全文获取类型
收费全文 | 2255篇 |
免费 | 28篇 |
专业分类
电工技术 | 9篇 |
综合类 | 1篇 |
化学工业 | 145篇 |
金属工艺 | 7篇 |
机械仪表 | 16篇 |
建筑科学 | 31篇 |
矿业工程 | 1篇 |
能源动力 | 14篇 |
轻工业 | 68篇 |
水利工程 | 2篇 |
武器工业 | 1篇 |
无线电 | 176篇 |
一般工业技术 | 138篇 |
冶金工业 | 1568篇 |
原子能技术 | 18篇 |
自动化技术 | 88篇 |
出版年
2021年 | 14篇 |
2020年 | 8篇 |
2019年 | 11篇 |
2018年 | 7篇 |
2017年 | 15篇 |
2016年 | 11篇 |
2015年 | 8篇 |
2014年 | 9篇 |
2013年 | 23篇 |
2012年 | 29篇 |
2011年 | 35篇 |
2010年 | 27篇 |
2009年 | 27篇 |
2008年 | 22篇 |
2007年 | 29篇 |
2006年 | 22篇 |
2005年 | 27篇 |
2004年 | 26篇 |
2003年 | 18篇 |
2002年 | 22篇 |
2001年 | 18篇 |
2000年 | 18篇 |
1999年 | 67篇 |
1998年 | 488篇 |
1997年 | 317篇 |
1996年 | 196篇 |
1995年 | 106篇 |
1994年 | 87篇 |
1993年 | 118篇 |
1992年 | 26篇 |
1991年 | 29篇 |
1990年 | 27篇 |
1989年 | 24篇 |
1988年 | 16篇 |
1987年 | 24篇 |
1986年 | 20篇 |
1985年 | 32篇 |
1984年 | 6篇 |
1983年 | 16篇 |
1982年 | 9篇 |
1981年 | 23篇 |
1980年 | 19篇 |
1979年 | 10篇 |
1978年 | 16篇 |
1977年 | 36篇 |
1976年 | 74篇 |
1975年 | 9篇 |
1973年 | 7篇 |
1971年 | 7篇 |
1955年 | 5篇 |
排序方式: 共有2283条查询结果,搜索用时 31 毫秒
1.
Phase contrast magnetic resonance imaging (MRI) can provide in vivo myocardial velocity field measurements. These data allow densely spaced material points to be tracked throughout the whole heart cycle using, for example, the Fourier tracking algorithm. To process the tracking results for myocardial deformation and strain quantification, we developed a method that is based on fitting the tracking results to an appropriate local deformation model. We further analyzed the accuracy and precision of the method and provided performance predictions for several local models. In order to validate the method and the theoretical performance analysis, we conducted controlled computer simulations and a phantom study. The results agreed well with expectations. Human heart data were also acquired and analyzed, and provided encouraging results. At the signal-to-noise ratio (SNR) level and spatial resolution expected in clinical settings, the study predicts strain quantification accuracy and precision that may allow the technique to become a practical and powerful noninvasive approach for the study of cardiac function, although clinically acceptable data acquisition strategies for three-dimensional (3-D) data are still a challenge. 相似文献
2.
Attempts to immunise sheep against natural infestations by Lucilia cuprina larvae have not been effective. Yet it is known that the larvae excrete the immunosuppressant ammonium bicarbonate. The effect of larval ammonium and nonionic ammonia on immunopathobiology was evaluated in 12 infested sheep. The concentration of ammonium in veins draining infested sites was measured in another group of four sheep. Mean jugular unionized ammonia concentration increased 3.5 to 5.6 times above pre-infested control levels. Mean venous ammonium concentrations draining infested sites were 13 times higher than pre-infested jugular or carotid levels. Increases in jugular ammonia concentrations correlated with increased number of larvae, area of infestation, earlier death, neutropenia, eosinopenia, lymphocytopenia, large declines in serum globulins and zinc, and large rises in toxic neutrophils. The high concentrations of toxic unionized ammonia in blood directly permanently damaged neutrophils and lymphocytes and depressed serum globulin production. The results show that the ammonium from the excreta of larvae of L. cuprina may be highly immunosuppressive. 相似文献
3.
4.
Lasers containing a nanopatterned active layer demonstrating excellent threshold characteristics are presented. The nanopatterned active layer is fabricated using high-resolution electron beam lithography and selective-area metal organic chemical vapour deposition crystal growth. Results demonstrating an order of magnitude improvement over previous results are reported. 相似文献
5.
In this work, we have created a new type of structure, the nanopore active layer, for achieving quantization of carrier states in a semiconductor. The nanopore structure consists of a periodic two-dimensional array of localized energy barriers perturbing an otherwise conventional quantum well. This perturbation leads to the formation of intraband forbidden energy gaps which are observed experimentally. 相似文献
6.
7.
Two experiments were conducted to explore the interaction of the two cerebral hemispheres in motor control, by examining hand, space and attentional asymmetries in goal-directed aiming. In Experiment 1, right-handed subjects moved to targets more quickly with their right hand than their left hand. In addition, each hand was faster when moving in its own hemispace. Although in a control condition, movements were initiated more quickly with the left hand, visual distractors disrupted left hand performance more than right hand performance. For contralateral aiming, ipsilateral distractors caused the greatest interference. In Experiment 2, when targets and distractors were all presented at the midline, a right hand advantage was found for movement time along with a left hand advantage for reaction time, independent of target and distractor location. Our findings are discussed in terms of a right hemisphere role in movement preparation and the allocation of attention in space, and greater left hemisphere involvement in movement execution. 相似文献
8.
9.
10.
The visual sector of the reticular thalamic nucleus has come under some intense scrutiny over recent years, principally because of the key role that the nucleus plays in the processing of visual information. Despite this scrutiny, we know very little of how the connections between the reticular nucleus and the different areas of visual cortex and the different visual dorsal thalamic nuclei are organized. This study examines the patterns of reticular connections with the visual cortex and the dorsal thalamus in the rat, a species where the visual pathways have been well documented. Biotinylated dextran, an anterograde and retrograde tracer, was injected into different visual cortical areas [17; rostral 18a: presumed area AL: (anterolateral); caudal 18a: presumed area LM (lateromedial); rostral 18b: presumed area AM (anteromedial); caudal 18b: presumed area PM (posteromedial)] and into different visual dorsal thalamic nuclei (posterior thalamic, lateral geniculate nuclei), and the patterns of anterograde and retrograde labelling in the reticular nucleus were examined. From the cortical injections, we find that the visual sector of the reticular nucleus is divided into subsectors that each receive an input from a distinct visual cortical area, with little or no overlap. Further, the resulting pattern of cortical terminations in the reticular nucleus reflects largely the patterns of termination in the dorsal thalamus. That is, each cortical area projects to a largely distinct subsector of the reticular nucleus, as it does to a largely distinct dorsal thalamic nucleus. As with each of the visual cortical areas, each of the visual dorsal thalamic (lateral geniculate, lateral posterior, posterior thalamic) nuclei relate to a separate territory of the reticular nucleus, with little or no overlap. Each of these dorsal thalamic territories within the reticular nucleus receives inputs from one or more of the visual cortical areas. For instance, the region to the reticular nucleus that is labelled after an injection into the lateral geniculate nucleus encompasses the reticular regions which receive afferents from cortical areas 17, rostral 18b and caudal 18b. These results suggest that individual cortical areas may influence the activity of different dorsal thalamic nuclei through their reticular connections. 相似文献