全文获取类型
收费全文 | 7279篇 |
免费 | 1684篇 |
国内免费 | 1688篇 |
专业分类
化学 | 4659篇 |
晶体学 | 408篇 |
力学 | 800篇 |
综合类 | 75篇 |
数学 | 106篇 |
物理学 | 4603篇 |
出版年
2024年 | 5篇 |
2023年 | 37篇 |
2022年 | 184篇 |
2021年 | 202篇 |
2020年 | 179篇 |
2019年 | 162篇 |
2018年 | 180篇 |
2017年 | 255篇 |
2016年 | 336篇 |
2015年 | 279篇 |
2014年 | 360篇 |
2013年 | 614篇 |
2012年 | 532篇 |
2011年 | 623篇 |
2010年 | 547篇 |
2009年 | 620篇 |
2008年 | 578篇 |
2007年 | 613篇 |
2006年 | 629篇 |
2005年 | 505篇 |
2004年 | 485篇 |
2003年 | 351篇 |
2002年 | 328篇 |
2001年 | 278篇 |
2000年 | 273篇 |
1999年 | 227篇 |
1998年 | 201篇 |
1997年 | 193篇 |
1996年 | 171篇 |
1995年 | 159篇 |
1994年 | 119篇 |
1993年 | 84篇 |
1992年 | 86篇 |
1991年 | 74篇 |
1990年 | 57篇 |
1989年 | 29篇 |
1988年 | 29篇 |
1987年 | 20篇 |
1986年 | 9篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
991.
992.
Rosaria Ciriminna Dr. Alexandra Fidalgo Prof. Laura M Ilharco Dr. Mario Pagliaro 《ChemistryOpen》2015,4(2):78-126
Porous silica-based microspheres encapsulating aqueous glycerol can be potential curing agents for one-component foams (OCFs). Such agents have the advantage of an enhanced sustainability profile on top of being environmentally friendly materials. A synthetically convenient and scalable sol-gel process was used to make silica and organosilica microspheres doped with aqueous glycerol. These methyl-modified silica microspheres, named “GreenCaps”, exhibit remarkable physical and chemical stability. The microspheres were characterized by scanning electron microscopy, transmission electron microscopy at reduced pressure, and cryogenic nitrogen adsorption—desorption analysis. The structure of the materials was also analyzed at the molecular level by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. As expected, the degree of methylation affects the degree of encapsulation and pore structure. Microspheres similarly methylated, however, can differ considerably in surface area and pore size due to the templating effect of glycerol on the organosilica structure. The results of the structure analysis reveal that glycerol is efficiently encapsulated, acts as a template, barely leaches over time, but is released by depressurization. A proper application of these microspheres can later on enhance both the environmental and health profile, as well as the technical performance (curing speed, foam quality, and froth thixotropy) of spray polyurethane foams. 相似文献
993.
The tribological performance of fullerene‐like hydrogenated carbon films under ionic liquid lubrication 下载免费PDF全文
Kunyao Wu Li Qiang Zhenbin Gong Gengrui Zhao Kaixiong Gao Bin Zhang Junyan Zhang 《Surface and interface analysis : SIA》2015,47(9):903-910
Fullerene‐like hydrogenated carbon films were deposited on Si substrate by plasma‐enhanced chemical vapor deposition. The microstructures of films were characterized by high‐resolution transmission electron microscopy and Raman spectrum. The tribological performance of films was tested by reciprocating ball‐on‐disc tester under 1‐ethyl‐3‐methylimidazolium tetrafluoroborate ionic liquid. The surface morphology and chemical composition of wear tracks and wear rates were investigated by optical microscope, X‐ray photoelectron spectroscopy, and 3D surface profiler. The results indicated that the film with a typical fullerene‐like structure embedded into the amorphous sp2 and sp3 carbon networks could be prepared successfully, and the film shows a higher hardness (26.7 GPa) and elastic recovery (89.9%) compared with the amorphous carbon film. Furthermore, the film shows a lower friction coefficient at low contact load and friction frequency, and excellent wear‐resistance performance at high load and frequency under ionic liquid lubrication. Meanwhile, the wear life of fullerene‐like hydrogenated carbon films could be improved significantly using ionic liquid as a lubrication material. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
994.
Influence of thermal annealing on the structural and optical properties of maghemite (γ‐Fe2O3) nanoparticle thin films 下载免费PDF全文
Ehsan Parsianpour Mohammad Gholami Nima Shahbazi Feridoun Samavat 《Surface and interface analysis : SIA》2015,47(5):612-617
In this study, maghemite (γ‐Fe2O3) nanoparticles were initially synthesized via chemical co‐precipitation and then deposited by spray pyrolysis as thin films on white glass substrates. The thin films were annealed for 8 h at 400, 450, 500, 550, and 600 °C in an oven. The structural studies of maghemite nanoparticles were carried out using X‐ray diffractometer. Structural properties that we investigated by X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, SEM, and Energy dispersive X‐ray analysis (EDS). Optical properties of the samples were also investigated by ultraviolet‐visible (UV–vis) spectroscopy. The results showed that maghemite nanoparticles have crystalline structure with domain that increases in size with increasing annealing temperature. The optical band gap values were found to reduce from 2.9 to 2.4 eV with increase in annealing temperature. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
995.
Strong Fluorescent Smart Organogel as a Dual Sensing Material for Volatile Acid and Organic Amine Vapors 下载免费PDF全文
Dr. Pengchong Xue Boqi Yao Panpan Wang Peng Gong Zhenqi Zhang Prof. Ran Lu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(48):17508-17515
An L ‐phenylalanine derivative ( C12PhBPCP ) consisting of a strong emission fluorophore with benzoxazole and cyano groups is designed and synthesized to realize dual responses to volatile acid and organic amine vapors. The photophysical properties and self‐assembly of the said derivative in the gel phase are also studied. C12PhBPCP can gelate organic solvents and self‐assemble into 1 D nanofibers in the gels. UV/Vis absorption spectral results show H‐aggregate formation during gelation, which indicates strong exciton coupling between fluorophores. Both wet gel and xerogel emit strong green fluorescence because the cyano group suppresses fluorescence quenching in the self‐assemblies. Moreover, the xerogel film with strong green fluorescence can be used as a dual chemosensor for quantitative detection of volatile acid and organic amine vapors with fast response times and low detection limits owing to its large surface area and amplified fluorescence quenching. The detection limits are 796 ppt and 25 ppb for gaseous aniline and trifluoroacetic acid (TFA), respectively. 相似文献
996.
997.
《中国化学》2017,35(12):1844-1852
The binder‐free composite films of reduced graphene oxide (rGO ) and activated carbon derived from cotton (aCFC ) have been fabricated and used as electrodes for electrochemical capacitors (ECs ) to avoid the decrease of capacitive performance in traditional process caused by the additional binder. The optimal aCFC is prepared at 850 °C when the mass ratio of carbon and potassium hydroxide is 1 to 4. The optimal composite film prepared from the mass ratio of aCFC /GO =2/1 exhibits porous structure, and has a specific surface area of 849.6 m2•g−1 and a total pore volume of 0.61 mL •g−1. Based on the two‐electrode system testing in 6.0 mol/L KOH electrolyte, the optimal composite has specific capacitance of about 202 F•g−1, 374 mF •cm−2 and 116 F•cm−3 in terms of mass, area and volume, and shows excellent rate capability and good cyclic stability (91.7% retention of the initial capacitance after 5000 cycles). Furthermore, the assembled solid‐state ECs by using KOH /polyvinyl alcohol as electrolyte show good mechanical stability and capacitive performances after repeated bending cycles. It is proved that this method is effective to fabricate binder‐free electrodes for ECs and will open up a novel route for the reuse of waste cotton. 相似文献
998.
光纤表面等离子共振(Fiber optic surface plasmon resonance,FO-SPR)传感器由于体积小、易携带、抗电磁干扰等优点在生物、化学、医学及食品领域均具有广阔的应用前景。该文综述了光纤SPR传感器的结构、膜材料及其应用进展。其中终端反射式和在线传输式是光纤SPR传感器最重要的两种结构;最常用的膜材料包括金膜、银膜、复合膜和金属纳米颗粒。基于光纤SPR的实时检测、抗干扰能力强、可多通道检测等特点展望了其未来发展与应用前景。 相似文献
999.
A novel method to prepare microcellular poly(vinyl alcohol) foam based on thermal processing and supercritical fluid 下载免费PDF全文
Combining the thermal processing and supercritical fluid technology develops a novel preparation method of microcellular poly(vinyl alcohol) (PVA). Water, as the plasticizer in system, can form the hydrogen bonding with pendant hydroxyl of PVA and weaken its strong intermolecular and intramolecular forces to realize the thermal processing. Supercritical carbon dioxide (sc‐CO2) can easily dissolve into water‐plasticized PVA (WPVA) because of the destruction of crystal region caused by water, and the enhanced sc‐CO2 solubility can greatly improve the foamability of WPVA. The porous structure generates through the saturation of sc‐CO2 in WPVA sample and followed by pressure drop‐induced phase separation. The foaming behavior of WPVA was studied as a function of saturation pressure, foaming temperature, and saturation time. The cell density, cell size, and distribution of the obtained foam can be controlled by tuning processing conditions. The results revealed that the cell size decreased, and its distribution narrowed with saturation pressure increasing, or decrease of foaming temperature. But excessively increasing the saturation time generated a negative effect on the foaming behavior owing to the deteriorated plasticization effect resulted from the loss of water. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
1000.