全文获取类型
收费全文 | 390974篇 |
免费 | 4416篇 |
国内免费 | 1236篇 |
专业分类
电工技术 | 7152篇 |
综合类 | 2658篇 |
化学工业 | 53764篇 |
金属工艺 | 19592篇 |
机械仪表 | 16206篇 |
建筑科学 | 9086篇 |
矿业工程 | 2273篇 |
能源动力 | 7977篇 |
轻工业 | 26550篇 |
水利工程 | 4429篇 |
石油天然气 | 5480篇 |
武器工业 | 68篇 |
无线电 | 48066篇 |
一般工业技术 | 79351篇 |
冶金工业 | 53473篇 |
原子能技术 | 6543篇 |
自动化技术 | 53958篇 |
出版年
2021年 | 2060篇 |
2019年 | 2057篇 |
2018年 | 22528篇 |
2017年 | 22175篇 |
2016年 | 15968篇 |
2015年 | 3284篇 |
2014年 | 4349篇 |
2013年 | 11560篇 |
2012年 | 11214篇 |
2011年 | 23622篇 |
2010年 | 20458篇 |
2009年 | 18350篇 |
2008年 | 19710篇 |
2007年 | 22123篇 |
2006年 | 8000篇 |
2005年 | 11294篇 |
2004年 | 9472篇 |
2003年 | 9055篇 |
2002年 | 7390篇 |
2001年 | 6627篇 |
2000年 | 6437篇 |
1999年 | 6340篇 |
1998年 | 14357篇 |
1997年 | 10331篇 |
1996年 | 8191篇 |
1995年 | 6445篇 |
1994年 | 5757篇 |
1993年 | 5630篇 |
1992年 | 4587篇 |
1991年 | 4264篇 |
1990年 | 4057篇 |
1989年 | 3792篇 |
1988年 | 3640篇 |
1987年 | 3174篇 |
1986年 | 3080篇 |
1985年 | 3628篇 |
1984年 | 3387篇 |
1983年 | 3034篇 |
1982年 | 2858篇 |
1981年 | 2954篇 |
1980年 | 2766篇 |
1979年 | 2649篇 |
1978年 | 2502篇 |
1977年 | 2959篇 |
1976年 | 3567篇 |
1975年 | 2318篇 |
1974年 | 2314篇 |
1973年 | 2321篇 |
1972年 | 1852篇 |
1971年 | 1745篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Ahmed Obaid M. Alzahrani M. Sh. Abdel-wahab Meshari Alayash M. S. Aida 《Journal of Materials Science: Materials in Electronics》2018,29(19):16317-16324
In this work, p-NiO/n-ZnO heterostructures were successfully prepared at room temperature using RF sputtering technique. The influence of ZnO layer thickness on the performance of the heterojunction was investigated. The deposited ZnO layers have a hexagonal Wurtzite structure with preferable growth orientations along (002) and (103) for thinner films. Increasing the thickness results in more crystallographic orientation randomness. The current–voltage measurements of the realized heterojunctions showed a clear rectifying behavior. The measured ideality factor varies from 2.5 to 1.6 according to the thickness of ZnO layer. The series resistance of the device is enlarged with increasing ZnO thickness. The deduced parameters from the I–V characteristics suggest that 200 nm is the optimal thickness of the ZnO layer according to our experimental conditions. We attribute the relatively better performance of this thickness to achieving reasonable compensation between serial resistance and ideality factor. The best heterojunction was tested and successfully used as a UV detector. 相似文献
72.
Video transmission over IEEE 802.11e wireless networks still shows poor performance for large bandwidth demand and frequently changed environments. Thus, several enhancements of IEEE 802.11e were proposed. On the other hand, big frames and simultaneous sending of adjacent frames always cause packet dropping for buffer overflow. In the past, we proposed an IEEE 802.11e enhancement named DFAA and a content aware mechanism to solve the above problems. The motivation of this paper is to find a proper way to integrate these two mechanisms. A DFAA enhancement (DFAA-E) is proposed to make up the insufficiency of content aware mechanism. Experiments results show that the combination of DFAA-E and content aware mechanism improves the video decoded quality greatly. And its performance can be further enhanced by selecting the suitable settings of certain parameters. 相似文献
73.
A. E. Kudryashov Zh. V. Eremeeva E. A. Levashov V. Yu. Lopatin A. V. Sevost’yanova E. I. Zamulaeva 《Surface Engineering and Applied Electrochemistry》2018,54(5):437-445
Electrospark treatment of OT4-1 titanium alloy was performed sequentially with a STIM-20N hard-alloy electrode (TiC–20% Ni) and carbon-containing material (graphite and carbon-based composite materials). Kinetics of the mass transfer of the hard-alloy electrode was studied. The cathode mass loss during the first minute of the treatment was established. The kinetics results were processed using the methods of mathematical statistics. The erosion resistance of the applied carbon-containing materials was determined. Phase composition and relief of the coatings formed were analyzed. It was found that the application of the carbon-containing material increases the content of refractory phases in the coatings. Increase in the time of the treatment using the carbon-containing materials decreases the roughness of the coatings. 相似文献
74.
The patent literature concerning thermal spraying for biomedical applications is reviewed in this contribution. The patents were compiled from multiple databases search spanning the 2005-2018 period. For clarity and ease of reading, the results have been grouped into sections according to four individual material groups (apatites, titanium, oxide ceramics, other), with the secondary sorting criterion being related to the specific bioapplication areas (maxillofacial, orthopedic, methods). Lastly, the patents are grouped according to the selected thermal spray method within the individual subsections. In the paper, recent R&D trends in this field are further identified and briefly commented. 相似文献
75.
Estimation of earth-fill dam height and dimension of spillway are strongly depend on accurate evaluation of dam overtopping reliability. Ideally, whole random and effective variables on overtopping should be considered for dam overtopping reliability assessment. However, taking into account all affecting random variables as well as overtopping reliability assessment using algorithms such as Monte Carlo (MC) could be excessively time consuming and impossible in some cases. In this study, new approach has been introduced as conditional reliability method and it has been tried to reduce the simulations time significantly by using combination of rainfall threshold theory, SUFI (Sequential Uncertainty Fitting) and MC methods. According two defined indexes, the obtain results shown, the relative error of new approach in computation of Jamishan dam overtopping reliability is less than 0.23%. Also, time saving in new method against to regular MC method is more than 87%. So, the new introduced method has more efficiency with acceptable accuracy for assessment of dam overtopping reliability. In addition, among hydrological and hydraulic uncertainties, hydrological uncertainties have more effect on overtopping reliability. 相似文献
76.
77.
78.
Yachao Dong Christos T. Maravelias Norman F. Jerome 《Optimization and Engineering》2018,19(4):937-976
We study a maritime inventory routing problem, in which shipments between production and consumption nodes are carried out by a fleet of vessels. The vessels have specific capacities and can be chartered under different agreements. The inventory levels of all consumption nodes and some production nodes should be maintained within specified bounds; for the remaining production nodes, orders should be picked up within pre-defined time windows. We propose a discrete-time mixed-integer programming model. In the face of new information and uncertainty, this optimization model has to be re-solved, as the horizon is rolled forward. We discuss how to account for different sources of uncertainty. We present a rolling-horizon reoptimization framework that allows us to study different policies that impact the quality of the implemented solution, so we can identify the optimal set of policies. 相似文献
79.
80.
In this paper, implementation of the Benchmark Simulation Model No 2 (BSM2) within Matlab-Simulink is presented. The BSM2 is developed for plant-wide WWTP control strategy evaluation on a long-term basis. It consists of a pre-treatment process, an activated sludge process and sludge treatment processes. Extended evaluation criteria are proposed for plant-wide control strategy assessment. Default open-loop and closed-loop strategies are also proposed to be used as references with which to compare other control strategies. Simulations indicate that the BM2 is an appropriate tool for plant-wide control strategy evaluation. 相似文献