全文获取类型
收费全文 | 7847篇 |
免费 | 368篇 |
国内免费 | 21篇 |
专业分类
电工技术 | 160篇 |
综合类 | 21篇 |
化学工业 | 1530篇 |
金属工艺 | 221篇 |
机械仪表 | 404篇 |
建筑科学 | 170篇 |
矿业工程 | 6篇 |
能源动力 | 298篇 |
轻工业 | 617篇 |
水利工程 | 42篇 |
石油天然气 | 22篇 |
无线电 | 1460篇 |
一般工业技术 | 1359篇 |
冶金工业 | 721篇 |
原子能技术 | 91篇 |
自动化技术 | 1114篇 |
出版年
2023年 | 62篇 |
2022年 | 86篇 |
2021年 | 126篇 |
2020年 | 110篇 |
2019年 | 132篇 |
2018年 | 168篇 |
2017年 | 148篇 |
2016年 | 218篇 |
2015年 | 189篇 |
2014年 | 314篇 |
2013年 | 545篇 |
2012年 | 444篇 |
2011年 | 485篇 |
2010年 | 353篇 |
2009年 | 428篇 |
2008年 | 366篇 |
2007年 | 336篇 |
2006年 | 337篇 |
2005年 | 289篇 |
2004年 | 277篇 |
2003年 | 252篇 |
2002年 | 277篇 |
2001年 | 206篇 |
2000年 | 188篇 |
1999年 | 178篇 |
1998年 | 375篇 |
1997年 | 221篇 |
1996年 | 162篇 |
1995年 | 133篇 |
1994年 | 114篇 |
1993年 | 114篇 |
1992年 | 61篇 |
1991年 | 72篇 |
1990年 | 56篇 |
1989年 | 58篇 |
1988年 | 41篇 |
1987年 | 44篇 |
1986年 | 39篇 |
1985年 | 31篇 |
1984年 | 29篇 |
1983年 | 20篇 |
1982年 | 14篇 |
1981年 | 23篇 |
1980年 | 16篇 |
1979年 | 9篇 |
1978年 | 15篇 |
1977年 | 14篇 |
1976年 | 21篇 |
1974年 | 6篇 |
1973年 | 8篇 |
排序方式: 共有8236条查询结果,搜索用时 0 毫秒
41.
Performance of the polymer- and oxide-supported triphase catalysts and effect of ultrasound on their stabilities 总被引:1,自引:0,他引:1
Hsieh-Ting Chung Hung-Shan Weng 《Journal of the Chinese Institute of Chemical Engineers》2008,39(5):449-455
In this study, several trialkylamines were immobilized on chloromethylated polystyrene (CMPS), silica gel, and alumina to prepare triphase catalysts for catalyzing the etherification reaction of allyl bromide (the organic reactant) and sodium phenolate (the aqueous reactant). The reactor was agitated mechanically or with the aid of ultrasonic vibration. Performances of the prepared catalysts were compared, and the effect of imposing ultrasound was investigated based on the activity, selectivity, and stability of the catalyst. Experimental results show that tri-n-propylamine is the best active species when CMPS is used as the support, while tri-n-butylamine is the best when SiO2 and Al2O3 are employed as the supports. The CMPS-supported catalyst is far better than the SiO2- and Al2O3-supported catalysts in activity and selectivity but not in stability. Imposing the ultrasound can effectively increase the reaction rate. Mechanical agitation at a low speed with the imposition of ultrasonic vibration not only results in a conversion slightly higher than the case with a high mechanical agitation speed without ultrasonic vibration, but also gives a constant stability for the CMPS-supported catalyst. 相似文献
42.
43.
Uniaxial tensile tests in various directions following uniaxial extension, equibiaxial stretching or plane strain rolling have been performed to study the effects of changes in strain path on the anisotropy of yield stresses of aluminium-killed low-carbon steel and 70-30 brass sheets. The anisotropy could be predicted from the specimen textures, if dislocation structure were equiaxed, as in the case of equibiaxial stretching. However, elongated dislocation cell structures, developed in the steel specimens prestrained in uniaxial tension or plane strain rolling, gave rise to the second-stage yield stresses higher than predicted from textures in the directions different from the maximum prestrain direction. Planar dislocation structures in the brass specimens prestrained in uniaxial tension or plane strain rolling gave the second-stage yield stresses lower than predicted from the textures in the directions different from the maximum prestrain direction. The phenomena are discussed based on textures and dislocation structures. 相似文献
44.
P Demoly D Jaffuel KF Chung J Bousquet FB Michel P Godard 《Canadian Metallurgical Quarterly》1996,25(40):2025-2030
The efficacy of corticosteroids in asthma has been recognized over 40 years ago. Since that time, the advent of inhaled forms has further improved the therapeutic of these drugs which are now recognized as the fundamental treatment for asthma, and described in detail by national and international consensus. Based on a large body of literature, it can now be recommended to prescribe inhaled corticosteroids for symptomatic asthma patients. Long-term treatment is required and dosage not exceeding 1000 micrograms/d (beclometasone dipropionate equivalent) in adults are safe. Differences in the pharmacological characteristics of the various systematic and inhaled corticosteroids can be used to adapt treatment and administration route to each patient and achieve good patient compliance with optimal therapeutic efficacy. 相似文献
45.
This paper describes a simple and effective way to modify an existing hard-switched flyback power converter into a circuit with zero-voltage switching (ZVS) and zero-current switching (ZCS). The key improvement is to turn the unattractive features of the coupled inductor leakage inductance and snubber capacitor into attractive ones. The coupled inductor leakage inductance and snubber are used to form a quasi-resonant circuit to facilitate ZVS/ZCS of all power devices. The operating principles of the power converter and experimental results are presented 相似文献
46.
Kow Ming Chang Yuan Hung Chung Gin Ming Lin 《Electron Device Letters, IEEE》2002,23(5):255-257
Studies the anomalous variations of the OFF-state leakage current (IOFF) in n-channel poly-Si thin-film transistors (TFTs) under static stress. The dominant mechanisms for the anomalous IOFF can be attributed to (1) IOFF increases due to channel hot electrons trapping at the gate oxide/channel interface and silicon grain boundaries and (2) IOFF decreases due to hot holes accumulated/trapped near the channel/bottom oxide interface near the source region. Under the stress of high drain bias, serious impact ionization effect will occur to generate hot electrons and hot holes near the drain region. Some of holes will be injected into the gate oxide due to the vertical field (~(V_Gstress V_Dstress)/T OX) near the drain and the others will be migrated from drain to source along the channel due to lateral electric field (~V_Dstress/LCH) 相似文献
47.
48.
P.-C. Chung Author Vitae C.-L. Huang Author Vitae E.-L. Chen Author Vitae 《Pattern recognition》2007,40(3):1066-1077
Motion vector plays one significant feature in moving object segmentation. However, the motion vector in this application is required to represent the actual motion displacement, rather than regions of visually significant similarity. In this paper, region-based selective optical flow back-projection (RSOFB) which back-projects optical flows in a region to restore the region's motion vector from gradient-based optical flows, is proposed to obtain genuine motion displacement. The back-projection is performed based on minimizing the projection mean square errors of the motion vector on gradient directions. As optical flows of various magnitudes and directions provide various degrees of reliability in the genuine motion restoration, the optical flows to be used in the RSOFB are optimally selected based on their sensitivity to noises and their tendency in causing motion estimation errors. In this paper a deterministic solution is also derived for performing the minimization and obtaining the genuine motion magnitude and motion direction. 相似文献
49.
Drawing Power Law Graphs Using a Local/Global Decomposition 总被引:1,自引:0,他引:1
50.
Young-Huang Chou Shew-Jon Lin Shyh-Jong Chung 《Vehicular Technology, IEEE Transactions on》2002,51(1):194-199
In this paper, grating metal structures with broad and flat back-scattering field patterns are studied for possible applications in a vehicle collision avoidance system. The two-dimensional TE scattering of a planar grating structure and a curved grating structure are analyzed at a frequency of 77 GHz. For the planar structure, the method of moments and Floquet's theorem are used to solve the induced current and the resultant back-scattering field. Based on the results of the planar structure, the scattering field of the curved grating structure is obtained by using a perturbation method. The influence on the field pattern of the curvature as well as other structure parameters, such as the width and geometry of each period in the grating structure, is investigated 相似文献