全文获取类型
收费全文 | 281175篇 |
免费 | 27443篇 |
国内免费 | 14149篇 |
专业分类
电工技术 | 20033篇 |
技术理论 | 34篇 |
综合类 | 28757篇 |
化学工业 | 37153篇 |
金属工艺 | 11897篇 |
机械仪表 | 16372篇 |
建筑科学 | 34680篇 |
矿业工程 | 14789篇 |
能源动力 | 13526篇 |
轻工业 | 18727篇 |
水利工程 | 17434篇 |
石油天然气 | 16899篇 |
武器工业 | 3889篇 |
无线电 | 16300篇 |
一般工业技术 | 21410篇 |
冶金工业 | 14882篇 |
原子能技术 | 3161篇 |
自动化技术 | 32824篇 |
出版年
2024年 | 1303篇 |
2023年 | 3838篇 |
2022年 | 7193篇 |
2021年 | 9265篇 |
2020年 | 9200篇 |
2019年 | 7138篇 |
2018年 | 6747篇 |
2017年 | 8420篇 |
2016年 | 10166篇 |
2015年 | 10797篇 |
2014年 | 18478篇 |
2013年 | 17320篇 |
2012年 | 19896篇 |
2011年 | 22238篇 |
2010年 | 16169篇 |
2009年 | 16675篇 |
2008年 | 15325篇 |
2007年 | 18670篇 |
2006年 | 17047篇 |
2005年 | 15005篇 |
2004年 | 12460篇 |
2003年 | 10892篇 |
2002年 | 8904篇 |
2001年 | 7388篇 |
2000年 | 6348篇 |
1999年 | 5075篇 |
1998年 | 3728篇 |
1997年 | 3284篇 |
1996年 | 2747篇 |
1995年 | 2313篇 |
1994年 | 1936篇 |
1993年 | 1419篇 |
1992年 | 1163篇 |
1991年 | 814篇 |
1990年 | 725篇 |
1989年 | 624篇 |
1988年 | 382篇 |
1987年 | 290篇 |
1986年 | 233篇 |
1985年 | 223篇 |
1984年 | 184篇 |
1983年 | 150篇 |
1982年 | 84篇 |
1981年 | 89篇 |
1980年 | 91篇 |
1979年 | 52篇 |
1978年 | 26篇 |
1977年 | 29篇 |
1959年 | 47篇 |
1951年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Coupled large eddy simulation and the discrete element method are applied to study turbulent particle–laden flows, including particle dispersion and agglomeration, in a channel. The particle–particle interaction model is based on the Hertz–Mindlin approach with Johnson–Kendall–Roberts cohesion to allow the simulation of van der Waals forces in a dry air flow. The influence of different particle surface energies, and the impact of fluid turbulence, on agglomeration behaviour are investigated. The agglomeration rate is found to be strongly influenced by the particle surface energy, with a positive relationship observed between the two. Particle agglomeration is found to be enhanced in two separate regions within the channel. First, in the near-wall region due to the high particle concentration there driven by turbophoresis, and secondly in the buffer region where the high turbulence intensity enhances particle–particle interactions. 相似文献
62.
Reliability based criteria are quite popular for optimal sensor network design. We present a modified definition of system reliability for sensor network design for two applications: reliable estimation of variables in a steady state linear flow process, and reliable fault detection and diagnosis for any process. Unlike the weakest-link based definition of system reliability in the literature, the proposed definition considers the entire system and is consistent with the reliability concept used in classical reliability literature. For each application, dual approaches for defining system reliability are proposed, and their analogy with the reliability problem in the classical reliability literature is established. Using examples and stochastic simulations, the advantage of using the proposed system reliability in contrast to the existing definition is illustrated. Part II of this series of articles presents methods for efficient generation of the system reliability function and its use in optimization-based approaches for designing optimal sensor networks. 相似文献
63.
Fault detection and isolation in water distribution networks is an active topic due to the nonlinearities of flow propagation and recent increases in data availability due to sensor deployment. Here, we propose an efficient two-step data driven alternative: first, we perform sensor placement taking the network topology into account; second, we use incoming sensor data to build a network model through online dictionary learning. Online learning is fast and allows tackling large networks as it processes small batches of signals at a time. This brings the benefit of continuous integration of new data into the existing network model, either in the beginning for training or in production when new data samples are gathered. The proposed algorithms show good performance in our simulations on both small and large-scale networks. 相似文献
64.
不同折流板结构螺旋折流板换热器传热性能的比较(英文) 总被引:1,自引:0,他引:1
Numerical simulations were performed on flow and heat transfer performances of heat exchangers having six helical baffles of different baffle shapes and assembly configurations, i.e., two trisection baffle schemes, two quadrant baffle schemes, and two continuous helical baffle schemes. The temperature contour or the pressure contour and velocity contour plots with superimposed velocity vectors on meridian, transverse and unfolded concentric hexagonal slices are presented to obtain a full angular view. For the six helix baffled heat exchangers, the different patterns of the single vortex secondary flow and the shortcut leakage flow were depicted as wel as the heat transfer properties were compared. The results show that the optimum scheme among the six configurations is a circumferential overlap trisection helix baffled heat exchanger with a baffle incline angle of 20° (20°TCO) scheme with an anti-shortcut baffle structure, which exhibits the second highest pressure dropΔpo, the highest overal heat transfer coefficient K, shel-side heat transfer coefficient ho and shel-side average comprehensive index ho/Δpo. 相似文献
65.
文章通过对黑龙江省高效节水现状,存在问题的分析,结合黑龙江省高效节水发展的支撑能力,阐述黑龙江省节水增粮目标、任务及总体布局,为黑龙江省2012—2015年节水增粮实施提供依据。 相似文献
66.
Robert Brooke Manrico Fabretto Samuel Pering Eliza Switalska Lachlan Reeks Drew Evans Peter Murphy 《应用聚合物科学杂志》2015,132(26)
A study using three different pairs of electrochromic polymers (ECPs) synthesized onto plaques by means of a modified vapor phase polymerization (VPP) technique is presented. Restriction of the respective polymerization times, allowed both faster and slower polymerizing monomers to be controlled, and produced blended plaques with visually diffuse interfaces. The ECPs within the blended plaques retain their individual electrochromic behavior and when encapsulated into an electrochromic device, show outstanding optical switching performance with little degradation evident over 10,000 cycles, coupled with a switching time of the order of 1 second. Blends also allow multiple diffuse color changes within an electrochromic device, due to the difference in oxidation potentials of the individual ECPs, making them candidates for adaptive camouflage use. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42158. 相似文献
67.
68.
Controllability and observability of multi-agent systems with heterogeneous and switching topologies
ABSTRACTThis paper focuses on controllability and observability of multi-agent systems with heterogeneous and switching topologies, where the first- and the second-order information interaction topologies are different and switching. First, based on the controllable state set, a controllability criterion is obtained in terms of the controllability matrix corresponding to the switching sequence. Next, by virtue of the subspace sequence, two necessary and sufficient algebraic conditions are established for controllability in terms of the system matrices corresponding to all the possible topologies. Furthermore, controllability is considered from the graphic perspective. It is proved that the system is controllable if the union graph of all the possible topologies is controllable. With respect to observability, two sufficient and necessary conditions are derived by taking advantage of the system matrices and the corresponding invariant subspace, respectively. Finally, some simulation examples are worked out to illustrate the theoretical results. 相似文献
69.
ABSTRACTIn this paper, we review some algebraic control system. Precisely, linear and bilinear systems on Euclidean spaces and invariant and linear systems on Lie groups. The fourth classes of systems have a common issue: to any class, there exists an associated subgroup. From this object, we survey the controllability property. Especially, from those coming from our contribution to the theory. 相似文献
70.
为测试倾斜摄影测量技术路线,并通过实际项目的应用,解决传统古建筑建模过程中存在的时间成本高、难以还原复杂场景等问题。按照倾斜摄影技术的技术路线,进行朱氏宗祠建筑测绘试验,并通过基于altizure软件建立三维模型来展现倾斜摄影测量技术流程。验证无人机倾斜摄影应用于古建筑三维建模的可行性和可操作性。 相似文献