全文获取类型
收费全文 | 830篇 |
免费 | 0篇 |
国内免费 | 5篇 |
专业分类
化学 | 691篇 |
力学 | 16篇 |
数学 | 79篇 |
物理学 | 49篇 |
出版年
2022年 | 9篇 |
2021年 | 9篇 |
2020年 | 7篇 |
2016年 | 10篇 |
2015年 | 5篇 |
2014年 | 5篇 |
2013年 | 20篇 |
2012年 | 34篇 |
2011年 | 51篇 |
2010年 | 25篇 |
2009年 | 13篇 |
2008年 | 40篇 |
2007年 | 44篇 |
2006年 | 48篇 |
2005年 | 45篇 |
2004年 | 47篇 |
2003年 | 37篇 |
2002年 | 29篇 |
2001年 | 8篇 |
2000年 | 5篇 |
1999年 | 10篇 |
1998年 | 15篇 |
1997年 | 19篇 |
1996年 | 19篇 |
1995年 | 14篇 |
1994年 | 8篇 |
1993年 | 14篇 |
1992年 | 18篇 |
1991年 | 16篇 |
1990年 | 16篇 |
1989年 | 8篇 |
1988年 | 15篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 10篇 |
1982年 | 7篇 |
1981年 | 8篇 |
1980年 | 13篇 |
1979年 | 12篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1976年 | 9篇 |
1975年 | 11篇 |
1974年 | 8篇 |
1973年 | 14篇 |
1972年 | 3篇 |
1971年 | 4篇 |
1967年 | 3篇 |
排序方式: 共有835条查询结果,搜索用时 15 毫秒
771.
772.
Ruben M Breuning E Barboiu M Gisselbrecht JP Lehn JM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(1):291-299
The [M(4)(II)L(4)](8+) [2 x 2]-grid-type complexes 1-8 present a set of features of particular interest for potential applications. All complexes exhibit multiple reduction levels at low reduction potentials paired with rather high stability. The modulation of the reduction potentials is possible by introduction of appropriate substituents on the ligands. The Co(II)(4) complexes 1-5 present a remarkable regularity in the disposition of the reduction levels, indicating the ability of the Co(II) sites to transmit electronic interactions between reduced ligands. In general, all investigated molecular systems 1-8 show characteristics typical for multilevel supramolecular electronic devices. 相似文献
773.
Jean-Marie Bourjolly 《Mathematical Programming》1988,41(1-3):375-384
Given a bidirected graphG and a vectorb of positive integral node-weights, an integer linear program IP is defined on (G, b). IP generalizes the node packing problem on a node-weighted (undirected) graph in the sense that it reduces to the latter whenG is undirected. A polynomial time algorithm is given that recognizes whether CP (the linear program obtained by relaxing the integrality constraints of IP) has an integral optimal solution. Also an efficient method for solving the linear programming dual of CP is described.Supported by the Natural Sciences and Engineering Research Council of Canada. 相似文献
774.
Pierre Granger Stella Chapelle Jean-Marie Poirier 《Magnetic resonance in chemistry : MRC》1980,14(1):69-73
The configurations of 16 different β-halogenoenamines have been determined using the proton NOE effect, and the same results were obtained as when the 2J(CH) coupling constants were used. A new procedure called the ‘repetitive shift frequency’ is presented for the NOE determinations which allows better reproducibility and improves the precision. 相似文献
775.
Antonio Echavarren Amalia Galn Javier de Mendoza Armando Salmern Jean-Marie Lehn 《Helvetica chimica acta》1988,71(4):685-693
The optically active (4S,8S)-4, 8-bis(hydroxymethyl)-1,5,7-triazabicyclo[4.4.0]dec-5-ene ((S,S)- 1 ) has been synthesized in nine steps from L -asparagine with a total yield of 5.1%. Similarly, the enantiomer (R,R)- 1 has been prepared from D -asparagine. (S,S)- and (S,S)- 1 are representative examples of rigid and functionalized bicyclic guanidine systems and constitute useful intermediates in the construction of chiral selective anion-receptor molecules. 相似文献
776.
777.
778.
779.
780.
Synthetic procedures have been developed for the preparation of ligands bearing two to six pendent, unsubstituted or substituted 2, 2′-bipyridine groups attached to acyclic (tripode, tetrapode) and macrocyclic (triazanonade-cane, cyclam, hexacyclen, bis(bipyrido)hexaazamacrocycle) polyamines. Ligands 1-5 have been obtained in high yield by condensation of 6-(bromomethyl)-2, 2′-bipyridine ( 9b ) with the corresponding amines in the presence of NaOH, H2O, and MeOH. Ligands 6-8 have been prepared in good yield by condensation of 9b or the di- or tetrasubstituted mono (bromomethyl) bipyridine 10b or 11b , respectively, with the corresponding amines in the presence of Na2CO3 and MeCN. Ligand 1 forms hemi-cage complexes with RuII, FeI, CrII, and CrIII cations and trinuclear complexes with [RuCl2(bpy)2] and [ReCl(CO)5]. Tetrapode 2 and hexapode 4 gave tetranuclear and dinuclear complexes, respectively, by reaction with Fe11 salts. These complexes possess a variety of interesting physical and chemical properties. 相似文献