全文获取类型
收费全文 | 1968篇 |
免费 | 112篇 |
国内免费 | 23篇 |
专业分类
化学 | 1537篇 |
晶体学 | 23篇 |
力学 | 41篇 |
数学 | 147篇 |
物理学 | 355篇 |
出版年
2024年 | 3篇 |
2023年 | 14篇 |
2022年 | 35篇 |
2021年 | 49篇 |
2020年 | 44篇 |
2019年 | 42篇 |
2018年 | 27篇 |
2017年 | 38篇 |
2016年 | 70篇 |
2015年 | 59篇 |
2014年 | 88篇 |
2013年 | 130篇 |
2012年 | 192篇 |
2011年 | 175篇 |
2010年 | 115篇 |
2009年 | 82篇 |
2008年 | 124篇 |
2007年 | 120篇 |
2006年 | 109篇 |
2005年 | 88篇 |
2004年 | 82篇 |
2003年 | 66篇 |
2002年 | 63篇 |
2001年 | 42篇 |
2000年 | 50篇 |
1999年 | 23篇 |
1998年 | 24篇 |
1997年 | 17篇 |
1996年 | 14篇 |
1995年 | 11篇 |
1994年 | 7篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 9篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1983年 | 7篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1974年 | 5篇 |
1973年 | 5篇 |
1933年 | 2篇 |
排序方式: 共有2103条查询结果,搜索用时 46 毫秒
941.
942.
943.
Salens, derived from 1,2‐ethylenediamine and salicylaldehydes, have been widely used as ligands for metal complexes which have been showing enormous potential in chemical properties of asymmetric catalysts as well as biological properties such as anticancer agents. Almost all of the salen–metal complexes with their corresponding metal (II)‐complexes show the evidences of chelation of two oxygens in salens. However, several metal (II) complexes, especially cobalt (II) complexes, could not show NMR spectra due to their paramagnetism. Recently, it has been reported that one of the cobalt (III) complexes was used for NMR spectroscopy to evaluate its stereoselectivity as a catalyst. Even though many salen ligands are known, their NMR data are not assigned completely. It was possible that modification in northern part of salen with 2‐hydroxyphenyl group afforded another oxygen chelation site in salen ligand. Here we report that synthesis and full NMR assignment of new salen ligands, which form meso 1,2‐bis(2‐hydroxyphenyl)ethylenediamine) and their cobalt (III) complexes. The assignments of 1H and 13C NMR data obtained in this experiment can help us to predict the NMR data of other salen ligands. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
944.
945.
946.
Woo Jin Bae Christopher Scilla Volodimyr V. Duzhko Won Ho Jo E. Bryan Coughlin 《Journal of polymer science. Part A, Polymer chemistry》2011,49(15):3260-3271
We report the facile synthesis and characterization of a class of thienothiophene polymers with various lengths of alkyl side chains. A series of 2‐alkylthieno[3,4‐b]thiophene monomers (Ttx) have been synthesized in a two‐step protocol in an overall yield of 28–37%. Poly(2‐alkylthieno[3,4‐b]thiophenes) (PTtx, alkyl: pentyl, hexyl, heptyl, octyl, and tridecyl) were synthesized by oxidative polymerization with FeCl3 or via Grignard metathesis (GRIM) polymerization methods. The polymers are readily soluble in common organic solvents. The polymers synthesized by GRIM polymerization method (PTtx‐G) have narrower molecular weight distribution (?) with lower molecular weight (Mn) than those synthesized by oxidative polymerization (PTtx‐O). The band structures of the polymers with various lengths of alkyl side chains were investigated by UV–vis spectroscopy, cyclic voltammetry, and ultraviolet photoelectron spectroscopy. These low‐bandgap polymers are good candidates for organic transistors, organic light‐emitting diodes, and organic photovoltaic cells. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
947.
A facile route for mono‐BOC protection of symmetrical and unsymmetrical diamines was developed by sequential additions of 1 mol of HCl and 1 mol of (BOC)2O followed by neutralization. 相似文献
948.
One-pot transformation of ketones into α-azido ketones has been achieved by successive treatment with HNIB and NaN3 in acetonitrile. 相似文献
949.
This paper proposes a simple factorization principle that can be used efficiently and effectively to derive the vector generating
function of the queue length at an arbitrary time of the BMAP/G/1/ queueing systems under variable service speed. We first
prove the factorization property. Then we provide moments formula. Lastly we present some applications of the factorization
principle. 相似文献
950.