全文获取类型
收费全文 | 490671篇 |
免费 | 5998篇 |
国内免费 | 1774篇 |
专业分类
化学 | 259810篇 |
晶体学 | 7495篇 |
力学 | 21790篇 |
综合类 | 8篇 |
数学 | 58522篇 |
物理学 | 150818篇 |
出版年
2020年 | 3488篇 |
2019年 | 3726篇 |
2018年 | 4410篇 |
2017年 | 4232篇 |
2016年 | 7192篇 |
2015年 | 5180篇 |
2014年 | 7758篇 |
2013年 | 21841篇 |
2012年 | 16495篇 |
2011年 | 20416篇 |
2010年 | 13530篇 |
2009年 | 13437篇 |
2008年 | 18788篇 |
2007年 | 19023篇 |
2006年 | 18249篇 |
2005年 | 16538篇 |
2004年 | 15039篇 |
2003年 | 13334篇 |
2002年 | 13164篇 |
2001年 | 14832篇 |
2000年 | 11374篇 |
1999年 | 9120篇 |
1998年 | 7491篇 |
1997年 | 7346篇 |
1996年 | 7221篇 |
1995年 | 6580篇 |
1994年 | 6324篇 |
1993年 | 6250篇 |
1992年 | 6735篇 |
1991年 | 6740篇 |
1990年 | 6299篇 |
1989年 | 6097篇 |
1988年 | 6443篇 |
1987年 | 6012篇 |
1986年 | 5746篇 |
1985年 | 8134篇 |
1984年 | 8319篇 |
1983年 | 6855篇 |
1982年 | 7267篇 |
1981年 | 7227篇 |
1980年 | 6913篇 |
1979年 | 7195篇 |
1978年 | 7240篇 |
1977年 | 7203篇 |
1976年 | 7189篇 |
1975年 | 6864篇 |
1974年 | 6781篇 |
1973年 | 6953篇 |
1972年 | 4443篇 |
1971年 | 3487篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Iodine(III)‐Catalyzed Rearrangements of Imides: A Versatile Route to α,α‐Dialkylated α‐Hydroxy Carboxylamides
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Anna Ulmer Dr. Maciej Stodulski Stefanie V. Kohlhepp Christoph Patzelt Dr. Alexander Pöthig Dr. Wolfgang Bettray Dr. Tanja Gulder 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(4):1444-1448
A tertiary hydroxy group α to a carboxyl moiety comprises a key structural motif in many bioactive substances. With the herein presented metal‐free rearrangement of imides triggered by hypervalent λ3‐iodane, an easy and selective way to gain access to such a compound class, namely α,α‐disubstituted‐α‐hydroxy carboxylamides, was established. Their additional methylene bromide side chain constitutes a useful handle for rapid diversification, as demonstrated by a series of further functionalizations. Moreover, the in situ formation of an iodine(III) species under the reaction conditions was proven. Our findings clearly corroborate that hypervalent λ3‐benziodoxolones are involved in these organocatalytic reactions. 相似文献
62.
63.
64.
A (di)graph is supereulerian if it contains a spanning eulerian sub(di)graph. This property is a relaxation of hamiltonicity. Inspired by this analogy with hamiltonian cycles and by similar results in supereulerian graph theory, we analyze a number of sufficient Ore type conditions for a digraph to be supereulerian. Furthermore, we study the following conjecture due to Thomassé and the first author: if the arc‐connectivity of a digraph is not smaller than its independence number, then the digraph is supereulerian. As a support for this conjecture we prove it for digraphs that are semicomplete multipartite or quasitransitive and verify the analogous statement for undirected graphs. 相似文献
65.
66.
67.
Timm Bergholz Dr. Benjamin Oelkers Dr. Benedikt Huber Prof. Bernhard Roling Prof. Dr. Jörg Sundermeyer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(6):2613-2620
New salts based on imidazolium, pyrrolidinium, phosphonium, guanidinium, and ammonium cations together with the 5‐cyanotetrazolide anion [C2N5]? are reported. Depending on the nature of cation–anion interactions, characterized by XRD, the ionic liquids (ILs) have a low viscosity and are liquid at room temperature or have higher melting temperatures. Thermogravimetric analysis, cyclic voltammetry, viscosimetry, and impedance spectroscopy display a thermal stability up to 230 °C, an electrochemical window of 4.5 V, a viscosity of 25 mPa s at 20 °C, and an ionic conductivity of 5.4 mS cm?1 at 20 °C for the IL 1‐butyl‐1‐methylpyrrolidinium 5‐cyanotetrazolide [BMPyr][C2N5]. On the basis of these results, the synthesized compounds are promising electrolytes for lithium‐ion batteries. 相似文献
68.
Applied Magnetic Resonance - The suggested approach allowed us to derive analytical expressions for modeling the shape of solid-echo signal and its time evolution for a system of three-spin groups... 相似文献
69.
70.