全文获取类型
收费全文 | 219264篇 |
免费 | 24652篇 |
国内免费 | 15912篇 |
专业分类
电工技术 | 24332篇 |
技术理论 | 18篇 |
综合类 | 22904篇 |
化学工业 | 24254篇 |
金属工艺 | 4741篇 |
机械仪表 | 8716篇 |
建筑科学 | 20201篇 |
矿业工程 | 8862篇 |
能源动力 | 8783篇 |
轻工业 | 8080篇 |
水利工程 | 21534篇 |
石油天然气 | 11966篇 |
武器工业 | 1617篇 |
无线电 | 25048篇 |
一般工业技术 | 11470篇 |
冶金工业 | 6624篇 |
原子能技术 | 2257篇 |
自动化技术 | 48421篇 |
出版年
2024年 | 1259篇 |
2023年 | 3590篇 |
2022年 | 6904篇 |
2021年 | 7862篇 |
2020年 | 8327篇 |
2019年 | 6435篇 |
2018年 | 5823篇 |
2017年 | 6982篇 |
2016年 | 7516篇 |
2015年 | 8032篇 |
2014年 | 13957篇 |
2013年 | 13485篇 |
2012年 | 16391篇 |
2011年 | 16871篇 |
2010年 | 12676篇 |
2009年 | 13338篇 |
2008年 | 12852篇 |
2007年 | 15387篇 |
2006年 | 13683篇 |
2005年 | 12179篇 |
2004年 | 9991篇 |
2003年 | 8983篇 |
2002年 | 7363篇 |
2001年 | 6116篇 |
2000年 | 5032篇 |
1999年 | 4056篇 |
1998年 | 3015篇 |
1997年 | 2427篇 |
1996年 | 1959篇 |
1995年 | 1649篇 |
1994年 | 1344篇 |
1993年 | 935篇 |
1992年 | 698篇 |
1991年 | 550篇 |
1990年 | 424篇 |
1989年 | 406篇 |
1988年 | 265篇 |
1987年 | 226篇 |
1986年 | 171篇 |
1985年 | 174篇 |
1984年 | 137篇 |
1983年 | 95篇 |
1982年 | 82篇 |
1981年 | 24篇 |
1980年 | 33篇 |
1979年 | 31篇 |
1977年 | 14篇 |
1976年 | 9篇 |
1959年 | 13篇 |
1951年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
鄱阳湖流域水土流失加剧了洪涝灾害。治理水土流失能增强山丘地涵养水源的能力,削洪减沙,减少库容损失,降低河床,具有明显的防洪效益。进行流域防洪规划时,应将防治水土流失与防洪治涝结合起来,因地制宣,综合治理。 相似文献
82.
83.
在讨论MPT1327信令的集群移动通信系统与国内No.7信令的PSTN网间互连,帝现两种信令配合中,研究了集群系统的仿真模型和模拟算法,同时模拟出整个集群系统的工作情况,运行结果证实了所提方案的可行性与准确性。 相似文献
84.
Air cleaning as a means of mitigating the risks arising from exposure to indoor radon progeny has been evaluated in a single-family house in the north eastem US. using an automated, semi-continuous activity-weighted size distribution measurement system. The measurements included radon concentration, condensation nuclei count, and activity-weighted size distribution of radon decay products. Measurements were made in the house with and without an operating air filtration system and with various particle sources common to normal indoor activities operating. Aerosols were generated by running water in a shower, candle burning, cigarette smoking, vacuuming, opening doors, and cooking. Using a room model, the changes in attachment rates, average attachment diameters, and deposition rates of the unattached fraction with and without the air cleaning system were calculated. In the presence of active aerosol sources, the air filtration unit typically reduced the concentration of particles within the hour following the end of particle generation. After candle burning, cigarette smoking, and vacuuming in the bedroom, the reductions of PAEC by air filtration are about 60% with the air filtration system operating in the bedroom. During cooking in the kitchen, the reductions of PAEC in the bedroom with the air filtration system were about 40%. However, for all cases the dose reductions were smaller than the particle and PAEC reductions. For those particles that were generated within the bedroom, there was a 20% to 50% reduction in dose. In the case of cooking where the door was open and particles infiltrated from the rest of the house, the dose reduction was only 5% on average and appears to be insignificant. Thus, the dose reductions were h e r than the reductions in activity concentration, but there were no cases where the estimated dose actually increased. 相似文献
85.
为提高环网的容错性能,文献(1)提出了一种基于事件驱动的故障重构算法,其缺点是该算法只能容忍连线故障。本文给出一种新的采用时钟起时驱动的重构算法,该算法既能容忍连线故障也能容忍站(或节点)故障,且令牌控制较文献(1)的简单。 相似文献
86.
高水固结尾砂充填采矿充填体合理配比的研究 总被引:7,自引:4,他引:3
高水固结尾砂充填采矿是一种新型充填采矿法。试验测定了高水固结尾矿充填体的强度和变形特征;研究分析了影响充填体强度的主要因素、高水充填工艺的特殊要求,以及上向,下向进路开采对充填体强度和稳定性的要求,提出了满足支护强度,工艺及经济需求的充填材料的合理配比范围。 相似文献
87.
单元系T—p相图的数学结构 总被引:1,自引:0,他引:1
作者以化学元素的稳定单质为基准,推演出了任意物质M_i(相态Ω)的热力学生成活度{相态Ω)的函数形式:?D_Ω数值的大小体现着相态Ω的热力学相对稳定性.根据集合论原理沿D(稳定性)座标取极大值的方法把物理性质互不连续的各个异相态连结在一起,建立了单元系在T-p面上的优势分布方程(PSDE):■作者以H_2O为实例,计算了T-p相图,与实验相图基本一致. 相似文献
88.
Evolution of the capillary network in a reactive powder concrete during hydration process 总被引:7,自引:0,他引:7
V. Morin F. Cohen-Tenoudji A. Feylessoufi P. Richard 《Cement and Concrete Research》2002,32(12):1907-1914
Ultrasonic waves in echographic mode, combined with autogenous shrinkage measurements, were used to study the evolution of the capillary network of reactive powder concrete (RPC) from the time after the mixing. Two characteristic porous classes have been identified: the first, between 10 and 20 nm, begins when the material reaches its solid hyperstatic state, and the second about 1 or 2 nm. The first class is associated with the porous space between the C-S-H hydrate clusters and the second with the internal porosity of the hydrate. The evolution of the active capillary radius as a function of the degree of hydration allows us to understand the strong interaction between the capillary network size and the chemical activity given by the dissipated calorimetric power curve. Indeed, the maximum point of the chemical activity marks the transition of the first class of pores to the second one. Finally, measurements of electrical conductivity through RPC samples show that after the maximum of the dissipated power, the curve of this electrical conductivity presents the same evolution as the capillary radius. As the electrical conductivity clearly depends on the evolution of the capillary network, the similarity between the results confirms our analysis in pore classes. 相似文献
89.
90.