全文获取类型
收费全文 | 2891篇 |
免费 | 303篇 |
国内免费 | 124篇 |
专业分类
化学 | 2165篇 |
晶体学 | 29篇 |
力学 | 64篇 |
数学 | 369篇 |
物理学 | 691篇 |
出版年
2023年 | 47篇 |
2022年 | 62篇 |
2021年 | 83篇 |
2020年 | 112篇 |
2019年 | 104篇 |
2018年 | 79篇 |
2017年 | 88篇 |
2016年 | 137篇 |
2015年 | 139篇 |
2014年 | 145篇 |
2013年 | 198篇 |
2012年 | 235篇 |
2011年 | 261篇 |
2010年 | 176篇 |
2009年 | 137篇 |
2008年 | 192篇 |
2007年 | 171篇 |
2006年 | 156篇 |
2005年 | 120篇 |
2004年 | 107篇 |
2003年 | 76篇 |
2002年 | 69篇 |
2001年 | 40篇 |
2000年 | 26篇 |
1999年 | 40篇 |
1998年 | 26篇 |
1997年 | 33篇 |
1996年 | 45篇 |
1995年 | 12篇 |
1994年 | 17篇 |
1993年 | 25篇 |
1992年 | 20篇 |
1991年 | 12篇 |
1990年 | 14篇 |
1989年 | 14篇 |
1988年 | 4篇 |
1987年 | 12篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 9篇 |
1982年 | 3篇 |
1980年 | 5篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1974年 | 3篇 |
1970年 | 3篇 |
1958年 | 6篇 |
1957年 | 2篇 |
排序方式: 共有3318条查询结果,搜索用时 15 毫秒
991.
Biodegradable polycarbonates containing side carboxyl groups—synthesis,properties, and degradation study 下载免费PDF全文
Joanna Jaworska Michal Kawalec Malgorzata Pastusiak Katarzyna Reczynska Henryk Janeczek Kamila Lewicka Elzbieta Pamula Piotr Dobrzynski 《Journal of polymer science. Part A, Polymer chemistry》2017,55(17):2756-2769
The main objective of the presented research was to synthesise biodegradable aliphatic polycarbonates containing reactive carboxyl pendant groups and to examine the influence of the copolymer chain microstructure and composition on the process of their hydrolytic degradation and cytocompatibility. The work describes copolymerization of cyclic trimethylene carbonate derivative containing benzyl‐ester pendant group (benzyl 5‐methyl‐2‐oxo‐1,3‐dioxane‐5‐carboxylate) with trimethylene carbonate. The copolymerization was conducted with the use of zinc (II) and lanthanum (III) acetylacetonates as ring‐opening polymerization coordination initiators. Detailed NMR analysis allowed to define the microstructure of the obtained copolymers, which depended on the composition and type of used initiator. The final tapered chain microstructure of the obtained copolymers was related to huge differences in comonomers reactivity and evidenced low level of transesterification of the main copolymer backbone. Chosen copolymers, with unprotected carbonyl groups, were subjected to in vitro degradation test and cytocompatibility studies. It was found that high concentration of carboxyl groups resulted in copolymers which formed hydrogels and were very prone to hydrolytic degradation; they were also cytotoxic toward osteoblast‐like MG 63 cells. Copolymers with lower content of carboxyl groups were found less susceptible to degradation and cytocompatible with studied cells. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2756–2769 相似文献
992.
993.
994.
995.
Jay B. Benziger May Jean Cheah Vaclav Klika Michal Pavelka 《Journal of Polymer Science.Polymer Physics》2015,53(22):1580-1589
Water and proton transport across a Nafion membrane are measured as functions of water activity and applied electric potential with a polymer electrolyte hydrogen pump. Water and proton transport across the membrane must match water and proton transport entering and leaving the electrode/membrane/vapor three phase interfaces at the anode and cathode. At low applied electric potential proton and water fluxes are correlated. At moderate to high applied electric potential the proton current is constant, independent of applied electric potential, while the water transport increases with increasing electric potential. At high applied electric potential water and proton transport become uncoupled at the membrane interfaces; water is transported across the membrane/vapor interface and protons are transported across the membrane/electrode interface. The applied electric potential drives electro‐osmosis to redistribute the water in the membrane. Water redistribution is limited by the interfacial transport of water across the membrane/vapor interface. © 2015 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2015 , 53, 1580–1589 相似文献
996.
997.
Xiaomin Zhang Heqin Dou Zhengbiao Zhang Wei Zhang Xiulin Zhu Jian Zhu 《Journal of polymer science. Part A, Polymer chemistry》2013,51(18):3907-3916
Vinyl‐conjugated monomer (methyl acrylate, MA) and allyl 2‐bromopropanoate (ABP)‐possessing unconjugated C?C and active C? Br bonds were polymerized via the Cu(0)‐mediated simultaneous chain‐ and step‐growth radical polymerization at ambient temperature using Cu(0) as catalyst, N,N,N′,N″,N″‐pentamethyldiethylenetriamine as ligand and dimethyl sulfoxide as solvent. The conversion was reached higher than 98% within 20 h. The obtained polymers showed block structure consisting of polyester and vinyl polymer moieties. The Cu(0)‐catalyzed simultaneous chain‐ and step‐growth radical polymerization mechanism was demonstrated by NMR, matrix‐assisted laser desorption ionization time‐of‐flight, and GPC analyses. Furthermore, the obtained copolymers of MA and ABP were further modified with poly(N‐isopropylamide) through radical thiol‐ene “click” chemistry from the terminal double bond. The thermoresponsive behavior of this block copolymer was investigated. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3907–3916 相似文献
998.
999.
1000.