全文获取类型
收费全文 | 23655篇 |
免费 | 2365篇 |
国内免费 | 5107篇 |
专业分类
化学 | 27332篇 |
晶体学 | 190篇 |
力学 | 279篇 |
综合类 | 128篇 |
数学 | 439篇 |
物理学 | 2759篇 |
出版年
2024年 | 65篇 |
2023年 | 377篇 |
2022年 | 717篇 |
2021年 | 832篇 |
2020年 | 1214篇 |
2019年 | 1028篇 |
2018年 | 1043篇 |
2017年 | 960篇 |
2016年 | 1060篇 |
2015年 | 1000篇 |
2014年 | 1478篇 |
2013年 | 2394篇 |
2012年 | 1334篇 |
2011年 | 1593篇 |
2010年 | 1218篇 |
2009年 | 1335篇 |
2008年 | 1424篇 |
2007年 | 1568篇 |
2006年 | 1461篇 |
2005年 | 1375篇 |
2004年 | 1345篇 |
2003年 | 1038篇 |
2002年 | 637篇 |
2001年 | 500篇 |
2000年 | 533篇 |
1999年 | 452篇 |
1998年 | 395篇 |
1997年 | 366篇 |
1996年 | 327篇 |
1995年 | 324篇 |
1994年 | 276篇 |
1993年 | 200篇 |
1992年 | 198篇 |
1991年 | 152篇 |
1990年 | 123篇 |
1989年 | 110篇 |
1988年 | 90篇 |
1987年 | 61篇 |
1986年 | 54篇 |
1985年 | 59篇 |
1984年 | 51篇 |
1983年 | 27篇 |
1982年 | 39篇 |
1981年 | 39篇 |
1980年 | 27篇 |
1979年 | 26篇 |
1978年 | 29篇 |
1977年 | 29篇 |
1976年 | 39篇 |
1974年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
We consider a spatially distributed hybrid system consisting of a convection/reaction system in which the reaction switches discontinuously in time between modes, independently at each spatial point on reaching “switching thresholds”. The model involves a novel formulation for evolution of the free boundary between the modal regions. 相似文献
92.
G. N. Merrill 《Journal of Physical Organic Chemistry》2007,20(1):19-29
Ab initio molecular orbital calculations were carried out on epibromohydrin (EBH) and epichlorohydrin (ECH) in an attempt to elucidate their reactivity with respect to a hard nucleophile, hydroxide. These systems were modeled in both the gas phase and a polar solvent under basic conditions. In the gas phase, it was determined that a direct displacement mechanism (nucleophilic attack at the C1 position) was operative for EBH, while an indirect pathway (nucleophilic attack at the C3 position and subsequent intramolecular displacement) was followed for ECH. In an acetone solution, only the indirect displacement mechanism was found to occur. An electrostatic argument is advanced to account for this behavior in polar solution. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
93.
94.
Vicenç Branchadell Roser Pleixats Claude Commandeur Max Malacria 《Journal of organometallic chemistry》2003,687(2):337-345
Regioselectivity of the Tsuji-Trost reaction on allyl acetates and carbonates substituted with silyl groups at the olefinic moiety has been analyzed. Silicon atom in the central carbon atom increases the stability of the intermediate π-allylpalladium cation with respect to the isomeric π-allylpalladium cation featuring the silicon in a terminal carbon atom. 相似文献
95.
Arata Yajima Ayumi Yamaguchi Fumihiro Saitou Tomoo Nukada Goro Yabuta 《Tetrahedron》2007,63(5):1080-1084
A convergent synthetic strategy for abietane diterpenoids via B-alkyl Suzuki-Miyaura coupling and Lewis acid-mediated cyclization reactions is established. Asymmetric total synthesis of 12-deoxyroyleanone, an antileishmanial diterpene, is described. 相似文献
96.
The synthesis of the title compounds has been achieved in concise, highly regiocontrolled fashion from commercially available (+)-sclareolide. In addition, we offer evidence that the structure of a newly reported natural product from Zingiber ottensii is incorrect. 相似文献
97.
Iodine has been found to be very effective catalyst for a Mannich reaction between an aryl aldehyde, an aryl ketone and benzyl carbamate, even though this is a less reactive amine, to produce Cbz-protected β-aryl β-amino carbonyl compounds in high yields. 相似文献
98.
氨酪酸(am inobutyric acid),化学名称为γ-氨基丁酸。本品在体内与血氨结合生成尿毒排出体外,有降低血氨及促进大脑新陈代谢的作用,能够增强葡萄糖磷酸酯化酶的活性,利于脑细胞功能的恢复。主要用于脑卒中后遗症、脑动脉硬化症、头部外伤后以及一氧化碳中毒所致昏迷的辅助治疗 相似文献
99.
100.
Surajit Some 《Tetrahedron letters》2006,47(7):1221-1224
A convenient synthetic approach to substituted benzene derivatives by modified Ullmann cross-coupling of 2-bromobenzaldehyde and bromovinylaldehydes followed by intramolecular McMurry coupling has been developed. 相似文献