全文获取类型
收费全文 | 2959篇 |
免费 | 570篇 |
国内免费 | 251篇 |
专业分类
电工技术 | 462篇 |
综合类 | 345篇 |
化学工业 | 190篇 |
金属工艺 | 71篇 |
机械仪表 | 450篇 |
建筑科学 | 270篇 |
矿业工程 | 64篇 |
能源动力 | 188篇 |
轻工业 | 86篇 |
水利工程 | 230篇 |
石油天然气 | 121篇 |
武器工业 | 21篇 |
无线电 | 270篇 |
一般工业技术 | 202篇 |
冶金工业 | 101篇 |
原子能技术 | 11篇 |
自动化技术 | 698篇 |
出版年
2024年 | 40篇 |
2023年 | 99篇 |
2022年 | 200篇 |
2021年 | 196篇 |
2020年 | 225篇 |
2019年 | 164篇 |
2018年 | 159篇 |
2017年 | 154篇 |
2016年 | 181篇 |
2015年 | 155篇 |
2014年 | 253篇 |
2013年 | 195篇 |
2012年 | 214篇 |
2011年 | 220篇 |
2010年 | 138篇 |
2009年 | 181篇 |
2008年 | 111篇 |
2007年 | 125篇 |
2006年 | 138篇 |
2005年 | 137篇 |
2004年 | 91篇 |
2003年 | 66篇 |
2002年 | 60篇 |
2001年 | 45篇 |
2000年 | 40篇 |
1999年 | 31篇 |
1998年 | 24篇 |
1997年 | 31篇 |
1996年 | 19篇 |
1995年 | 11篇 |
1994年 | 7篇 |
1993年 | 18篇 |
1992年 | 8篇 |
1991年 | 7篇 |
1990年 | 6篇 |
1989年 | 2篇 |
1988年 | 9篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1964年 | 1篇 |
1961年 | 1篇 |
1960年 | 1篇 |
1959年 | 2篇 |
1957年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有3780条查询结果,搜索用时 15 毫秒
121.
Ignition of the external combustible elements of a building is one of the key factors leading to house loss in bushfires. Timber elements contain moisture that migrates into and out from the timber surface, depending on the surrounding ambient conditions. In extreme hot and dry conditions, such as those associated with severe bushfire weather, the moisture contents (MCs) in building timbers can drop well below the normal levels. In this paper, we not only qualify a methodology to assess the likely MCs of timbers under typical bushfire conditions, but also quantify the low levels of moisture that can be expected for the climatic conditions experienced in Melbourne—one of Australia's bushfire‐prone regions. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
122.
为了有效解决低温敏化乳化炸药在低温天气下产品质量不稳定的现状,分别从工艺参数的调整、工装条件的改善、贮存条件的改善三方面入手进行改进,使低温敏化乳化炸药在低温天气下的产品质量稳定性得到明显改善。结果表明,通过对生产线的一系列改进,在低温天气下产品质量得到明显提升,改进效果明显。 相似文献
123.
V. Srinivas Ch. Kodanda Rama Rao N. Mohan Rao 《Tribology - Materials, Surfaces & Interfaces》2018,12(2):107-114
This paper studies the effect of surface modification of multiwall carbon nanotubes (MWCNTs) prior to dispersion in engine oil to improve the tribological properties. The MWCNTs are stabilised in the lubricant with two different surfactants cetrimonium bromide (CTAB) and sorbitan monooleate (SPAN 80) and the effect of surfactants on the tribological properties has been studied. Pristine and surface modified MWCNTs in weight per cent range of 0·5% are dispersed in CI4 plus diesel engine oil. The foaming tendency and other physico-chemical properties of test lubricant have been studied to investigate the effect of nano materials and surfactants. The anti-wear and anti-friction properties are tested on a four ball wear tester and the comparison is made to assess the relative performance of pristine MWCNTs over surface modified MWCNTs. A strong influence of the surface modification technique is found on lubricating and physico-chemical properties. Both CTAB and SPAN 80 could keep the MWCNTs stable in the lubricant without compromising the foaming tendency of lubricant and other physico-chemical properties. The friction and wear characteristics of lubricants have improved with the dispersion of surface modified MWCNTs while there is no improvement in the properties of lubricant dispersed with pristine MWCNTs. 相似文献
124.
This study presents the optimization of biodiesel engine performance that can achieve the goal of fewer emissions, low fuel cost and wide engine operating range. A new biodiesel engine modeling and optimization framework based on extreme learning machine (ELM) is proposed. As an accurate model is required for effective optimization result, kernel-based ELM (K-ELM) is used instead of basic ELM because K-ELM can provide better generalization performance, and the randomness of basic ELM does not occur in K-ELM. By using K-ELM, a biodiesel engine model is first created based on experimental data. Logarithmic transformation of dependent variables is used to alleviate the problems of data scarcity and data exponentiality simultaneously. With the K-ELM engine model, cuckoo search (CS) is then employed to determine the optimal biodiesel ratio. A flexible objective function is designed so that various user-defined constraints can be applied. As an illustrative study, the fuel price in Macau is used to perform the optimization. To verify the modeling and optimization framework, the K-ELM model is compared with a least-squares support vector machine (LS-SVM) model, and the CS optimization result is compared with particle swarm optimization and experimental results. The evaluation result shows that K-ELM can achieve comparable performance to LS-SVM, resulting in a reliable prediction result for optimization. It also shows that the optimization results based on CS is effective. 相似文献
125.
Giovanni Rinaldi George Crossley Ed Mackay Ian Ashton Max Campbell Tim Wood Lars Johanning 《国际能源研究杂志》2019,43(13):7316-7335
The Maldives is a group of tropical atolls, considered globally to be one of the most desirable holiday destinations. There is an urgent requirement to decrease their dependency on fossil fuels that are currently the main source of energy, and a number of renewable energy alternatives are being evaluated. Among these, due to the favorable oceanographic and bathymetric conditions, ocean thermal energy conversion (OTEC) systems represent a viable opportunity for clean and reliable power. However, the stresses the OTEC platform will need to endure during adverse environmental conditions are not well defined. The magnitude of these stresses will then have a direct influence on the design of the OTEC device. In order to overcome this uncertainty, this paper uses hindcast data sets from global weather and ocean models to assess the metocean conditions of the Maldives, with particular reference to extreme conditions. After selecting a suitable location for the deployment of the devices, return values calculated using the peaks‐over‐threshold (POT) methodology are estimated for wind, waves, and currents. The 100‐year return value for the significant wave height is found to be 4.5 m, with a joint occurrence of energy periods between 7.5 and 8.5 seconds, whereas the 100‐year return wind has a velocity of 17.8 m/s and the 100‐year return current of 1.9 m/s. The directionality of these extreme events is also considered, showing the southern and western sub‐quadrants as the prevailing sources, which provides essential information for positioning of the platform. Additional evaluations of tropical revolving storms (TRS) and variations in temperature and salinity patterns are also provided over a 1500‐m water column; temperature varies by approximately 24°C, and salinity by around 2 ppt, showing the suitability of OTEC platforms in the Maldives. This work is therefore of interest to offshore renewable energy stakeholders interested in developing a project in the Maldives or those conducting an analogous analysis in other locations. 相似文献
126.
127.
Jie Zheng Heikki Kallio Baoru Yang 《Journal of the science of food and agriculture》2009,89(12):2011-2023
BACKGROUND: Sugars, acids and vitamin C are essential components influencing the sensory and nutritional properties of currants (Ribes sp.). In this study the effects of growth latitude and weather conditions on these components in red, white and green currant cultivars were systematically investigated for the first time. RESULTS: Red Dutch (a red Ribes rubrum cultivar) contained more malic acid but fewer sugars and had a lower sugar/acid ratio than Vertti (a green Ribes nigrum cultivar) and White Dutch (a white R. rubrum cultivar). Fructose (27–56 g L?1 juice) and glucose (21–54 g L?1) were the major sugars in all currant samples, but sucrose (7–20 g L?1) was present only in Vertti. Vertti contained the most ascorbic acid. Sugars, malic acid and the sugar/acid ratio in Red Dutch were 11–28% higher in southern Finland than in northern Finland. The corresponding values in Vertti were 6–16% lower in the south than in the north, but no differences were found in White Dutch. As the relative humidity decreased, the amounts of citric acid and total acid increased in all cultivars, while the amount of sugars increased in Vertti but decreased in White Dutch and Red Dutch. In Red Dutch, high temperature and radiation levels increased the sugar content. CONCLUSION: The influence of latitude and weather conditions on qualitative parameters of currants varies with the cultivar. This study provides important guidance for currant cultivation and for further physiological and enzymological studies. Copyright © 2009 Society of Chemical Industry 相似文献
128.
129.
MIKLAS SCHOLZ 《The International journal of environmental studies》2013,70(4):471-483
The aim was to assess the influence of a full silt trap at the end of a stormwater drainage pipe on the water quality of stormwater discharged into a semi‐natural urban watercourse. For approximately eleven weeks, the water qualities of the preliminarily treated stormwater and of the receiving watercourse (Braid Burn) were studied. The mean outflow concentrations of suspended solids were 2.0 mg/l and 34.1 mg/l during dry and wet weather conditions, respectively. Suspended solids concentrations of up to 141.6 mg/l were recorded during storm events. Suspended solids values for treated stormwater were often too high compared to international secondary wastewater treatment standards of around 30 mg/l. Pollutants including heavy metals (e.g., zinc, copper and nickel) accumulated in the silt trap. However, high outflow velocities during heavy rainfall events did not result in clearly defined sediment layers due to sediment re‐suspension. Metals did not accumulate in the receiving watercourse. 相似文献
130.
Hospitals play a critical role in helping communities respond effectively to extreme weather events (EWEs). Despite predictions of more EWEs, little is known about the process by which hospital infrastructure resilience to such events can be built. Using Gunderson and Holling’s Adaptive Cycle, a new theoretical perspective based on socio-ecological resilience theory is provided to understand this process. Data were collected using semi-structured interviews, observations of disaster drills and disaster planning meetings, as well as additional documentary analysis of past incident reports. The research findings were then refined and validated in a focus group meeting with respondents. The findings indicate that there are significant organizational barriers which prevent facilities managers improving the resilience of hospital facilities to future EWEs. It was found that the disaster planning process is ad hoc and non-inclusive, focused on man-made disasters and compliance driven, top-down approach, under-resourced and is driven by a general ignorance of the importance of resilient-built facilities to health care delivery during an EWE. It is concluded that to produce more resilient hospital infrastructure, there needs to be a more well-resourced, integrated and collaborative approach to disaster management planning which enables health facilities managers to play a more central role in disaster planning decisions. There also need to be better systems, technologies and training implemented to manage information about health infrastructure performance before, during and after EWEs. 相似文献