全文获取类型
收费全文 | 13165篇 |
免费 | 435篇 |
国内免费 | 45篇 |
专业分类
化学 | 10521篇 |
晶体学 | 73篇 |
力学 | 210篇 |
数学 | 1668篇 |
物理学 | 1173篇 |
出版年
2023年 | 88篇 |
2022年 | 303篇 |
2021年 | 503篇 |
2020年 | 282篇 |
2019年 | 332篇 |
2018年 | 253篇 |
2017年 | 213篇 |
2016年 | 433篇 |
2015年 | 442篇 |
2014年 | 418篇 |
2013年 | 833篇 |
2012年 | 859篇 |
2011年 | 972篇 |
2010年 | 587篇 |
2009年 | 579篇 |
2008年 | 819篇 |
2007年 | 798篇 |
2006年 | 681篇 |
2005年 | 620篇 |
2004年 | 526篇 |
2003年 | 442篇 |
2002年 | 431篇 |
2001年 | 164篇 |
2000年 | 132篇 |
1999年 | 110篇 |
1998年 | 113篇 |
1997年 | 98篇 |
1996年 | 131篇 |
1995年 | 86篇 |
1994年 | 84篇 |
1993年 | 77篇 |
1992年 | 61篇 |
1991年 | 75篇 |
1990年 | 55篇 |
1989年 | 74篇 |
1988年 | 62篇 |
1987年 | 49篇 |
1986年 | 52篇 |
1985年 | 63篇 |
1984年 | 82篇 |
1983年 | 43篇 |
1982年 | 66篇 |
1981年 | 58篇 |
1980年 | 55篇 |
1979年 | 46篇 |
1978年 | 54篇 |
1977年 | 38篇 |
1976年 | 33篇 |
1975年 | 24篇 |
1963年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
In the pursuit to enlarge the library of polyimide materials for energy applications, new polyimide/MWCNTs composite films have been developed by MWCNTs-assisted polycondensation reaction of a hydroxyl and triphenylmethane-containing diamine with benzophenone tetracarboxylic dianhydride targeting to highlight their electrical storage capability as flexible electrodes in micro-supercapacitors (mSCs). The Fourier-transform infrared spectroscopy, proton nuclear magnetic resonance, UV–vis, fluorescence, and Raman spectroscopies were used to demonstrate the evolution of interfacial interactions between MWCNTs and the precursors (diamine monomer and intermediate polyamidic acid) and polyimide matrix that proved to be the origin of MWCNTs homogeneous dispersion. Thus, composite films incorporating 1, 3, 5, and 10 w.t.% MWCNTs were obtained and thoroughly investigated with regard to their morphology, mechanical behavior, thermal stability, and electrical conductivity. The electrochemical performance of these composites was first analyzed in a classical three-electrode cell by cyclic voltammetry and galvanostatic charge-discharge in both aqueous and organic electrolyte systems. By far, the best electrical storage capacity was obtained with the composite polyimide film containing 10% MWCNTs that was further used as both active material and current collector in a flexible symmetric mSC realized by a straightforward and low-cost procedure. In the attempt to better exploit the advantages of this composite film, it was layered with a graphite-containing paint and tested as an electrode in a flexible mSC, which provided satisfactory results. To our knowledge, this is the first report on the electrical charge storage capability of a polyimide/MWCNTs free-standing film as a flexible electrode in mSCs, which do not require time- and resource-consuming processing steps. 相似文献
2.
3.
Journal of Fourier Analysis and Applications - We develop a theory of Sobolev orthogonal polynomials on the Sierpiński gasket ( $$SG$$ ), which is a fractal set that can be viewed as a limit... 相似文献
4.
5.
6.
Synthesis of Highly Substituted γ‐Butyrolactones by a Gold‐Catalyzed Cascade Reaction of Benzyl Esters
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)
Maria Camila Blanco Jaimes Alexander Ahrens Daniel Pflästerer Dr. Matthias Rudolph Prof. Dr. A. Stephen K. Hashmi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):427-433
Easily accessible benzylic esters of 3‐butynoic acids in a gold‐catalyzed cyclization/rearrangement cascade reaction provided 3‐propargyl γ‐butyrolactones with the alkene and the carbonyl group not being conjugated. Crossover experiments showed that the formation of the new C?C bond is an intermolecular process. Initially propargylic–benzylic esters were used, but alkyl‐substituted benzylic esters worked equally well. In the case of the propargylic–benzylic products, a simple treatment of the products with aluminum oxide initiated a twofold tautomerization to the allenyl‐substituted γ‐butyrolactones with conjugation of the carbonyl group, the olefin, and the allene. The synthetic sequence can be conducted stepwise or as a one‐pot cascade reaction with similar yields. Even in the presence of the gold catalyst the new allene remains intact. 相似文献
7.
8.
9.
10.