全文获取类型
收费全文 | 135篇 |
免费 | 8篇 |
国内免费 | 1篇 |
专业分类
化学 | 99篇 |
晶体学 | 7篇 |
力学 | 1篇 |
数学 | 14篇 |
物理学 | 23篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 1篇 |
2020年 | 4篇 |
2019年 | 3篇 |
2018年 | 8篇 |
2017年 | 3篇 |
2016年 | 6篇 |
2015年 | 2篇 |
2014年 | 10篇 |
2013年 | 15篇 |
2012年 | 8篇 |
2011年 | 11篇 |
2010年 | 8篇 |
2009年 | 4篇 |
2008年 | 7篇 |
2007年 | 10篇 |
2006年 | 8篇 |
2005年 | 14篇 |
2004年 | 9篇 |
2003年 | 1篇 |
2002年 | 3篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1996年 | 1篇 |
排序方式: 共有144条查询结果,搜索用时 312 毫秒
41.
Ismail Akgun Markus Ganzera Canan Gur Serdar Senol Kemal Korkmaz Erdal Bedir 《Chromatographia》2009,70(5-6):963-967
As part of our ongoing studies, a new and validated method for analysis of isohexenyl-naphthazarines in Turkish Alkanna species was developed. By using reversed phase material (Synergi MAX RP) it was possible to determine four known isohexenylnaphthazarin-derivatives, namely alkannin, acetylalkannin, deoxyalkannin, and β,β-dimethylacrylalkannin within 25 min in n-hexane extracts of the roots. The quantification of these compounds in 16 Anatolian Alkanna species is described for the first time. In order to assure peak identity LC-MS experiments were performed. Quantitative results revealed that the most dominant compound in the extracts was β,β-dimethylacrylalkannin. 相似文献
42.
β‐Amino alcohols derived from (1R,2S)‐norephedrine were synthesized and used as ligands in the catalytic enantioselective diethylzinc addition to benzaldehydes. N‐alkylated (1R,2S)‐norephedrine‐based derivative 3a gave the highest enantioselectivity. The effects of different parameters on the enantioselectivity of the product were investigated. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
43.
Jarzynski's relation and the fluctuation theorem have established important connections between nonequilibrium statistical mechanics and equilibrium thermodynamics. In particular, an exact relationship between the equilibrium free energy and the nonequilibrium work is useful for computer simulations. In this paper, we exploit the fact that the free energy is a state function, independent of the pathway taken to change the equilibrium ensemble. We show that a generalized expression is advantageous for computer simulations of free energy differences. Several methods based on this idea are proposed. The accuracy and efficiency of the proposed methods are evaluated with a model problem. 相似文献
44.
Okan Zafer Yeilela Halis
lmez brahim Uar Ahmet Bulut Canan Kazak 《无机化学与普通化学杂志》2005,631(15):3100-3103
The aquaorotatotriethanolaminenickel(II) monohydrate, [Ni(HOr)(H2O)(tea)]·H2O ( 1 ), was synthesized and characterized by means of elementel analysis, IR and UV‐Vis, spectroscopy, magnetic susceptibility, thermal analysis and X‐ray diffraction techniques. The nickel ion in [Ni(C5H2N2O4)(H2O)(N(C2H4OH)3)] is chelated to the deprotonated N3 pyrimidine atom and to the carboxylate oxygen atom of the bidentate orotate dianion, and to the one nitrogen and two oxygen atoms of the tridentate triethanolamine molecule and its octahedral geometry is completed by an aqua ligand. It crystallizes in the monoclinic system, space group P21/c with lattice parameters a = 7.1528(5) Å, b = 19.4903(14) Å, c = 11.8085(8) Å, β = 106.237(5)°, V = 1580.55(19) Å3, Z = 4. An extensive three dimensional network of Ow‐H…O, N‐H…O and O‐H…O hydrogen bonds, π‐π and π‐ring interactions are responsible for crystal stabilization. The decomposition reaction take places in the temperature range 20‐1000 °C in the static air atmosphere. Thermal decomposition of 1 proceeds in three stages. 相似文献
45.
Clarithromycin (6-O-methylerythromycin A) is a 14-membered macrolide antibiotic which is active in vitro against clinically important gram-positive and gram-negative bacteria. The selectivity of the methylation of the C-6 OH group is studied on erythromycin A derivatives. To understand the effect of the solvent on the methylation process, detailed molecular dynamics (MD) simulations are performed in pure DMSO, pure THF and DMSO:THF (1:1) mixture by using the anions at the C-6, C-11 and C-12 positions of 2',4"-[O-bis(TMS)]erythromycin A 9-[O-(dimethylthexylsilyl)oxime] under the assumption that the anions are stable on the sub-nanosecond time scale. The conformations of the anions are not affected by the presence of the solvent mixture. The radial distribution functions are computed for the distribution of different solvent molecules around the 'O-' of the anions. At distances shorter than 5 A, DMSO molecules are found to cluster around the C-11 anion, whereas the anion at the C-12 position is surrounded by the THF molecules. The anion at the C-6 position is not blocked by the solvent molecules. The results are consistent with the experimental finding that the methylation yield at the latter position is increased in the presence of a DMSO:THF (1:1) solvent mixture. Thus, the effect of the solvent in enhancing the yield during the synthesis is not by changing the conformational properties of the anions, but rather by creating a suitable environment for methylation at the C-6 position. 相似文献
46.
Novel 2-alkylated pyrrole derivatives were synthesized regioselectively by Gd(OTf)3 catalyzed addition reactions of pyrrole to substituted dimethyl 2-benzylidenemalonate derivatives under mild reaction conditions. 2-Alkylated pyrrole derivatives are used for the construction of the 3-oxo pyrrolizine skeleton. Intramolecular cyclization of alkylated pyrrole derivatives afforded new diastereoselective 3-oxo-2,3-dihydro-1H-pyrrolizine derivatives with good to high yields. 相似文献
47.
A turn-on fluorescent chemosensor strategy based on the change in the polarity of aggregation induced emission active tetraphenylethene is presented for the detection of Hg2+ in aqueous medium and in living cells. The sensing mechanism involves the formation of nonpolar fluorescent aggregates of tetraphenylethene molecules by elimination of polar moieties of TPE with Hg2+ interaction. 相似文献
48.
49.
Murat Celtek Sedat Sengul Unal Domekeli Cem Canan 《The European Physical Journal B - Condensed Matter and Complex Systems》2016,89(3):65
In this study, the temperature effects on the structural evolution of theZr70Pd30 binary alloy in the glassy and liquid states werestudied using the molecular dynamics simulations based on the many-body type tight-bindingpotential. We considered the following properties in detail: the temperature dependence ofthe volume, the partial and total pair distribution functions and the simulated glasstransition temperature. The effects of the cooling rates on the glass transitiontemperature were examined. The Wendt-Abraham parameter was calculated to determine theglass transition temperature of Zr70Pd30 glassy alloy. The pair analysis technique ofHoneycutt-Andersen was applied to define local atomic arrangements produced from moleculardynamics simulations. The results show that the icosahedral ordering in glassy state hasbeen composed during quenching period, and the simulated glass transition temperature andthe total pair distribution functions are in good agreement with the experimental data. 相似文献
50.
Dr. Çiğdem Hopa Raif Kurtaran Akın Azizoğlu Mahir Alkan N. Burcu Arslan Canan Kazak 《无机化学与普通化学杂志》2011,637(9):1238-1245
Monomeric zinc(II) and mercury(II) complexes containing tripodal nitrogen donor ligand 2,6‐bis(3,4,5‐trimethyl‐N‐pyrazolyl)pyridine (btmpp) were synthesized, and characterized by elemental and spectroscopic (IR, UV/Vis) analyses, TG‐DTA and single‐crystal X‐ray diffraction studies. X‐ray analyses of the complexes [Zn(btmpp)Cl2] ( 2 ) and [Hg(btmpp)(SCN)2] ( 3 ) showed that both structures crystallize in space group P21/c with a = 7.9722(6), b = 18.3084(13), c = 13.3117(9) Å and Z = 4 for 2 and a = 8.7830(3), b = 21.1489(7), c = 12.0682(4) Å and Z = 4 for 3 . Both monomeric units contain pentacoordinate metal ions in distorted square‐pyramidal arrangement. The structures of complexes 2 and 3 were also computed with DFT methods at B3LYP/LanL2DZ level and are in good agreement with the experimental values obtained from X‐ray analysis. The NPa charge distributions, HOMO–LUMO gaps, and dipole moments for 1 , 2 , and 3 were also reported. Natural bond orbital analyses were performed to reveal local charges and charge transfers in 1 , 2 , and 3 . 相似文献