全文获取类型
收费全文 | 1860篇 |
免费 | 53篇 |
国内免费 | 4篇 |
专业分类
化学 | 1130篇 |
晶体学 | 4篇 |
力学 | 110篇 |
数学 | 341篇 |
物理学 | 332篇 |
出版年
2023年 | 16篇 |
2022年 | 20篇 |
2021年 | 64篇 |
2020年 | 38篇 |
2019年 | 39篇 |
2018年 | 34篇 |
2017年 | 32篇 |
2016年 | 67篇 |
2015年 | 61篇 |
2014年 | 54篇 |
2013年 | 92篇 |
2012年 | 103篇 |
2011年 | 147篇 |
2010年 | 61篇 |
2009年 | 61篇 |
2008年 | 117篇 |
2007年 | 110篇 |
2006年 | 107篇 |
2005年 | 81篇 |
2004年 | 73篇 |
2003年 | 59篇 |
2002年 | 72篇 |
2001年 | 22篇 |
2000年 | 15篇 |
1999年 | 22篇 |
1998年 | 15篇 |
1997年 | 23篇 |
1996年 | 34篇 |
1995年 | 20篇 |
1994年 | 14篇 |
1993年 | 21篇 |
1992年 | 9篇 |
1991年 | 6篇 |
1990年 | 12篇 |
1989年 | 13篇 |
1988年 | 9篇 |
1987年 | 17篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 10篇 |
1978年 | 14篇 |
1977年 | 12篇 |
1976年 | 11篇 |
1975年 | 5篇 |
1972年 | 4篇 |
排序方式: 共有1917条查询结果,搜索用时 551 毫秒
991.
By means of ab initio simulations we here provide a comprehensive scenario for hydrogen oxidation reactions at the Ni/zirconia anode of solid oxide fuel cells. The simulations have also revealed that in the presence of water chemisorbed at the oxide surface, the active region for H oxidation actually extends beyond the metal/zirconia interface unraveling the role of water partial pressure in the decrease of the polarization resistance observed experimentally. 相似文献
992.
In a previous paper the structure and the physical properties of melt mixed polyamide 66 (PA66)/polyamide 12 (PA12) blends characterized by different compositions have been investigated by means of morphological and physical analyses. A low amount of organically‐modified layered silicate (OMLS, 4 wt%) was introduced in order to evaluate its effect on blends structure and components miscibility. This paper completes the characterization of these materials investigating their thermal properties by means of standard and modulated differential scanning calorimetry (DSC, MDSC), dynamic‐mechanical analysis (DMA), and thermogravimetric analysis (TGA). The partial miscibility of PA66 and PA12, with phase separation depending on blend composition, has been confirmed by analyzing the glass transition temperature (Tg) dependence on composition as well as the existence of strong segmental interactions between polymer components. A compatibilizing action of OMLS has been observed because of a lowering of interfacial tension avoiding coalescence phenomena between particles during melt mixing process. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
993.
Xue C Yonet-Tanyeri N Brouette N Sferrazza M Braun PV Leckband DE 《Langmuir : the ACS journal of surfaces and colloids》2011,27(14):8810-8818
The protein resistance of poly(N-isopropylacrylamide) brushes grafted from silicon wafers was investigated as a function of the chain molecular weight, grafting density, and temperature. Above the lower critical solution temperature (LCST) of 32 °C, the collapse of the water-swollen chains, determined by ellipsometry, depends on the grafting density and molecular weight. Ellipsometry, radio assay, and fluorescence imaging demonstrated that, below the lower critical solution temperature, the brushes repel protein as effectively as oligoethylene oxide-terminated monolayers. Above 32 °C, very low levels of protein adsorb on densely grafted brushes, and the amounts of adsorbed protein increase with decreasing brush-grafting-densities. Brushes that do not exhibit a collapse transition also bind protein, even though the chains remain extended above the LCST. These findings suggest possible mechanisms underlying protein interactions with end-grafted poly(N-isopropyl acrylamide) brushes. 相似文献
994.
Dessy A Kubowicz S Alderighi M Bartoli C Piras AM Schmid R Chiellini F 《Colloids and surfaces. B, Biointerfaces》2011,87(2):236-242
Therapeutic properties of Dead Sea Water (DSW) in the treatment of skin diseases such as atopic dermatitis, psoriasis and photo aging UV damaged skin have been well established. DSW is in fact rich in minerals such as calcium, magnesium, sodium, potassium, zinc and strontium which are known to exploit anti-inflammatory effects and to promote skin barrier recovery. In order to develop a Dead Sea Minerals (DSM) based drug delivery system for topical therapy of skin diseases, polymeric nanoparticles based on Poly (maleic anhydride-alt-butyl vinyl ether) 5% grafted with monomethoxy poly(ethyleneglycol) 2000 MW (PEG) and 95% grafted with 2-methoxyethanol (VAM41-PEG) loaded with DSM were prepared by means of a combined miniemulsion/solvent evaporation process. The resulting nanoparticles were characterized in terms of dimension, morphology, biocompatibility, salt content and release. Cytocompatible spherical nanoparticles possessing an average diameter of about 300 nm, a time controlled drug release profile and a high formulation yield were obtained. 相似文献
995.
Stefano Toffanin Raffaella Capelli Wouter Koopman Gianluca Generali Susanna Cavallini Andrea Stefani Davide Saguatti Giampiero Ruani Michele Muccini 《Laser \u0026amp; Photonics Reviews》2013,7(6):1011-1019
Organic light‐emitting transistors (OLETs) are multifunctional optoelectronic devices that hold great promise for a variety of applications, including flat panel displays, integrated light sources for sensing and optical communication systems. The narrow illumination area within the device channel is considered intrinsic to the device architecture and is a severe technological drawback for all those applications where a controlled, wide and homogeneous emission area is required. Here it is shown that not only the position but also the extension of the emission area is voltage‐tunable, and the entire channel of the transistor can be homogeneously illuminated. The modeling of the exciton distribution within the channel at the different bias conditions coupled to the modeling of the device emission profile highlights that excitons are spread through the entire channel width and across the bulk of the central emission layer of the p‐channel/emitter/n‐channel trilayer active heterostructure. 相似文献
996.
Hamza Bouzid Mario Prosa Margherita Bolognesi Nadia Chehata Desta Gedefaw Cristiano Albonetti Mats R. Andersson Michele Muccini Abdelaziz Bouazizi Mirko Seri 《Journal of polymer science. Part A, Polymer chemistry》2019,57(4):487-494
High‐performance polymer solar cells (PSCs) are typically fabricated by spin coating in inert atmosphere from toxic halogenated solvents such as 1,2‐dichlorobenzene (o‐DCB) and chlorobenzene. This fabrication process is potentially hazardous for both the humans and the environment and dramatically impacts the possibility for the organic photovoltaic technology to be adopted at large scale. In this work, efficient PSCs blade coated in air using nonhalogenated 1,2,4‐trimethylbenzene (TMB) as processing solvent are demonstrated. The active layer, based on a previously synthesized benchmark polymer PFQ2T‐benzodithiophene blended with [6,6]‐phenyl‐C61‐butyric acid methyl ester (PC61BM), showed an enhanced solid‐state aggregation induced by the use of TMB. Compared to o‐DCB‐processed devices, the solar cells fabricated from TMB resulted 10% more efficient with a power conversion efficiency of 4.20%. Interestingly, the improved photovoltaic performance resulted from the combination of synergic effects promoted by a more favorable film morphology, such as high exciton dissociation efficiency and lower bimolecular recombinations resulting in higher charge collection efficiency at the electrodes. The positive effect of TMB, compared to that of commonly employed halogenated solvents, confirms the great potential of this approach for the development of efficient PSCs for practical applications with reduced environmental impact. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 487–494 相似文献
997.
De Filippo Michele Kuang Jun Shang 《Journal of Optimization Theory and Applications》2021,190(2):540-564
Journal of Optimization Theory and Applications - Nowadays, large part of the technical knowledge associated with collapses of slabs is based on past failures of bridges, floors, flat roofs and... 相似文献
998.
Michele Cacioppo Tobias Scharl Luka orevi Alejandro Cadranel Francesca Arcudi Dirk M. Guldi Maurizio Prato 《Angewandte Chemie (International ed. in English)》2020,59(31):12779-12784
Carbon dots (CDs) and their derivatives are useful platforms for studying electron‐donor/acceptor interactions and dynamics therein. Herein, we couple amorphous CDs with phthalocyanines (Pcs) that act as electron donors with a large extended π‐surface and intense absorption across the visible range of the solar spectrum. Investigations of the intercomponent interactions by means of steady‐state and pump‐probe transient absorption spectroscopy reveal symmetry‐breaking charge transfer/separation and recombination dynamics within pairs of phthalocyanines. The CDs facilitate the electronic interactions between the phthalocyanines. Thus, our findings suggest that CDs could be used to support electronic couplings in multichromophoric systems and further increase their applicability in organic electronics, photonics, and artificial photosynthesis. 相似文献
999.
Alex Lanzutti Francesco Andreatta Michele Magnan Lorenzo Fedrizzi 《Surface and interface analysis : SIA》2019,51(12):1165-1172
AA 3XXX alloys are widely used in heating, ventilation, and air conditioning (HVAC) field. Diffusion joining using a filler metal together with flux is employed in some applications as for heat exchangers. In this work, the effect of diffusion of a Zn-based flux on both microstructure and electrochemical behavior has been investigated. In particular, an AA3xxx was coated with a Zn-rich flux and subjected to controlled atmosphere brazing (CAB). Glow discharge optical emission spectroscopy (GDOES) composition profiles were acquired in order to determine the Zn distribution in the diffusion layer. The GDOES was also employed to produce a controlled erosion of the surface in order to obtain craters with defined depths in the Zn diffusion layer, in which electrochemical analyses could be performed. The Volta potential maps at different depths in the Zn diffusion layer were obtained by scanning Kelvin probe force microscope (SKPFM). The Zn diffusion layer was also investigated by means of Scanning Electron Microscope-Energy Dispersive X-ray Spectroscopy (SEM-EDXS) and the chemical composition of the phases present in the regions was investigated by SKPFM. Finally, the electrochemical microcell was used in the produced craters in order to determine the electrochemical behavior along the Zn diffusion profile. SKPFM and microcell results showed a correlation between the Zn content and the electrochemical properties. In particular, a higher Zn content in the diffusion layer leads to an increase of the Volta potential difference between the intermetallic particles and the matrix. The electrochemical measurements also showed that the Zn diffusion layer provides galvanic protection to the underlaying aluminum alloy. 相似文献
1000.
Stefano Rossi Mirco Bizzotto Flavio Deflorian Michele Fedel 《Surface and interface analysis : SIA》2019,51(12):1194-1206
Aluminium foam is obtained by the production of air into metallic melt. This material shows a very low density together with good mechanical properties, high impact energy absorption, and fire resistance. Different production ways to obtain metallic foam are possible. Considering the cost, the Alporas process is particularly interesting. By means of this production method, a block of metallic foam with close cells is obtained. By slicing, foam panels are obtained. The mechanical cut promotes the formation of an open cells texture on the surface. In this last case, the complex morphology of aluminium foam could be a critical point considering the corrosion behavior in aggressive environments, where localized corrosion phenomena, as pitting or crevice corrosion, are likely to occur. The anodizing treatment is one of the most used methods to improve the corrosion resistance of aluminium and aluminium alloys. The aim of this paper is to perform an anodization treatment to enhance the corrosion resistance of aluminium foam. Constant voltage anodization (12 V for 60 min) and pulsed current anodization (0.04 A/cm2 for 60 seconds and 0.01 A/cm2 for 15 seconds, repeated for 15 cycles) have been carried out in 15 wt% H2SO4 at 20°C. The anodized samples are observed in cross section by optical and electronic microscopes to investigate the structure of the anodic oxide layer and the presence of defects and to measure the thickness of the layer. The corrosion protection performance and the compactness of layers are evaluated using acetic salt spray test and electrochemical impedance spectroscopy. 相似文献