全文获取类型
收费全文 | 1626篇 |
免费 | 138篇 |
国内免费 | 60篇 |
专业分类
电工技术 | 110篇 |
综合类 | 93篇 |
化学工业 | 810篇 |
金属工艺 | 32篇 |
机械仪表 | 15篇 |
建筑科学 | 38篇 |
矿业工程 | 39篇 |
能源动力 | 253篇 |
轻工业 | 86篇 |
水利工程 | 7篇 |
石油天然气 | 35篇 |
武器工业 | 8篇 |
无线电 | 82篇 |
一般工业技术 | 78篇 |
冶金工业 | 64篇 |
原子能技术 | 21篇 |
自动化技术 | 53篇 |
出版年
2023年 | 26篇 |
2022年 | 31篇 |
2021年 | 49篇 |
2020年 | 42篇 |
2019年 | 53篇 |
2018年 | 41篇 |
2017年 | 34篇 |
2016年 | 39篇 |
2015年 | 49篇 |
2014年 | 54篇 |
2013年 | 52篇 |
2012年 | 68篇 |
2011年 | 107篇 |
2010年 | 76篇 |
2009年 | 103篇 |
2008年 | 90篇 |
2007年 | 130篇 |
2006年 | 72篇 |
2005年 | 81篇 |
2004年 | 69篇 |
2003年 | 94篇 |
2002年 | 96篇 |
2001年 | 91篇 |
2000年 | 67篇 |
1999年 | 50篇 |
1998年 | 39篇 |
1997年 | 22篇 |
1996年 | 31篇 |
1995年 | 11篇 |
1994年 | 13篇 |
1993年 | 11篇 |
1992年 | 13篇 |
1991年 | 4篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有1824条查询结果,搜索用时 15 毫秒
1.
Zaidatul Akmal Othman Zaida Zakaria Joseph Bagi Suleiman Victor Udo Nna Aminah Che Romli Wan Syaheedah Wan Ghazali Mahaneem Mohamed 《International journal of molecular sciences》2021,22(8)
Obesity and hyperlipidemia are major risk factors for developing vascular diseases. Bee bread (BB) has been reported to exhibit some biological actions, including anti-obesity and anti-hyperlipidemic. This study aims to investigate whether bee bread can ameliorate vascular inflammation and impaired vasorelaxation activity through eNOS/NO/cGMP pathway in obese rats. Forty male Sprague-Dawley rats were randomly divided into four groups (n = 10/group), namely: control (normal group), obese rats (OB group), obese rats treated with bee bread (0.5 g/kg/day, OB/BB group) and obese rats treated with orlistat (10 mg/kg/day, OB/OR group). The latter three groups were given a high-fat diet (HFD) for 6 weeks to induced obesity before being administered with their respective treatments for another 6 weeks. After 12 weeks of the total experimental period, rats in the OB group demonstrated significantly higher Lee obesity index, lipid profile (total cholesterol, triglyceride, low-density lipoprotein), aortic proinflammatory markers (tumor necrosis factor-α, nuclear factor-κβ), aortic structural damage and impairment in vasorelaxation response to acetylcholine (ACh). Bee bread significantly ameliorated the obesity-induced vascular damage manifested by improvements in the lipid profile, aortic inflammatory markers, and the impaired vasorelaxation activity by significantly enhancing nitric oxide release, promoting endothelial nitric oxide synthase (eNOS) and cyclic guanosine monophosphate (cGMP) immunoexpression. These findings suggest that the administration of bee bread ameliorates the impaired vasorelaxation response to ACh by improving eNOS/NO/cGMP-signaling pathway in obese rats, suggesting its vascular therapeutic role. 相似文献
2.
Young Been Kim Sung Hyeon Jung Dong Su Kim Nishad G. Deshpande Hee Won Suh Hak Hyeon Lee Ji Hoon Choi Ho Seong Lee Hyung Koun Cho 《Advanced functional materials》2021,31(38):2102439
Antimony triselenide (Sb2Se3) nanoflake-based nitrogen dioxide (NO2) sensors exhibit a progressive bifunctional gas-sensing performance, with a rapid alarm for hazardous highly concentrated gases, and an advanced memory-type function for low-concentration (<1 ppm) monitoring repeated under potentially fatal exposure. Rectangular and cuboid shaped Sb2Se3 nanoflakes, comprising van der Waals planes with large surface areas and covalent bond planes with small areas, can rapidly detect a wide range of NO2 gas concentrations from 0.1 to 100 ppm. These Sb2Se3 nanoflakes are found to be suitable for physisorption-based gas sensing owing to their anisotropic quasi-2D crystal structure with extremely enlarged van der Waals planes, where they are humidity-insensitive and consequently exhibit an extremely stable baseline current. The Sb2Se3 nanoflake sensor exhibits a room-temperature/low-voltage operation, which is noticeable owing to its low energy consumption and rapid response even under a NO2 gas flow of only 1 ppm. As a result, the Sb2Se3 nanoflake sensor is suitable for the development of a rapid alarm system. Furthermore, the persistent gas-sensing conductivity of the sensor with a slow decaying current can enable the development of a progressive memory-type sensor that retains the previous signal under irregular gas injection at low concentrations. 相似文献
3.
Graphene-based heterostructure composite is a new type of advanced sensing material that includes composites of graphene with noble metals/metal oxides/metal sulfides/polymers and organic ligands. Exerting the synergistic effect of graphene and noble metals/metal oxides/metal sulfides/polymers and organic ligands is a new way to design advanced gas sensors for nitrogen-containing gas species including NH3 and NO2 to solve the problems such as poor stability, high working temperature, poor recovery, and poor selectivity. Different fabrication methods of graphene-based heterostructure composite are extensively studied, enabling massive progress in developing chemiresistive-type sensors for detecting the nitrogen-containing gas species. With the components of noble metals/metal oxides/metal sulfides/polymers and organic ligands which are composited with graphene, each material has its attractive and unique electrical properties. Consequently, the corresponding composite formed with graphene has different sensing characteristics. Furthermore, working ambient gas and response type can affect gas-sensitive characteristic parameters of graphene-based heterostructure composite sensing materials. Moreover, it requires particular attention in studying gas sensing mechanism of graphene-based heterostructure composite sensing materials for nitrogen-containing gas species. This review focuses on related scientific issues such as material synthesis methods, sensing performance, and gas sensing mechanism to discuss the technical challenges and several perspectives. 相似文献
4.
《能源学会志》2020,93(2):496-507
Hydrocarbons could be used as the reductant for elimination of NOx emissions. Liquid petroleum gas, with higher carbon hydrocarbons and cheaper costs, may be of practical value as reducing agents. Due to the consumption of hydrocarbons by oxygen, the NOx reduction efficiency is significantly inhibited by oxygen in the flue gas. In this research, a novel rotary reactor, realizing the alternating cycle of adsorption zone and reduction zone, was proposed to overcome this negative effect. Co–Ce–Ti mixed oxide catalysts synthesized by a sol–gel method were tested in a simulated rotary reactor for NOx removal by liquid petroleum gas and characterized by SEM, BET, XRD and XPS. The results showed that catalysts exhibited better NO conversion efficiency at higher temperature but were highly susceptible to oxygen. Catalysts achieved nearly full removal of NOx from flue gas at 300 °C in a simulated rotary reactor, and 300 °C is considered to be the most optimum temperature with lower energy consumption and excellent flue gas purification performance. 相似文献
5.
果蔬在采后以及贮藏过程中易发生氧化褐变、组织软化、腐烂变质等生理生化变化,造成果蔬品质下降、经济损失和资源的浪费,因此,果蔬保鲜技术的研究与应用显得尤为重要。熏蒸技术主要是利用熏蒸剂在密闭空间内以气态形式扩散并与果蔬作用,通过调控多酚氧化酶(PPO)、过氧化物酶(POD)和超氧化物歧化酶(SOD)等酶活性、抑制细菌生长等方面发挥保鲜作用。本文主要综述了近年来普遍使用的乙醇、一氧化氮和植物精油等熏蒸剂在果蔬保鲜中应用研究进展,为果蔬保鲜研究中熏蒸剂的选择与熏蒸技术的应用提供理论依据。 相似文献
6.
《International Journal of Hydrogen Energy》2020,45(39):20491-20500
The unburned H2 can be used to reduce NO emission in conventional TWC (three-way catalyst) for a hydrogen internal combustion engine when it works at equivalence ratio marginally higher than the stoichiometric ratio. To explore the effects and feasibility of this reaction, a Perfectly Stirred Reactor simulation model of TWC has been built with simplified mechanisms. Experiments on a 2.3 L turbocharged hydrogen engine are used to verify the conclusion. It shows that rising initial temperature accelerates the reduction of NO and the maximum reaction rate occurs at 400 °C temperature. The conversion efficiency of NO remains approximately 0 when temperatures below 300 °C. The efficiency reaches a peak value of approximately 98% with 400 °C and declines gradually. The unburned H2 to NO mixing ratio greater than 1.5 in TWC guarantees 100% NO conversion efficiency. The experiments indicate that the NOx concentration decreases from 2056 ppm to 41 ppm at the stoichiometric ratio after the treatment of TWC and NOx reaches 0 ppm with a rich ratio. Results also demonstrate that the suitable reaction temperatures for TWC locate in the range of 400 °C–500 °C. Therefore, if the temperature and the mixing ratio are appropriate, it can achieve zero emissions with NOx reduction by unburned H2 in conventional TWC for a hydrogen engine. 相似文献
7.
G.M. Kosmadakis D.C. Rakopoulos C.D. Rakopoulos 《International Journal of Hydrogen Energy》2021,46(34):17955-17968
The cyclic variability in a spark-ignition (SI) engine is examined fueled with methane/hydrogen blends with the use of an in-house computational fluid dynamics (CFD) code. A recent methodology is followed, which has been developed with the main aim at providing accurate predictions of the coefficient of variation (COV) of the indicated mean effective pressure (IMEP) in a fraction of time. Instead of simulating several tens of engine cycles, the methodology is based on the numerical results obtained from just 5 cycles, which are then processed for developing suitable fitted correlations of the main parameters as a function of a normalized distance. The latter expresses the distance of the spheres of the initial flame within the computational cell at the spark-plug region with the local turbulent eddy, and provides a smooth transition from the laminar burning regime to the fully turbulent one. This sub-model is included in the ignition numerical approach and is applied here in a SI engine with 3 different hydrogen contents, 10%, 30% and 50%, and three equivalence ratios, 1, 0.8 and 0.7, showing that the COV of IMEP is well predicted compared to the available measured data. Other parameters of engine cycle variations are also examined, such as the distribution of the IMEP. The variability of NO (nitric oxide) emissions is also examined, showing that for the stoichiometric cases it follows a distribution similar to a normal (Gaussian) one, while for lower ratios it is positively skewed. Overall, the methodology seems to provide reliable results for the whole range of the operating conditions examined, while the next steps of this activity will focus on similar cases for engine with variable speed and load, with the final goal to include additional mechanisms that contribute to the engine cycle variations. 相似文献
8.
《International Journal of Hydrogen Energy》2022,47(24):12421-12431
This study reports the impacts of dual fuel mixtures on the theoretical performance characteristics of a spark ignition engine (SIE). The effects of addition of liquefied hydrogen, methane, butane, propane (additive fuels) into gasoline, iso-octane, benzene, toluene, hexane, ethanol and methanol fuels (primary fuels) on the variation of power, indicated mean effective pressure (IMEP), thermal efficiency, exergy efficiency, were examined by using a combustion model. The fuel additives were ranged from 10 to 50% by mass. The results exhibited that the ratios of hydrogen, methane, butane, propane noticeably affect the performance of the engine. The maximum increase ratio of power is 82.59% with 50% of toluene ratio and its maximum decrease ratio is 10.84% with 50% of methanol ratio in hydrogen mixtures. The maximum increase ratio of thermal efficiency and exergy efficiency are observed as 26.75% and 32.23% with the combustion of benzene-hydrogen mixtures. The maximum decrease ratio of thermal efficiency is 29.71% with the combustion of 50% of methanol ratio and it is 21.95% for the exergy efficieny with the combustion of 50% of ethanol ratio in hydrogen mixtures. The power, IMEP, thermal efficiency and exergy efficiency of primary fuels demonstrate different variation characteristics with respect to type and ratio of additive fuels. 相似文献
9.
10.