全文获取类型
收费全文 | 958篇 |
免费 | 26篇 |
国内免费 | 4篇 |
专业分类
化学 | 656篇 |
晶体学 | 7篇 |
力学 | 21篇 |
数学 | 137篇 |
物理学 | 167篇 |
出版年
2022年 | 10篇 |
2021年 | 14篇 |
2020年 | 13篇 |
2019年 | 13篇 |
2017年 | 8篇 |
2016年 | 12篇 |
2015年 | 19篇 |
2014年 | 17篇 |
2013年 | 32篇 |
2012年 | 42篇 |
2011年 | 57篇 |
2010年 | 33篇 |
2009年 | 23篇 |
2008年 | 42篇 |
2007年 | 38篇 |
2006年 | 47篇 |
2005年 | 40篇 |
2004年 | 39篇 |
2003年 | 33篇 |
2002年 | 42篇 |
2001年 | 27篇 |
2000年 | 23篇 |
1999年 | 23篇 |
1998年 | 13篇 |
1997年 | 13篇 |
1996年 | 17篇 |
1994年 | 10篇 |
1993年 | 18篇 |
1992年 | 23篇 |
1991年 | 9篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 11篇 |
1987年 | 10篇 |
1986年 | 9篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 8篇 |
1981年 | 16篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1976年 | 9篇 |
1975年 | 8篇 |
1974年 | 7篇 |
1973年 | 14篇 |
1969年 | 8篇 |
1934年 | 4篇 |
排序方式: 共有988条查询结果,搜索用时 0 毫秒
1.
2.
In previous work the authors consider the dynamic assignment problem, which involves solving sequences of assignment problems over time in the presence of uncertain information about the future. The algorithm proposed by the authors provides generally high-quality but non-optimal solutions. In this work, though, the authors prove that if the optimal solution to a dynamic assignment problem in one of two problem classes is unique, then the optimal solution is a fixed point under the algorithm. 相似文献
3.
4.
5.
C. Linda Powell 《Tetrahedron letters》2007,48(7):1251-1254
1-(2-Nitrophenyl)-1,2-dicarba-closo-dodecaborane(12) shows C-H?O intramolecular hydrogen bonding in chloroform. The reaction of isomeric 1-(nitrophenyl)-1,2-dicarba-closo-dodecaborane(12)s and of 1-(4-fluorophenyl)-1,2-dicarba-closo-dodecaborane(12) with wet DMSO causes the removal of 3-B or 6-B, leading cleanly to nido-carboranes. The rank order of rates of these deboronations is consistent with developing negative charge in the rate-determining step. 相似文献
6.
7.
Powell BJ Baruah T Bernstein N Brake K McKenzie RH Meredith P Pederson MR 《The Journal of chemical physics》2004,120(18):8608-8615
We report first-principles density-functional calculations for hydroquinone (HQ), indolequinone (IQ), and semiquinone (SQ). These molecules are believed to be the basic building blocks of the eumelanins, a class of biomacromolecules with important biological functions (including photoprotection) and with the potential for certain bioengineering applications. We have used the difference of self-consistent fields method to study the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, Delta(HL). We show that Delta(HL) is similar in IQ and SQ, but approximately twice as large in HQ. This may have important implications for our understanding of the observed broadband optical absorption of the eumelanins. The possibility of using this difference in Delta(HL) to molecularly engineer the electronic properties of eumelanins is discussed. We calculate the infrared and Raman spectra of the three redox forms from first principles. Each of the molecules have significantly different infrared and Raman signatures, and so these spectra could be used in situ to nondestructively identify the monomeric content of macromolecules. It is hoped that this may be a helpful analytical tool in determining the structure of eumelanin macromolecules and hence in helping to determine the structure-property-function relationships that control the behavior of the eumelanins. 相似文献
8.
Kang SO VanderVelde D Powell D Bowman-James K 《Journal of the American Chemical Society》2004,126(39):12272-12273
Multiple deuterium exchange between DMSO-d6 and amide hydrogens in two hexaamido cryptand fluoride receptors has been verified by 19F and 2H NMR and FAB mass spectral studies. Structural results for one of the complexes indicate a tricapped trigonal prism hydrogen bond coordination geometry around an encapsulated fluoride, with hydrogen bonds from fluoride to six amide and three phenyl hydrogens. 相似文献
9.
10.
The metallochromic reagent chrome azurol S, when used in hexamine buffer at pH 4.9, reacts rapidly with monomeric and small polymeric forms of aluminium(III) in aged hydrolysed solutions. It is unreactive toward the polymer Al13(OH)7+32 and colloidal Al(OH)3 and the hydroxyaluminosilicates, imogolite and allophane. The reagent is appropriate for rapid semi-quantitative analysis of labile aluminium in acid lake waters or acid soils. 相似文献