全文获取类型
收费全文 | 868篇 |
免费 | 71篇 |
国内免费 | 10篇 |
专业分类
化学 | 497篇 |
力学 | 52篇 |
数学 | 104篇 |
物理学 | 174篇 |
无线电 | 122篇 |
出版年
2024年 | 2篇 |
2023年 | 6篇 |
2022年 | 28篇 |
2021年 | 50篇 |
2020年 | 63篇 |
2019年 | 57篇 |
2018年 | 54篇 |
2017年 | 58篇 |
2016年 | 69篇 |
2015年 | 61篇 |
2014年 | 67篇 |
2013年 | 77篇 |
2012年 | 88篇 |
2011年 | 87篇 |
2010年 | 40篇 |
2009年 | 29篇 |
2008年 | 30篇 |
2007年 | 15篇 |
2006年 | 15篇 |
2005年 | 13篇 |
2004年 | 12篇 |
2003年 | 3篇 |
2002年 | 6篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1994年 | 2篇 |
1990年 | 1篇 |
1986年 | 4篇 |
1984年 | 2篇 |
1983年 | 1篇 |
排序方式: 共有949条查询结果,搜索用时 15 毫秒
31.
The fluids containing nanoparticles have enhanced thermo-physical characteristics in comparison with conventional fluids without nanoparticles. Thermal conductivity and viscosity are thermo-physical properties that strongly determine heat transfer and momentum. In this study, the response surface method was firstly used to derive an equation for the thermal conductivity and another one for the viscosity of bioglycol/water mixture (20:80) containing silicon dioxide nanoparticles as a function of temperature as well as the volume fraction of silicon dioxide. Then, NSGA-II algorithm was used for the optimization and maximizing thermal conductivity and minimizing the nanofluid viscosity. Different fronts were implemented and 20th iteration number was selected as Pareto front. The highest thermal conductivity (0.576 W/m.K) and the lowest viscosity (0.61 mPa.s) were obtained at temperature on volume concentration of (80 °C and 2%) and (80 °C without nanoparticle) respectively. It was concluded that the optimum thermal conductivity and viscosity of nanofluid could be obtained at maximum temperature (80 °C) or a temperature close to this temperature. An increase in the volume fraction of silicon dioxide led to the enhancement of thermal conductivity but the solution viscosity was also increased. Therefore, the optimum point should be selected based on the system requirement. 相似文献
32.
Ghasemi Mahdi Niknejadi Mohammadreza Toghraie Davood 《Journal of Thermal Analysis and Calorimetry》2021,144(6):2483-2495
Journal of Thermal Analysis and Calorimetry - The thermal behavior of CuO-water nanofluid is examined on an aluminum surface. The dimensions of simulation boxes are... 相似文献
33.
34.
Saied Ahmadjo Hassan Arabi Gholamhossien Zohuri Mehdi Nekoomanesh Gholamreza Nejabat Seyed Mohammad Mahdi Mortazavi 《Journal of Thermal Analysis and Calorimetry》2014,116(1):417-426
(2-RInd)2ZrCl2 (R:Ph,H) catalyst was supported on MCM-41 and ethylene copolymerization behavior as well as microstructure of copolymers were studied. A steady rate–time profile behavior was observed for homo and copolymerization of ethylene using supported catalysts. It was noticed that increasing the comonomer content can result in lower physical properties. The obtained results indicated that (2-PhInd)2ZrCl2/MCM-41 had higher ability of comonomer incorporation than the non-substituted supported catalysts. The CCC, CCE, and ECC (C: comonomer, E: ethylene) triad sequence distribution in backbone of copolymers were negligible, that means no evidence could be detected for comonomer blocks. The polymer characterization revealed that utilizing 1-octene instead of 1-hexene as the comonomer leads to more heterogeneous distribution of chemical composition. The heterogeneity of the chemical composition distribution and the physical properties were influenced by the type of comonomer and catalyst. (2-PhInd)2ZrCl2/MCM-41 produced copolymers containing narrower distribution of lamellae (0.3–1 nm) than the copolymer produce using Ind2ZrCl2/MCM-41 (0.3–1.6 nm). 相似文献
35.
New Polydentate Trimethylsilyl Chalcogenide Reagents for the Assembly of Polyferrocenyl Architectures 下载免费PDF全文
Mahmood Azizpoor Fard Bahareh Khalili Najafabadi Mahdi Hesari Prof. Dr. Mark S. Workentin Prof. Dr. John F. Corrigan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(23):7037-7047
A series of polychalcogenotrimethylsilane complexes Ar(CH2ESiMe3)n, (Ar=aryl; E=S, Se; n=2, 3, and 4) can be prepared from the corresponding polyorganobromide and M[ESiMe3] (M=Na, Li). These represent the first examples of the incorporation of such a large number of reactive ?ESiMe3 moieties onto an organic molecular framework. They are shown to be convenient reagents for the preparation of the polyferrocenylseleno‐ and thioesters from ferrocenoyl chloride. The synthesis, structures, and spectroscopic properties of the new silyl chalcogen complexes 1,4‐(Me3SiECH2)2(C6Me4) (E=S, 1 ; E=Se, 2 ), 1,3,5‐(Me3SiECH2)3(C6Me3) (E=S, 3 ; E=Se, 4 ) and 1,2,4,5‐(Me3SiECH2)4(C6H2) (E=S, 5 ; E=Se, 6 ) and the polyferrocenyl chalcogenoesters [1,4‐{FcC(O)ECH2}2(C6Me4)] (E=S, 7 ; E=Se, 8 ), [1,3,5‐{FcC(O)ECH2}3(C6Me3)] (E=S, 9 ; E=Se, 10 ) and [1,2,4,5‐{FcC(O)ECH2}4(C6H2)] (E=S, 11 illustrated; E=Se, 12 ) are reported. The new polysilylated reagents and polyferrocenyl chalcogenoesters have been characterized by multinuclear NMR spectroscopy (1H, 13C, 77Se), electrospray ionization mass spectrometry and, for complexes 1 , 2 , 3 , 4 , 7 , 8 , and 11 , single‐crystal X‐ray diffraction. The cyclic voltammograms of complexes 7 – 11 are presented. 相似文献
36.
A simple, efficient, and ecofriendly procedure has been developed using propane-l,2,3-triyl tris(hydrogen sulfate) as a catalyst for the synthesis of biscoumarin derivatives in water and solvent-free conditions. The significant features of the present protocol are simplicity, environmentally benign, high yields, no chromatographic separation, and recyclability of the catalyst. 相似文献
37.
Hosseinikhah Seyed Mahdi Beigzadeh Borhan Siavashi Majid Halabian Mahdi 《Journal of Thermal Analysis and Calorimetry》2020,141(5):1543-1558
Journal of Thermal Analysis and Calorimetry - High interstitial fluid pressure in the tumor is among the most important barriers to drug delivery. The use of the static magnetic field is one of the... 相似文献
38.
Nili-Ahmadabadi Mahdi Nematollahi Omid Fatehi Mostafa Cho Dae Seung Kim Kyung Chun 《显形杂志》2020,23(4):591-603
Journal of Visualization - Airfoils are mostly inefficient in their off-design conditions. In order to improve the aerodynamic performance of airfoils in these conditions, using an optimized cavity... 相似文献
39.
Nikoo Saveh‐Shemshaki Masoud Latifi Roohollah Bagherzadeh Mahdi Malekshahi Byranvand Naimeh Naseri Ali Dabirian 《先进技术聚合物》2016,27(3):358-365
Iron(III) oxide (hematite, Fe2O3) nanofibers, as visible light‐induced photoanode for water oxidation reaction of a water splitting process, were fabricated through electrospinning method followed by calcination treatment. The prepared samples were characterized with scanning electron microscopy, and three‐electrode galvanostat/potentiostat for evaluating their photoelectrochemical (PEC) properties. The diameter of the as‐spun fibers is about 300 nm, and calcinated fibers have diameter less than 110 nm with mesoporous structure. Optimized multilayered electrospun α‐Fe2O3 nanostructure mats showed photocurrent density of 0.53 mA/cm2 under dark and visible illumination conditions at voltage 1.23 V and constant intensity (900 mW/cm2). This photovoltaic performance of nanostructure mats makes it suitable choice for using in the PEC water splitting application as an efficient photoanode. This method, if combined with appropriate flexible conductive substrate, has the potential for producing flexible hematite solar fuel generators. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
40.
Ligand‐Free Synthesis of Aluminum‐Doped Zinc Oxide Nanocrystals and their Use as Optical Spacers in Color‐Tuned Highly Efficient Organic Solar Cells 下载免费PDF全文
Meriem Gaceur Sadok Ben Dkhil David Duché Fatima Bencheikh Jean‐Jacques Simon Ludovic Escoubas Mahdi Mansour Antonio Guerrero Germà Garcia‐Belmonte Xianjie Liu Mats Fahlman Walid Dachraoui Abdou Karim Diallo Christine Videlot‐Ackermann Olivier Margeat Jörg Ackermann 《Advanced functional materials》2016,26(2):243-253
The color of polymer solar cells using an opaque electrode is given by the reflected light, which depends on the composition and thickness of each layer of the device. Metal‐oxide‐based optical spacers are intensively studied in polymer solar cells aiming to optimize the light absorption. However, the low conductivity of materials such as ZnO and TiO2 limits the thickness of such optical spacers to tenths of nanometers. A novel synthesis route of cluster‐free Al‐doped ZnO (AZO) nanocrystals (NCs) is presented for solution processing of highly conductive layers without the need of temperature annealing, including thick optical spacers on top of polymer blends. The processing of 80 nm thick optical spacers based on AZO nanocrystal solutions on top of 200 nm thick polymer blend layer is demonstrated leading to improved photocurrent density of 17% compared to solar cells using standard active layers of 90 nm in combination with thin ZnO‐based optical spacers. These AZO NCs also open new opportunities for the processing of high‐efficiency color tuned solar cells. For the first time, it is shown that applying solution‐processed thick optical spacer with polymer blends of different thicknesses can process solar cells of similar efficiency over 7% but of different colors. 相似文献