全文获取类型
收费全文 | 249219篇 |
免费 | 22628篇 |
国内免费 | 12998篇 |
专业分类
电工技术 | 16249篇 |
技术理论 | 19篇 |
综合类 | 18332篇 |
化学工业 | 39665篇 |
金属工艺 | 13685篇 |
机械仪表 | 15415篇 |
建筑科学 | 19129篇 |
矿业工程 | 7352篇 |
能源动力 | 7038篇 |
轻工业 | 20991篇 |
水利工程 | 5196篇 |
石油天然气 | 13497篇 |
武器工业 | 2123篇 |
无线电 | 29390篇 |
一般工业技术 | 28208篇 |
冶金工业 | 11138篇 |
原子能技术 | 2738篇 |
自动化技术 | 34680篇 |
出版年
2024年 | 1324篇 |
2023年 | 4608篇 |
2022年 | 8824篇 |
2021年 | 11746篇 |
2020年 | 8975篇 |
2019年 | 6885篇 |
2018年 | 7751篇 |
2017年 | 8792篇 |
2016年 | 7879篇 |
2015年 | 10847篇 |
2014年 | 13600篇 |
2013年 | 16139篇 |
2012年 | 17870篇 |
2011年 | 18962篇 |
2010年 | 16442篇 |
2009年 | 15374篇 |
2008年 | 14894篇 |
2007年 | 13768篇 |
2006年 | 13368篇 |
2005年 | 11189篇 |
2004年 | 7597篇 |
2003年 | 6349篇 |
2002年 | 5929篇 |
2001年 | 5243篇 |
2000年 | 4591篇 |
1999年 | 4967篇 |
1998年 | 3886篇 |
1997年 | 3277篇 |
1996年 | 3073篇 |
1995年 | 2431篇 |
1994年 | 1972篇 |
1993年 | 1426篇 |
1992年 | 1168篇 |
1991年 | 862篇 |
1990年 | 624篇 |
1989年 | 513篇 |
1988年 | 394篇 |
1987年 | 275篇 |
1986年 | 227篇 |
1985年 | 136篇 |
1984年 | 124篇 |
1983年 | 96篇 |
1982年 | 95篇 |
1981年 | 77篇 |
1980年 | 80篇 |
1979年 | 40篇 |
1978年 | 26篇 |
1977年 | 26篇 |
1976年 | 26篇 |
1951年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
Zhenghong Yang Yongjian Hu 《Automatic Control, IEEE Transactions on》2004,49(10):1783-1792
In this note, a generalized Bezoutian matrix with respect to a polynomial sequence of interpolatory type is introduced. The operator representation relative to a pair of dual bases and the generalized Barnett-type factorization formula are derived. An intertwining relation and a Bezoutian reduction to a block diagonal form by congruence via a generalized Vandermonde matrix are presented. Fujiwara-Hermite and Routh-Hurwitz criteria in terms of this generalized Bezout matrix are obtained. 相似文献
63.
CHENSheng-ping LUKe-cheng LIYi-gang LIJia-fang ZHUJian-ping FENGMing LIJing 《半导体光子学与技术》2004,10(2):122-126
The effects of the variations in fiber length, fiber mirror reflectance on efficiency and output power are experimentally investigated for erbium-doped double pass backward superfluorescent fiber sources (SFSs). The influence of fiber length on mean wavelength stability (MWS) has also been demonstrated. By incorporating a short section of un-pumped erbium-doped fiber (EDF) at the output port, the pump power dependent on MWS becomes independent of pumped EDF length. This is a novel phenomenon that hasn‘t been reported up to now,and should be helpful to SFS fabrication and theory analysis. By using a fiber Michelson interferometer as spectrum slicing component,a multi-wavelength fiber source (MWFS) with ~20 channels (from 1542nm to 1559nm) is got. The MWFS has a channel spacing of ~0. 8 nm which satisfies ITUstandard. The intensity fluctuation among channels is less than 0.5dB,and the extinction ratio of all channels is above 14dB. This kind of MWFS should be useful to wavelength division multiplexing systems. 相似文献
64.
65.
66.
Similarity retrieval of iconic image database 总被引:3,自引:0,他引:3
The perception of spatial relationships among objects in a picture is one of the important selection criteria to discriminate and retrieve the images in an iconic image database system. The data structure called 2D string, proposed by Chang et al., is adopted to represent symbolic pictures. The 2D string preserves the objects' spatial knowledge embedded in images. Since spatial relationship is a fuzzy concept, the capability of similarity retrieval for the retrieval by subpicture is essential. In this paper, similarity measure based on 2D string longest common subsequence is defined. The algorithm for similarity retrieval is also proposed. Similarity retrieval provides the iconic image database with the distinguishing function different from a conventional database. 相似文献
67.
68.
Off-Site Exposure to Respirable Aerosols Produced during the Disk-Incorporation of Class B Biosolids
Swee Yang Low Tania Paez-Rubio Carolina Baertsch Matthew Kucharski Jordan Peccia 《Canadian Metallurgical Quarterly》2007,133(10):987-994
Field experiments were conducted at a Class B biosolids land application site in central Arizona to measure, model, and source-track the off-site transport of aerosols emitted when biosolids were disk-incorporated into soils. Real-time PM10 monitoring provided time-resolved aerosol information sufficient for verifying both off-site concentration and off-site exposure time model results. Under the conditions considered and at a distance of 165?m from the aerosol source, biosolids disk-incorporation resulted in an intermittent exposure to biosolids-derived aerosol concentration between 15 and 40?μg/m3 and an inhalable biosolids dose between 2 and 8?μg. Transport modeling predicted that these doses will decrease with increasing wind speed. In addition, three DNA sequence-based biosolids source tracking methods were applied to aerosol samples and confirmed the presence of biosolids in aerosols at 5, 65, and 165?m from the aerosol source. Field measurements and modeling indicate that the nature of biosolids-derived aerosol exposure is a series of intermittent high concentration puffs, rather than a continuous low concentration. 相似文献
69.
Perceptual Temporal Quality Metric for Compressed Video 总被引:2,自引:0,他引:2
Kai-Chieh Yang Guest C.C. El-Maleh K. Das P.K. 《Multimedia, IEEE Transactions on》2007,9(7):1528-1535
This paper presents a metric to quantify frame loss according to the impact on perceived temporal quality. This metric particularly aims at measuring the temporal quality degradation caused by both regular and irregular frame loss. Experimental results with subjective viewing demonstrate high performance on prediction of perceptual temporal quality. 相似文献
70.