全文获取类型
收费全文 | 5483篇 |
免费 | 1038篇 |
国内免费 | 743篇 |
专业分类
化学 | 5676篇 |
晶体学 | 12篇 |
力学 | 206篇 |
综合类 | 10篇 |
数学 | 213篇 |
物理学 | 563篇 |
综合类 | 584篇 |
出版年
2024年 | 12篇 |
2023年 | 62篇 |
2022年 | 108篇 |
2021年 | 147篇 |
2020年 | 279篇 |
2019年 | 130篇 |
2018年 | 199篇 |
2017年 | 145篇 |
2016年 | 289篇 |
2015年 | 375篇 |
2014年 | 371篇 |
2013年 | 474篇 |
2012年 | 426篇 |
2011年 | 400篇 |
2010年 | 384篇 |
2009年 | 382篇 |
2008年 | 466篇 |
2007年 | 392篇 |
2006年 | 374篇 |
2005年 | 331篇 |
2004年 | 301篇 |
2003年 | 349篇 |
2002年 | 126篇 |
2001年 | 104篇 |
2000年 | 109篇 |
1999年 | 70篇 |
1998年 | 51篇 |
1997年 | 88篇 |
1996年 | 78篇 |
1995年 | 65篇 |
1994年 | 33篇 |
1993年 | 29篇 |
1992年 | 27篇 |
1991年 | 19篇 |
1990年 | 16篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1977年 | 1篇 |
排序方式: 共有7264条查询结果,搜索用时 0 毫秒
991.
Johannes F. Teichert Ben L. Feringa Prof. Dr. 《Angewandte Chemie (International ed. in English)》2010,49(14):2486-2528
Asymmetric catalysis with transition‐metal complexes is the basis for a vast array of stereoselective transformations and has changed the face of modern synthetic chemistry. Key to this success has been the design of chiral ligands to control the regio‐, diastereo‐, and enantioselectivity. Phosphoramidites have emerged as a highly versatile and readily accessible class of chiral ligands. Their modular structure enables the formation of ligand libraries and easy fine‐tuning for a specific catalytic reaction. Phosphoramidites frequently show exceptional levels of stereocontrol, and their monodentate nature is essential in combinatorial catalysis, where a ligand‐mixture approach is used. In this Review, recent developments in asymmetric catalysis with phosphoramidites used as ligands are discussed, with a focus on the formation of carbon–carbon and carbon–heteroatom bonds. 相似文献
992.
993.
994.
995.
996.
997.
Pignataro L Boghi M Civera M Carboni S Piarulli U Gennari C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(5):1383-1400
A library of 19 binol-derived chiral monophosphites that contain a phthalic acid diamide group (PhthalaPhos) has been designed and synthesized in four steps. These new ligands were screened in the rhodium-catalyzed enantioselective hydrogenation of prochiral dehydroamino esters and enamides. Several members of the library showed excellent enantioselectivity with methyl 2-acetamido acrylate (6 ligands gave >97% ee), methyl (Z)-2-acetamido cinnamate (6 ligands gave >94% ee), and N-(1-phenylvinyl)acetamide (9 ligands gave >95% ee), whilst only a few representatives afforded high enantioselectivities for challenging and industrially relevant substrates N-(3,4-dihydronaphthalen-1-yl)-acetamide (96% ee in one case) and methyl (E)-2-(acetamidomethyl)-3-phenylacrylate (99% ee in one case). In most cases, the new ligands were more active and more stereoselective than their structurally related monodentate phosphites (which are devoid of functional groups that are capable of hydrogen-bonding interactions). Control experiments and kinetic studies were carried out that allowed us to demonstrate that hydrogen-bonding interactions involving the diamide group of the PhthalaPhos ligands strongly contribute to their outstanding catalytic properties. Computational studies carried out on a rhodium precatalyst and on a conceivable intermediate in the hydrogenation catalytic cycle shed some light on the role played by hydrogen bonding, which is likely to act in a substrate-orientation effect. 相似文献
998.
999.
该文报道了一种具有结构复杂性和生物学特性的功能化螺旋吲哚酮的简便合成方法.以二苯乙烯基甲酮和氧化吲哚为原料,用结构上下对称的多氢键型催化剂轴手性胍-酰胺催化不对称串联[5+1]环加成反应,采用一锅法合成了15种螺[环己酮-氧化吲哚]衍生物,并对反应条件进行了优化.研究结果表明:在以物质的量分数20%的手性胍(1a)为催化剂、CH2Cl2为溶剂、在40 ℃下反应72 h的条件下,以91%的产率、93%的ee值获得螺环己酮吲哚啉酮. 相似文献
1000.
Chen W McCormack PJ Mohammed K Mbafor W Roberts SM Whittall J 《Angewandte Chemie (International ed. in English)》2007,46(22):4141-4144