全文获取类型
收费全文 | 2380篇 |
免费 | 272篇 |
国内免费 | 151篇 |
专业分类
电工技术 | 128篇 |
技术理论 | 1篇 |
综合类 | 338篇 |
化学工业 | 95篇 |
金属工艺 | 66篇 |
机械仪表 | 87篇 |
建筑科学 | 203篇 |
矿业工程 | 46篇 |
能源动力 | 51篇 |
轻工业 | 76篇 |
水利工程 | 20篇 |
石油天然气 | 64篇 |
武器工业 | 51篇 |
无线电 | 949篇 |
一般工业技术 | 121篇 |
冶金工业 | 55篇 |
原子能技术 | 27篇 |
自动化技术 | 425篇 |
出版年
2024年 | 6篇 |
2023年 | 13篇 |
2022年 | 31篇 |
2021年 | 48篇 |
2020年 | 67篇 |
2019年 | 38篇 |
2018年 | 33篇 |
2017年 | 82篇 |
2016年 | 60篇 |
2015年 | 82篇 |
2014年 | 120篇 |
2013年 | 155篇 |
2012年 | 172篇 |
2011年 | 204篇 |
2010年 | 160篇 |
2009年 | 155篇 |
2008年 | 133篇 |
2007年 | 209篇 |
2006年 | 168篇 |
2005年 | 147篇 |
2004年 | 122篇 |
2003年 | 128篇 |
2002年 | 84篇 |
2001年 | 77篇 |
2000年 | 74篇 |
1999年 | 40篇 |
1998年 | 41篇 |
1997年 | 34篇 |
1996年 | 30篇 |
1995年 | 22篇 |
1994年 | 18篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 1篇 |
1983年 | 3篇 |
排序方式: 共有2803条查询结果,搜索用时 62 毫秒
181.
Upward flame spread experiments were conducted on long thin composite fabric fuels made of 75% cotton and 25% fiberglass of various widths between 2 and 8.8 cm and lengths greater than 1.5 m. Symmetric ignition at the bottom edge of the fuel resulted in two sided upward flame growth initially. As flame grew to a critical length (15–30 cm depending on sample width) fluctuation or instability of the flame base was observed. For samples 5 cm or less in width, this instability lead to flame blow off on one side of the sample (can be either side in repeated tests). The remaining flame on the other side would quickly shrink in length and spread all the way to the end of the sample with a constant limiting length and steady spread rate. Flame blow off from the increased buoyancy induced air velocity (at the flame base) with increasing flame length is proposed as the mechanism for this interesting phenomenon. Experimental details and the proposed explanation, including sample width effect, are offered in the paper. 相似文献
182.
We experimentally burn thin solid fuels and obtain the speed of the flame front when it propagates (1) within a narrow channel (closed cross section), (2) within a channel with lateral walls only and (3) through a free cross section (plain case). The latter configuration is the classical one and it has been extensively studied with analytical, numerical and experimental methods by other authors. Our experiments have been carried out at different geometrical configurations and angles of inclination of the sample and also at several values of oxygen molar fraction. All experiments are restricted to purely buoyant flow. Our main results are as follows: (1) sidewalls reduce the flame spread rate in a non-monotonous trend when varying its height; (2) in horizontal flame spread, two simultaneous flame fronts that propagate at different velocities may arise in the channel case at high oxygen levels. The fastest flame front speed may be higher than that obtained in the plain case; (3) in upward flame spread, the channel effect configuration produces the highest flame front speed. We finally analyze the correlation of the downward flame front speed data in terms of the Damkohler number. 相似文献
183.
Richard Howey Melvyn Quan Nicholas J. Savill Louise Matthews S?ren Alexandersen Mark Woolhouse 《Journal of the Royal Society Interface》2009,6(39):835-847
This paper investigates the early viral dynamics of foot-and-mouth disease (FMD) within infected pigs. Using an existing within-host model, we investigate whether individual variation can be explained by the effect of the initial dose of FMD virus. To do this, we consider the experimental data on the concentration of FMD virus genomes in the blood (viral load). In this experiment, 12 pigs were inoculated with one of three different doses of FMD virus: low; medium; or high. Measurements of the viral load were recorded over a time course of approximately 11 days for every 8 hours. The model is a set of deterministic differential equations with the following variables: viral load; virus in the interstitial space; and the proportion of epithelial cells available for infection, infected and uninfected. The model was fitted to the data for each animal individually and also simultaneously over all animals varying only the initial dose. We show that the general trend in the data can be explained by varying only the initial dose. The higher the initial dose the earlier the development of a detectable viral load. 相似文献
184.
185.
直接序列扩频信号的周期谱密度检测法 总被引:1,自引:0,他引:1
本文针对直接序列扩频(DS/SS)通信系统的可截获性问题,提出了一种新方法,即用周期谱密度检测法,来获取该系统的重要参数,如载波频率、扩频码速率以及信号的调制方式等,从而实现对 DS/SS 信号的识别.最后,对 BPSK 和 QPSK 两种信号的调制方式进行了分析.由于计算中采用了FFT 算法,因此,便于进行实时处理。计算机模拟结果表明,此法是切实可行的。 相似文献
186.
扩频通信具有抗干扰能力强、易于实现码分多址等优点 ,特别适合煤矿通信 ,因此引进扩频通信技术 ,能够推动煤矿通信的发展 ,达到现代化的要求。文章分析了扩频系统对各种干扰的抵抗能力 ,计算了系统对这些干扰的处理增益 相似文献
187.
188.
神经网络集成通过训练多个神经网络并将其结论进行适当的合成,可以显著地提高学习系统的泛化能力.然而,设计一个好的神经网络集成必须在个体准确性与彼此差异性之间取得一个平衡.本文提出了一种改进的神经网络集成构造方法--基于噪声传播的神经网络集成算法(NSENN). 相似文献
189.
190.
CDMA通信系统多址干扰的仿真研究 总被引:1,自引:0,他引:1
许丽艳 《青岛大学学报(工程技术版)》2005,20(2):87-90
为了研究cDMA通信系统的多址干扰,本文利用Matlab提供的可视化仿真工具Sireunnk建立了CDMA通信系统仿真模型,详细讲述各模块的设计及参数设置,并对仿真结果进行分析。结果表明,多址干扰是CDMA系统的固有干扰,当同时通信的用户数增多时,多址干扰电平增大,导致系统的误码率也增大。因此,多址干扰是CDMA通信系统本身存在的自我干扰,它限制了蜂窝系统的通信容量。 相似文献