全文获取类型
收费全文 | 7553篇 |
免费 | 237篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 119篇 |
综合类 | 31篇 |
化学工业 | 1914篇 |
金属工艺 | 175篇 |
机械仪表 | 131篇 |
建筑科学 | 378篇 |
矿业工程 | 29篇 |
能源动力 | 143篇 |
轻工业 | 622篇 |
水利工程 | 48篇 |
石油天然气 | 3篇 |
无线电 | 630篇 |
一般工业技术 | 1299篇 |
冶金工业 | 1422篇 |
原子能技术 | 95篇 |
自动化技术 | 763篇 |
出版年
2022年 | 62篇 |
2021年 | 93篇 |
2020年 | 72篇 |
2019年 | 96篇 |
2018年 | 104篇 |
2017年 | 96篇 |
2016年 | 145篇 |
2015年 | 138篇 |
2014年 | 166篇 |
2013年 | 318篇 |
2012年 | 259篇 |
2011年 | 391篇 |
2010年 | 264篇 |
2009年 | 270篇 |
2008年 | 314篇 |
2007年 | 261篇 |
2006年 | 217篇 |
2005年 | 220篇 |
2004年 | 195篇 |
2003年 | 177篇 |
2002年 | 166篇 |
2001年 | 150篇 |
2000年 | 148篇 |
1999年 | 163篇 |
1998年 | 370篇 |
1997年 | 268篇 |
1996年 | 190篇 |
1995年 | 169篇 |
1994年 | 155篇 |
1993年 | 160篇 |
1992年 | 122篇 |
1991年 | 121篇 |
1990年 | 118篇 |
1989年 | 92篇 |
1988年 | 90篇 |
1987年 | 90篇 |
1986年 | 69篇 |
1985年 | 105篇 |
1984年 | 94篇 |
1983年 | 78篇 |
1982年 | 71篇 |
1981年 | 66篇 |
1980年 | 56篇 |
1979年 | 62篇 |
1978年 | 60篇 |
1977年 | 93篇 |
1976年 | 99篇 |
1975年 | 61篇 |
1974年 | 70篇 |
1972年 | 59篇 |
排序方式: 共有7802条查询结果,搜索用时 31 毫秒
1.
Leibetseder Andreas Schoeffmann Klaus Keckstein Jörg Keckstein Simon 《Multimedia Tools and Applications》2022,81(5):6191-6215
Multimedia Tools and Applications - Endometriosis is a common gynecologic condition typically treated via laparoscopic surgery. Its visual versatility makes it hard to identify for non-specialized... 相似文献
2.
Klaus Reinhardt Hans Georg Breunig Aisada Uchugonova Karsten K?nig 《Journal of the Royal Society Interface》2015,12(110)
We explore the possibility of characterizing sperm cells without the need to stain them using spectral and fluorescence lifetime analyses after multi-photon excitation in an insect model. The autofluorescence emission spectrum of sperm of the common bedbug, Cimex lectularius, was consistent with the presence of flavins and NAD(P)H. The mean fluorescence lifetimes showed smaller variation in sperm extracted from the male (tau m, τm = 1.54–1.84 ns) than in that extracted from the female sperm storage organ (tau m, τm = 1.26–2.00 ns). The fluorescence lifetime histograms revealed four peaks. These peaks (0.18, 0.92, 2.50 and 3.80 ns) suggest the presence of NAD(P)H and flavins and show that sperm metabolism can be characterized using fluorescence lifetime imaging. The difference in fluorescence lifetime variation between the sexes is consistent with the notion that female animals alter the metabolism of sperm cells during storage. It is not consistent, however, with the idea that sperm metabolism represents a sexually selected character that provides females with information about the male genotype. 相似文献
3.
Potential mGAT4 inhibitors derived from the lead substance (S)-SNAP-5114 have been synthesized and characterized for their inhibitory potency. Variations from the parent compound included the substitution of one of its aromatic 4-methoxy and 4-methoxyphenyl groups, respectively, with a more polar moiety, including a carboxylic acid, alcohol, nitrile, carboxamide, sulfonamide, aldehyde or ketone function, or amino acid partial structures. Furthermore, it was investigated how the substitution of more than one of the aromatic 4-methoxy groups affects the potency and selectivity of the resulting compounds. Among the synthesized test substances (S)-1-{2-[(4-formylphenyl)bis(4-methoxyphenyl)-methoxy]ethyl}piperidine-3-carboxylic acid, that features a carbaldehyde function in place of one of the aromatic 4-methoxy moieties of (S)-SNAP-5114, was found to have a pIC50 value of 5.89±0.07, hence constituting a slightly more potent mGAT4 inhibitor than the parent substance while showing comparable subtype selectivity. 相似文献
4.
5.
Adaptive decision making requires that contingencies between decision options and their relative assets be assessed accurately and quickly. The present research addresses the challenging notion that contingencies may be more visible from small than from large samples of observations. An algorithmic account for such a seemingly paradoxical effect is offered within a satisficing-choice framework. Accordingly, a choice is only made when the sample contingency describing the relative evaluation of the 2 options exceeds a critical threshold. Small samples, because of the high dispersion of their sampling distribution, facilitate above-threshold contingencies. Across a broad range of parameters, the resulting small-sample advantage in terms of hits is stronger than their disadvantage in false alarms. Computer simulations and experiments support the model predictions. The relative advantage of small samples is most apparent when information loss is low, when the threshold is high relative to the ecological contingency, and when the sampling process is self-truncated. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
6.
7.
Limited-trial Chase decoding 总被引:1,自引:0,他引:1
Arico G. Weber J.H. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2003,49(11):2972-2975
Chase decoders permit flexible use of reliability information in algebraic decoding algorithms for error-correcting block codes of Hamming distance d. The least complex version of the original Chase algorithms uses roughly d/2 trials of a conventional binary decoder, after which the best decoding result is selected as the final output. On certain channels, this approach achieves asymptotically the same performance as maximum-likelihood (ML) decoding. In this correspondence, the performance of Chase-like decoders with even less trials is studied. Most strikingly, it turns out that asymptotically optimal performance can be achieved by a version which uses only about d/4 trials. 相似文献
8.
Separation tests using hollow-fibre modules were performed for the difficult selective extraction of trivalent actinides over fission lanthanides from acidic media. This article shows that with 2,6-di(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine as the extractant, up to 94% americium could be extracted from 1.0 kmol/m3 HNO3, with minimal lanthanide co-extraction. Using a synergistic mixture of bis(chlorophenyl)dithiophosphinic acid and tri-n-octyl phosphine oxide, tests were performed on extraction, lanthanide scrubbing and stripping. In the extraction test, up to 99.99% americium could be extracted from 0.5 kmol/m3 HNO3, with approximately one third of the lanthanides being co-extracted. Mass transfer calculations using a consistent set of input data showed good agreement with the experiments. 相似文献
9.
The purpose of this study was to determine whether retention of fetal lung liquid is more prevalent in polyalveolar congenital lobar emphysema than in conventional congenital lobar emphysema. Two patients with congenital lobar emphysema were prospectively identified in a 3-year period. Twenty-five such patients were identified in a retrospective study covering 39 years. Medical records were available for 22 patients who had 23 emphysematous lobes. Both babies from the prospective study and six subjects from the retrospective group had respiratory symptoms and underwent chest X-ray in the first day of life. Six of the eight babies with respiratory symptoms and chest imaging in the first day of life had retention of fetal lung liquid in an emphysematous lobe. All six of these lobes were polyalveolar. The lobe in one child was a polyalveolar lobe but without retained fetal lung liquid, and one child exhibited conventional lobar emphysema also without retained fetal lung liquid. One polyalveolar lobe caused no neonatal symptoms and was not imaged until the child was 3 months old. No baby with conventional lobar emphysema was shown to have retained fetal lung liquid. There seems to be a correlation between polyalveolar lobe and onset of respiratory symptoms in the first day of life. Retention of fetal lung liquid within the affected lobe was documented only in cases of polyalveolar lobe. 相似文献
10.