全文获取类型
收费全文 | 1968篇 |
免费 | 52篇 |
国内免费 | 1篇 |
专业分类
化学 | 1326篇 |
晶体学 | 27篇 |
力学 | 67篇 |
数学 | 148篇 |
物理学 | 453篇 |
出版年
2023年 | 12篇 |
2022年 | 17篇 |
2021年 | 42篇 |
2020年 | 58篇 |
2019年 | 51篇 |
2018年 | 30篇 |
2017年 | 38篇 |
2016年 | 66篇 |
2015年 | 39篇 |
2014年 | 44篇 |
2013年 | 104篇 |
2012年 | 113篇 |
2011年 | 122篇 |
2010年 | 70篇 |
2009年 | 62篇 |
2008年 | 104篇 |
2007年 | 127篇 |
2006年 | 104篇 |
2005年 | 94篇 |
2004年 | 67篇 |
2003年 | 57篇 |
2002年 | 62篇 |
2001年 | 33篇 |
2000年 | 26篇 |
1999年 | 24篇 |
1998年 | 21篇 |
1997年 | 17篇 |
1996年 | 20篇 |
1995年 | 15篇 |
1994年 | 21篇 |
1993年 | 14篇 |
1992年 | 21篇 |
1991年 | 20篇 |
1990年 | 15篇 |
1989年 | 17篇 |
1988年 | 18篇 |
1987年 | 14篇 |
1986年 | 13篇 |
1985年 | 17篇 |
1983年 | 12篇 |
1982年 | 16篇 |
1980年 | 13篇 |
1978年 | 16篇 |
1976年 | 12篇 |
1974年 | 12篇 |
1973年 | 12篇 |
1972年 | 11篇 |
1971年 | 11篇 |
1970年 | 15篇 |
1967年 | 10篇 |
排序方式: 共有2021条查询结果,搜索用时 484 毫秒
31.
Schroeder G. Rybachenko V. I. Chotii K. Yu. Kovalenko V. V. Grebenyuk L. V. Lenska B. Eitner K. 《Russian Journal of General Chemistry》2003,73(3):455-462
Dimethylcarbamoyl transfer from N-acyloxypyridinium salts to pyridine N-oxides in acetonitrile occurs in one stage by the forced concerted SN2 mechanism. The rate and equilibrium of the reaction are fairly described by the Brönsted equation. The Marcus equation provides a much higher quality of reactivity predictions. 相似文献
32.
Fisher KA Huddersman KD Taylor MJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(23):5873-5878
The uptake of the three species of the drug model fluorescein (fluorescein sodium salt (FNa), fluorescein free acid (F), and fluorescein diacetate (FDA)) by zeolite NaX and the mesoporous zeotype MCM-41 was investigated as well as their release rates into solutions at pH 7 and pH 4.5. UV/Vis analysis was carried out at a wavelength of 490 nm. Uptakes of the sodium salt of 9 % for zeolite X and 14 % for MCM suggest little penetration of the pores. The use of ethanol as the loading solvent for F resulted in little uptake for both zeolitic materials due to the successful competition of the ethanol for binding sites. Use of acetone (weaker proton acceptor) as loading solvent significantly improved the uptake of F to 17 % and 12 % for zeolite X and MCM, respectively, whilst the uptake of FDA in acetone increased still further to 22 % and 17 % for zeolite X and MCM, respectively. Generally there was a large initial release of the fluorescein analogues from the surface of the zeolites with very little further increase over time. The prescence of an esterase enzyme in the release medium of FDA tripled the release from MCM to 15 % but left the release from zeolite X unaffected at 6 %. The results obtained show that uptake of fluorescein and its analogues is dependent on the loading solvent used, the amount released is influenced by not only the solvent but the pH and the presence of enzymes in the release medium. 相似文献
33.
V. V. Zverev V. I. Kovalenko 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2006,80(1):99-105
Hartree-Fock and density functional theory calculations showed that the B, C, D, and E fullerene C70 cycles were not coplanar. The interrelation between acoplanarity and pyramidality of atoms was studied. The bond lengths, valence and torsion angles, and charges and chemical shifts of fullerene C70 atoms were jointly analyzed. Most attention was given to the acoplanarity of hexagons E in the aromatic belt. 相似文献
34.
Effect of Hydration–Dehydration Processes on the Structure and Porosity of Detemplated Silica Fibers
Kovalenko V. V. Tel'biz G. M. Bobonich F. M. 《Theoretical and Experimental Chemistry》2004,40(1):64-68
A study was carried out on the conditions of template removal (calcination or extraction by solvents) and hydration–dehydration processes on the hexagonal structure and porosity of detemplated fibers. The hydration–dehydration cycle leads to a decrease in fiber porosity, especially in fiber detemplation by extraction with surfactant solvents such as ethanol and acetic acid. 相似文献
35.
In this report, first use of size-selected gold nanoparticles (AuNPs) as matrixes for matrix assisted laser desorption/ionization (MALDI) is described for peptides and proteins. In comparison with conventional organic acid MALDI matrixes, the optimum matrix-to-analyte ratio with AuNP matrixes is reduced by 10-14 orders of magnitude. Significant differences in the relative abundances of the ions observed in positive and negative mode MALDI-time-of-flight mass spectrometry (TOFMS) are revealed as the AuNP size distribution is decreased from 10 to 2 nm, whereby 2-nm AuNPs exhibit quantum confinement effects prevalent in quantum dots. AuNP matrixes allow for selective analyte ionization, as demonstrated in the selective MALDI-TOFMS of phosphotyrosine in a background of phosphoserine and phosphothreonine peptides. 相似文献
36.
Bodnarchuk M. I. Kovalenko M. V. Stroyuk A. L. Kuchmii S. Ya. 《Theoretical and Experimental Chemistry》2004,40(5):287-292
The photochemical behavior of solutions containing a mixture of CdS and CdTe nanoparticles under pulsed irradiation conditions was investigated. It was shown that electron transfer from the CdS particles to the CdTe nanoparticles occurs during the photoexcitation of such systems. The effectiveness of the process is increased with increase in the size of the CdTe nanoparticles. Such behavior is due to decrease in the potential of the CdTe conduction band with increase in the size of the nanoparticles as a result of the appearance of quantum-dimensional effects. 相似文献
37.
Katherine E. BashfordMatthew B. Burton Stuart CameronAnthony L. Cooper Rebecca D. HoggPeter D. Kane David A. MacManusChristopher A. Matrunola Christopher J. Moody Avril A.B. Robertson Mark R. Warne 《Tetrahedron letters》2003,44(8):1627-1629
The Bohlmann-Rahtz reaction has been used to prepare 2,3,6-trisubstituted pyridines suitable for use in library synthesis. The synthesis of piperidine substituted nicotinic acid derivative 9 has been optimised and carried out on a large scale to give ca. 500 g of scaffold which was used in the generation of the pyridine library 11. 相似文献
38.
Katherine Yu. Bezsoudnova Anatoly K. Yatsimirsky 《Reaction Kinetics and Catalysis Letters》1997,62(1):63-69
α- and β-Cyclodextrins accelerate the Smiles rearrangement of 4-nitrophenyl salicylate which proceeds through the mechanism
of intramolecular aromatic nucleophilic substitution. The binding and catalytic rate constants were calculated from the dependences
of the observed pseudo-first-order rate constants of the rearrangement reaction on cyclodextrin concentration obtained at
various pH values. The catalysis was interpreted in terms of a tighter binding of the anionic, highly delocalized δ-complex
intermediate than that of the substrate to cyclodextrins. 相似文献
39.
Yu. B. Sinkevich A. E. Shchekotikhin Yu. N. Luzikov V. N. Buyanov L. V. Kovalenko 《Chemistry of Heterocyclic Compounds》2007,43(10):1252-1259
4,11-Dihydroxyanthra[2,3-b]thiophene-5,10-dione (thiophenoquinizarine) and its 3-methyl derivative were obtained by the cyclization
of quinizarin-2-yl derivatives of mercaptoacetaldehyde or mercaptoacetone in acid medium. 4,11-Dimethoxy-and 4,11-dibutoxyanthra[2,3-b]thiophene-5,10-dione
were synthesized by the alkylation of the hydroxyl group in the synthesized anthrathiophenes with dimethylformamide dimethylacetal
or butyl iodide respectively. Radical bromination of 4,11-dimethoxy-3-methylanthra[2,3-b]thiophene-5,10-dione, depending on
the amount of N-bromo-succinimide taken, leads to the formation of 3-bromomethyl-or 3-dibromomethyl-4,11-dimethoxy-anthra[2,3-b]thiophene-5,10-diones.
The action of sodium acetate on the obtained bromo derivatives with subsequent hydrolysis of the intermediate acetates led
to the synthesis of 3-hydroxymethyl-or 3-formyl-4,11-dimethoxy-anthra[2,3-b]thiophene-5,10-diones.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1478–1485, October, 2007. 相似文献
40.
V.L. Furer A.E. Vandyukov J.P. Majoral A.M. Caminade V.I. Kovalenko 《Vibrational Spectroscopy》2006,40(2):155-160
The Raman (10–3500 cm−1) and infrared (150–3500 cm−1) spectra have been recorded for tris(4-oxibenzaldehyde)thiophosphate. This compound includes structural parts of elementoorganic dendrimers: a core and terminal aldehyde groups. The structural optimization and normal mode analysis are performed for elementoorganic dendrimer on the basis of the ab initio density functional theory. It is found that the dendrimer exist in a single stable conformation with planar C6H4CHO fragments. Our calculations show that conformer with one trans and two gauche 4-oxibenzaldehyde groups is realized. All these observations suggest that steric congestion does not disturb the construction of dendrimers even for the highest generations, and that terminal groups are readily available for further reactions. Relying on DFT calculations a complete vibrational assignment is proposed for different parts of the studied dendrimers. 相似文献