全文获取类型
收费全文 | 763篇 |
免费 | 23篇 |
国内免费 | 16篇 |
专业分类
化学 | 552篇 |
晶体学 | 11篇 |
力学 | 46篇 |
数学 | 31篇 |
物理学 | 162篇 |
出版年
2023年 | 3篇 |
2022年 | 10篇 |
2021年 | 11篇 |
2020年 | 14篇 |
2019年 | 10篇 |
2018年 | 10篇 |
2017年 | 7篇 |
2016年 | 10篇 |
2015年 | 14篇 |
2014年 | 20篇 |
2013年 | 54篇 |
2012年 | 43篇 |
2011年 | 37篇 |
2010年 | 17篇 |
2009年 | 46篇 |
2008年 | 43篇 |
2007年 | 48篇 |
2006年 | 39篇 |
2005年 | 47篇 |
2004年 | 46篇 |
2003年 | 35篇 |
2002年 | 35篇 |
2001年 | 10篇 |
2000年 | 12篇 |
1999年 | 9篇 |
1998年 | 12篇 |
1997年 | 9篇 |
1996年 | 11篇 |
1995年 | 13篇 |
1994年 | 8篇 |
1993年 | 5篇 |
1992年 | 10篇 |
1991年 | 10篇 |
1990年 | 7篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 7篇 |
1974年 | 5篇 |
1973年 | 7篇 |
1972年 | 3篇 |
1971年 | 6篇 |
1970年 | 3篇 |
1967年 | 4篇 |
排序方式: 共有802条查询结果,搜索用时 0 毫秒
801.
Hideyuki Kaneko Shingo Matsuo Nobuo Kawahara Junji Saito Tomoaki Matsugi Norio Kashiwa 《Macromolecular Symposia》2007,260(1):9-14
Isotactic polypropylene-based graft copolymers linking poly(methyl methacrylate), poly(n-butyl acrylate) and polystyrene were successfully synthesized by a controlled radical polymerization with isotactic polypropylene (iPP) macroinitiator. The hydroxylated iPP, prepared by propylene/10-undecen-1-ol copolymerization with a metallocene/methyl-aluminoxane/triisobutylaluminum catalyst system, was treated with 2-bromoisobutyryl bromide to produce a Br-group containing iPP (PP-g-Br). The resulting PP-g-Br could initiate controlled radical polymerization of methyl methacrylate, n-butyl acrylate and styrene by using a copper catalyst system, leading to a variety of iPP-based graft copolymers with a different content of the corresponding polar segment. These graft copolymers demonstrated unique mechanical properties dependent upon the kind and content of the grafted polar segment. 相似文献
802.
Construction of α-phosphonolactams via rhodium (II)-catalyzed intramolecular C?H insertion reactions
Yoshiharu Okada Toru Minami Masahiro Miyamoto Tsuneyuki Otaguro Sumiko Sawasaki Junji Ichikawa 《Heteroatom Chemistry》1995,6(3):195-210
The Rh(II)-catalyzed intramolecular C H insertion reactions of N,N-dialkyl-α-diazo-α-(diethylphosphono)acetamides 2a , f–j in CHCl3 or ClCH2CH2Cl were found to give monocyclic and bicyclic α-phosphono-β-lactams, 3a and 3f–j , in 43–67% yields via regiospecific α-C H insertion of the N-alkyl groups. Similar treatment of N-benzyl-N-isopropyl-α-diazo-α-(diethylphosphono)acetamide ( 2b ) and the corresponding N-isobutyl-N-methylacetamide 2d in ClCH2CH2Cl afforded mixtures of β-lactams 3b (35%) and and 3b ′ (16%), β-lactam 3d (47%), and γ-lactam 4d (10%), respectively, each of which is formed by the competitive C H insertion reaction between benzylic and isopropyl α-C H bonds and between methyl α-C H and methine β-C H bonds, respectively. For the formation of β-lactams, the selectivity in the rhodium-mediated C H insertion in ClCH2CH2Cl follows the order methyl > methine > benzylic α-C H bond on N-substituents. The N,N-dibutyl-α-diazo homologue 2c and Nα[α-diazo-α-(diethylphosphono)acetyl]-2-methylindoline ( 2k ) exclusively produced γ-lactams 4c (67%) and 4k (81%) via insertion into the methylene β-C H and methyl β-C H bonds. tert-Butyl N-[α-diazo-α-(dibenzylphosphono)acetyl]-piperidine-2-carboxylate ( 2m ) on similar treatment, followed by deprotection of the benzyl ester afforded the 7-phosphono carbacepham 6 in 32% overall yield. Similar Rh(II)-catalyzed cyclization of N-methyl-N[4-benzyloxy-α-(diethylphosphono)-phenyl(diethyl-phosphono)methyl]-α-diazo-acetamide ( 2n ) led to 1-[4′-benzylphenyl(diethylphosphono)methyl] -3-(diethyl-phosphono)azetidin-2-one ( 3n ) in 78% yicld. The phosphono group at C-7 of 3f was converted into the acetylamino group via a four-step reaction. Application of chiral rhodium(II) carboxylates 12a–c to the insertion reactions of 2b , c produced α-phosphono-β-and γ-lactams, 3b and 4c , in 6–24% ee and 25–29% ee, respectively. 相似文献