全文获取类型
收费全文 | 38826篇 |
免费 | 2968篇 |
国内免费 | 1680篇 |
专业分类
电工技术 | 2145篇 |
综合类 | 1403篇 |
化学工业 | 9257篇 |
金属工艺 | 1254篇 |
机械仪表 | 1599篇 |
建筑科学 | 581篇 |
矿业工程 | 308篇 |
能源动力 | 11694篇 |
轻工业 | 2932篇 |
水利工程 | 100篇 |
石油天然气 | 1177篇 |
武器工业 | 236篇 |
无线电 | 3002篇 |
一般工业技术 | 3450篇 |
冶金工业 | 1185篇 |
原子能技术 | 1764篇 |
自动化技术 | 1387篇 |
出版年
2024年 | 122篇 |
2023年 | 849篇 |
2022年 | 2023篇 |
2021年 | 2398篇 |
2020年 | 1616篇 |
2019年 | 1509篇 |
2018年 | 1229篇 |
2017年 | 1422篇 |
2016年 | 1340篇 |
2015年 | 1222篇 |
2014年 | 2178篇 |
2013年 | 2740篇 |
2012年 | 2344篇 |
2011年 | 3464篇 |
2010年 | 2478篇 |
2009年 | 2207篇 |
2008年 | 2134篇 |
2007年 | 2119篇 |
2006年 | 1800篇 |
2005年 | 1426篇 |
2004年 | 1179篇 |
2003年 | 954篇 |
2002年 | 879篇 |
2001年 | 749篇 |
2000年 | 573篇 |
1999年 | 434篇 |
1998年 | 375篇 |
1997年 | 319篇 |
1996年 | 256篇 |
1995年 | 200篇 |
1994年 | 169篇 |
1993年 | 142篇 |
1992年 | 125篇 |
1991年 | 86篇 |
1990年 | 65篇 |
1989年 | 61篇 |
1988年 | 46篇 |
1987年 | 30篇 |
1986年 | 34篇 |
1985年 | 40篇 |
1984年 | 26篇 |
1983年 | 14篇 |
1982年 | 26篇 |
1981年 | 11篇 |
1980年 | 19篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1975年 | 2篇 |
1959年 | 11篇 |
1951年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
《International Journal of Hydrogen Energy》2022,47(52):22114-22146
Direct methanol fuel cells (DMFC), among the most suited and prospective alternatives for portable electronics, have lately been treated with nanotechnology. DMFCs may be able to remedy the energy security issue by having low operating temperatures, high conversion efficiencies, and minimal emission levels. Though, slow reaction kinetics are a significant restriction of DMFC, lowering efficiency and energy output. Nowadays, research is more focused on fundamental studies that are studying the factors that can improve the capacity and activity of catalysts. In DMFC, among the most widely explored catalysts are platinum and ruthenium which are enhanced in nature by the presence of supporting materials such as nanocarbons and metal oxides. As a result, this research sheds light on nanocatalyst development for DMFCs based on Platinum noble metal. To summarize, this research focuses on the structure of nanocatalysts, as well as support materials for nanocatalysts that can be 3D, 2D, 1D, or 0D. The support material described is made up of CNT, CNF, and CNW, which are the most extensively used because they improve the performance of catalysts in DMFCs. In addition, cost estimations for fuel cell technology are emphasized to show the technology's status and requirements. Finally, challenges to nanocatalyst development have been recognized, as well as future prospects, as recommendations for more innovative future research. 相似文献
32.
33.
《International Journal of Hydrogen Energy》2022,47(75):32303-32314
Membrane electrode assembly (MEA) is considered a key component of a proton exchange membrane fuel cell (PEMFC). However, developing a new MEA to meet desired properties, such as operation under low-humidity conditions without a humidifier, is a time- and cost-consuming process. This study employs a machine-learning-based approach using K-nearest neighbor (KNN) and neural networks (NN) in the MEA development process by identifying a suitable catalyst layer (CL) recipe in MEA. Minimum redundancy maximum relevance and principal component analysis were implemented to specify the most important predictor and reduce the data dimension. The number of predictors was found to play an essential role in the accuracy of the KNN and NN models although the predictors have self-correlations. The KNN model with a K of 7 was found to minimize the model loss with a loss of 11.9%. The NN model constructed by three corresponding hidden layers with nine, eight, and nine nodes can achieve the lowest error of 0.1293 for the Pt catalyst and 0.031 for PVA as a good additive blending in the CL of the MEA. However, even if the error is low, the prediction of PVA seems to be inaccurate, regardless of the model structure. Therefore, the KNN model is more appropriate for CL recipe prediction. 相似文献
34.
《International Journal of Hydrogen Energy》2022,47(36):16165-16178
This study deals with the manufacturing of catalyst-coated membranes (CCMs) for newcomers in the field of coating. Although there are many studies on electrode ink composition for improving the performance of proton-exchange membrane fuel cells (PEMFCs), there are few papers dealing with electrode coating itself. Usually, it is a know-how that often remains secret and constitutes the added value of scientific teams or the business of industrialists. In this paper, we identify and clarify the role of key parameters to improve coating quality and also to correlate coating quality with fuel cell performance via polarization curves and electrochemical active surface area measurements. We found that the coating configurations can affect the performance of lab-made CCMs in PEMFCs. After the repeatability of the performance obtained by our coating method has been proved, we show that: (i) edge effects, due to mask shadowing - cannot be neglected when the active surface area is low, (ii) a heterogeneous thickness electrode produces performance lower than a homogeneous thickness electrode, and (iii) the origin and storage of platinum on carbon powders are a very important source of variability in the obtained results. 相似文献
35.
《International Journal of Hydrogen Energy》2022,47(18):10409-10419
The utilization of renewable gaseous fuels in the diesel engine has gained significant interest in recent years due to its clean-burning nature and higher availability. In this study, hydrogen-rich reformed biogas was used as a gaseous fuel in a common rail diesel engine with diesel as pilot fuel. The hydrogen-rich reformed gas was synthesized through dry-oxidative reforming. The experimentations were performed in the load range from 6 to 24 N m with two different flow rates of gaseous fuel (0.5 and 1.5 kg/h) at a constant speed of 1800 RPM. The effects on engine performance parameters (brake thermal efficiency, brake specific energy consumption, and brake specific diesel consumption), combustion parameters (rate of pressure rise and maximum heat release rate) and emission parameters (Unburnt hydrocarbons, nitrogen oxides, carbon monoxide, and carbon dioxide) were assessed. The induction of gaseous fuel led to an increase in brake thermal efficiency by 10.5%, reduction in brake specific energy consumption by 13.6%, and a reduction of 26.4% in brake specific diesel consumption with a flow rate of 0.5 kg/h when compared to diesel-only mode at 24 N m load. The HC, NOX and CO2 emissions were reduced by 18.2%, 7.4% and 1.4% with a flow rate of 0.5 kg/h when compared to diesel-only mode at 24 N m load due to lower availability of carbon content in the combustible mixture. The utilization of renewable fuel like hydrogen-rich reformed biogas has great potential for overcoming the issue related to both biogas and hydrogen in diesel engines. Moreover, the higher diesel substitution also demonstrates the potential for cost-saving and fossil fuel conservation. 相似文献
36.
37.
Lucía Beltrn-Camacho Marta Rojas-Torres M
Carmen Durn-Ruiz 《International journal of molecular sciences》2021,22(5)
Critical limb ischemia (CLI) constitutes the most severe form of peripheral arterial disease (PAD), it is characterized by progressive blockade of arterial vessels, commonly correlated to atherosclerosis. Currently, revascularization strategies (bypass grafting, angioplasty) remain the first option for CLI patients, although less than 45% of them are eligible for surgical intervention mainly due to associated comorbidities. Moreover, patients usually require amputation in the short-term. Angiogenic cell therapy has arisen as a promising alternative for these “no-option” patients, with many studies demonstrating the potential of stem cells to enhance revascularization by promoting vessel formation and blood flow recovery in ischemic tissues. Herein, we provide an overview of studies focused on the use of angiogenic cell therapies in CLI in the last years, from approaches testing different cell types in animal/pre-clinical models of CLI, to the clinical trials currently under evaluation. Furthermore, recent alternatives related to stem cell therapies such as the use of secretomes, exosomes, or even microRNA, will be also described. 相似文献
38.
39.
Indoor surfaces may be adsorptive sinks with the potential to change Indoor Air Quality. To estimate this effect, the sorption parameters of formaldehyde and toluene were assessed on five floorings by an experimental method using solid-phase microextraction in an airtight emission cell. Adsorption rate constants ranged from 0.003 to 0.075 m·h−1, desorption rate constants from 0.019 to 0.51 h−1, and the partition coefficient from 0.005 to 3.9 m, and these parameters vary greatly from one volatile organic compound/material couple to another indicating contrasted sorption behaviors. A rubber was identified as a sink of formaldehyde characterized by a very low desorption constant close to 0. For these sorbent floorings identified, the adsorption rates of formaldehyde are from 2 to 4 times higher than those of toluene. Two models were used to evaluate the sink effects of floorings on indoor pollutant concentrations in one room from different realistic conditions. The scenarios tested came to the conclusion that the formaldehyde sorption on one rubber (identified as a sink) has a maximum contribution from 15% to 21% for the conditions of low air exchange rate. For other floorings, the sorption has a minor contribution less than or equal to 5%, regardless of the air exchange rate. 相似文献
40.
Fluorescence‐Activated Cell Sorters: Standing Surface Acoustic Wave (SSAW)‐Based Fluorescence‐Activated Cell Sorter (Small 40/2018) 下载免费PDF全文