全文获取类型
收费全文 | 4048篇 |
免费 | 313篇 |
国内免费 | 194篇 |
专业分类
化学 | 2718篇 |
晶体学 | 70篇 |
力学 | 156篇 |
综合类 | 12篇 |
数学 | 608篇 |
物理学 | 991篇 |
出版年
2024年 | 5篇 |
2023年 | 52篇 |
2022年 | 94篇 |
2021年 | 107篇 |
2020年 | 129篇 |
2019年 | 149篇 |
2018年 | 159篇 |
2017年 | 130篇 |
2016年 | 198篇 |
2015年 | 158篇 |
2014年 | 212篇 |
2013年 | 396篇 |
2012年 | 290篇 |
2011年 | 314篇 |
2010年 | 241篇 |
2009年 | 179篇 |
2008年 | 268篇 |
2007年 | 237篇 |
2006年 | 181篇 |
2005年 | 147篇 |
2004年 | 101篇 |
2003年 | 89篇 |
2002年 | 102篇 |
2001年 | 68篇 |
2000年 | 55篇 |
1999年 | 40篇 |
1998年 | 43篇 |
1997年 | 44篇 |
1996年 | 41篇 |
1995年 | 34篇 |
1994年 | 28篇 |
1993年 | 21篇 |
1992年 | 30篇 |
1991年 | 15篇 |
1990年 | 25篇 |
1989年 | 22篇 |
1988年 | 16篇 |
1987年 | 16篇 |
1986年 | 10篇 |
1985年 | 14篇 |
1984年 | 23篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1970年 | 4篇 |
排序方式: 共有4555条查询结果,搜索用时 15 毫秒
101.
102.
103.
Wang Xiwen Liu Suqin Wang Haiyan Tu Feiyue Fang Dong Li Yanhua 《Journal of Solid State Electrochemistry》2012,16(11):3593-3602
Journal of Solid State Electrochemistry - A series of Co3O4 nanoplates/graphene nanosheets (GNS) composites are fabricated using a facile and green method by hydrothermal treatment and subsequent... 相似文献
104.
105.
Liyong Chen Mingzu Zhang Zhuang Liu Zixu Gu Yingfeng Tu Peihong Ni 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(11):862-871
A biocompatible complex has been prepared as gene carrier via electrostatic interaction, which is composed of a polycation, that is, poly[(dimethylamino)ethyl methacrylate] end-capped with cholesterol moiety (Chol-PDMAEMA30), along with a polyanion named poly(aspartic acid)-grafted-poly(ethylene glycol) (PASP-g-PEG). The complexes have less cytotoxicity compared to the case of alone Chol-PDMAEMA30 or branched polyethylenimine (PEI) system. In the present study, biocompatible complexes have been prepared as gene carrier via electrostatic interaction, which is composed of a polycation, that is, poly[(dimethylamino)ethyl methacrylate] end-capped with cholesterol moiety (Chol-PDMAEMA30), along with a polyanion named poly(aspartic acid)-grafted-poly(ethylene glycol) (PASP-g-PEG). We first synthesized polysuccinimide (PSI) via condensation polymerization of aspartic acid, and then used PEG-NH2 to react with the partial pentacyclic rings of PSI to yield a kind of graft copolymer polysuccinimide-grafted-poly(ethylene glycol) (PSI-g-PEG). After hydrolysis of the residual succinimide units, a new biodegradable and biocompatible graft copolymer PASP-g-PEG was prepared successfully. Chol-PDMAEMA30 was synthesized via oxyanion-initiated polymerization, as reported in our previous literature. We investigated the interactions between every pair among calf thymus DNA, Chol-PDMAEMA30, and PASP-g-PEG by agarose gel retardation assay. The results indicate that the prepared complexes could completely bind DNA and may become more stable during systemic circulation. The complexes have less cytotoxicity compared to the case of alone Chol-PDMAEMA30 or branched polyethylenimine (PEI) system. Furthermore, the physicochemical properties of the complexes were also investigated by zeta potential, transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements. These biodegradable and biocompatible polymeric carriers have potential applications in gene delivery. 相似文献
106.
Electrically conductive composite systems based on polyvinyl chloride (PVC) and polymethyl methacrylate (PMMA) filled with metal powders of Al and Cu have been studied. The composite preparation conditions allow the formation of a random distribution of metallic particles in the polymer matrix. Dependence of the dielectric and conductivity properties of the PVC and PMMA/fillers was studied over a broad range of frequency and volume fraction of metal fillers. The experimental results could be explained by means of the conductivity of fillers and the interface polarization between polymers and fillers. Percolation was also seen in this study when the volume fraction of conducting fillers was close to critical value, in which the composites undergo an insulator‐conductor transition. The relation among the dielectric property and the fillers with different conductivity was proposed. 相似文献
107.
Conductive polythiophene (PTh)/poly(ethylene terephthalate) (PET) composite fibers were prepared by polymerization of thiophene in the presence of PET fibers in acetonitrile medium using FeCl3. The effects of polymerization conditions such as oxidant/monomer mol ratio and polymerization temperature and time on PTh content and surface electrical resistivity of PTh/PET composite fiber were investigated in detail. It was observed that the usage of preswelled PET fibers in dichloromethane increased the PTh content and decreased surface resistivity of composite fiber. Composite fiber having the highest PTh content (5.7%) and the lowest surface resistivity (80 kΩ) was obtained at 20°C with 1.25 M FeCl3 and 0.42 M thiophene concentrations. The washing effects of laundering detergent and dry cleaning liquid on surface resistivity of composite fibers were investigated. The electromagnetic shielding effectiveness (EMSE) and relative shielding efficiency by absorption and reflection of composite fibers were measured in the radio and microwave frequency range. The results show that the EMSE values decreased with increasing frequency from radio waves to microwaves with an attenuation of 21 dB to 4 dB. 相似文献
108.
Four cone calix[4]arene-1,2-crown ethers each with two ionisable side arms containing dansyl groups are synthesised. The crown ether ring on the lower rim is varied from crown-4 to crown-5 with hydrogen or tert-butyl groups on the para position of the upper rim. Di(tetramethylammonium) salts of the di-ionised ligands are utilised for spectrofluorimetric titration experiments in MeCN. The influence of alkali metal, alkaline earth metal and selected transition and heavy metal (Co2+, Fe2+, Hg2+, Mn2+, Pb2+, Zn2+ and Fe3+) cations on the spectroscopic properties of the two dansyl groups linked to the lower rim of the conformationally locked, di-ionised calix[4]arene-1,2-crown ether frameworks is investigated by emission spectrophotometry. All of the metal cations induce red shifts in the emission spectra of the di-ionised ligands. The metal cations produce enhancement or quenching of the fluorescence emissions. Changes in the fluorescence emission as a function of the metal cation identity, the lower rim crown ether ring size and the absence or presence of upper rim tert-butyl groups are investigated. 相似文献
109.
Sonochemical synthesis and electrochemical characterization of α-nickel hydroxide: precursor effects
F. Sinem Ertaş Recep Kaş Uğur Ünal Özgür Birer 《Journal of Solid State Electrochemistry》2013,17(5):1455-1462
Sonochemical degradation of urea was employed to synthesize alpha-nickel hydroxide from different nickel salts. Utilization of ultrasound yielded products with properties significantly different than the products obtained by thermal degradation of urea. The effect of intercalating chloride, nitrate, acetate, and sulfate anions on morphology and electrochemical performance was studied. The sulfate-intercalated sample had the smallest interlayer spacing when obtained by the sonochemical method, contradicting all the previous thermal synthesis results. The specific capacitance trend also differed from the literature values, and the value for the sulfate-intercalated sample was larger than that of acetate- and nitrate-intercalated samples. Ultrasonic synthesis increased the specific capacitance of the sulfate-intercalated sample significantly. This sample was also the most reversible and had the highest charge efficiency. 相似文献