全文获取类型
收费全文 | 1931篇 |
免费 | 16篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 12篇 |
化学工业 | 82篇 |
金属工艺 | 17篇 |
机械仪表 | 29篇 |
建筑科学 | 19篇 |
矿业工程 | 2篇 |
能源动力 | 19篇 |
轻工业 | 91篇 |
水利工程 | 5篇 |
无线电 | 61篇 |
一般工业技术 | 117篇 |
冶金工业 | 1388篇 |
原子能技术 | 7篇 |
自动化技术 | 99篇 |
出版年
2022年 | 8篇 |
2021年 | 8篇 |
2020年 | 10篇 |
2019年 | 9篇 |
2018年 | 6篇 |
2017年 | 9篇 |
2016年 | 9篇 |
2015年 | 6篇 |
2014年 | 11篇 |
2013年 | 45篇 |
2012年 | 27篇 |
2011年 | 29篇 |
2010年 | 19篇 |
2009年 | 20篇 |
2008年 | 33篇 |
2007年 | 17篇 |
2006年 | 25篇 |
2005年 | 17篇 |
2004年 | 22篇 |
2003年 | 18篇 |
2002年 | 13篇 |
2001年 | 18篇 |
2000年 | 9篇 |
1999年 | 45篇 |
1998年 | 447篇 |
1997年 | 210篇 |
1996年 | 170篇 |
1995年 | 88篇 |
1994年 | 73篇 |
1993年 | 83篇 |
1992年 | 18篇 |
1991年 | 24篇 |
1990年 | 12篇 |
1989年 | 14篇 |
1988年 | 16篇 |
1987年 | 16篇 |
1986年 | 18篇 |
1985年 | 25篇 |
1984年 | 7篇 |
1983年 | 11篇 |
1982年 | 14篇 |
1981年 | 12篇 |
1980年 | 16篇 |
1979年 | 10篇 |
1978年 | 11篇 |
1977年 | 53篇 |
1976年 | 120篇 |
1975年 | 8篇 |
1974年 | 6篇 |
1973年 | 4篇 |
排序方式: 共有1948条查询结果,搜索用时 15 毫秒
71.
Matthew Sharp 《Urban Forum》2013,24(2):251-268
Much policy-orientated research in South Africa relies solely on large-scale surveys. Little or no case study research is undertaken as part of studies despite broad international acknowledgement of the benefits of mixing methods. In the South African poverty and demographic literature, strong arguments have been made for the incorporation of case study approaches to arrive at a deeper and more accurate understanding of social phenomena. This paper, which draws on an ethnographic study of ‘day labourers’ (both South African and foreign) in Cape Town, together with an extensive range of relevant literature, extends this line of argument to research on casual employment and relations between South Africans and foreign nationals. It highlights a number of questionable assumptions and superficial analyses present in previous survey-based research on these topics. It also discusses the potential contribution of more case study work and some of the practical issues associated with linking methodologies in development research. 相似文献
72.
Bandgap Tunability in Sb‐Alloyed BiVO4 Quaternary Oxides as Visible Light Absorbers for Solar Fuel Applications 下载免费PDF全文
73.
S. Weichenthal G. Mallach R. Kulka A. Black A. Wheeler H. You M. St‐Jean R. Kwiatkowski D. Sharp 《Indoor air》2013,23(3):175-184
Few studies have examined indoor air quality in First Nations communities and its impact on cardiorespiratory health. To address this need, we conducted a crossover study on a First Nations reserve in Manitoba, Canada, including 37 residents in 20 homes. Each home received an electrostatic air filter and a placebo filter for 1 week in random order, and lung function, blood pressure, and endothelial function measures were collected at the beginning and end of each week. Indoor air pollutants were monitored throughout the study period. Indoor PM2.5 decreased substantially during air filter weeks relative to placebo (mean difference: 37 μg/m3, 95% CI: 10, 64) but remained approximately five times greater than outdoor concentrations owing to a high prevalence of indoor smoking. On average, air filter use was associated with a 217‐ml (95% CI: 23, 410) increase in forced expiratory volume in 1 s, a 7.9‐mm Hg (95% CI: ?17, 0.82) decrease in systolic blood pressure, and a 4.5‐mm Hg (95% CI: ?11, 2.4) decrease in diastolic blood pressure. Consistent inverse associations were also observed between indoor PM2.5 and lung function. In general, our findings suggest that reducing indoor PM2.5 may contribute to improved lung function in First Nations communities. 相似文献
74.
Plasma ignition threshold of nanoparticle-based and bulk silver targets was measured in air. The plasma was initiated by a Nd:YAG laser at wavelengths of 355, 532, and 1064 nm. The plasma ignition was monitored utilizing the prominent Ag I line at 546.5 nm. Lower ignition thresholds of the nanoparticle-based silver target were estimated at 0.4?±?0.02, 0.34?±?0.04, and 0.27?±?0.035 J cm~(-2) coupled with the different laser wavelengths, respectively. In contrast, the bulk silver target plasma exhibited an order of magnitude higher ignition threshold. A three orders of magnitude enhanced emission intensity from the nano-based target over the bulk target was achieved at lower levels of laser irradiation. A reduction of the thermal diffusion length of the nanosilver was assumed in order to theoretically predict this reduction in the plasma threshold. In addition, the effect of self-reversal on the resonance lines was taken into consideration. 相似文献
75.
Abstract: Phenolic compounds and anthocyanins in muscadines have attracted much attention due to their diverse biological activities. With bioassays of antioxidant activities in terms of total phenolic content (TPC), total anthocyanin content (TAC), total procyanidin content (TPA), oxygen radical absorbance capacity (ORAC), and ferric reducing antioxidant power (FRAP) of different parts of the Noble muscadine, the butanol (BuOH) extract of the muscadine skin showed the highest TPC (317.91 ± 1.83 mg GAE/100 g FW), which might be ascribed to its high TAC of 227.06 ± 1.29 mg/100 g fresh weight (FW). The ethyl acetate (EtOAc) extract of the muscadine seed contained the highest TPA (55.30 ± 0.63 mg CE/100 g FW). Correlation analyses demonstrated a significant linear relationship of TPC and TAC compared to their ORAC and FRAP values within the range of R2 from 0.9283 to 0.9936, which suggested that phenolics and anthocyanins in the extracts contributed significantly to their antioxidant potential. Nineteen individual phenolics and 5 anthocyanins were identified by HPLC‐MS, which indicated different chemical profiles of anthocyanins and other phenolics in the muscadine extracts. Practical Application: The paper has provided rich information of bioactive phytochemical profiles in different solvent extracts and their correlation with the antioxidant activity in the muscadine that is a very special regional fruit in U.S. Its high content of phenolic compounds demonstrates that muscadine could be beneficial to human health. 相似文献
76.
Jon R Saunders Heather Allison Chloe E James Alan J McCarthy Richard Sharp 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2001,76(7):662-666
Bacteriophages as accessory genetic elements play a crucial role in the dissemination of genes and the promotion of genetic diversity within bacterial populations. Such horizontal transfer of DNA is critical in the emergence of new pathogenic organisms, through the dissemination of genes encoding virulence factors such as toxins, adhesins and agressins. Phages can transfer genes that are not necessary for bacteriophage persistence and are generally recognised by their ability to convert their host bacteria to new phenotypes. This phenomenon is known as phage conversion. If such converting genes encode for virulence factors, the consequences of phage infection may include increased virulence of the host bacteria, and the conversion of a non‐pathogenic strain to a potentially dangerous pathogen. A number of virulence factors in bacteria causing diseases in plants, animals and humans are encoded by converting phages, the vast majority of which are temperate as opposed to lytic in nature. © 2001 Society of Chemical Industry 相似文献
77.
Amy I. Nathanson Molly L. Sharp Fashina Aladé Eric E. Rasmussen Katheryn Christy 《The Journal of communication》2013,63(6):1088-1108
This study explored the relation between preschoolers' television exposure and one important indicator of cognitive processing called theory of mind (ToM). A total of 107 preschoolers and their parents provided data on the preschoolers' television exposure (including both intentional viewing and exposure via background television), parent–child discussion of television, and preschoolers' ToM. The results indicated that preschoolers who were exposed to more background television and who had a television in their bedroom performed more poorly on ToM assessments compared with other children. Parent–child discussion of television was positively related to ToM performance, however. These results have implications for how we understand the effects of television on preschoolers. 相似文献
78.
Laurus nobilis is one of the most broadly used spices in Moroccan gastronomy. Its antimicrobial activity against both gram-positive and gram-negative bacterial species was demonstrated. Likewise, its toxicity was investigated on Swiss albinos' mice . Daily, mice were treated orally with 0.003 and 0.3 mg during 7 days. Plasmatic markers and enzymatic systems were assessed and histological alterations were evaluated. A significant increase in creatine phosphokinase level was observed. The microscopic evaluation showed that L. nobilis induces morphological perturbation in mice's liver. The results also showed an inhibitory effect of glyceraldehydes 3-phosphate dehydrogenase and an important increase in the level of thiobarbituric acid reactive substances and succinate dehydrogenase and no change in catalase activities. The results showed that L. nobilis induces toxicity at 0.3 mg/g mouse and affects energy metabolism and oxidative stress.
The aim of the present study is to determine the antimicrobial effect of Laurus nobilis on pathogens for potential application as herbal medicine in infusion or oral preparation. The effect of the spice extract was investigated on the metabolic markers, stress biomarkers and clinical parameters. This study was completed with histological coupes. To our knowledge, this is the first report to demonstrate the laurel effect on energy metabolism and oxidative stress. 相似文献
PRACTICAL APPLICATIONS
The aim of the present study is to determine the antimicrobial effect of Laurus nobilis on pathogens for potential application as herbal medicine in infusion or oral preparation. The effect of the spice extract was investigated on the metabolic markers, stress biomarkers and clinical parameters. This study was completed with histological coupes. To our knowledge, this is the first report to demonstrate the laurel effect on energy metabolism and oxidative stress. 相似文献
79.
80.
O. A. SEBAKHY M. I. EL SINGABY I. F. EL ARABAWY 《International journal of control》2013,86(4):1171-1186
An iterative algorithm, developed by the authors to compute the finite zeros of a linear multivariable system (Sebakhy et al. 1983), is extended to compute the infinite zeros of the system as well. The method is simple, efficient and suitable for programming on a digital computer 相似文献