全文获取类型
收费全文 | 168531篇 |
免费 | 7401篇 |
国内免费 | 3352篇 |
专业分类
电工技术 | 5146篇 |
技术理论 | 9篇 |
综合类 | 6844篇 |
化学工业 | 26729篇 |
金属工艺 | 9117篇 |
机械仪表 | 8203篇 |
建筑科学 | 9266篇 |
矿业工程 | 2573篇 |
能源动力 | 3569篇 |
轻工业 | 8487篇 |
水利工程 | 2701篇 |
石油天然气 | 4884篇 |
武器工业 | 489篇 |
无线电 | 19458篇 |
一般工业技术 | 27211篇 |
冶金工业 | 7278篇 |
原子能技术 | 1082篇 |
自动化技术 | 36238篇 |
出版年
2024年 | 328篇 |
2023年 | 1337篇 |
2022年 | 2311篇 |
2021年 | 3136篇 |
2020年 | 2361篇 |
2019年 | 2051篇 |
2018年 | 16343篇 |
2017年 | 15554篇 |
2016年 | 12074篇 |
2015年 | 3551篇 |
2014年 | 4262篇 |
2013年 | 5290篇 |
2012年 | 8333篇 |
2011年 | 14767篇 |
2010年 | 13007篇 |
2009年 | 10125篇 |
2008年 | 11091篇 |
2007年 | 12053篇 |
2006年 | 4786篇 |
2005年 | 5345篇 |
2004年 | 3891篇 |
2003年 | 3667篇 |
2002年 | 2735篇 |
2001年 | 2124篇 |
2000年 | 2478篇 |
1999年 | 2638篇 |
1998年 | 2449篇 |
1997年 | 1922篇 |
1996年 | 1799篇 |
1995年 | 1465篇 |
1994年 | 1237篇 |
1993年 | 893篇 |
1992年 | 671篇 |
1991年 | 570篇 |
1990年 | 411篇 |
1989年 | 367篇 |
1988年 | 328篇 |
1987年 | 176篇 |
1986年 | 166篇 |
1985年 | 112篇 |
1984年 | 98篇 |
1983年 | 63篇 |
1982年 | 60篇 |
1981年 | 54篇 |
1980年 | 38篇 |
1968年 | 45篇 |
1966年 | 43篇 |
1965年 | 45篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Neural Computing and Applications - More and more enterprises hope to achieve cooperation and win–win. However, many companies often have problems such as insufficient partner credit, which... 相似文献
82.
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
83.
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
84.
Petre Badica Dan Batalu Mihail Burdusel Mihai A. Grigoroscuta Gheorghe V. Aldica Monica Enculescu Raluca A. Gabor Zhiyong Wang Ruoxuan Huang Peifeng Li 《Ceramics International》2018,44(9):10181-10191
Pristine and (SiC+Te)-added MgB2 powders, green and spark plasma sintered (SPS) compacts were investigated from the viewpoint of quasi-static and dynamic (Split-Hopkinson Pressure Bar, SHPB) compressive mechanical properties The amount of the additive (SiC+Te) was selected to be the optimum one for maximization of the superconducting functional parameters. Pristine and added MgB2 show very similar compressive parameters (tan δ, fracture strength, Vickers hardness, others) and fragment size in the SHPB test. However, for the bulk SPSed samples the ratio of intergranular to transgranular fracturing changes, the first one being stronger in the added sample. This is reflected in the quasi-static KIC that is higher for the added sample. Despite this result, sintered samples are brittle and have roughly similar fragmentation behavior as for brittle engineering ceramics. In the fragmentation process, the composite nature of our samples should be considered with a special focus on MgB2 blocks (colonies) that show the major contribution to fracturing. The Glenn-Chudnovsky model of fracturing under dynamic load provides the closest values to our experimental fragment size data. 相似文献
85.
86.
87.
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
88.
90.
Wei-Cheng Tang Yi-Che Su Yun-Shan Huang Ya-Tin Yu Hsin-Lung Chen I-Ming Chu 《应用聚合物科学杂志》2019,136(39):48003
While perfluoroalkyl acids (PFAAs), also known as C8s, are used extensively in textile repellent coatings, concerns have arisen for their carcinogenicity and hazardous effects on the environment. In this study, a novel water-based, nonfluoro, and nanobrush textile repelling agent was prepared by conventional sol–gel chemistry using amorphous fumed silica and n-octyltriethoxysilane as the starting materials. Minimal interaction between the designed repelling agent and marketed water-based resins was confirmed using linear viscosity region (LVR) analysis and asymmetric-flow field-flow fractionation (AF4), suggesting the self-stratification potential of the repelling agent. More specifically, the repelling agent exhibited excellent compatibility and self-stratifying ability with a force-emulsified acrylic-based resin, affording a water contact angle of 104.3° when incorporated at 7% solid content. Performance tests carried out on thermoplastic polyurethane (TPU) revealed excellent adhesion (100/100) of a final formulation, and a significant increase in water contact angle from 80.1° to 103.8° after treatment. In addition, the fouling area after the removal of a submerged sample from a mixture of slurry, polymer, and oil decreased from 48 to 1% when the repelling agent was added. Moreover, the sludge-fouling property remained unchanged after 1000 cycles of abrasion. These findings demonstrate the potential of the described nonfluoro, nanobrush repelling agent as an environmentally safe alternative for use with commercial resins, in turn realizing a fully water-based hydrophobic coating. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48003. 相似文献