全文获取类型
收费全文 | 2020篇 |
免费 | 162篇 |
国内免费 | 9篇 |
专业分类
化学 | 1442篇 |
晶体学 | 25篇 |
力学 | 65篇 |
数学 | 275篇 |
物理学 | 384篇 |
出版年
2023年 | 15篇 |
2022年 | 90篇 |
2021年 | 62篇 |
2020年 | 51篇 |
2019年 | 82篇 |
2018年 | 61篇 |
2017年 | 46篇 |
2016年 | 105篇 |
2015年 | 73篇 |
2014年 | 78篇 |
2013年 | 144篇 |
2012年 | 121篇 |
2011年 | 110篇 |
2010年 | 91篇 |
2009年 | 89篇 |
2008年 | 117篇 |
2007年 | 125篇 |
2006年 | 97篇 |
2005年 | 70篇 |
2004年 | 67篇 |
2003年 | 55篇 |
2002年 | 51篇 |
2001年 | 47篇 |
2000年 | 35篇 |
1999年 | 28篇 |
1998年 | 11篇 |
1997年 | 13篇 |
1996年 | 13篇 |
1995年 | 11篇 |
1994年 | 8篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 7篇 |
1990年 | 9篇 |
1988年 | 5篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 19篇 |
1983年 | 8篇 |
1981年 | 11篇 |
1980年 | 17篇 |
1979年 | 8篇 |
1978年 | 11篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1973年 | 6篇 |
1971年 | 6篇 |
1901年 | 4篇 |
1862年 | 8篇 |
排序方式: 共有2191条查询结果,搜索用时 15 毫秒
941.
José Fuentes Nader R. Al Bujuq Manuel Angulo Consolación Gasch 《Tetrahedron letters》2008,49(5):910-913
The iminosugar thioglycosides are used as glycosyl donors in glycosidation reactions. Thereby, iminosugar glycosides and disaccharide analogues with an iminosugar moiety are prepared. The yields are high and the method is stereoselective. 相似文献
942.
Mahmoud M. Al Omari Mohammad B. Zughul J. Eric D. Davies Adnan A. Badwan 《Journal of solution chemistry》2008,37(6):875-893
Guest–host interaction of astemizole (Astm) with cyclodextrins (CDs) has been investigated using phase solubility diagrams
(PSD), differential scanning calorimetry (DSC), X-ray powder diffractometry (XRPD), proton nuclear magnetic resonance (1H-NMR) and molecular mechanical modeling (MM+). Estimates of the complex formation constant, K
11, show that the tendency of Astm to complex with CDs follows the order: β-CD>HP-β-CD>γ-CD, α-CD. 1:1 Astm/β-CD complex formation at pH=5.0 was largely driven by the hydrophobic effect (desolvation), which was quantitatively estimated
at −16.5 kJ⋅mol−1, whereas specific interactions contribute only −5.3 kJ⋅mol−1 to 1:1 complex stability (ΔG
11o=−22.7 kJ⋅mol−1). The percentage contributions of the hydrophobic effect and specific interactions were therefore 73 and 27%, respectively.
Both enthalpic and entropic factors contribute equally well (−11 kJ⋅mol−1 each) to 1:1 Astm/β-CD complex stability. 1H-NMR and MM+ molecular modeling studies indicate the formation of different isomeric 1:1 and 1:2 complexes. The dominant driving force
for complexation is evidently van der Waals with very little electrostatic contribution. PSD, 1H-NMR, DSC, XRPD and MM+ studies proved the formation of inclusion complexes in solution and the solid state. 相似文献
943.
The UV irradiation effects on stability of polystyrene, poly(4-methoxystyrene), poly(4-methylstyrene), poly(α-methylstyrene), poly(4-tert-butylstyrene), poly(4-chlorostyrene), and poly(4-bromostyrene) in dichloromethane, dichloromethane, tetrahydrofuran, and N,N-dimethylformamide solutions were studied in the presence of oxygen at different intervals of irradiation time. The photodegradation was studied at 293 K using fluorescence spectroscopy. Solutions of these polymers were accompanied by quenching of monomer and excimer emissions during the exposure of their solutions to UV light, and by a change in the structure of the fluorescence spectrum. Irradiation of poly(4-methylstyrene) and poly(α-methylstyrene) at excitation wavelength of 265 nm showed an increase of fluorescence intensity of a broad band, at longer wavelength without clear maxima. This may indicate that photodestruction of these polymers by irradiation with light of frequency absorbed by the polymer, may start from a random chain scission, with the possibility of formation of polyene and carbonyl compounds. 相似文献
944.
Naim H. Al‐Said Khaled Q. Shawakfeh Baha A. Hammad 《Journal of heterocyclic chemistry》2008,45(5):1333-1336
Free‐radical generated at C‐7 position of indole derivative bearing N‐(3′‐chloroallyl) group prompted a regioselective intramolecular cyclization to furnish pyrroloindoline derivative, through the more favorable 5‐exo‐trig cyclization mode. The pyrroloindoline compound smoothly rearranged to pyrroloquinoline under mild conditions. 相似文献
945.
Osman M. E. El‐Dusouqui Nouria A. Al‐Awadi Mohamed H. Elnagdi Mervat M. Abdelkhalik 《Journal of heterocyclic chemistry》2008,45(6):1751-1753
1,2,3‐Triazolylpropanone was prepared and coupled with aryldiazonium salts yielding the corresponding arylhydrazones. Gas‐phase pyrolysis of the hydrazono derivative produced N‐arylamino‐2‐acetylimidazole as well as 2‐acetylimidazole. The latter is the product of further pyrolysis of the former. 相似文献
946.
E. D. Totchasov M. Yu. Nikiforov G. A. Al’per 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2008,82(1):68-70
The kinematic viscosity of the methanol-n-heptane system was measured at various temperatures at low methanol concentrations (over the range of miscibility). The dynamic viscosities of this system at 298.15 K were calculated according to free volume theory taking into account molecular association. No anomaly (negative Δlnη values) was observed for the system. 相似文献
947.
İ. Özdemir B. Alıcı N. Gürbüz B. Çetinkaya E. Çetinkaya 《Russian Journal of Coordination Chemistry》2005,31(2):142-145
Three palladium(II) complexes of the type [PdCl2(PPh3)L] (L—1-alkylperimidine) have been prepared by reactions of [PdCl2(PPh3)]2 with 1-alkylperimidine. The complexes were characterized by conventional spectroscopic methods and elemental analyses. The incorporation of N-coordinated perimidine complexes of palladium(II) gave high catalytic activity in the Suzuki coupling deactivated aryl chloride substrates.From Koordinatsionnaya Khimiya, Vol. 31, No. 2, 2005, pp. 153–156. Original English Text Copyright © 2005 by Özdemir, Alýcý, Gürbüz, B. Çetinkaya, E. Çetinkaya.This article was submitted by the authors in English. 相似文献
948.
I. V. Terekhova O. V. Kulikov R. S. Kumeev M. Yu. Nikiforov G. A. Al’per 《Russian Journal of Coordination Chemistry》2005,31(3):218-220
Reactions of - and -cyclodextrins with some biologically active acids were studied by 1H NMR spectroscopy. Inclusion complexes are found to be formed only with aromatic amino acids (phenylalanine and tryptophan) and ascorbic acid. The complexes of cyclodextrin with citric acid are obtained through interactions between the polar groups of the guest molecule and the OH groups of the host molecule located on the outside.Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 3, 2005, pp. 234–236.Original Russian Text Copyright © 2005 by Terekhova, Kulikov, Kumeev, Nikiforov, Alper.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date. 相似文献
949.
We present the concept of circuit nanoelements in the optical domain using plasmonic and nonplasmonic nanoparticles. Three basic circuit elements, i.e., nanoinductors, nanocapacitors, and nanoresistors, are discussed in terms of small nanostructures with different material properties. Coupled nanoscale circuits and parallel and series combinations are also envisioned, which may provide road maps for the synthesis of more complex circuits in the IR and visible bands. Ideas for the optical implementation of right-handed and left-handed nanotransmission lines are also forecasted. 相似文献
950.