全文获取类型
收费全文 | 19481篇 |
免费 | 1982篇 |
国内免费 | 1120篇 |
专业分类
电工技术 | 710篇 |
综合类 | 928篇 |
化学工业 | 4760篇 |
金属工艺 | 3450篇 |
机械仪表 | 809篇 |
建筑科学 | 114篇 |
矿业工程 | 231篇 |
能源动力 | 604篇 |
轻工业 | 1731篇 |
水利工程 | 9篇 |
石油天然气 | 184篇 |
武器工业 | 152篇 |
无线电 | 2427篇 |
一般工业技术 | 3366篇 |
冶金工业 | 1210篇 |
原子能技术 | 1456篇 |
自动化技术 | 442篇 |
出版年
2024年 | 55篇 |
2023年 | 435篇 |
2022年 | 743篇 |
2021年 | 863篇 |
2020年 | 760篇 |
2019年 | 757篇 |
2018年 | 761篇 |
2017年 | 788篇 |
2016年 | 682篇 |
2015年 | 630篇 |
2014年 | 931篇 |
2013年 | 1337篇 |
2012年 | 1048篇 |
2011年 | 1381篇 |
2010年 | 939篇 |
2009年 | 1073篇 |
2008年 | 1010篇 |
2007年 | 1198篇 |
2006年 | 1158篇 |
2005年 | 898篇 |
2004年 | 864篇 |
2003年 | 681篇 |
2002年 | 545篇 |
2001年 | 474篇 |
2000年 | 438篇 |
1999年 | 350篇 |
1998年 | 294篇 |
1997年 | 267篇 |
1996年 | 240篇 |
1995年 | 169篇 |
1994年 | 140篇 |
1993年 | 139篇 |
1992年 | 124篇 |
1991年 | 92篇 |
1990年 | 66篇 |
1989年 | 51篇 |
1988年 | 57篇 |
1987年 | 23篇 |
1986年 | 21篇 |
1985年 | 14篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 31篇 |
1981年 | 23篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1959年 | 1篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
111.
112.
某型无人机的导引系统需要具备可靠、精密、可用等特点。文中首先对比了现行的三种导引系统,接着说明微波着陆系统(MLS)和所有的无线电测量系统一样,不可避免地存在系统误差。从微波着陆系统工作原理出发,分析讨论了角度测量过程中存在的误差源,及其所影响到的角度计算因子。进而给出了来自不同误差源的误差概算,最终结合系统测角精度要求,得出了相关设备的参数选择参考。 相似文献
113.
XU Ying LIAO Xianbo DIAO Hongwei Li Xudong ZENG Xiangbo LIU Xiaoping WANG Minhua WANG Wenjing 《稀有金属(英文版)》2006,25(Z1)
Hetero-junction solar cells with an mc-Si:H window layer were achieved. The open voltage is increased while short current is decreased with increasing the mc-Si:H layer's thickness of emitter layer. The highest of V oc of 597 mV has obtained. When fixed the thickness of 30 nm, changing the N type from amorphous silicon layer to micro-crystalline layer, the efficiency of the hetero-junction solar cells is increased. Although the hydrogen etching before deposition enables the c-Si substrates to become rough by AFM images, it enhances the formation of epitaxial-like micro-crystalline silicon and better parameters of solar cell can be obtained by implying this process. The best result of efficiency is 13.86% with the V oc of 549.8 mV, J sc of 32.19 mA·cm-2 and the cell's area of 1cm2. 相似文献
114.
This paper mainly focuses on the influence of three kinds of media: air, air-10%PA (Nylon) and air-10% POM (polyoxymethylene) on low-voltage circuit breaker arcs. A threedimensional (3-D) model of arc motioa under the effect of external magnetic field is built based on magnetohydrodynamics (MHD) equations. By adopting the commercial computational fluid dynamics (CFD) package based on the control-volume method, the above MHD equations are solved. For the media of air-10%PA and air-10%POM, the distributions of stationary temperature and electrical potential and the transient motion processes are compared with those of air arc. The research shows that both air-10%PA and air -10% POM can cool the arc plasma and the former is more effective. Both of them can increase the stationary voltage as well. Moreover, the presence of the two mixtures can accelerate the arc motion toward the quenching area and ensures the arc quenched in time. 相似文献
115.
The surface of polyethyleneterephthalate (PET) nonwoven fabric was modified by He/O2 atmospheric pressure plasma treatment, varying plasma exposure time. The plasma treated PET surfaces have been analyzed to investigate the chemical nature and morphology of surface by X‐ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), respectively. The change of wettability was measured depending on plasma exposure time. XPS results indicated the presence of oxygen‐based functional groups on the PET nonwoven fabric surface after plasma treatment and oxygen content increased as exposure time increased. The mean roughness increased after 30 s exposure and further increase in exposure to 60 s led to decrease of the roughness and then again increase. The root mean square roughness followed the similar trend to mean roughness. The average difference in height, Rz, increased after plasma exposure for 30 s, while it slightly decreased after 60 s exposure. Despite of redeposition, the Rz of 90 s exposed sample increased more than two times compared with those of 30 and 60 s exposed. Wettability increased progressively up to 10 times after 90 s exposure compared with the untreated. It is attributed to the increases of hydrophilicity and surface roughness. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
116.
117.
In this work the synergistic effects of microwave (MW) irradiation induced oxidation processes and CoFe2O4 were studied for the degradation of brilliant green (BG) from aqueous solutions. Under the optimum condition, the ratio of solid to liquid was 1:167 (0.3 g CoFe2O4 mixed with 50 mL of 20 mg L−1 BG solution), MW power 600 W, and the time of the irradiation 2 min. And the decolorization rate could reach up to 100%. Further investigation showed that BG was degraded by MW-induced oxidation combined with CoFe2O4 surface adsorption. The CoFe2O4 could increase the efficiencies of MW degradation and be used repeatedly. The experimental results indicated that the method of MW degradation BG in the presence of CoFe2O4 could reduce reaction time and increase product yield. 相似文献
118.
取样门管的特性对微波取样器性能影响的分析 总被引:1,自引:1,他引:0
本文在概述微波取样器原理的基础上,重点研究了取样门管的特性对取样器性能的影响。并通过计算机辅助分析,为取样门管参数的选取提供了理论依据。 相似文献
119.
Plasmapropertiesoflaser-ablatedSttargetinairWangXiang-Tai(王象泰);ManBao-Yuan(满宝元);WangGong-Tang(王公堂);FanXi-Jun(樊锡君);WangJun(王军)... 相似文献
120.