全文获取类型
收费全文 | 288篇 |
免费 | 11篇 |
专业分类
电工技术 | 2篇 |
化学工业 | 46篇 |
机械仪表 | 4篇 |
建筑科学 | 7篇 |
能源动力 | 2篇 |
轻工业 | 17篇 |
无线电 | 41篇 |
一般工业技术 | 76篇 |
冶金工业 | 28篇 |
原子能技术 | 4篇 |
自动化技术 | 72篇 |
出版年
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 2篇 |
2019年 | 5篇 |
2018年 | 5篇 |
2017年 | 2篇 |
2016年 | 7篇 |
2015年 | 3篇 |
2014年 | 9篇 |
2013年 | 22篇 |
2012年 | 14篇 |
2011年 | 24篇 |
2010年 | 25篇 |
2009年 | 14篇 |
2008年 | 18篇 |
2007年 | 14篇 |
2006年 | 8篇 |
2005年 | 5篇 |
2004年 | 12篇 |
2003年 | 7篇 |
2002年 | 5篇 |
2001年 | 9篇 |
2000年 | 6篇 |
1999年 | 2篇 |
1998年 | 7篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 1篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 4篇 |
1984年 | 4篇 |
1983年 | 6篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1976年 | 3篇 |
1974年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有299条查询结果,搜索用时 15 毫秒
141.
Accurate indoor localization has long been an objective of the ubiquitous computing research community, and numerous indoor localization solutions based on 802.11, Bluetooth, ultrasound and infrared technologies have been proposed. This paper presents the first accurate GSM indoor localization system that achieves median within floor accuracy of 4 m in large buildings and is able to identify the floor correctly in up to 60% of the cases and is within 2 floors in up to 98% of the cases in tall multi-floor buildings. We report evaluation results of two case studies conducted over a course of several years, with data collected from 6 buildings in 3 cities across North America. The key idea that makes accurate GSM-based indoor localization possible is the use of wide signal-strength fingerprints. In addition to the 6-strongest cells traditionally used in the GSM standard, the wide fingerprint includes readings from additional cells that are strong enough to be detected, but are too weak to be used for efficient communication. We further show that selecting a subset of highly relevant channels for fingerprinting matching out of all available channels, further improves the localization accuracy. 相似文献
142.
We investigate theoretically the effect of layering of concrete shields using a wide class of semi-empirical models. We have found that (i) the ballistic limit velocity (BLV) of the multilayered shield does not depend on the order of the plates in the shield, (ii) monolithic shield is superior to any layered shield with the same thickness, and (iii) the largest decrease of the BLV occurs when a shield is divided into a number of plates having the same thickness. 相似文献
143.
Eyal Bergman/CEVA产品市场总监/胡凯/CEVA中国区技术支持经理中国作为目前世界上最大的移动市场,对移动标准的发展,希望制定不同于西方的自己的标准.这就是目前的3G标准TD-SCDMA以及未来的4G标准TD-LTE. 相似文献
144.
An impulsive cognitive style may affect behaviour in several different ways, including rapid decision making, intolerance of the delay of reward and a tendency to terminate chains of responses prematurely. It has been proposed to measure the last of these in rats using fixed consecutive number (FCN) schedules. The present study uses a modified version of the FCN procedure in which responding was paced by retracting the response lever for short periods between presses. In this way, the experimenter can control the maximum rate of responding. The procedure was made up of two components. In both, the schedule requirement was FCN 8, but in the Fast component lever presses were spaced by a minimum of 2.5 s and in the Slow component by a minimum of 5 s. Alterations in impulsivity were inferred from changes in the mean chain length and the distribution of chain lengths. The 5-HT1A agonist, 8-OH-DPAT (0.03-0.3 mg/kg), increased chain lengths within a narrow dose range, whereas the 5-HT1A antagonist, WAY 100 635 (0.03-0.3 mg/kg), reduced chain lengths. The 5-HT2 agonist, DOI (0.1-1.0 mg/kg), markedly reduced chain lengths, whereas the 5-HT2 antagonist, ritanserin (0.03-0.3 mg/kg), had no effect. The 5-HT1A/1b agonist, RU 24969 (0.03-0.3 mg/kg), reduced chain lengths. The 5-HT releaser, p-chloramphetamine (0.1-1.0 mg/kg), had a weak, biphasic effect, slightly reducing the number of short chains at the lowest dose tested and slightly increasing this number at the highest dose. Other drugs tested, citalopram (1.0-10.0 mg/kg), metergoline (0.3-3.0 mg/kg) and MDL-72222 (0.1-3.0 mg/kg), had no significant effects. These results suggest that stimulation of 5-HT1A receptors reduces impulsivity, whereas stimulation of 5-HT2 receptors increases it. These data are in agreement with previous results using the DRL-72 schedule, and indicate that there is no simple role for serotonin in the control of impulsivity. 相似文献
145.
146.
Sameer Abu Saleh Yehuda Eyal 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2005,230(1-4):246-250
Continuous density decreases of 50% within 98 μm long and 3.2 nm wide cylindrical ion damage trails, latent ion tracks, created in a {1 0 0} LiF platelet by 2.31 GeV Pb ions, have been measured by small-angle X-ray scattering. Structural alteration is attributed mainly to radiolytic decomposition of the crystal into Li atoms and fluorine molecules, and subsequent transport and release of the fluorine gas through the low-density tracks. Free volume and Li residues undoubtedly account for the observed enhanced etchability of the track-core region. 相似文献
147.
A max-2-connected Bayes network is one where there are at most 2 distinct directed paths between any two nodes. We show that even for this restricted topology, null-evidence belief updating is hard to approximate. 相似文献
148.
Porogen derived membranes, formed on decomposition of porogen molecules homogeneously dispersed in premembranes, were divided into two groups according to permeability and permeation mechanism. The more open membranes were formed when premembranes were cast on nonwoven polyester cloth support, or when decomposition products were extracted by solvent. The molecular cut off found for these membranes was at about 1000 Daltons and permeability was mainly determined by permeants' diffusivity and concentration. Permeability through the denser membrane was mainly determined by the permeants' partial vapor pressure, leading to high permselectivities. These denser membranes allowed relatively high osmotic water permeation while practically blocking permeation of solutes, such as salt, in the opposite direction. These membranes were thus also suitable for concentration of aqueous solutions by water removal into concentrated electrolyte solutions. © John Wiley & Sons, Inc. 相似文献
149.
In 5 experiments, participants read text that was briefly replaced by a transient image for 33 ms at random intervals. A decrease in saccadic frequency, referred to as saccadic inhibition, occurred as early as 60-70 ms following the onset of abrupt changes in visual input. It was demonstrated that the saccadic inhibition was influenced by the saliency of the visual event (Experiment 3) and was not produced in response to abrupt but irrelevant auditory stimuli (Experiment 1). Display changes restricted to an area either inside or outside the perceptual span required for normal reading produced strong saccadic inhibition (Experiment 2). Finally, Experiments 4 and 5 demonstrated higher level cognitive or attentional modulation of the saccadic inhibition effect. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
150.
We describe a new design approach for broad-band polarization-mode dispersion (PMD) compensation filters. An efficient algorithm for minimization of the maximum differential group delay within a given frequency band is described. 相似文献