全文获取类型
收费全文 | 1688篇 |
免费 | 20篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 4篇 |
化学工业 | 256篇 |
金属工艺 | 30篇 |
机械仪表 | 56篇 |
建筑科学 | 8篇 |
能源动力 | 26篇 |
轻工业 | 105篇 |
水利工程 | 3篇 |
石油天然气 | 2篇 |
无线电 | 112篇 |
一般工业技术 | 167篇 |
冶金工业 | 868篇 |
原子能技术 | 10篇 |
自动化技术 | 63篇 |
出版年
2023年 | 4篇 |
2022年 | 7篇 |
2021年 | 19篇 |
2020年 | 8篇 |
2019年 | 5篇 |
2018年 | 10篇 |
2017年 | 10篇 |
2016年 | 9篇 |
2015年 | 7篇 |
2014年 | 28篇 |
2013年 | 35篇 |
2012年 | 41篇 |
2011年 | 43篇 |
2010年 | 39篇 |
2009年 | 43篇 |
2008年 | 45篇 |
2007年 | 37篇 |
2006年 | 21篇 |
2005年 | 33篇 |
2004年 | 44篇 |
2003年 | 48篇 |
2002年 | 45篇 |
2001年 | 29篇 |
2000年 | 43篇 |
1999年 | 63篇 |
1998年 | 260篇 |
1997年 | 169篇 |
1996年 | 120篇 |
1995年 | 84篇 |
1994年 | 60篇 |
1993年 | 54篇 |
1992年 | 17篇 |
1991年 | 24篇 |
1990年 | 30篇 |
1989年 | 19篇 |
1988年 | 23篇 |
1987年 | 17篇 |
1986年 | 15篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 3篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1978年 | 5篇 |
1977年 | 17篇 |
1976年 | 18篇 |
1975年 | 4篇 |
1974年 | 5篇 |
1973年 | 6篇 |
1970年 | 4篇 |
排序方式: 共有1710条查询结果,搜索用时 31 毫秒
1.
2.
BACKGROUND: The effect of topical corticosteroids after excimer laser photorefractive keratectomy (PRK) remains a matter of some controversy. Refractive effects may be different according to the amount of myopia and timing of instillation. METHODS: Two groups of patients were studied: Study A consisted of 215 eyes (128 patients) with PRK (mean baseline myopia, -6.53 +/- 2.22 D) that received no corticosteroids (No Corticosteroid Group) unless significant regression or corneal haze appeared (Delayed Corticosteroid Group), and in Study B, we randomly assigned eyes to the Initial Corticosteroid Group (mean baseline myopia, -6.39 +/- 1.84 D) or the No/delayed Corticosteroid Group (mean baseline myopia -5.78 +/- 2.02 D). Clinical results after PRK for low-to-moderate and high myopia were compared. RESULTS: In the first group, 70.9% (73 eyes) of moderately myopic eyes (mean, -4.56 +/- 1.10 D) belonged to the No Corticosteroid Group that had a mean refraction of -5.39 +/- 1.77 D. Delayed Corticosteroid Group eyes were more myopic (mean, -7.52 +/- 2.10 D), and showed more severe haze than those in the No Corticosteroid Group. In study B, only in high myopes with more than -6.00 D (mean, -7.76 +/- 1.15 D) did refraction and corneal haze outcomes show significant difference between the Initial Corticosteroid Group and the No/delayed Corticosteroid Group. CONCLUSIONS: The effects of topical corticosteroids after PRK were less in moderate myopes compared to high myopes. Delayed instillation of corticosteroids did not reverse the regression or haze whereas initial instillation showed a beneficial effect on high myopes but not on moderate myopes. 相似文献
3.
M Beltramo N Stella A Calignano SY Lin A Makriyannis D Piomelli 《Canadian Metallurgical Quarterly》1997,277(5329):1094-1097
Anandamide, an endogenous ligand for central cannabinoid receptors, is released from neurons on depolarization and rapidly inactivated. Anandamide inactivation is not completely understood, but it may occur by transport into cells or by enzymatic hydrolysis. The compound N-(4-hydroxyphenyl)arachidonylamide (AM404) was shown to inhibit high-affinity anandamide accumulation in rat neurons and astrocytes in vitro, an indication that this accumulation resulted from carrier-mediated transport. Although AM404 did not activate cannabinoid receptors or inhibit anandamide hydrolysis, it enhanced receptor-mediated anandamide responses in vitro and in vivo. The data indicate that carrier-mediated transport may be essential for termination of the biological effects of anandamide, and may represent a potential drug target. 相似文献
4.
JW Rhee 《The Journal of communication》1997,47(3):26-48
This study examines how news frames in campaign coverage affect individuals' interpretation of campaigns. Framing effects are conceptualized in terms of the process by which textual features in news stories set limits on knowledge use in the construction of a discourse model - a mental model constructed through the interaction between news frames and the interpreter's social knowledge. Examining message structures in campaign news stories led to identifying two major frames in campaign coverage: strategy and issue. Narrative data collected from two field experiments were analyzed. The findings suggest that both strategy-framed and issue-framed print news stories are effective in influencing campaign interpretation. 相似文献
5.
OBJECTIVE: We hypothesized that institutionalized patients with dementia, who frequently have feeding problems and require supervised and assisted feeding, would lose more weight during their residency than nondemented, independently functioning residents and have compromised survival. To test this hypothesis, we examined the survival and longitudinal changes in weight of two cohorts of institutionalized residents with dementia and compared these cohorts with a cohort of nondemented residents. We also measured the resting energy expenditures of a subset of the subjects with dementia as an indicator of their energy needs. DESIGN: A longitudinal cohort study with retrospective baseline chart review and subsequent follow-up of monthly weights and mortality over 4 years. SETTING: A 725-bed long-term care institution with specified levels of care. SUBJECTS: Two cohorts of residents with dementia, one consisting of subjects who required total care throughout their institutional stay (n = 31) and another group who did not initially require total care (n = 48); these were compared with a cohort with normal mentation who were functionally independent in their daily activities (n = 26). The total number of subjects was 105. MEASUREMENTS: Demographics, medical problems, and medications by chart review; functional and mental status evaluations; longitudinal monthly weights and mortality for the 48-month study period; and resting energy expenditures by indirect calorimetry. MAIN RESULTS: Residents with dementia had lower weights on admission and throughout their stay than nondemented, independently functioning residents, and they were more likely to have a weight loss of 10 lbs or more at some point during the 4-year study period. However, their mean weights did not change during the study period. The mean survival from admission of those demented residents who died was more than 3 years. Resting energy expenditures of women residents with advanced dementia were 12% lower than predicted from the Harris Benedict equations. CONCLUSION: Dementia is not necessarily associated with unremitting weight loss during institutionalization despite the frequent occurrence of feeding difficulties and temporary weight loss. This may be caused partly by the lower than expected resting energy expenditures and, hence, energy needs of affected residents as their dementia progresses. Demented residents weighed significantly less than nondemented, independently functioning residents throughout their institutional stay. Nevertheless, nursing staff are able to maintain weight and survival for extended periods even in very impaired residents. 相似文献
6.
7.
8.
Low dielectric poly[methylsilsesquioxane‐ran‐trifluoropropylsilsesquioxane‐ran‐(2,4,6,8‐tetramethyl‐2,4,6,8‐tetraethylenecyclotetrasiloxane)silsesquioxane]s {P[M‐ran‐TFP‐ran‐(TCS)]SSQs} having various compositions were synthesized using trifluoropropyl trimethoxysilane, methyl trimethoxysilane and 2,4,6,8‐tetramethyl‐2,4,6,8‐tetra(trimethoxysilylethyl)cyclotetrasiloxane. The chemical composition of the polymers and the content of SiOH end‐groups were controlled by adjusting the reaction conditions, and they were characterized by 1H‐NMR. The thermally decomposable trifluoropropyl groups on the P[M‐ran‐TFP‐ran‐(TCS)]SSQ backbone and heptakis(2,3,6‐tri‐O‐methyl)‐β‐cyclodextrin (CD) were employed as pore generators. The dielectric constants of the porous CD/P[M‐ran‐TFP‐ran‐(TCS)]SSQ films were in the range 2.0–2.7 (at 100 kHz) depending on the concentration of the porogens, and showed no change over 4 days under aqueous conditions. The pore size of the films showed a bimodal distribution, with diameters of ca 0.5–1.0 nm for those originating from the trifluoropropyl groups and 1.7 nm from the CD. The elastic modulus and hardness of the 30 vol% CD‐blended film with a dielectric constant of 2.26 were 2.40 and 0.38 GPa, respectively, as determined by a nanoindenter. Copyright © 2005 Society of Chemical Industry 相似文献
9.
10.