全文获取类型
收费全文 | 13245篇 |
免费 | 2126篇 |
国内免费 | 1034篇 |
专业分类
电工技术 | 1232篇 |
综合类 | 1226篇 |
化学工业 | 1914篇 |
金属工艺 | 837篇 |
机械仪表 | 1042篇 |
建筑科学 | 956篇 |
矿业工程 | 755篇 |
能源动力 | 395篇 |
轻工业 | 1338篇 |
水利工程 | 389篇 |
石油天然气 | 451篇 |
武器工业 | 191篇 |
无线电 | 1630篇 |
一般工业技术 | 1327篇 |
冶金工业 | 499篇 |
原子能技术 | 197篇 |
自动化技术 | 2026篇 |
出版年
2024年 | 176篇 |
2023年 | 463篇 |
2022年 | 964篇 |
2021年 | 1279篇 |
2020年 | 971篇 |
2019年 | 700篇 |
2018年 | 707篇 |
2017年 | 779篇 |
2016年 | 626篇 |
2015年 | 862篇 |
2014年 | 979篇 |
2013年 | 963篇 |
2012年 | 1131篇 |
2011年 | 1103篇 |
2010年 | 914篇 |
2009年 | 783篇 |
2008年 | 727篇 |
2007年 | 597篇 |
2006年 | 454篇 |
2005年 | 327篇 |
2004年 | 217篇 |
2003年 | 142篇 |
2002年 | 138篇 |
2001年 | 104篇 |
2000年 | 105篇 |
1999年 | 52篇 |
1998年 | 20篇 |
1997年 | 25篇 |
1996年 | 19篇 |
1995年 | 20篇 |
1994年 | 9篇 |
1993年 | 8篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 6篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1959年 | 1篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
This paper mainly focuses on the influence of three kinds of media: air, air-10%PA (Nylon) and air-10% POM (polyoxymethylene) on low-voltage circuit breaker arcs. A threedimensional (3-D) model of arc motioa under the effect of external magnetic field is built based on magnetohydrodynamics (MHD) equations. By adopting the commercial computational fluid dynamics (CFD) package based on the control-volume method, the above MHD equations are solved. For the media of air-10%PA and air-10%POM, the distributions of stationary temperature and electrical potential and the transient motion processes are compared with those of air arc. The research shows that both air-10%PA and air -10% POM can cool the arc plasma and the former is more effective. Both of them can increase the stationary voltage as well. Moreover, the presence of the two mixtures can accelerate the arc motion toward the quenching area and ensures the arc quenched in time. 相似文献
2.
依据丰满漉域的水文气象资料,计算丰满流域可能最大暴雨,推求白丰区间的可能最大洪水并进行成果合理性分析. 相似文献
3.
Chemical looping combustion (CLC) is a clean and efficient flame-free combustion technology,which combust the fuels by lattice oxygen from a solid oxygen carrier with inherent CO2 capture.The develop-ment of oxygen carriers with low cost and high redox performance is crucial to the whole efficiency of CLC process.As the solid by-product from the sulfuric acid production,pyrite cinder presented excellent redox performance as an oxygen carrier in CLC process.The main components in pyrite cinder are Fe2O3,CaSO4,Al2O3 and SiO2 in which Fe2O3 is the active component to provide lattice oxygen.In order to sys-tematic investigate the functions of supports (CaSO4,Al2O3 and SiO2) in pyrite cinder,three oxygen car-riers (Fe2O3-CaSO4,Fe2O3-Al2O3 and Fe2O3-SiO2) were prepared and evaluated in this study.The results showed that Fe2O3-CaSO4 displayed high redox activity and cycling stability in the multiple redox cycles.However,both Fe2O3-Al2O3 and Fe2O3-SiO2 experienced serious deactivation during redox reactions.It indicated that the inert Fe-Si solid solution (Fe2SiO4) was formed in the spent Fe2O3-SiO2 sample,which decreased the oxygen carrying capacity of this sample.The XPS results showed that the oxygen species on the surface of Fe2O3-CaSO4 could be fully recovered after the 20 redox cycles.It can be concluded that CaSO4 is the key to the high redox activity and cycling stability of pyrite cinder. 相似文献
4.
5.
Hydrogenolysis of biomass-derived glycerol is an alternative route to sustainable production of propylene glycol. Cu–ZnO catalysts
were prepared by coprecipitation with a range of Cu/Zn atomic ratio (0.6–2.0) and examined in glycerol hydrogenolysis to propylene
glycol at 453–513 K and 4.2 MPa H2. These catalysts possess acid and hydrogenation sites required for bifunctional glycerol reaction pathways, most likely involving
glycerol dehydration to acetol and glycidol intermediates on acidic ZnO surfaces, and their subsequent hydrogenation on Cu
surfaces. Glycerol hydrogenolysis conversions and selectivities depend on Cu and ZnO particle sizes. Smaller ZnO and Cu domains
led to higher conversions and propylene glycol selectivities, respectively. A high propylene glycol selectivity (83.6%), with
a 94.3% combined selectivity to propylene glycol and ethylene glycol (also a valuable product) was achieved at 22.5% glycerol
conversion at 473 K on Cu–ZnO (Cu/Zn = 1.0) with relatively small Cu particles. Reaction temperature effects showed that optimal
temperatures (e.g. 493 K) are required for high propylene glycol selectivities, probably as a result of optimized adsorption
and transformation of the reaction intermediates on the catalyst surfaces. These preliminary results provide guidance for
the synthesis of more efficient Cu–ZnO catalysts and for the optimization of reaction parameters for selective glycerol hydrogenolysis
to produce propylene glycol. 相似文献
6.
Neural Processing Letters - Online sequential extreme learning machine (OS-ELM) is one of the most popular real-time learning strategy for feedforward neural networks with single hidden layer due... 相似文献
7.
Cheng Jiaqi Gong Junyi Yue Shuai Jiang Yao Hou Xiangjun Ma Jianjun Yao Yali Jiang Cairong 《Journal of Applied Electrochemistry》2021,51(8):1175-1188
Journal of Applied Electrochemistry - La-doped titanate materials have been widely investigated as alternative Ni-free anodes for solid oxide fuel cells (SOFCs). In this study, La0.4Sr0.6TiO3 (LST)... 相似文献
8.
Shaohui Mei Genliang Guan Zhiyong Wang Shuai Wan Mingyi He David Dagan Feng 《Pattern recognition》2015
The rapid growth of video data demands both effective and efficient video summarization methods so that users are empowered to quickly browse and comprehend a large amount of video content. In this paper, we formulate the video summarization task with a novel minimum sparse reconstruction (MSR) problem. That is, the original video sequence can be best reconstructed with as few selected keyframes as possible. Different from the recently proposed convex relaxation based sparse dictionary selection method, our proposed method utilizes the true sparse constraint L0 norm, instead of the relaxed constraint L2,1 norm, such that keyframes are directly selected as a sparse dictionary that can well reconstruct all the video frames. An on-line version is further developed owing to the real-time efficiency of the proposed MSR principle. In addition, a percentage of reconstruction (POR) criterion is proposed to intuitively guide users in obtaining a summary with an appropriate length. Experimental results on two benchmark datasets with various types of videos demonstrate that the proposed methods outperform the state of the art. 相似文献
9.
10.
Bartels–Stewart algorithm is an effective and widely used method with an O(n 3) time complexity for solving a static Sylvester equation. When applied to time-varying Sylvester equation, the computation burden increases intensively with the decrease of sampling period and cannot satisfy continuous realtime calculation requirements. Gradient-based recurrent neural network are able to solve the time-varying Sylvester equation in real time but there always exists an estimation error. In contrast, the recently proposed Zhang neural network has been proven to converge to the solution of the Sylvester equation ideally when time goes to infinity. However, this neural network with the suggested activation functions never converges to the desired value in finite time, which may limit its applications in realtime processing. To tackle this problem, a sign-bi-power activation function is proposed in this paper to accelerate Zhang neural network to finite-time convergence. The global convergence and finite-time convergence property are proven in theory. The upper bound of the convergence time is derived analytically. Simulations are performed to evaluate the performance of the neural network with the proposed activation function. In addition, the proposed strategy is applied to online calculating the pseudo-inverse of a matrix and nonlinear control of an inverted pendulum system. Both theoretical analysis and numerical simulations validate the effectiveness of proposed activation function. 相似文献