全文获取类型
收费全文 | 705篇 |
免费 | 33篇 |
国内免费 | 1篇 |
专业分类
化学 | 555篇 |
晶体学 | 3篇 |
力学 | 25篇 |
数学 | 61篇 |
物理学 | 95篇 |
出版年
2023年 | 5篇 |
2022年 | 8篇 |
2021年 | 17篇 |
2020年 | 13篇 |
2019年 | 13篇 |
2018年 | 5篇 |
2017年 | 6篇 |
2016年 | 29篇 |
2015年 | 22篇 |
2014年 | 25篇 |
2013年 | 35篇 |
2012年 | 57篇 |
2011年 | 71篇 |
2010年 | 33篇 |
2009年 | 20篇 |
2008年 | 54篇 |
2007年 | 31篇 |
2006年 | 38篇 |
2005年 | 27篇 |
2004年 | 29篇 |
2003年 | 18篇 |
2002年 | 23篇 |
2001年 | 3篇 |
2000年 | 7篇 |
1998年 | 3篇 |
1995年 | 4篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 8篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 8篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 15篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1975年 | 1篇 |
1974年 | 8篇 |
1973年 | 10篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1924年 | 2篇 |
排序方式: 共有739条查询结果,搜索用时 15 毫秒
71.
72.
Cyril Odianose Usifoh 《Journal of heterocyclic chemistry》2001,38(3):597-600
Isoquinolinones were brominated using N‐bromosuccinimide in dimethylformamide at room temperature to give 4‐bromo‐3‐substituted isoquinolin‐1‐(2H)‐ones. The reaction of these isoquinolinones with propargyl bromide in the presence of anhydrous potassium carbonate yielded N and O‐alkylated products. 相似文献
73.
The paper considers how to choose the joint distribution of several random variables each with a given marginal distribution so that their sum has a variance as small as possible. A theorem is given that allows the solution of this and of related problems for normal random variables. Several specific applications are given. Additional results are provided for radially symmetric joint distributions of three random variables when the sum is identically zero. 相似文献
74.
Nicolas Cocherel Cyril Poriel Dr. Joëlle Rault‐Berthelot Dr. Frédéric Barrière Dr. Nathalie Audebrand Dr. Alexandra M. Z. Slawin Prof. Dr. Laurence Vignau Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(36):11328-11342
New routes to ladder‐type phenylene materials 1 and 2 are described. The oligomers 1 and 2 , which possess a “3π‐2spiro” architecture, have been synthesized by using extended diketone derivatives 3 and 10 as key intermediates. The physicochemical properties of the new blue‐light emitter 2 were studied in detail and compared with those of the less‐extended 1 . Owing to the recent development of fluorenone derivatives and their corresponding more conjugated analogues as potential electron‐transport materials in organic light‐emitting diodes (OLEDs) and as n‐type materials for photovoltaic applications, we also report herein the thermal, optical and electrochemical behavior of the key intermediates, diketones 3 and 10 . Finally, the application of dispiro 2 as a new light‐emitting material in OLEDs is reported. 相似文献
75.
76.
Peter Flury Cyril A. Grob Guang Yi Wang Hans-Werner Lennartz Wolfgang R. Roth 《Helvetica chimica acta》1988,71(5):1017-1024
Further evidence is presented that the 2-norbornyl cation is stabilized primarily by C(2)–C(6) bridging, and that C(2)–C(7) bridging leads to prohibitive strain. Thus, a comparison of the heats of hydrogenation of nortricyclene 17 and bicyclo[3. 2. 0. 0.2,7]heptane 18 indicates that the strain energy of the latter is ca. 21.5 kcal/mol higher that that of 17 . Furthermore, 6-exo-2-oxabicyclo[2. 2. 1]heptyl sulfonates 8 ionize with strong O(2) participation to the bridged oxonium ion 12. In contrast, 2-endo-7-oxabicyclo[2.2.1]heptyl sulfonates 11 ionize without O(7) participation to form the unbridged carbenium ion 15 . 相似文献
77.
The pKa of 2-, 3- and 4-substituted quinuclidinium perchlorates and the solvolysis rates of the corresponding bicyclo[2.2.2]octyl-l-p-nitrobenzenesulfonates reveal the dispersal of charge in ammonium ions and carbocations. 相似文献
78.
79.
The preparation of several 4-heterosubstituted quinuclidines and the pKa values of their hydroperchlorates in water are reported. 相似文献
80.
pKa Values of 42 quinuclidinium perchlorates I have been measured in 0.1 M aqueous KCl-solution. In a few cases small corrections of earlier thermodynamic pKa values are indicated. These measurements, in conjunction with recent X-ray structure determinations, confirm the reliability of the inductive substituent constants σIq derived from them. 相似文献