全文获取类型
收费全文 | 1770篇 |
免费 | 21篇 |
专业分类
电工技术 | 13篇 |
综合类 | 2篇 |
化学工业 | 248篇 |
金属工艺 | 77篇 |
机械仪表 | 22篇 |
建筑科学 | 28篇 |
矿业工程 | 3篇 |
能源动力 | 20篇 |
轻工业 | 638篇 |
水利工程 | 3篇 |
石油天然气 | 6篇 |
无线电 | 55篇 |
一般工业技术 | 166篇 |
冶金工业 | 316篇 |
原子能技术 | 15篇 |
自动化技术 | 179篇 |
出版年
2021年 | 18篇 |
2020年 | 13篇 |
2019年 | 16篇 |
2018年 | 18篇 |
2016年 | 17篇 |
2014年 | 17篇 |
2013年 | 50篇 |
2012年 | 22篇 |
2011年 | 41篇 |
2010年 | 33篇 |
2009年 | 40篇 |
2008年 | 40篇 |
2007年 | 25篇 |
2006年 | 20篇 |
2005年 | 25篇 |
2004年 | 30篇 |
2003年 | 35篇 |
2002年 | 32篇 |
2001年 | 20篇 |
2000年 | 22篇 |
1999年 | 33篇 |
1998年 | 101篇 |
1997年 | 65篇 |
1996年 | 40篇 |
1995年 | 32篇 |
1994年 | 16篇 |
1993年 | 22篇 |
1992年 | 14篇 |
1991年 | 15篇 |
1990年 | 17篇 |
1989年 | 20篇 |
1988年 | 16篇 |
1987年 | 19篇 |
1986年 | 14篇 |
1985年 | 27篇 |
1984年 | 15篇 |
1977年 | 16篇 |
1976年 | 19篇 |
1921年 | 21篇 |
1920年 | 30篇 |
1919年 | 22篇 |
1918年 | 27篇 |
1917年 | 84篇 |
1916年 | 45篇 |
1915年 | 43篇 |
1914年 | 39篇 |
1913年 | 68篇 |
1912年 | 115篇 |
1911年 | 31篇 |
1910年 | 31篇 |
排序方式: 共有1791条查询结果,搜索用时 15 毫秒
61.
Comparative investigation of the biocompatibility of various silicon nitride ceramic qualities in vitro 总被引:8,自引:0,他引:8
Neumann A Reske T Held M Jahnke K Ragoss C Maier HR 《Journal of materials science. Materials in medicine》2004,15(10):1135-1140
There is a controversy about the biocompatibility of silicon nitride ceramics contained in the literature, which appears to be related to a factor of the individual chemical composition of different qualities of silicon nitride ceramics and of the different surface properties. This study attempts to investigate the cytotoxicity of different qualities of industrial silicon nitride ceramics applying an L929-cell culture model in a direct contact assay combined with a cell viability assessment. Five different qualities of industrial standard silicon nitride ceramics were chosen for in vitro testing. The chemical composition was determined by EDS analysis. Different biomedically approved aluminium oxide qualities, a titanium alloy, glass and polyvinylchloride (PVC) served as control materials. L929 mice fibroblasts were incubated directly on the materials for 24 h, stained with bisbenzimide and propidium iodine for double fluorochromasia viability testing, and evaluated by inversion-fluorescence microscopy to control cell morphology, viability and cell counts compared to empty well values. Scanning electron microscopy was applied to additionally investigate cell morphology. There was no observation of cytotoxic effects on the silicon nitride ceramic samples; moreover cell morphology remained the same as on aluminium oxide and titanium. Viability testing revealed the presence of avital cells exclusively on PVC, which served as a negative control. Cell counts on all polished surfaces showed significantly higher numbers, whereas some rough surface samples showed significantly lower numbers. We conclude that silicon nitride ceramics show no cytotoxic effects and should be considered for biomedical application owing to its favourable physiochemical properties, especially its superior resistance to mechanical stress, which would be useful for compression loaded conditions. Polished surfaces would appear to promote advanced biocompatibility. 相似文献
62.
We demonstrate a continuous-wave deuterium Raman laser that generates more than 160 mW of Stokes output power despite severe thermal effects. This output power represents nearly an order-of-magnitude increase over any previously reported continuous-wave Raman laser and is the first such system to our knowledge that uses deuterium gas as the Raman medium. The high output power is achieved through careful consideration of the electronic feedback design, frequency actuators, and pump-laser intensity noise. 相似文献
63.
64.
65.
Digitisation of images recorded on film is a crucial part of data acquisition in electron microscopy, particularly for electron cryo-microscopy of biological specimens where the contrast and signal-to-noise ratio are low. A quantitative method to evaluate and compare the quality of densitometers, as measured by the modulation transfer function (MTF), is described here. The densitometer is modelled as a linear system, the output being the convolution of the input image and a point spread function. The MTF is the magnitude of the Fourier transform of the point spread function. The relative MTF describes the quality of signal transfer with spatial frequency. It is important that fine structural details in the micrograph are digitised with a high value for the MTF which does not vary with direction. A test pattern has been generated by projecting an electron image of a grid pattern onto film. The film is scanned and a computer program measures the intensities of the diffraction orders of the repeating pattern. Three different scanners are compared, one is a point scanner and the other two are line scanners. The test can be used to check if a scanner is set up optimally, and how it compares with another scanner. 相似文献
66.
The neural mechanisms underlying motion segregation and integration still remain unclear to a large extent. Local motion estimates
often are ambiguous in the lack of form features, such as corners or junctions. Furthermore, even in the presence of such
features, local motion estimates may be wrong if they were generated near occlusions or from transparent objects. Here, a
neural model of visual motion processing is presented that involves early stages of the cortical dorsal and ventral pathways.
We investigate the computational mechanisms of V1-MT feedforward and feedback processing in the perception of coherent shape
motion. In particular, we demonstrate how modulatory MT-V1 feedback helps to stabilize localized feature signals at, e.g.
corners, and to disambiguate initial flow estimates that signal ambiguous movement due to the aperture problem for single
shapes. In cluttered environments with multiple moving objects partial occlusions may occur which, in turn, generate erroneous
motion signals at points of overlapping form. Intrinsic-extrinsic region boundaries are indicated by local T-junctions of
possibly any orientation and spatial configuration. Such junctions generate strong localized feature tracking signals that
inject erroneous motion directions into the integration process. We describe a simple local mechanism of excitatory form-motion
interaction that modifies spurious motion cues at T-junctions. In concert with local competitive-cooperative mechanisms of
the motion pathway the motion signals are subsequently segregated into coherent representations of moving shapes. Computer
simulations demonstrate the competency of the proposed neural model. 相似文献
67.
68.
Salekin Randall T.; Yff Rachel M. A.; Neumann Craig S.; Leistico Anne-Marie R.; Zalot Alecia A. 《Canadian Metallurgical Quarterly》2002,8(4):373
Juvenile court judges are often required to make distinctions as to whether certain adolescents should remain in the juvenile justice system or be transferred to adult courts. Typically, 3 broad factors weigh into juvenile court judges' decision making: (a) the level of danger the juvenile poses to the community, (b) the level of sophistication-maturity of the juvenile, and (c) the extent to which the juvenile is viewed as treatable. In an earlier study, knowledge of forensic and child psychologists was tapped to elucidate core characteristics related to the transfer process (R. T. Salekin et al, 2001). The current study augments that investigation. Judges provided (a) their perspective regarding the core criteria for dangerousness, sophistication-maturity, and amenability to treatment, and (b) data on the core characteristics of juveniles who were evaluated and subsequently judged to be appropriate for transfer to adult criminal courts. Policy implications for this increasingly critical interface between law and psychology are threefold: (a) Individualized assessments are key; (b) the adoption of a national standard for transfer to adult court is required; and (c) the development of treatment programs to improve the socialization of youth is necessary. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
69.
Karsten Neumann 《Datenschutz und Datensicherheit - DuD》2008,32(10):644-644
Ohne Zusammenfassung 相似文献
70.
Representation techniques are important issues when designing successful evolutionary algorithms. Within this field the use
of neutrality plays an important role. We examine the use of bit-wise neutrality introduced by Poli and López (2007) from a theoretical point of view and show that this mechanism only enhances mutation-based evolutionary algorithms if not
the same number of genotypic bits for each phenotypic bit is used. Using different numbers of genotypic bits for the bits
in the phenome we point out by rigorous runtime analyses that it may reduce the optimization time significantly. 相似文献