全文获取类型
收费全文 | 39441篇 |
免费 | 5910篇 |
国内免费 | 3855篇 |
专业分类
电工技术 | 3085篇 |
技术理论 | 1篇 |
综合类 | 3948篇 |
化学工业 | 3457篇 |
金属工艺 | 2730篇 |
机械仪表 | 2922篇 |
建筑科学 | 4226篇 |
矿业工程 | 723篇 |
能源动力 | 1852篇 |
轻工业 | 3059篇 |
水利工程 | 495篇 |
石油天然气 | 770篇 |
武器工业 | 241篇 |
无线电 | 6059篇 |
一般工业技术 | 5005篇 |
冶金工业 | 1128篇 |
原子能技术 | 204篇 |
自动化技术 | 9301篇 |
出版年
2024年 | 325篇 |
2023年 | 1291篇 |
2022年 | 1739篇 |
2021年 | 1934篇 |
2020年 | 1923篇 |
2019年 | 1615篇 |
2018年 | 1569篇 |
2017年 | 1804篇 |
2016年 | 1794篇 |
2015年 | 2144篇 |
2014年 | 2828篇 |
2013年 | 3410篇 |
2012年 | 4761篇 |
2011年 | 4610篇 |
2010年 | 3379篇 |
2009年 | 3357篇 |
2008年 | 1830篇 |
2007年 | 2537篇 |
2006年 | 2254篇 |
2005年 | 814篇 |
2004年 | 323篇 |
2003年 | 243篇 |
2002年 | 276篇 |
2001年 | 279篇 |
2000年 | 250篇 |
1999年 | 267篇 |
1998年 | 137篇 |
1997年 | 87篇 |
1996年 | 161篇 |
1995年 | 132篇 |
1994年 | 119篇 |
1993年 | 114篇 |
1992年 | 80篇 |
1991年 | 65篇 |
1990年 | 71篇 |
1989年 | 54篇 |
1988年 | 76篇 |
1987年 | 155篇 |
1986年 | 163篇 |
1985年 | 42篇 |
1984年 | 34篇 |
1983年 | 13篇 |
1982年 | 18篇 |
1981年 | 15篇 |
1980年 | 15篇 |
1979年 | 28篇 |
1978年 | 17篇 |
1976年 | 16篇 |
1959年 | 7篇 |
1951年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
61.
异构数据集成方法研究与实现 总被引:4,自引:4,他引:0
王行荣 《微电子学与计算机》2006,23(4):172-173,176
为解决异构数据集成的复杂性问题,文章提出了一种异构数据同步的新方法——半集成式中间件法。该方法成功地应用在重庆市社会保障综合信息系统中,具有易于实现、可扩展性、跨平台性和效率高等特点。 相似文献
62.
63.
玻璃微珠的表面化学镀银及红外辐射性能研究 总被引:6,自引:1,他引:5
采用化学镀方法在玻璃微珠表面镀银,考察了预处理条件、反应温度和反应时间等因素对玻璃微珠表面镀银的影响,并通过扫描电镜和X-射线衍射分析仪,对镀银后玻璃微珠的表面形貌和结构进行了观察和表征。将镀银玻璃微珠用于涂料中,考察了玻璃微珠在涂料中的应用及其红外辐射率的变化,探讨了化学镀条件对涂料红外辐射率的影响,结果表明,在控制反应温度和浓度的条件下,可使镀银玻璃微珠的红外辐射率由原来的1.02降为0.70,将其应用于涂料后,涂层的红外辐射率为0.80。 相似文献
64.
65.
66.
《Ad hoc Networks》2008,6(8):1258-1280
We present a method for more uniformly distributing the energy burden across a wireless ground-based sensor network communicating with an overhead unmanned aerial vehicle (UAV). A subset of sensor nodes, termed a transmit cluster, receives and aggregates data gathered by the entire network, and forms a distributed antenna array, concentrating the radiated transmission into a narrow beam aimed towards the UAV. Because these duties are power-intensive, the role of transmit cluster must be shifted to different nodes as time progresses. We present an algorithm to reassign the transmit cluster, specifying the time that should elapse between reassignments and the number of hops that should be placed between successive transmit clusters in order to achieve three competing goals: first, we wish to better and more broadly spread the energy load across the sensor network while, second, minimizing the energy expended in moving the transmit cluster, all the while, third, reducing to the extent practicable the time to bring the UAV and the sensor network’s beam into alignment. Additionally, we present a method for reconfiguring the communication burden between the ground-based sensor network and the UAV. We describe and analyze two alternative strategies to bring the UAV and the sensor network’s beam into alignment, while minimizing the energy expended by the sensor network. The performance of the two strategies is compared in terms of probability of beam-UAV alignment as a function of time, and the expected time to alignment. We examine the performance tradeoff between the choice of strategy and parameters of the sensor network that affect power conservation. 相似文献
67.
MIMO (Multiple-Input Multiple-Output)的显著优点就是在不增加带宽的情况下,能够成倍地提高通信系统容量和频谱利用率,是未来移动通信与个人通信系统实现高速率数据传输,提高高传输质量的重要途径,也是未来移动通信系统广泛采用的关键技术.文中简要介绍了MIMO系统及其一种新的MIMO系统中的应用技术,即PARC(Per-antenna Rate Control)技术. 相似文献
68.
《Construction and Building Materials》2007,21(5):958-964
Firstly, the performance-based properties of rejuvenated aged asphalt binders, i.e., the blends of aged binders containing a rejuvenator at various percentages, were investigated under high, intermediate and low temperatures. The tests were conducted on the blends at three stages as follows: no aging, rolling thin film oven (RTFO) residuals and as well RTFO + pressure aging vessel (PAV) residuals through dynamic shear rheometer (DSR) and bending beam rheometer (BBR) tests. Optimum concentrations of the rejuvenator needed for the blends to reach a target PG grade were obtained from the blending charts of the rejuvenated aged binders in terms of performance properties. The rejuvenator is a soft binder containing a low asphaltene content of 2 wt%. Secondly, selected performance-based properties were conducted on hot mix asphalt (HMA) using the rejuvenated aged binder and a virgin HMA as a control mixture. Results showed that the rejuvenator affected significantly the performance-based properties of both the rejuvenated aged binders and the mixtures containing the rejuvenated aged binders. It was possible to get optimum concentrations of the rejuvenator using the blending charts so that the rejuvenated binders reach a target PG grade. The mean value of the concentrations was proved to be more reliable through the performance-based properties of the mixtures if it is used for a design value for recycling. The properties of the asphalt paving mixtures with the rejuvenated binders were even improved or in the same level as the properties of the virgin mixtures. 相似文献
69.
《Cement and Concrete Composites》2006,28(9):790-799
This paper presents the results of an investigation of the properties of mortar in which a calcined clay was employed as a pozzolan. Mortars were prepared using either heat treated clay or ground waste clay bricks (from the same clay subjected to 1000 °C calcining) as a pozzolanic partial replacement for cement at replacement levels of 10%, 20% and 30%. The compressive strengths of the mortars were monitored up to 90 days and the resistance to sodium sulphate solution and synthetic seawater was monitored up to 300 days. The specimens were also monitored for weight changes. Partially replacing cement by ground brick or heat-treated brick clay gives early strengths that are lower than that of the control. At 90 days, however, the strengths are the same as or are greater than that of the control. Heat-treated clay is effective in reducing expansion during exposure of the mortar to sulphate solution and synthetic seawater. The rapidly cooled clay gives better performance, in terms of strength development and resistance to harmful solutions, than the slow cooled clay. 相似文献
70.
《Journal of the European Ceramic Society》2005,25(9):1629-1636
Ultimate tensile strength of five different continuous fiber-reinforced ceramic matrix composites (CMCs), including SiCf/BSAS (two dimensional (2D), 2 types), SiCf/MAS (2D), SiCf/SiC (2D), and Cf/SiC (2D, 2 types), was determined as a function of test rate at 1100–1200 °C in air. All five CMCs exhibited a significant dependency of ultimate tensile strength on test rate such that the ultimate tensile strength decreased with decreasing test rate. The dependency of ultimate tensile strength on test rate, the applicability of preload technique, and the predictability of life from one loading configuration (constant stress-rate loading) to another (constant stress loading) all suggested that the overall, phenomenological delayed failure of the CMCs would be governed by a power-law type of slow crack growth. 相似文献