全文获取类型
收费全文 | 6407篇 |
免费 | 263篇 |
国内免费 | 23篇 |
专业分类
电工技术 | 93篇 |
综合类 | 14篇 |
化学工业 | 1151篇 |
金属工艺 | 274篇 |
机械仪表 | 143篇 |
建筑科学 | 286篇 |
矿业工程 | 5篇 |
能源动力 | 190篇 |
轻工业 | 460篇 |
水利工程 | 66篇 |
石油天然气 | 44篇 |
无线电 | 783篇 |
一般工业技术 | 983篇 |
冶金工业 | 1227篇 |
原子能技术 | 42篇 |
自动化技术 | 932篇 |
出版年
2023年 | 40篇 |
2022年 | 71篇 |
2021年 | 124篇 |
2020年 | 84篇 |
2019年 | 103篇 |
2018年 | 126篇 |
2017年 | 117篇 |
2016年 | 136篇 |
2015年 | 126篇 |
2014年 | 155篇 |
2013年 | 390篇 |
2012年 | 259篇 |
2011年 | 304篇 |
2010年 | 233篇 |
2009年 | 264篇 |
2008年 | 315篇 |
2007年 | 306篇 |
2006年 | 240篇 |
2005年 | 210篇 |
2004年 | 217篇 |
2003年 | 189篇 |
2002年 | 165篇 |
2001年 | 126篇 |
2000年 | 118篇 |
1999年 | 137篇 |
1998年 | 263篇 |
1997年 | 188篇 |
1996年 | 159篇 |
1995年 | 118篇 |
1994年 | 119篇 |
1993年 | 117篇 |
1992年 | 76篇 |
1991年 | 58篇 |
1990年 | 79篇 |
1989年 | 83篇 |
1988年 | 76篇 |
1987年 | 73篇 |
1986年 | 73篇 |
1985年 | 69篇 |
1984年 | 70篇 |
1983年 | 55篇 |
1982年 | 48篇 |
1981年 | 45篇 |
1980年 | 51篇 |
1979年 | 47篇 |
1978年 | 39篇 |
1977年 | 35篇 |
1976年 | 41篇 |
1975年 | 30篇 |
1974年 | 23篇 |
排序方式: 共有6693条查询结果,搜索用时 15 毫秒
11.
Kun-Wah Yip Tung-Sang Ng 《Communications Letters, IEEE》2003,7(2):58-60
This letter analyzes Bluetooth's power-control algorithm with a goal to study the mean transmit power required in the presence of lognormal shadowing. The following results are found. 1) A smaller power-control step size yields a lower mean transmit power. 2) When the standard deviations of lognormal shadowing are 3 and 6 dB, respectively, a Bluetooth device needs to consume 11.1 dB and 15.0 dB more in the transmit energy than the minimum one required in the absence of shadowing. 3) The transmit energy consumption varies by around 6 dB among Bluetooth devices as a result of the /spl plusmn/6 dB tolerance in the golden receive power range, which has a nominal size of 20 dB. 相似文献
12.
Finite element piezothermoelasticity analysis and the active control of FGM plates with integrated piezoelectric sensors and actuators 总被引:3,自引:0,他引:3
An efficient finite element model is presented for the static and dynamic piezothermoelastic analysis and control of FGM
plates under temperature gradient environments using integrated piezoelectric sensor/actuator layers. The properties of an FGM plate are functionally graded in the thickness
direction according to a volume fraction power law distribution. A constant displacement-cum-velocity feedback control algorithm that couples the direct and inverse piezoelectric effects is applied to provide active feedback
control of the integrated FGM plate in a closed loop system. Numerical results for the static and dynamic control are presented
for the FGM plate, which consists of zirconia and aluminum. The effects of the constituent volume fractions and the influence
of feedback control gain on the static and dynamic responses of the FGM plates are examined.
Received: 13 March 2002 / Accepted: 5 March 2003
The work described in this paper was supported by a grant awarded by the Research Grants Council of the Hong Kong Special
Administrative Region, China (Project No. CityU 1024/01E). 相似文献
13.
Accidents in different complex sociotechnical systems are rarely compared using the same theoretical framework for risk management. We conducted a comparative analysis of two Canadian public health disasters involving drinking water distribution systems, the North Battleford Cryptosporidium parvum outbreak in April 2001 and the Walkerton E. coli outbreak in May 2000. Both accidents resulted from a complex interaction between all levels of a complex sociotechnical system. However, the low-level physical and individual factors differed in the two cases, whereas, the high-level governmental and regulatory factors tended to be the same. These findings may have implications for the design of public policies to minimize risk in complex sociotechnical systems. 相似文献
14.
15.
D Averill D Blockus B Brabson J Brom C Jung H Ogren DR Rust M Derrick P Kooijman JS Loos B Musgrave LE Price J Repond K Sugano B Cork C Akerlof J Chapman D Errede MT Ken DI Meyer H Neal D Nitz R Thun R Tschirhart S Abachi P Baringer BG Bylsma R DeBonte D Koltick EH Low RL McIlwain DH Miller CR Ng EI Shibata 《Canadian Metallurgical Quarterly》1989,39(1):123-137
16.
17.
PHYSICS-BASED SIMULATION OF HIGH SPEED MACHINING 总被引:3,自引:0,他引:3
Eu-Gene Ng Tahany I. El-Wardany Mihaela Dumitrescu Mohamed A. Elbestawi 《Machining Science and Technology》2002,6(3):301-329
Computer simulation of high speed machining processes can provide a unique insight and reduce the number of design iterations required to advance and optimize the process. Predictive modeling of high speed machining of exotic materials has been hindered by the nonlinear behavior of this type of materials at extremely high strain, strain rate, and temperatures. This paper presents a physics-based modeling technology that includes the change in the material constitutive equation and the friction characterization at cutting speeds up to 400 m min-1. The dependence of the accuracy of the predicted parameters, such as the chip formation on cutting forces, chip/tool/workpiece interface temperature, stress and strain distributions are also discussed. The fundamentals of metal cutting were utilized to understand the effect of parameter changes in regimes that are outside current empirical knowledge databases. 相似文献
18.
Amanda Alliband Daniel W. Lenz Laura E. Stevenson Travis Whitmer Rex Cash Dennis Burns Sarah Hall William T.K. Stevenson 《Progress in Organic Coatings》2008
A model has been proposed to explain the failure of the original BMS10-39 epoxy paint on upper vertical surfaces in B-52 fuel tanks. The model involves interaction of the paint with DIEGME, a fuel system ice inhibitor (FSII) in jet fuel, that is distilled from the liquid fuel. In this communication, distillation experiments used to support the model are refined to better match the mass transfer of vapor from fuel in a B-52 fuel tank at close to room temperature. The interaction of these lower temperature distillates with the paint affirms the earlier model. On the basis of these experiments it is proposed that paint failure may be controlled or eliminated by reducing the level of DIEGME in the fuel. Proposed changes in military jet fuel composition are detailed. 相似文献
19.
Halo effects in rating specific pieces of work, as in educational grading, have received little attention. Grades awarded by 2 independent graders to undergraduate projects were analyzed with a correlated uniqueness model. Grades showed substantial halo despite being awarded by expert assessors at the time of reading the work. There was greater halo between different grades applying to the same section of the project than between grades applying to different sections. Supervisors who had regular contact with the student whose work they were grading showed no more halo than other graders. More reliable graders showed less within-section halo than graders of lower reliability but equal between-sections halo. The halo effects observed cannot be entirely attributable to a unitary general impression. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
20.
The synthesis of hydrocarbons via hydrogenation of carbon monoxide was investigated over cobalt—nickel—zirconia catalysts of various compositions in combination with zeolite HZSM-5 in “mixed bed” and “follow bed” arrangements. These combinations resulted in the formation of aromatics in amounts as high as 30-35 wt% under relatively mild operating conditions (1 atm, 250–280°C). Although the olefinicity of C2 and C3 fractions in the product stream was higher in the mixed bed compared to the follow bed arrangement, the selectivities to aromatics were comparable in the two bed arrangements. The aromatic selectivity was found to be sensitive to operating conditions. The formation of aromatics was favored at high HZSM-5/metal catalyst ratios, low space velocities and high reaction temperatures. The product distributions obtained using various metal/zeolite bifunctional catalysts have been discussed. 相似文献