全文获取类型
收费全文 | 356篇 |
免费 | 8篇 |
专业分类
电工技术 | 4篇 |
化学工业 | 21篇 |
金属工艺 | 7篇 |
机械仪表 | 3篇 |
建筑科学 | 75篇 |
能源动力 | 2篇 |
轻工业 | 31篇 |
无线电 | 44篇 |
一般工业技术 | 77篇 |
冶金工业 | 70篇 |
原子能技术 | 3篇 |
自动化技术 | 27篇 |
出版年
2022年 | 2篇 |
2021年 | 5篇 |
2019年 | 6篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 8篇 |
2015年 | 13篇 |
2014年 | 8篇 |
2013年 | 14篇 |
2012年 | 14篇 |
2011年 | 26篇 |
2010年 | 15篇 |
2009年 | 17篇 |
2008年 | 21篇 |
2007年 | 27篇 |
2006年 | 12篇 |
2005年 | 12篇 |
2004年 | 4篇 |
2003年 | 10篇 |
2002年 | 6篇 |
2001年 | 7篇 |
2000年 | 4篇 |
1999年 | 6篇 |
1998年 | 30篇 |
1997年 | 10篇 |
1996年 | 14篇 |
1995年 | 8篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1973年 | 3篇 |
1972年 | 1篇 |
1971年 | 2篇 |
1969年 | 2篇 |
1966年 | 1篇 |
1913年 | 1篇 |
1912年 | 1篇 |
排序方式: 共有364条查询结果,搜索用时 0 毫秒
71.
Lutich AA Mauser C Da Como E Huang J Vaneski A Talapin DV Rogach AL Feldmann J 《Nano letters》2010,10(11):4646-4650
CdSe/CdS semiconductor nanocrystal heterostructures are currently of high interest for the peculiar electronic structure offering unique optical properties. Here, we show that nanorods and tetrapods made of such material combination enable efficient multiexcitonic emission, when the volume of the nanoparticle is maximized. This condition is fulfilled by tetrapods with an arm length of 55 nm and results in a dual emission with comparable intensities from the CdS arms and CdSe core. The relative intensities of the dual emission, originating from exciton phase-space filling and reduced Auger recombination, can be effectively modulated by the photon fluence of the pump laser. The results, obtained under steady-state detection conditions, highlight the properties of tetrapods as multiexciton dual-color emitters. 相似文献
72.
73.
74.
We demonstrate that optical trapping of multiple silver nanoparticles is strongly influenced by plasmonic coupling of the nanoparticles. Employing dark-field Rayleigh scattering imaging and spectroscopy on multiple silver nanoparticles optically trapped in three dimensions, we experimentally investigate the time-evolution of the coupled plasmon resonance and its influence on the trapping stability. With time the coupling strengthens, which is observed as a gradual red shift of the coupled plasmon scattering. When the coupled plasmon becomes resonant with the trapping laser wavelength, the trap is destabilized and nanoparticles are released from the trap. Modeling of the trapping potential and its comparison to the plasmonic heating efficiency at various nanoparticle separation distances suggests a thermal mechanism of the trap destabilization. Our findings provide insight into the specificity of three-dimensional optical manipulation of plasmonic nanostructures suitable for field enhancement, for example for surface-enhanced Raman scattering. 相似文献
75.
Molecular cloning of CIF1, a yeast gene necessary for growth on glucose. 总被引:13,自引:0,他引:13
M I González R Stucka M A Blázquez H Feldmann C Gancedo 《Yeast (Chichester, England)》1992,8(3):183-192
The cif1 mutation of Saccharomyces cerevisiae (Navon et al., Biochemistry 18, 4487-4499, 1979) causes inability to grow on glucose and absence of catabolite inactivation. We have cloned the CIF1 gene by complementation of function and located it in a 2.75 kb SphI-BstEII fragment situated at ca. 18 kb centromere distal of LYS2 and ca. 80 kb centromere proximal of TYR1 on chromosome II. Southern analysis demonstrated that CIF1 is present in a single copy in the yeast genome. Northern analysis revealed that the corresponding mRNA of 1.8 kb is more abundant in cells grown on galactose than in those grown on glucose. A protein of ca. 54 kDa was predicted from the open reading frame in the sequenced fragment. In strains carrying the cif1 mutation the intracellular concentration of ATP decreased immediately after addition of glucose while the intracellular concentration of cAMP did not increase. cAMP concentration increased in response to galactose or 2,4-dinitrophenol. Disruption of BCY1 or overexpression of CDC25 in a cif1 background did not restore growth on glucose, suggesting that the absence of cAMP signal is not the primary cause of lack of growth on glucose. Complementation tests showed that cif1 is not allelic to fdp1 although the two genes seem to be functionally related. 相似文献
76.
Caumette G Ouypornkochagorn S Scrimgeour CM Raab A Feldmann J 《Environmental science & technology》2007,41(8):2673-2679
Trace elements often accumulate in keratin-rich tissues. Hair, nails, and horns grow steadily but once formed are metabolically inactive and provide an archive of trace element exposure when analyzed in segments. Here we demonstrate the use of laser ablation ICP-MS for the high-resolution monitoring of trace elements in the horns of seaweed-eating sheep from North Ronaldsay, which live on grass only during lambing time. Due to this peculiar husbandry/dietary pattern and the fact that seaweed is rich in arsenic and iodine, we hoped to use iodine and arsenic as markers for seaweed ingestion. Cross sections and scans along the growing axis (representing the first 8-10 months of the sheep's life) revealed that these elements were not homogeneously distributed in the horn, with arsenic representing the amount of seaweed intake. The scans show the periods in which the lambs were fed on milk and grass and the change to seaweed ingestion with the successive replacement of milk with seaweed; this was supported by the carbon and nitrogen isotope signatures (delta13C and delta15N) of the horn and the arsenic speciation in the horn. The period of low arsenic accumulation in the horn had terrestrial isotope signatures and accumulated arsenic of mainly inorganic origin. The period of high arsenic accumulation was characterized by isotope signatures of marine origin, and the majority of accumulated arsenic in the horn was the main arsenosugar metabolite dimethylarsinic acid. Although we have investigated only four different horns of individual sheep, this study shows that arsenic is not significantly transported with milk. However, the high concentration of arsenic in the oldest part of the horn, which was formed in utero, points to a relatively high placental transport of arsenic while the ewe was eating seaweed. In contrast to arsenic, iodine is transported not only through milk ingestion but also through the placenta in large quantities. 相似文献
77.
78.
79.
80.
Feldmann A. Greenberg A. Lund C. Reingold N. Rexford J. True F. 《Networking, IEEE/ACM Transactions on》2001,9(3):265-279
Engineering a large IP backbone network without an accurate network-wide view of the traffic demands is challenging. Shifts in user behavior, changes in routing policies, and failures of network elements can result in significant (and sudden) fluctuations in load. We present a model of traffic demands to support traffic engineering and performance debugging of large Internet service provider networks. By defining a traffic demand as a volume of load originating from an ingress link and destined to a set of egress links, we can capture and predict how routing affects the traffic traveling between domains. To infer the traffic demands, we propose a measurement methodology that combines flow-level measurements collected at all ingress links with reachability information about all egress links. We discuss how to cope with situations where practical considerations limit the amount and quality of the necessary data. Specifically, we show how to infer interdomain traffic demands using measurements collected at a smaller number of edge links-the peering links connecting to neighboring providers. We report on our experiences in deriving the traffic demands in the AT&T IP Backbone, by collecting, validating, and joining very large and diverse sets of usage, configuration, and routing data over extended periods of time. The paper concludes with a preliminary analysis of the observed dynamics of the traffic demands and a discussion of the practical implications for traffic engineering 相似文献