Shao Edward C. Kirby 《Fullerenes, Nanotubes and Carbon Nanostructures》1994,2(4):481-497
An algorithm to generate the molecular graphs of the trivalent clusters is presented. All the polyhedral trivalent cages with 4-16 vertices are enumerated, with particular attention being given to their symmetry, spectra and stability. The relative stability of isomers is not decided solely by their symmetry. A new kind of spectral phenomenon is reported. This is the occurrence of graphs having the same HOMO-LUMO gap, the same E and the same even-order moments. We refer to it as 'pseudo-isospectrality'. 相似文献
172.
173.
This work reports the fabrication and the characterization of a new composite consisting of multiwalled carbon nanotubes (CNTs) and conducting titanium nitride (TiN) with a higher specific surface area ( S BET ), enhanced electrical conductivity (σ), and specific capacitance. With increasing CNT content, the electrical conductivity and electrochemical performance of the CNT–TiN composites gradually increase. In the presence of 5 wt% (12.0 vol%) CNTs, the electrical conductivity and the weight-specific capacitance of CNT–TiN composite are increased by 3.6 times and 54.8% compared with pure TiN, respectively. 相似文献
174.
粗面岩油藏是一种特殊油气藏,已受到国内外油田的广泛关注,但目前国内对粗面岩力学特性的研究还很少。分析了粗面岩的岩性和裂缝发育情况,以岩石力学和弹性力学为理论基础,从岩石的应力-应变曲线和试验的基本原理出发,结合辽河油田小龙湾地区现场实际,通过粗面岩岩心单轴试验,得到了粗面岩的抗压强度、弹性模量、泊松比和抗拉强度等基本岩石力学参数。根据试验得到的应力-应变曲线,结合弹性力学相关理论,得出小龙湾地区粗面岩的力学特性为线弹性,并给出了其基本力学参数的取值范围。谊结果对辽河油田小龙湾地区粗面岩油气藏的压裂设计和油气田开发具有重要的指导意义和参考价值。 相似文献
175.
Ma Weidong Liu Wen Wenmin Wang Luo Yong Bu Qinlian Xiouli Zhao Jiang Shan Li Wei 《Photonics Technology Letters, IEEE》2007,19(15):1115-1117
An athermal 40-channel dense wavelength-division-multiplexing multi/demultiplexer using a novel combination technology is proposed. It consists of one 1times4 100- to 400-GHz spacing interleaver filter and four sub-arrayed-waveguide gratings (AWGs). The temperature-dependent wavelength shift of the combined device is successfully suppressed to 0.058 nm in the -20degC to 70degC temperature range. Moreover, the combined device's adjacent crosstalk (typically -35 dB) is much better than conventional AWGs (typically -25 dB). 相似文献
176.
On the basis of Odum's ecological economic measure of emergy as embodied solar energy, a system account of biomass resource exploitation by agriculture in China 2004 is developed in this paper, which supplements a former study on corresponding long-term historical trends during 1978 to 2000 (Chen et al., 2006. Emergy-based analysis of the Chinese agriculture. Agriculture, Ecosystems and Environment 115, 161–173). The aggregate fluxes and indicators for biomass resource exploitation in China 2004 are calculated and illustrated when compared with those for 2000 to elucidate the latest status of the Chinese agriculture as the exploitation sector for biomass resource. Data sources and algorithm are presented in detail as basic references for related analysis involving the ecological economy of biomass exploitation in agriculture. 相似文献
177.
Ming Jiang Qiang Ji Bruce F McEwen 《IEEE transactions on information technology in biomedicine》2006,10(3):608-617
We propose a model-based automated approach to extracting microtubules from noisy electron tomography volume. Our approach consists of volume enhancement, microtubule localization, and boundary segmentation to exploit the unique geometric and photometric properties of microtubules. The enhancement starts with an anisotropic invariant wavelet transform to enhance the microtubules globally, followed by a three-dimensional (3-D) tube-enhancing filter based on Weingarten matrix to further accentuate the tubular structures locally. The enhancement ends with a modified coherence-enhancing diffusion to complete the interruptions along the microtubules. The microtubules are then localized with a centerline extraction algorithm adapted for tubular objects. To perform segmentation, we novelly modify and extend active shape model method. We first use 3-D local surface enhancement to characterize the microtubule boundary and improve shape searching by relating the boundary strength with the weight matrix of the searching error. We then integrate the active shape model with Kalman filtering to utilize the longitudinal smoothness along the microtubules. The segmentation improved in this way is robust against missing boundaries and outliers that are often present in the tomography volume. Experimental results demonstrate that our automated method produces results close to those by manual process and uses only a fraction of the time of the latter. 相似文献
178.
A novel dynamic survivable routing in WDM optical networks with/without sparse wavelength conversion
Vinh Trong Le Xiaohong Jiang Son Hong Ngo Susumu Horiguchi Yasushi Inoguchi 《Optical Switching and Networking》2006,3(3-4):173-190
In this paper, we study the dynamic survivable routing problem, both in optical networks without wavelength conversion and in optical networks with sparse wavelength conversion, and propose a novel hybrid algorithm for it based on the combination of mobile agents technique and genetic algorithms (GA). By keeping a suitable number of mobile agents in the network to cooperatively explore the network states and continuously report cycles (that are formed by two disjoint-link routes) into the routing tables, our new hybrid algorithm can promptly determine the first population of cycles for a new request based on the routing table of its source node, without the time consuming process associated with current GA-based lightpath protection schemes. We further improve the performance of our algorithm by introducing a more advanced fitness function that is suitable for both the above networks. Extensive simulation studies on the ns-2 network simulator show that our hybrid algorithm achieves a significantly lower blocking probability than the conventional survivable routing algorithms for all the cases we studied. 相似文献
179.
近十年来,浙江玩具产业异军突起,逐渐成为一个玩具大省。但是,国内玩具界已进入一个群雄逐鹿的时代。浙江玩具业发展何去何从?本文从战略的高度,提出关键在于玩具业内人士把握良机,创建有中国特色、浙江特色的自主品牌.值得业界人士一读。[编者按] 相似文献
180.