全文获取类型
收费全文 | 1081篇 |
免费 | 4篇 |
国内免费 | 2篇 |
学科分类
工业技术 | 1087篇 |
出版年
2020年 | 1篇 |
2017年 | 1篇 |
2016年 | 2篇 |
2015年 | 4篇 |
2014年 | 1篇 |
2013年 | 7篇 |
2012年 | 1篇 |
2011年 | 4篇 |
2009年 | 7篇 |
2008年 | 4篇 |
2007年 | 3篇 |
2006年 | 13篇 |
2005年 | 1篇 |
2004年 | 9篇 |
2003年 | 8篇 |
2002年 | 7篇 |
2001年 | 1篇 |
2000年 | 5篇 |
1999年 | 35篇 |
1998年 | 298篇 |
1997年 | 171篇 |
1996年 | 114篇 |
1995年 | 82篇 |
1994年 | 50篇 |
1993年 | 54篇 |
1992年 | 11篇 |
1991年 | 13篇 |
1990年 | 12篇 |
1989年 | 16篇 |
1988年 | 11篇 |
1987年 | 12篇 |
1986年 | 8篇 |
1985年 | 15篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 9篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 20篇 |
1976年 | 33篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1971年 | 1篇 |
1970年 | 3篇 |
1968年 | 1篇 |
排序方式: 共有1087条查询结果,搜索用时 171 毫秒
1.
2.
Ixent Galpin Alvaro A. A. Fernandes Norman W. Paton 《The VLDB Journal The International Journal on Very Large Data Bases》2013,22(4):495-517
The resource-constrained nature of mote-level wireless sensor networks (WSNs) poses challenges for the design of a general-purpose sensor network query processors (SNQPs). Existing SNQPs tend to generate query execution plans (QEPs) that are selected on the basis of a fixed, implicit expectation, for example, that energy consumption should be kept as small as possible. However, in WSN applications, the same query may be subject to several, possibly conflicting, quality-of-service (QoS) expectations concomitantly (for example maximizing data acquisition rates subject to keeping energy consumption low). It is also not uncommon for the QoS expectations to change over the lifetime of a deployment (for example from low to high data acquisition rates). This paper describes optimization algorithms that respond to stated QoS expectations (about acquisition rate, delivery time, energy consumption and lifetime) when making routing, placement, and timing decisions for in-WSN query processing. The paper shows experimentally that QoS-awareness offers significant benefits in responding to, and reconciling, diverse QoS expectations, thereby enabling QoS-aware SNQPs to generate efficient QEPs for a broader range WSN applications than has hitherto been possible. 相似文献
3.
Velikson B; Cohen P; Rholam M; Rose JP; Wang BC; Smith JC 《Protein engineering, design & selection : PEDS》1998,11(10):909-916
The hormonal precursor pro-ocytocin-neurophysin is activated by selective
cleavage at Arg2-Ala13, producing mature ocytocin and neurophysin. To
understand the cleavage mechanism better, and in particular the recognition
of the cleavage site, it is necessary to characterize the three-dimensional
structure of the precursor molecule. Here we combine a variety of
experimental data with molecular modeling and dynamics calculations to
derive possible precursor conformations. In the models obtained, the
N-terminus of the precursor, corresponding to the ocytocin segment, is
hydrogen bonded in a pocket of the neurophysin moiety in a similar manner
to a crystallographically obtained non-covalent complex between the two
molecules. The calculations suggest that although the ocytocin segment is
relatively flexible, it adopts a stable, broad loop structure in the
vicinity of the cleavage region, which may constitute the structural
element recognized by the cleaving enzyme. The calculations also suggest a
possible widening of the distance between the two neurophysin domains in
the precursor relative to that in the non-covalent neurophysin- ocytocin
complex.
相似文献
4.
5.
The shear properties of woven carbon fabric 总被引:6,自引:0,他引:6
This paper presents experimental and theoretical studies of the shearing properties of carbon plain weave fabrics and prepregs. The shearing characteristics of these materials are determined by the use of a picture frame shear rig which is loaded by a mechanical test machine. The shear force/angle curves are presented for the experiments conducted with the various test materials. A proposed shear model based on previous research which idealizes the fabric yarns as beam elements is presented. Using fabric geometric and material parameters, the model predicts the initial slip region of the fabric, as well as the more dominant elastic deformation range. Comparisons of the experimental and theoretical results were conducted to validate the model. A discussion of the findings from the analysis is also given, with particular focus relating to the accuracy, limitations and advantages offered by such a model. Results indicated that the slip model gives modestly accurate predictions, whilst the elastic modulus model showed very good correlation with experimental data. 相似文献
6.
7.
Efficient microwave energy absorption by carbon nanotubes 总被引:1,自引:0,他引:1
Keith R. Paton 《Carbon》2008,46(14):1935-1941
The absorption of energy from microwave frequency electromagnetic fields by carbon nanotubes is investigated by measuring the heating rate of dispersions of carbon nanotubes in silicone oil. Microwave absorbance of silicone oil is enhanced by 500 times with the addition of as little as 0.04 wt% carbon nanotubes. The removal of residual iron catalyst is found to have little effect on the microwave absorbance; an acid based surface modification however causes the enhancement to be lost, with the performance little better than carbon black. As-synthesized tubes showed a percolation threshold of ∼0.025 wt% for both conductivity and microwave absorbance. The efficient energy absorption is explained by a mechanism of conduction loss in the samples. 相似文献
8.
9.
BC Kone 《Canadian Metallurgical Quarterly》1997,30(3):311-333
Nitric oxide (NO) is a labile radical gas that is widely acclaimed as one of the most important molecules in biology. Through covalent modifications of target proteins and redox reactions with oxygen and superoxide radical and transition metal prosthetic groups, NO plays a critical role in many vital biological processes, including the control of vascular tone, neurotransmission, ventilation, hormone secretion, inflammation, and immunity. Moreover, NO has been shown to influence a host of fundamental cellular functions, such as RNA synthesis, mitochondrial respiration, glycolysis, and iron metabolism. NO is formed from L-arginine by NO synthases (NOSs), a family of related enzymes encoded by separate unlinked genes. The different NOS isozymes exhibit disparate tissue and intrarenal distributions and are governed by unique regulatory mechanisms. In the kidney, NO participates in several vital processes, including the regulation of glomerular and medullary hemodynamics, the tubuloglomerular feedback response, renin release, and the extracellular fluid volume. While NO serves beneficial roles as a messenger and host defense molecule, excessive NO production can be cytotoxic, the result of NO's reaction with reactive oxygen and nitrogen species, leading to peroxynitrite anion formation, protein tyrosine nitration, and hydroxyl radical production. Indeed, NO may contribute to the evolution of several commonly encountered renal diseases, including immune-mediated glomerulonephritis, postischemic renal failure, radiocontrast nephropathy, obstructive nephropathy, and acute and chronic renal allograft rejection. Moreover, impaired NO production has been implicated in the pathogenesis of volume-dependent hypertension. This duality of NO's beneficial and detrimental effects has created extraordinary interest in this molecule and the need for a detailed understanding of NO biosynthesis. 相似文献
10.