全文获取类型
收费全文 | 260篇 |
免费 | 5篇 |
专业分类
化学 | 142篇 |
晶体学 | 7篇 |
力学 | 4篇 |
数学 | 24篇 |
物理学 | 88篇 |
出版年
2024年 | 5篇 |
2023年 | 2篇 |
2022年 | 10篇 |
2021年 | 4篇 |
2020年 | 3篇 |
2019年 | 6篇 |
2018年 | 7篇 |
2017年 | 6篇 |
2016年 | 14篇 |
2015年 | 8篇 |
2014年 | 9篇 |
2013年 | 19篇 |
2012年 | 19篇 |
2011年 | 19篇 |
2010年 | 11篇 |
2009年 | 7篇 |
2008年 | 9篇 |
2007年 | 14篇 |
2006年 | 13篇 |
2005年 | 9篇 |
2004年 | 8篇 |
2003年 | 7篇 |
2002年 | 5篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有265条查询结果,搜索用时 15 毫秒
251.
This study was aimed at evaluating the antioxidant and hepatoprotective effects of the ethanol extract of Vitex glabrata (EEVG) in a CCl(4)-induced liver damage model in rats; and to isolate and characterise the bioactive constituent from EEVG. Hepatoprotective activity was evaluated by changes in the levels of the serum enzymes viz. AST, ALT, ALP and total bilirubin, and further by histopathological examinations of liver tissues. Antioxidant activity was measured in terms of superoxide dismutase, GSH, lipid peroxidation (LPO), catalase and peroxidase levels in liver homogenate. The pentamethoxy flavonoid artemetin was isolated and characterised from EEVG. Artemetin and EEVG pre-treatment significantly (p?0.001) inhibited LPO in CCl(4)-intoxicated livers and reduced the elevated serum levels of AST, ALT, ALP and bilirubin to normal; it also brought back the normal architecture of liver tissues. Antioxidant activity of EEVG was found to be comparable with silymarin (p?0.05). In conclusion, EEVG possesses significant hepatoprotective activity, which may be mediated by the antioxidant mechanisms of its components, predominantly artemetin. 相似文献
252.
Prabhu VM Kang S Sha J Bonnesen PV Satija S Wu WL Ober CK 《Langmuir : the ACS journal of surfaces and colloids》2012,28(20):7665-7678
Lithographic feature size requirements have approached a few radius of gyration of photoresist polymers used in thin-film patterning. Furthermore, the feature dimensions are commensurate with the photoacid diffusion length that defines the underlying latent image. Smaller imaging building blocks may enable reduced feature sizes; however, resolution limits are also dependent upon the spatial extent of the photoacid-catalyzed reaction diffusion front and subsequent dissolution mechanism. The reaction-diffusion front was characterized by neutron reflectivity for ccc stereoisomer-purified, deuterium-labeled tert-butoxycarbonyloxy calix[4]resorcinarene molecular resists. The spatial extent of the reaction front exceeds the size of the molecular resist with an effective diffusion constant of (0.13 ± 0.06) nm(2)/s for reaction times longer than 60 s, with the maximum at shorter times. Comparison to a mean-field reaction-diffusion model shows that a photoacid trapping process provides bounds to the spatial and extent of reaction via a reaction-limited mechanism whereas the ratio of the reaction rate to trapping rate constants recovers the effective diffusion peak. Under the ideal step-exposure conditions, surface roughness was observed after either positive- or negative-tone development. However, negative-tone development follows a surface-restructuring mechanism rather than etch-like dissolution in positive-tone development. 相似文献
253.
Gore KR Nawale GN Harikrishna S Chittoor VG Pandey SK Höbartner C Patankar S Pradeepkumar PI 《The Journal of organic chemistry》2012,77(7):3233-3245
The linear syntheses of 4'-C-aminomethyl-2'-O-methyl uridine and cytidine nucleoside phosphoramidites were achieved using glucose as the starting material. The modified RNA building blocks were incorporated into small interfering RNAs (siRNAs) by employing solid phase RNA synthesis. Thermal melting studies showed that the modified siRNA duplexes exhibited slightly lower T(m) (~1 °C/modification) compared to the unmodified duplex. Molecular dynamics simulations revealed that the 4'-C-aminomethyl-2'-O-methyl modified nucleotides adopt South-type conformation in a siRNA duplex, thereby altering the stacking and hydrogen-bonding interactions. These modified siRNAs were also evaluated for their gene silencing efficiency in HeLa cells using a luciferase-based reporter assay. The results indicate that the modifications are well tolerated in various positions of the passenger strand and at the 3' end of the guide strand but are less tolerated in the seed region of the guide strand. The modified siRNAs exhibited prolonged stability in human serum compared to unmodified siRNA. This work has implications for the use of 4'-C-aminomethyl-2'-O-methyl modified nucleotides to overcome some of the challenges associated with the therapeutic utilities of siRNAs. 相似文献
254.
Three-component one pot silica gel promoted synthesis of 2,3-disubstituted 4-thiazolidinones is described. The method provides rapid and easy access to thiazolidinone compounds in good to excellent yields. 相似文献
255.
Saha UC Chattopadhyay B Dhara K Mandal SK Sarkar S Khuda-Bukhsh AR Mukherjee M Helliwell M Chattopadhyay P 《Inorganic chemistry》2011,50(4):1213-1219
A new 2,6-bis(5,6-dihydrobenzo[4,5]imidazo[1,2-c]quinazolin-6-yl)-4-methylphenol (1) serves as a highly selective and sensitive fluorescent probe for Zn(2+) in a HEPES buffer (50 mM, DMSO:water = 1:9 (v/v), pH = 7.2) at 25 °C. The increase in fluorescence in the presence of Zn(2+) is accounted for by the formation of dinuclear Zn(2+) complex [Zn(2)(C(35)H(25)N(6)O)(OH)(NO(3))(2)(H(2)O)] (2), characterized by X-ray crystallography. The fluorescence quantum yield of the chemosensor 1 is only 0.019, and it increases more than 12-fold (0.237) in the presence of 2 equiv of the zinc ion. Interestingly, the introduction of other metal ions causes the fluorescence intensity to be either unchanged or weakened. By incubation of cultured living cells (A375 and HT-29) with the chemosensor 1, intracellular Zn(2+) concentrations could be monitored through selective fluorescence chemosensing. 相似文献
256.
Santosh K. Tripathi Bishan L. Khandelwal Sushil K. Gupta 《Phosphorus, sulfur, and silicon and the related elements》2013,188(10):2285-2293
A new series of 24- and 28-membered macrocyclic systems associated with "hard" (N and O) and "soft" (Se or Te) donor atoms have been developed via template free (2 + 2) condensation reactions of bis(aminoalkyl)selenides/tellurides, {NH 2 (CH 2 ) n } 2 E (E = Se, Te; n = 2,3) with 2,6-diacetyl-4-methylphenol. A macroacycle, Se{(CH 2 ) 2 N=C(CH 3 )C 6 H 2 (OH)(CH 3 )C=O(CH 3 )} 2 , has also been obtained. These compounds have been characterized by ESMS, IR, and 1 H, 13 C, and 77 Se NMR spectroscopy. 相似文献
257.
Enantiopure ferrocenyl-β, and bis-β-amino acids [(R)-(+)-1 and (R, R)-(+)-2] were prepared from (S)-(+)-sulfinimine (3) and (S, S)-(+)-bis-sulfinimine (4) respectively. The desired sulfinimines [(S)-(+)-3 and (S, S)-(+)-4] were prepared from (S)-Andersen reagent (5) and ferrocenecarboxaldehyde (6) and 1, 1 -ferrocenedicarboxaldehyde (7). 相似文献
258.
Jain Reshma Rajput S. J. Sethiya Neeraj Kumar Chauddhary Sushil K. 《平面色谱法杂志一现代薄层色谱法》2022,35(6):571-577
JPC – Journal of Planar Chromatography – Modern TLC - Quantification of bioactive markers through modern analytical methods is very essential for establishing the authenticity and... 相似文献
259.
Freezing temperatures of dilute aqueous mixtures of: formamide with myo-inositol, d-mannitol, and cyclohexanol; N,N-dimethylformamide with inositol, mannitol, and cyclohexanol; and acetamide with inositol and mannitol have been measured. These data have been analyzed to yield the pairwise molecular Gibbs energies of interaction between the molecules in an aqueous solution. Using the group additivity principle, the results yield the pairwise functional group Gibbs energies of interaction of the amide group with the hydroxyl group, G
OH,CONH
=–31 J-kg-mol–2. 相似文献
260.
Lu H Akgun B Wei X Li L Satija SK Russell TP 《Langmuir : the ACS journal of surfaces and colloids》2011,27(20):12443-12450
In situ neutron reflectivity was used to study thermally induced structural changes of the lamellae-forming polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) block copolymer thin films floating on the surface of an ionic liquid (IL). The IL, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, is a nonsolvent for PS and a temperature-tunable solvent for P2VP, and, as such, micellization can be induced at the air-IL interface by changing the temperature. Transmission electron microscopy and scanning force microscopy were used to investigate the resultant morphologies of the micellar films. It was found that highly ordered nanostructures consisting of spherical micelles with a PS core surrounded by a P2VP corona were produced. In addition, bilayer films of PS homopolymer on top of a PS-b-P2VP layer also underwent micellization with increasing temperature but the micellization was strongly dependent on the thickness of the PS and PS-b-P2VP layers. 相似文献