全文获取类型
收费全文 | 624篇 |
免费 | 18篇 |
国内免费 | 6篇 |
专业分类
化学 | 325篇 |
晶体学 | 1篇 |
力学 | 5篇 |
数学 | 249篇 |
物理学 | 68篇 |
出版年
2023年 | 2篇 |
2022年 | 6篇 |
2021年 | 16篇 |
2020年 | 5篇 |
2019年 | 11篇 |
2018年 | 20篇 |
2017年 | 19篇 |
2016年 | 23篇 |
2015年 | 27篇 |
2014年 | 19篇 |
2013年 | 42篇 |
2012年 | 41篇 |
2011年 | 38篇 |
2010年 | 31篇 |
2009年 | 21篇 |
2008年 | 39篇 |
2007年 | 40篇 |
2006年 | 23篇 |
2005年 | 26篇 |
2004年 | 23篇 |
2003年 | 20篇 |
2002年 | 20篇 |
2001年 | 13篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1998年 | 5篇 |
1997年 | 12篇 |
1996年 | 12篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1992年 | 10篇 |
1991年 | 4篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 8篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1965年 | 2篇 |
1963年 | 1篇 |
1962年 | 1篇 |
1958年 | 4篇 |
1933年 | 2篇 |
1921年 | 1篇 |
排序方式: 共有648条查询结果,搜索用时 198 毫秒
51.
Attila Makó Zsolt Rapi György Keglevich Áron Szöllősy László Drahos László Hegedűs Péter Bakó 《Tetrahedron: Asymmetry》2010,21(8):919-925
The chiral monoaza-15-crown-5 lariat ethers annellated to methyl-4,6-O-benzylidene-α-d-glucopyranoside-1 or mannopyranoside 2 have been applied as phase-transfer catalysts in the epoxidation of substituted chalcones and chalcone analogues with tert-butylhydroperoxide resulting in significant asymmetric induction. It was found that the position of the substituents in the aromatic ring of the chalcone had an influence both on the chemical yields and enantiomeric excesses. The lowest enantioselectivities (62–83% ee) were found in the case of ortho-substituted model compounds. The highest ee values (ee of 83–97%) were obtained in the case of para-substituted models. From among the chalcone analogues, the maximum ee (90–92%) was detected for the model compound having α-tert-butyl- and β-aryl groups. Using glucose-based crown ether 1, formation of the (?)-enantiomer was preferred, while applying mannose-based 2 as the catalyst, the (+)-enantiomer was in excess. 相似文献
52.
In this review structural and reactivity studies on the co-ligand containing model complexes for the flavonol 2,4-dioxygenase (FDO) are covered. The main focus is on the relationship between the structural features of the copper-containing model complexes, and their activity in the enzyme-like reactions. Some radical initiated reactions and catalytic systems will also be discussed. 相似文献
53.
We discuss problems and results on the maximum number of colors in combinatorial structures under the assumption that no totally multicolored sets of a specified type occur. 相似文献
54.
55.
T. Kàmàn E. Lähderanta S. Leppävuori I. Halàsz I. Dòdony G. Zsolt T. Porjesz R. Laiho A. Uusimäki I. Kirschner Gy. Kovács 《Zeitschrift für Physik B Condensed Matter》1990,78(2):169-173
Tl–Ca–Ba–Cu–O compounds of the nominal composition of (1, 1, 1, 1) have been prepared from different starting materials and with the same heat treatment process. During the investigation of their properties a diamagnetic signal has been found up to the temperature of 132 K. This hints at the existence of a certain material content distributed into discrete superconducting domains. The parameters of it reflect a superstructure of the (2, 2, 2, 3) and (2, 1, 2, 2) compositions having a time-dependent behaviour. On the basis of the signal levels at 132 K and 4.2 K, the quantity of the high temperature superconducting material is about 0.01% of the total one at liquid He temperatures. 相似文献
56.
57.
58.
Gyula Pap 《Semigroup Forum》2002,64(1):130-158
An explicit form is derived for the Fourier transform of symmetric Gauss measures on the Heisenberg group at the Schrödinger
representation. Using this explicit formula, necessary and sufficient conditions are given for the convolution of two symmetric
Gauss measures to be a symmetric Gauss measure and for commutability of two symmetric Gauss measures. Moreover, necessary
and sufficient conditions are presented for the convolution of two symmetric Gauss convolution semigroups to be a convolution
semigroup.
May 8, 2001 相似文献
59.
Zsolt Zsótér Tibor Tímár Krisztina Kónya Tamás Patonay József Jekő 《Journal of heterocyclic chemistry》2015,52(6):1677-1683
4,4‐Dimethylchromeno[4,3‐d]selenadiazoles 8 with insecticide activities have been synthesized via oxidative ring closure of the corresponding semicarbazone derivatives 7 by treatment with selenium dioxide. Reaction of various alkoxy‐2,2‐dimethyl‐2H‐benzopyrans with phenylselenyl chloride was utilized to prepare different phenylselenyl‐ and 3‐chloro precocene analogs. 相似文献
60.
Zoltán-István Szabó Réka Gál Zsolt Gáll Szende Vancea Emőke Rédai Ibolya Fülöp Emese Sipos Gabriella Donáth-Nagy Béla Noszál Gergő Tóth 《Journal of inclusion phenomena and macrocyclic chemistry》2017,88(1-2):43-52
Rufinamide (RUF) was characterized in terms of cyclodextrin (CD) complexation in order to improve its aqueous solubility. Binary systems of RUF with three CDs—β-cyclodextrin (β-CD), randomly methylated-β-cyclodextrin (RAMEB) and sulfobutylether-β-cyclodextrin (SBE-β-CD)—were characterized with a wide variety of analytical techniques. Liquid state characterization was carried out by complementary techniques such as nuclear magnetic resonance spectroscopy (NMR), capillary electrophoresis (CE), mass spectrometry (MS) and phase solubility studies. The latter revealed that the stability of the complexes decreased in the order of RAMEB?>?β-CD?>?SBE-β-CD. AL-type diagrams were obtained in all cases, characteristic of 1:1 stoichiometry, with a maximum of over 15-fold increase in RUF solubility, when complexed with RAMEB. NMR Job plot and MS studies confirmed phase solubility results, regarding the binding stoichiometry. 1H NMR and 2D ROESY investigations revealed the inclusion of the triazole moiety of RUF, confirmed by molecular modeling. Solid state complexation in 1:1 molar ratio was carried out by kneading method and investigated by differential scanning calorimetry (DSC) and infrared spectroscopy (IR). Comparative dissolution studies indicated an over two-fold improvement in dissolution efficacy of the kneaded products, when compared to the pure drug. Results of the present study might pave the way for a drug formulation with improved bioavailability. 相似文献