全文获取类型
收费全文 | 268255篇 |
免费 | 25538篇 |
国内免费 | 13377篇 |
专业分类
电工技术 | 18185篇 |
技术理论 | 32篇 |
综合类 | 28091篇 |
化学工业 | 31495篇 |
金属工艺 | 10876篇 |
机械仪表 | 14042篇 |
建筑科学 | 35349篇 |
矿业工程 | 14367篇 |
能源动力 | 9225篇 |
轻工业 | 17897篇 |
水利工程 | 12035篇 |
石油天然气 | 12923篇 |
武器工业 | 3555篇 |
无线电 | 20137篇 |
一般工业技术 | 21362篇 |
冶金工业 | 13395篇 |
原子能技术 | 1949篇 |
自动化技术 | 42255篇 |
出版年
2024年 | 747篇 |
2023年 | 3312篇 |
2022年 | 5876篇 |
2021年 | 8417篇 |
2020年 | 8187篇 |
2019年 | 6465篇 |
2018年 | 6142篇 |
2017年 | 7690篇 |
2016年 | 9419篇 |
2015年 | 10407篇 |
2014年 | 18307篇 |
2013年 | 16664篇 |
2012年 | 19711篇 |
2011年 | 21435篇 |
2010年 | 16110篇 |
2009年 | 16504篇 |
2008年 | 15361篇 |
2007年 | 18351篇 |
2006年 | 16460篇 |
2005年 | 14395篇 |
2004年 | 12004篇 |
2003年 | 10382篇 |
2002年 | 8433篇 |
2001年 | 7041篇 |
2000年 | 5936篇 |
1999年 | 4711篇 |
1998年 | 3369篇 |
1997年 | 2953篇 |
1996年 | 2408篇 |
1995年 | 2035篇 |
1994年 | 1704篇 |
1993年 | 1227篇 |
1992年 | 1012篇 |
1991年 | 736篇 |
1990年 | 622篇 |
1989年 | 580篇 |
1988年 | 348篇 |
1987年 | 275篇 |
1986年 | 203篇 |
1985年 | 217篇 |
1984年 | 176篇 |
1983年 | 145篇 |
1982年 | 81篇 |
1981年 | 101篇 |
1980年 | 109篇 |
1979年 | 57篇 |
1978年 | 27篇 |
1977年 | 27篇 |
1975年 | 28篇 |
1959年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
61.
62.
随着网络建设以及信息化教学方法在高校教学过程中的应用普及,越来越多的高校使用在线巡课系统对教师的教学过程进行跟踪和管理,以便发现课堂教学中的亮点、问题和不足。文章提出的在线巡课系统,基于声源定位的技术,对传统的在线巡课系统做出了改进,解决了已有巡课系统中“只闻其声,不见其人”的问题,能够更直观地跟踪到教师的教学过程,包括教学行为以及师生互动过程,有效提升教务人员巡课效果和体验感受。 相似文献
63.
The existing analytical average bit error rate (ABER) expression of conventional generalised spatial modulation (CGSM) does not agree well with the Monte Carlo simulation results in the low signal‐to‐noise ratio (SNR) region. Hence, the first contribution of this paper is to derive a new and easy way to evaluate analytical ABER expression that improves the validation of the simulation results at low SNRs. Secondly, a novel system termed CGSM with enhanced spectral efficiency (CGSM‐ESE) is presented. This system is realised by applying a rotation angle to one of the two active transmit antennas. As a result, the overall spectral efficiency is increased by 1 bit/s/Hz when compared with the equivalent CGSM system. In order to validate the simulation results of CGSM‐ESE, the third contribution is to derive an analytical ABER expression. Finally, to improve the ABER performance of CGSM‐ESE, three link adaptation algorithms are developed. By assuming full knowledge of the channel at the receiver, the proposed algorithms select a subset of channel gain vector (CGV) pairs based on the Euclidean distance between all CGV pairs, CGV splitting, CGV amplitudes, or a combination of these. 相似文献
64.
65.
66.
《International Journal of Hydrogen Energy》2019,44(5):2905-2917
In this study, a multi-tubular thermally coupled packed bed reactor in which simultaneous production of ammonia and methyl ethyl ketone (MEK) takes place is simulated. The simulation results are presented in two co-current and counter-current flow modes. Based on this new configuration, the released heat from the ammonia synthesis reaction as an extremely exothermic reaction in the inner tube is employed to supply the required heat for the endothermic 2-butanol dehydrogenation reaction in the outer tube. On the other hand, MEK and hydrogen are produced by the dehydrogenation reaction of 2-butanol in the endothermic side, and the produced hydrogen is used to supply a part of the ammonia synthesis feed in the exothermic side. Thus, 30.72% and 31.88% of the required hydrogen for the ammonia synthesis are provided by the dehydrogenation reaction in the co-current and counter-current configurations, respectively. Also, according to the thermal coupling, the required cooler and furnace for the ammonia synthesis and 2-butanol dehydrogenation conventional plants are eliminated, respectively. As a result, operational costs, energy consumption and furnace emissions are considerably decreased. Finally, a sensitivity analysis and optimization are applied to study the effect of the main process parameters variation on the system performance and obtain the minimum hydrogen make-up flow rate, respectively. 相似文献
67.
Transmission system restoration with co-optimization of repairs,load pickups,and generation dispatch
This paper studies the restoration of a transmission system after a significant disruption such as a natural disaster. It considers the co-optimization of repairs, load pickups, and generation dispatch to produce a sequencing of the repairs that minimizes the size of the blackout over time. The core of this process is a Restoration Ordering Problem (ROP), a non-convex mixed-integer nonlinear program that is outside the capabilities of existing solver technologies. To address this computational barrier, the paper examines two approximations of the power flow equations: The DC model and the recently proposed LPAC model. Systematic, large-scale testing indicates that the DC model is not sufficiently accurate for solving the ROP. In contrast, the LPAC power flow model, which captures line losses, reactive power, and voltage magnitudes, is sufficiently accurate to obtain restoration plans that can be converted into AC-feasible power flows. An experimental study also suggests that the LPAC model provides a robust and appealing tradeoff between accuracy and computational performance for solving the ROP. 相似文献
68.
Redundancy allocation problem (RAP) is one of the best-developed problems in reliability engineering studies. This problem follows to optimize the reliability of a system containing s sub-systems under different constraints, including cost, weight, and volume restrictions using redundant components for each sub-system. Various solving methodologies have been used to optimize this problem, including exact, heuristic, and meta-heuristic algorithms. In this paper, an efficient multi-objective meta-heuristic algorithm based on simulated annealing (SA) is developed to solve multi-objective RAP (MORAP). This algorithm is knowledge-based archive multi-objective simulated annealing (KBAMOSA). KBAMOSA applies a memory matrix to reinforce the neighborhood structure to achieve better quality solutions. The results analysis and comparisons demonstrate the performance of the proposed algorithm for solving MORAP. 相似文献
69.
70.
《International Journal of Hydrogen Energy》2021,46(69):34449-34462
Three-dimensional Bödewadt flow (fluid rotates at a large enough distance from the stationary plate) of carbon nanomaterial is examined. Single walled and multi walled CNTs are dissolved in water and gasoline oil baseliquids. Darcy-Forchheimer porous medium is considered. Stationary disk is further stretched linearly in radial direction. Heat transfer effect is examined in presence of radiation and convection. Effect of viscous dissipation is accounted. Entropy generation rate is studied. By using adequate transformation (von Kármán relations), the flow field equations (PDEs) are transmitted into ODEs. Solutions to these ODEs are constructed via implementation of shooting method (bvp4c). In addition to Entropy generation rate, Bejan number, heat transfer rate (Nusselt number), skin friction and temperature of fluid are examined through involved physical parameters. Axial component of velocity intensifies with increment in nanoparticles volume fraction and ratio of stretching rate to angular velocity parameter while it decays with higher porosity parameter. Higher nanoparticles volume fraction and porosity parameter lead to decay in radial as well as tangential component of velocity. However it enhances with higher ratio of stretching rate to angular velocity parameter. Temperature of fluid directly varies with higher ratio of stretching rate to angular velocity parameter, radiation parameter, Eckert number, Biot number and nanoparticles volume fraction. Rate of Entropy generation is reduced with higher estimations of porosity parameter, nanoparticles volume fraction and radiation parameter. Skin friction coefficient decays with higher porosity parameter and ratio of stretching rate to angular velocity parameter. Intensification in porosity parameter, nanoparticles volume fraction and Biot number leads to higher Nusselt number. Prominent impact is shown by multiple-walled CNTs with gasoline oil basefluid than single-walled CNTs with water basefluid. 相似文献