全文获取类型
收费全文 | 1708篇 |
免费 | 29篇 |
专业分类
电工技术 | 9篇 |
化学工业 | 151篇 |
金属工艺 | 7篇 |
机械仪表 | 16篇 |
建筑科学 | 30篇 |
矿业工程 | 1篇 |
能源动力 | 14篇 |
轻工业 | 69篇 |
水利工程 | 2篇 |
无线电 | 176篇 |
一般工业技术 | 136篇 |
冶金工业 | 1021篇 |
原子能技术 | 18篇 |
自动化技术 | 87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 | 22篇 |
2012年 | 29篇 |
2011年 | 34篇 |
2010年 | 27篇 |
2009年 | 27篇 |
2008年 | 23篇 |
2007年 | 29篇 |
2006年 | 22篇 |
2005年 | 27篇 |
2004年 | 28篇 |
2003年 | 18篇 |
2002年 | 22篇 |
2001年 | 18篇 |
2000年 | 18篇 |
1999年 | 47篇 |
1998年 | 305篇 |
1997年 | 192篇 |
1996年 | 126篇 |
1995年 | 87篇 |
1994年 | 70篇 |
1993年 | 73篇 |
1992年 | 22篇 |
1991年 | 20篇 |
1990年 | 19篇 |
1989年 | 21篇 |
1988年 | 15篇 |
1987年 | 19篇 |
1986年 | 20篇 |
1985年 | 22篇 |
1984年 | 6篇 |
1983年 | 15篇 |
1982年 | 6篇 |
1981年 | 18篇 |
1980年 | 17篇 |
1979年 | 10篇 |
1978年 | 15篇 |
1977年 | 38篇 |
1976年 | 53篇 |
1975年 | 8篇 |
1973年 | 7篇 |
1971年 | 7篇 |
1970年 | 5篇 |
排序方式: 共有1737条查询结果,搜索用时 0 毫秒
1.
2.
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
3.
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
4.
5.
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
6.
In anesthetized intact rats, cerebral blood flow is autoregulated until mean arterial blood pressure (MAP) exceeds 150 mmHg. At higher pressures cerebral blood flow breaks through autoregulation and rapidly increases. However, interruption of the arterial baroreceptor reflex eliminates breakthrough of autoregulation. Thus, breakthrough may reflect active rather than passive vasodilatation. We, therefore, sought to determine if breakthrough depends upon synthesis of the vasodilator nitric oxide. Thirty-eight anesthetized adult male Sprague-Dawley rats were studied. In all, MAP was raised by slow i.v. infusion of phenylephrine. In rats pretreated with the nitric oxide synthase inhibitor L-nitroarginine (L-NA; 22 mg/kg i.v.) or with a combination of L-NA plus D-arginine (D-Arg; 240 mg/kg i.v.), breakthrough did not occur even when MAP exceeded 185 mmHg (L-NA) and 165 mmHg (D-Arg). In contrast, breakthrough occurred in rats treated with L-NA plus L-arginine (L-Arg; 240 mg/kg i.v.) and in rats whose basal vascular tone had been increased by pretreatment with arginine vasopressin prior to infusion of phenylephrine. Removal of sympathetic innervation to cerebral vessels attenuated, but did not eliminate, effects of L-NA on breakthrough. Thus, vasodilatation seen with breakthrough of autoregulation depends upon release of nitric oxide or a nitric oxide donor. 相似文献
7.
This study examined concordance between self-reported drug use and urinalysis data among 341 applicants for methadone treatment in Sydney, Australia. Rates of under-reporting of use of specific drugs were low (0% to 10%). Irregular drug use, short half-life of some abused drugs, and relatively low sensitivity of the TLC assay procedure led to most detected drugs being found in only one of two urine samples collected. Subjects reported having recently used nearly twice as many drugs as were detected in their urine. Agreement (kappa) between self-report and urinalysis results was in the fair to good range for most drugs. None of the six predictors of misreporting examined were found to be of practical value. 相似文献
8.
9.
10.