全文获取类型
收费全文 | 260篇 |
免费 | 1篇 |
专业分类
化学 | 143篇 |
晶体学 | 2篇 |
力学 | 12篇 |
数学 | 49篇 |
物理学 | 55篇 |
出版年
2022年 | 4篇 |
2020年 | 3篇 |
2019年 | 3篇 |
2018年 | 3篇 |
2016年 | 3篇 |
2015年 | 3篇 |
2014年 | 2篇 |
2013年 | 23篇 |
2012年 | 4篇 |
2011年 | 10篇 |
2010年 | 7篇 |
2009年 | 7篇 |
2008年 | 9篇 |
2007年 | 5篇 |
2006年 | 6篇 |
2005年 | 9篇 |
2004年 | 5篇 |
2003年 | 3篇 |
2002年 | 8篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 8篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1985年 | 2篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1975年 | 5篇 |
1974年 | 6篇 |
1973年 | 7篇 |
1972年 | 2篇 |
1968年 | 5篇 |
1967年 | 4篇 |
1961年 | 2篇 |
1956年 | 8篇 |
排序方式: 共有261条查询结果,搜索用时 31 毫秒
1.
A scheme for the detection of rare quadrupolar nuclei based on off-resonant pulse excitation of the abundant quadrupolar nuclei coupled to the rare ones in the sample has been outlined and demonstrated. Pure quadrupole resonance spectrum of 23Na in poly-crystalline samples of sodium chlorate has been thus recorded at room temperature. The present double resonance scheme in the pure quadrupole regime is marked by a substantial reduction in spectrometer transmitter power and hardware requirements. 相似文献
2.
Agwu Anthony Harris Phillip James Kevin Kannan Siddarth Li Huixi 《The Ramanujan Journal》2022,58(1):75-120
The Ramanujan Journal - For an elliptic curve $$E/{\mathbb {Q}}$$ , let $$a_p$$ denote the trace of its Frobenius endomorphism over $${\mathbb {F}}_p$$ , where p is a prime of good reduction for E.... 相似文献
3.
4.
This paper presents DSC and NMR study of how the kerotolytic drug, salicylic acid (SA), affects the thermotropic and morphological behavior of a model membrane, dipalmitoyl phosphatidic acid (DPPA). The membrane-drug system has been studied in the multilamellar vesicular (MLV) and in the unilamellar vesicular (ULV) forms, for SA/DPPA molar ratios from 0 to 0.5. The mode of interaction of SA molecules with DPPA is similar in MLV and ULV. Chain-melting transition becomes sharper and shifts to higher temperatures in the presence of the drug, implying an enhanced co-operativity of the acyl chains. NMR and DSC data indicate that the drug molecules are located in the aqueous interfacial region neighboring the lipid headgroups. The membrane becomes more rigid in the presence of the drug molecules, due to a stronger interaction between the lipid headgroups leading to reduced permeability. ULVs are destroyed by even a short equilibration at room temperature, whereas prolonged equilibration of the MLV only leads to a slightly reduced interaction between the lipid headgroups due to sequestering of the drug molecules in the interfacial aqueous region. 相似文献
5.
Valency is defined for each molecular orbital. The molecular orbital valency values are shown to be a good measure of the bonding nature of the molecular orbital. Comparisons are made with photoelectron spectral studies and Mulliken overlap population analysis.The variation of molecular valency and molecular orbital valency with bond angle is studied. It is found that for all the molecules presently considered, energy is linearly related to valency and that the molecular valency reaches a maximum at the equilibrium bond angle. It is also shown that the molecular orbital valency can serve as a quantitatively reliable ordinate for Mulliken-Walsh diagrams. 相似文献
6.
1-Amino-3-methoxypropane (3MPA) and 2-dimethylaminoethanol (DMAE) are potential volatile amines for boiler water treatment and were investigated for their complexation behaviour with copper. Their pKb values were 3.67 and 4.52 at 25°C and they formed coloured complexes with absorption in the region of 644 and 510 nm, respectively. In the pH range 10–11, the Cu-3MPA complex exhibited stepwise reduction and [Cu(3MPA)2]+ was identified, with a stability constant of 109.52. In the pH range 8–10.5, the Cu-DMAE complex exhibited 2e? reduction and the species [Cu(DMAE)2(OH)2] was identified, with a stability constant of 1020.39. A correlation between visible and ESR spectra and reduction behaviour was established. 相似文献
7.
Nurani S. Narasimhan Heinz Heimgartner Hans-Jürgen Hansen Hans Schmid 《Helvetica chimica acta》1973,56(4):1351-1370
Benzonitrile p-nitrobenzylide ( 5 ) undergoes 1,3-dipolar cyclo-additions in the presence of 3-phenyl-2H-azirines ( 1 ), yielding in benzene at 0° 2-(p-nitrophenyl)-4,5-diphenyl-1,3-diazabicyclo[3.1.0]hex-3-enes ( 7 , scheme 2). Under the basic conditions of the reaction mixture, 7 a and 7 b are partially converted to 2-(p-nitrophenyl)-4,5-diphenyl-1,6-dihydropyrimidines ( 8a, b ) which are dehydrogenated by oxygen to the corresponding pyrimidines 9a and 9b , respectively. 3-Phenyl-2H-azirines ( 1 ) form, on heating at 145° in xylene in the presence of the azalactone 32 (2,4-diphenyl-Δ2-oxazolin-5-one), 4-(aziridin-2′-yl)-2,4-diphenyl-Δ2-oxazolin-5-ones ( 33 , scheme 11). 33 arises from an ene reaction of the enol form of 32 with 1 . Similar ene reactions are observed with the azirines 1 and dimedone ( 37 , scheme 12). Under the ene reaction conditions (xylene, 145°), the non-isolated intermediate primary adducts ( 38a and 38b ) undergo rearrangements of the vinylcyclopane-cyclopentene type to give 6,6-dimethyl-4-oxo-1,3-diphenyl-4, 5, 6, 7-tetrahydroisoindole ( 40 ) and 6, 6-dimethyl-4-oxo-3-phenyl-4, 5, 6, 7-tetrahedroindole ( 42 ), respectively. 相似文献
8.
Vicinal proton couplings in cyclopropane have been calculated using Dirac-Van Vleck and variational methods in valence bond formalism. The couplings may be considered as taking place along a path comprising either three or four intervening bonds. Inclusion of all exchange integrals in the appropriate fragment models leads to a satisfactory ratio of Jcis/Jtrans . In this respect valence bond results appear to be superior to those obtained using a molecular orbital approach. The present valence bond results on couplings in cyclopropane are not affected by the choice of models for bonding in cyclopropane, namely the Coulson-Moffitt model or the Walsh model. 相似文献
9.
Tetraalkylammonium borohydride reduces carboxylic acids to the corresponding alcohols in good yields utilizing only stoichiometric quantities of hydride and also in the absence of any Lewis acids. 相似文献
10.
Zirconium borohydride, a potential reducing agent, reduces acids, esters, imines to the corresponding alcohols and secondary amines in good yield at room temperature within two hours. This facile reducing property was taken advantage off in the synthesis of pheromones and some novel chiral precursors for asymmetric synthesis. 相似文献