全文获取类型
收费全文 | 2949篇 |
免费 | 108篇 |
国内免费 | 429篇 |
专业分类
化学 | 2721篇 |
晶体学 | 8篇 |
力学 | 80篇 |
综合类 | 10篇 |
数学 | 331篇 |
物理学 | 336篇 |
出版年
2024年 | 2篇 |
2023年 | 9篇 |
2022年 | 28篇 |
2021年 | 32篇 |
2020年 | 57篇 |
2019年 | 54篇 |
2018年 | 44篇 |
2017年 | 79篇 |
2016年 | 82篇 |
2015年 | 84篇 |
2014年 | 128篇 |
2013年 | 219篇 |
2012年 | 166篇 |
2011年 | 180篇 |
2010年 | 169篇 |
2009年 | 181篇 |
2008年 | 194篇 |
2007年 | 208篇 |
2006年 | 160篇 |
2005年 | 178篇 |
2004年 | 171篇 |
2003年 | 141篇 |
2002年 | 100篇 |
2001年 | 91篇 |
2000年 | 91篇 |
1999年 | 71篇 |
1998年 | 75篇 |
1997年 | 75篇 |
1996年 | 59篇 |
1995年 | 70篇 |
1994年 | 66篇 |
1993年 | 59篇 |
1992年 | 45篇 |
1991年 | 22篇 |
1990年 | 20篇 |
1989年 | 24篇 |
1988年 | 10篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有3486条查询结果,搜索用时 46 毫秒
61.
62.
For use in micro-patterned scaffolds in tissue engineering, novel diacrylated triblock macromers (PLA-b-PCL-b-PLA, PGA-b-PCL-b-PGA and PCL-b-PEO-b-PCL) were synthesized and characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR) and gel permeation chromatography (GPC). All diacrylated polymers were designed as triblock copolymers and involved biodegradable blocks of relatively non-polar epsilon-caprolactone (CL) and polar monomers such as glycolide (GA), lactide (LA) or ethylene oxide (EO). All triblock polymers were prepared in molecular weights of a few kilo daltons via the anionic ring-opening polymerization (ROP) of the corresponding lactide, glycolide or caprolactone using stannous octoate [Sn(Oct)(2)] as catalyst. The polymers had low polydispersity indices, ranging from 1.23 to 1.56. Biodegradable polymeric networks were prepared with conversions of 72-84% via photopolymerization of the triblock diacrylated polymers with 2,2-dimethoxy-2-phenylacetophenone (DMPA) as photoinitiator. PLA-b-PCL-b-PLA copolymers crumbled easily and were not suitable for micro-patterning. PGA-b-PCL-b-PGA copolymers had higher water contact angles than PCL-b-PEO-b-PCL and were also cytocompatible with Fibroblasts 3T3. 相似文献
63.
Preparation and surface properties of latexes with fluorine enriched in the shell by silicon monomer crosslinking 总被引:1,自引:0,他引:1
Ping ting Xiong Pei zhi Chen Hong zhi Huang Rong Guan 《European Polymer Journal》2007,43(5):2117-2126
A series of core-shell acrylic copolymer latexes containing fluorine enriched in the shell have been prepared by emulsion polymerization of a variety of hydrocarbon monomers with (perfluoroalkyl)methyl methacrylate and vinyltriethoxysilicone. In the presence of a reactive anionic and a long chain anionic-nonionic emulsifier, the core-shell latexes were prepared and characterized by transmission electron microscopy (TEM) and tapping-mode atomic force microscopy (AFM). From AFM and contact angle measurements, it was observed that the resulting fluorine and silicon-containing acrylic copolymers with surface energy as low as 15.5 mN/m formed a dense and gradient film containing a surface layer with high a fluorine content, and that the fluorinated particles can be fixed on the surface due to the crosslinking reaction of multi-functional silicon monomer even though the fluorinated carbon number was not enough to crystallize. 相似文献
64.
65.
66.
JunJieKANG ShiBiFANG 《中国化学快报》2004,15(1):87-89
Network polymer electrolytes with free oligo(oxyethylene) chains as internal plasticizers were prepared by cross-linking poly(ethylene glycol) acrylates. The effects of salt concentration and properties of internal plasticizers on ionic conductivity were studied. 相似文献
67.
疏水缔合型增稠剂聚(丙烯酰胺-丙烯酸高级酯)的合成及增稠性能研究 总被引:5,自引:0,他引:5
采用沉淀聚合法合成了聚(丙烯酰胺-丙烯酸十四酯),聚(丙烯酰胺-丙烯酸十六酯)和聚(丙烯酰胺-丙烯酸十八酯),重点讨论了共聚物中疏水基团数量及疏水基团链长对增稠性能的影响。采用凯达尔定氮法和动态热分析(DMTA)测定了共聚物的组成及玻璃化温度。 相似文献
68.
Natalia N. Dioubankova 《Tetrahedron》2004,60(21):4617-4626
The synthesis of two novel fluorescent uridine-2′-carbamate phosphoramidites is described. The reagents carrying fluorescent polyaromatic hydrocarbons 1-phenylethynylpyrene (PEPy) or 9,10-bis(phenylethynyl)anthracene (BPEA) are suitable for oligonucleotide synthesis. Prepared oligonucleotide conjugates show strong dye emissions at 401 and 485 nm, but low FRET rate when located in the oligonucleotide duplex. The dyes show considerable compensation of the usual carbamate duplex destabilization. The possible explanation of both effects is binding of PEPy and BPEA to the minor groove of the DNA duplex. 相似文献
69.
The viscosity of PEG-modified urethane acrylate (PMUA) showed peculiar behavior in the course of soap-free emulsification. Moreover, the viscosity change with added amounts of water was influenced by the reaction molar ratio of polyethylene glycol (PEG). The rate of increase in viscosity slowed and the ratio of increase in viscosity increased as the reaction molar ratio of PEG increased. This peculiar viscosity behavior was due to the microphase separation between hydrophilic and hydrophobic segments of PMUA, and the orientation of polyoxyethylene groups at O/W interface which influenced droplet size of the soap-free PMUA emulsion. The location of polyoxyethylene groups of this resin at O/W interface was confirmed using the adsorption isotherm measurement of PMUA molecules containing polyoxyethylene groups at water/benzene interface. The microphase separation behavior of PMUA between hydrophilic and hydrophobic segments could apply to the preparation of the PMUA gels containing peculiar structure. PMUA gels were prepared using dioxane (UAG) and the swelling behavior of these gels were compared to that of gels prepared using water (UAHG) in the same medium. In the same medium, the swelling behavior of UAHG gels differed from that of UAG gels because of the difference in the microstructure of gel due to the microphase separation between hydrophilic and hydrophobic segments. This phase separation in the course of gelation in water could be confirmed using contact angle measurement. 相似文献
70.
Mi-Young Song En-Young Kim Kyung Il Kim Hong-Seok Kim Chang-Hee Lee 《Tetrahedron letters》2004,45(2):299-301
Furans, thiazoles, fluorene or thiophene incorporated calix[4]pyrrole analogues were synthesized and characterized. The synthesis was achieved by utilization of various building blocks such as 7, 13, 14, 18 and 21. Acid catalyzed condensation of those building blocks with acetone or meso-disubstituted dipyrromethanes afforded desired macrocycles. 相似文献