全文获取类型
收费全文 | 83892篇 |
免费 | 8482篇 |
国内免费 | 5546篇 |
专业分类
电工技术 | 7165篇 |
技术理论 | 3篇 |
综合类 | 8467篇 |
化学工业 | 11433篇 |
金属工艺 | 5352篇 |
机械仪表 | 5838篇 |
建筑科学 | 6192篇 |
矿业工程 | 3068篇 |
能源动力 | 2398篇 |
轻工业 | 8196篇 |
水利工程 | 2688篇 |
石油天然气 | 3078篇 |
武器工业 | 1173篇 |
无线电 | 8462篇 |
一般工业技术 | 7785篇 |
冶金工业 | 3403篇 |
原子能技术 | 1273篇 |
自动化技术 | 11946篇 |
出版年
2024年 | 356篇 |
2023年 | 1038篇 |
2022年 | 2587篇 |
2021年 | 3327篇 |
2020年 | 2568篇 |
2019年 | 1855篇 |
2018年 | 2001篇 |
2017年 | 2410篇 |
2016年 | 2159篇 |
2015年 | 3475篇 |
2014年 | 4460篇 |
2013年 | 5333篇 |
2012年 | 6570篇 |
2011年 | 6936篇 |
2010年 | 6596篇 |
2009年 | 6610篇 |
2008年 | 6591篇 |
2007年 | 6432篇 |
2006年 | 5878篇 |
2005年 | 4843篇 |
2004年 | 3543篇 |
2003年 | 2433篇 |
2002年 | 2413篇 |
2001年 | 2213篇 |
2000年 | 1686篇 |
1999年 | 955篇 |
1998年 | 477篇 |
1997年 | 429篇 |
1996年 | 357篇 |
1995年 | 256篇 |
1994年 | 232篇 |
1993年 | 184篇 |
1992年 | 128篇 |
1991年 | 125篇 |
1990年 | 78篇 |
1989年 | 76篇 |
1988年 | 56篇 |
1987年 | 37篇 |
1986年 | 39篇 |
1985年 | 26篇 |
1984年 | 14篇 |
1983年 | 15篇 |
1982年 | 9篇 |
1981年 | 13篇 |
1980年 | 43篇 |
1979年 | 14篇 |
1965年 | 7篇 |
1959年 | 11篇 |
1958年 | 3篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
通过电镀法制备片状磁性吸收剂,用SEM、XRD等手段对其进行表征。用网络分析仪测试了不同工艺条件下吸收剂样品2~18GHz的电磁参数,并结合晶粒尺寸因素研究了不同工艺条件下对吸收剂电磁参数的影响.结果表明,不同的工艺条件对吸收剂电磁参数的影响具有规律性,可通过合理配置工艺参数来提高吸收剂的吸波性能。 相似文献
22.
Xue‐Bing Zhao Lei Wang De‐Hua Liu 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(6):950-956
Previous work has shown that the enzymatic hydrolysis of sugarcane bagasse could be greatly enhanced by peracetic acid (PAA) pretreatment. There are several factors affecting the enzymatic digestibility of the biomass, including lignin and hemicelluloses content, cellulose crystallinity, acetyl group content, accessible surface area and so on. The objective of this work is to analyze the mechanism of the enhancement of enzymatic digestibility caused by PAA pretreatment. Delignification resulted in an increase of the surface area and reduction of the irreversible absorption of cellulase, which helped to increase the enzymatic digestibility. The Fourier transform infrared (FTIR) spectrum showed that the absorption peaks of aromatic skeletal vibrations were weakened or disappeared after PAA pretreatment. However, the infrared crystallization index (N.O'KI) was increased. X‐ray diffraction (XRD) analysis indicated that the crystallinity of PAA‐treated samples was increased owing to the partial removal of amorphous lignin and hemicelluloses and probable physical change of cellulose. The effect of acetyl group content on enzymatic digestibility is negligible compared with the degree of delignification and crystallinity. The results indicate that enhancement of enzymatic digestibility of sugarcane bagasse by PAA pretreatment is achieved mainly by delignification and an increase in the surface area and exposure of cellulose fibers. Copyright © 2008 Society of Chemical Industry 相似文献
23.
Local residence time,residence revolution,and residence volume distributions in twin‐screw extruders
Xian‐Ming Zhang Lian‐Fang Feng Sandrine Hoppe Guo‐Hua Hu 《Polymer Engineering and Science》2008,48(1):19-28
This work was aimed at studying the overall, partial, and local residence time distributions (RTD); overall, partial and local residence revolution distributions (RRD) and overall, partial and local residence volume distributions (RVD) in a co‐rotating twin screw extruder, on the one hand; and establishing the relationships among them, on the other hand. Emphasis was placed on the effects of the type and geometry of mixing elements (a gear block and various types of kneading elements differing in staggering angle) and process parameters on the RTD, RRD and RVD. The overall and partial RTD were directly measured in‐line during the extrusion process and the local ones were calculated by deconvolution based on a statistical theory. The local RTD allowed comparing the mixing performance of mixing elements. Also it was confirmed both experimentally and theoretically that specific throughput, defined as a ratio of throughput (Q) over screw speed (N), controlled all the above three types of residence distributions, be they local, partial or overall. The RRD and RVD do not provide more information on an extrusion process than the corresponding RTD. Rather they are different ways of representing the same phenomena. POLYM. ENG. SCI., 48:19–28, 2008. © 2007 Society of Plastics Engineers 相似文献
24.
试图构建企业以顾客为中心的营销策略过程的一般模型,并利用已有的研究成果对其构成要素进行了深入分析.在此基础上,对此模型所形成的企业营销策略循环进行分类分析,并以实例说明它们所代表的现实意义,从而为企业的决策提供帮助. 相似文献
25.
Wei Li Zhang Wei Pan Bin Luo Xi Hua Zou Meng Yao Wang 《Photonics Technology Letters, IEEE》2008,20(9):712-714
A theoretical construction of one-to-many (OTM) and many-to-one (MTO) chaos synchronization communications using semiconductor lasers is presented. One center laser provides strong injections (strong link) to other side lasers, and the side lasers also provide weak injections (weak link) to the center one. Simulation results show that the side lasers synchronize with the center laser through injection-locking. In addition, messages transmitted via the strong links or the weak links experience strong chaos pass filtering, enabling us to realize OTM and MTO communications. 相似文献
26.
Yue Rong Yingbo Hua Swami A. Swindlehurst A.L. 《Signal Processing, IEEE Transactions on》2008,56(2):686-701
A space-time optimal power schedule for multiple distributed multiple-input multiple-output (MIMO) links without the knowledge of the instantaneous channel state information (CSI) at the transmitting nodes is proposed. A readily computable expression for the ergodic sum capacity of the MIMO links is derived. Based on this expression, which is a non-convex function of power allocation vectors, a projected gradient algorithm is developed to optimize the power allocation. For a symmetric set of MIMO links with independent identically distributed channels, it is observed that the space-time optimal power schedule reduces to a uniform isotropic power schedule when nominal interference is low, or to an orthogonal isotropic power schedule when nominal interference is high. Furthermore, the transition region between the latter two schedules is seen to be very sharp in terms of nominal interference-to-noise ratio (INR). For MIMO links with correlated channels, the corresponding space-time optimal power schedule is developed based on the knowledge of the channel correlation matrices. It is shown that the channel correlation has a great impact on the ergodic capacity and the optimality of different power scheduling approaches. 相似文献
27.
塔顶放大器在移动通信领域有较为广泛的应用,它通过降低(改善)等效接收噪声系数,从而提高上行接收灵敏度。本文将简要介绍塔顶放大器的应用和提高接收机灵敏度的计算。 相似文献
28.
29.
CHENG Xiang 《半导体光子学与技术》2004,(4)
Amorphous carbon (a-C) films and amorphous carbon films incorporating with the nitrogen (a-C∶N) were deposited on silicon substrates in a radio-frequency driven plasma enhanced chemical vapour deposition system, while the surface electrical properties of films were investigated by electrochemical capacitance-voltage measurements. It was examined the effect of the interface defects on the properties and deduced that the conducting type of a-C∶N films was n-type. Subsequently, a comparative studies of a-C and a-C∶N films were performed by photoluminescence spectra depending on the temperature. With the decrease of the temperature, the main band with peak energy of 2.48 eV in the a-C∶N films was more intense compared with the other three bands caused by amorphous C in the a-C films. 相似文献
30.