全文获取类型
收费全文 | 856篇 |
免费 | 23篇 |
国内免费 | 1篇 |
专业分类
化学 | 739篇 |
晶体学 | 2篇 |
力学 | 18篇 |
数学 | 42篇 |
物理学 | 79篇 |
出版年
2023年 | 6篇 |
2021年 | 8篇 |
2020年 | 4篇 |
2019年 | 12篇 |
2017年 | 4篇 |
2016年 | 14篇 |
2015年 | 12篇 |
2014年 | 10篇 |
2013年 | 23篇 |
2012年 | 57篇 |
2011年 | 55篇 |
2010年 | 19篇 |
2009年 | 15篇 |
2008年 | 43篇 |
2007年 | 49篇 |
2006年 | 43篇 |
2005年 | 42篇 |
2004年 | 37篇 |
2003年 | 31篇 |
2002年 | 51篇 |
2001年 | 14篇 |
2000年 | 7篇 |
1999年 | 10篇 |
1998年 | 12篇 |
1997年 | 21篇 |
1996年 | 14篇 |
1995年 | 18篇 |
1994年 | 11篇 |
1993年 | 11篇 |
1992年 | 9篇 |
1991年 | 14篇 |
1990年 | 8篇 |
1989年 | 16篇 |
1988年 | 17篇 |
1987年 | 11篇 |
1986年 | 7篇 |
1985年 | 17篇 |
1984年 | 14篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 10篇 |
1980年 | 11篇 |
1979年 | 14篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 10篇 |
1975年 | 12篇 |
1974年 | 13篇 |
1973年 | 6篇 |
1972年 | 3篇 |
排序方式: 共有880条查询结果,搜索用时 15 毫秒
41.
42.
43.
[reaction: see text] An enmeshed supramolecular complex, based on a semi-dumbbell-shaped component containing an asymmetrically substituted tetrathiafulvalene site and a 1,5-dioxynaphthalene site for encirclement by a cyclobis(paraquat-p-phenylene) ring component and with a "speed bump" in the form of an thiomethyl group situated between the two recognition sites, has been self-assembled. This complex is a mixture in acetone solution of two slowly interconverting [2]pseudorotaxanes, one of which is on the verge of being a [2]rotaxane at room temperature. 相似文献
44.
[reaction: see text] A dendrimer wherein the branching points are mechanical in nature has been synthesized. It contains two identical covalently linked bis-dendrons and a core unit fused to two rings that encircle the two bis-dendrons. A "threading-followed-by-stoppering" approach is used in the template-directed synthesis of a precursor bis[2]rotaxane, which undergoes stopper exchange four times to yield the dendrimer in which the two bis-dendrons act as stoppers within the two [2]rotaxane subunits. 相似文献
45.
Ballardini R Balzani V Clemente-León M Credi A Gandolfi MT Ishow E Perkins J Stoddart JF Tseng HR Wenger S 《Journal of the American Chemical Society》2002,124(43):12786-12795
We have designed, synthesized, and investigated a self-assembling supramolecular system which mimics, at a molecular level, the function performed by a macroscopic electrical extension cable. The system is made up of three components, 12+, 2-H3+, and 3. Component 12+ consists of two moieties: a [Ru(bpy)3]2+ unit, which plays the role of an electron donor under light excitation, and a DB24C8 crown ether, which fulfills the function of a socket. The wire-type component 2-H3+ is also composed of two moieties, a secondary dialkylammonium-ion center and a bipyridinium unit, which thread into the DB24C8 crown-ether socket of 12+ and the 1/5DN38C10 crown-ether socket 3, respectively. The photochemical, photophysical, and electrochemical properties of the three separated components, of the 12+ superset 2-H3+ and 2-H3+ subset 3 dyads, and of the 12+ superset 2-H3+ subset 3 triad have been investigated in CH2Cl2 solution containing 2% MeCN. Reversible connection/disconnection of the two plug/socket systems can be controlled independently by acid/base and redox stimulation. The behavior of the various different dyads and triad has been monitored by light absorption and emission spectroscopies, as well as by electrochemical techniques. In the fully connected 12+ superset 2-H3+ subset 3 triad, light excitation of the [Ru(bpy)3]2+ unit of component 12+ is followed by electron transfer (k = 2.8 x 108 s-1) to the bipyridinium unit of component 2-H3+, which is plugged into component 3. Possible schemes to obtain improved molecular-level electrical extension cables are discussed. 相似文献
46.
47.
48.
R.R. Fraser N. Chuaqui-Offermanns K.N. Houk N.G. Rondan 《Journal of organometallic chemistry》1981,206(2):131-138
The N-isopropyl imine of lithioacetaldehyde, I, was found to exist as a 50 : 50 mixture of two isomers, as seen below 20°C by 1H and 13C NMR. Comparison of the population ratio and spectral characteristics of the isomers of this and related lithiated imines leads to the conclusion that they are rotamers all of which possess the syn configuration. This conclusion is supported by calculations of the barriers to interconversion. 相似文献
49.
A tolerance region is a map from the sample space of one statistical model to the event space of a second statistical model having the same parameter. This paper derives an optimum β-expectation tolerance region for the multivariate regression model. A measure of power is proposed and evaluated. 相似文献
50.