全文获取类型
收费全文 | 1256篇 |
免费 | 46篇 |
国内免费 | 8篇 |
专业分类
化学 | 909篇 |
晶体学 | 33篇 |
力学 | 29篇 |
数学 | 69篇 |
物理学 | 270篇 |
出版年
2024年 | 2篇 |
2023年 | 14篇 |
2022年 | 17篇 |
2021年 | 18篇 |
2020年 | 39篇 |
2019年 | 43篇 |
2018年 | 31篇 |
2017年 | 39篇 |
2016年 | 56篇 |
2015年 | 38篇 |
2014年 | 91篇 |
2013年 | 99篇 |
2012年 | 92篇 |
2011年 | 125篇 |
2010年 | 60篇 |
2009年 | 72篇 |
2008年 | 88篇 |
2007年 | 85篇 |
2006年 | 60篇 |
2005年 | 43篇 |
2004年 | 47篇 |
2003年 | 45篇 |
2002年 | 36篇 |
2001年 | 12篇 |
2000年 | 9篇 |
1999年 | 4篇 |
1998年 | 8篇 |
1997年 | 7篇 |
1996年 | 8篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1981年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有1310条查询结果,搜索用时 531 毫秒
991.
Dramatic influence of the orientation of linker between hydrophilic and hydrophobic lipid moiety in liposomal gene delivery 总被引:1,自引:0,他引:1
Rajesh M Sen J Srujan M Mukherjee K Sreedhar B Chaudhuri A 《Journal of the American Chemical Society》2007,129(37):11408-11420
A number of prior studies have demonstrated that the DNA-binding and gene transfection efficacies of cationic amphiphiles crucially depend on their various structural parameters including hydrophobic chain lengths, headgroup functionalities, and the nature of the linker-functionality used in tethering the polar headgroup and hydrophobic tails. However, to date addressing the issue of linker orientation remains unexplored in liposomal gene delivery. Toward probing the influence of linker orientation in cationic lipid mediated gene delivery, we have designed and synthesized two structurally isomeric remarkably similar cationic amphiphiles 1 and 2 bearing the same hydrophobic tails and the same polar headgroups connected by the same ester linker group. The only structural difference between the cationic amphiphiles 1 and 2 is the orientation of their linker ester functionality. While lipid 1 showed high gene transfer efficacies in multiple cultured animal cells, lipid 2 was essentially transfection incompetent. Findings in both transmission electron microscopic and dynamic laser light scattering studies revealed no significant size difference between the lipoplexes of lipids 1 and 2. Findings in confocal microscopic and fluorescence resonance energy transfer (FRET) experiments, taken together, support the notion that the remarkably higher gene transfer efficacies of lipid 1 compared to those of lipid 2 presumably originate from higher biomembrane fusogenicity of lipid 1 liposomes. Differential scanning calorimetry (DSC) and fluorescence anisotropy studies revealed a significantly higher gel-to-liquid crystalline temperature for the lipid 2 liposomes than that for lipid 1 liposomes. Findings in the dye entrapment experiment were also consistent with the higher rigidity of lipid 2/cholesterol (1:1 mole ratio) liposomes. Thus, the higher biomembrane fusibility of lipid 1 liposomes than that of lipid 2 liposomes presumably originates from the more rigid nature of lipid 2 cationic liposomes. Taken together, the present findings demonstrate for the first time that even as minor a structural variation as linker orientation reversal in cationic amphiphiles can profoundly influence DNA-binding characteristics, membrane rigidity, membrane fusibility, cellular uptake, and consequently gene delivery efficacies of cationic liposomes. 相似文献
992.
993.
Sengupta O Chakrabarty R Mukherjee PS 《Dalton transactions (Cambridge, England : 2003)》2007,(40):4514-4516
A new 3D framework [Mn4(5-pmc)4(1,1-N3)4]n () composed of a rare MnII4 square as the repeating secondary building unit, representing the first coordination polymer of 5-pyrimidinecarboxylate (5-pmc) has been successfully synthesized and characterized by X-ray single crystal structure analysis. 相似文献
994.
The synthetic correlation between two different antibiotic frameworks, the beta-lactams and 2-oxazolidinones, is described for the first time. In this approach, 2-oxazolidinones are prepared in stereomerically pure form from 3-hydroxy beta-lactams by a ring-opening-cyclization isomerization process. Application of this methodology to the total synthesis of the cytokine modulator, (-)-cytoxazone, and its three stereoisomers is demonstrated. [reaction: see text]. 相似文献
995.
A glycine Schiff base Michael addition is used in sequence with free radical-mediated aryl amination to ultimately arrive at the ambiguine G ABC-tricycle convergently. Additionally, thermal Diels-Alder cycloaddition of beta-chloromethacrolein with Cohen's diene is used to diastereoselectively construct the D-cyclohexane ring bearing a neopentyl chloride. 相似文献
996.
Heterobimetallic complexes of the type R2Si(HL)Cl2 and R2SiL2 (where R = Me, Et, Ph; L = ferrocenyl aroylhydrazone) have been synthesized at 40 °C to 50 °C and at room temperature (25
°C), respectively, and characterized by elemental analysis, molar conductance, infrared and NMR (1H, 13C and 29Si) spectral data. The ligands behave as bidentate, coordinating through the azomethine nitrogen and the oxygen in the amidic
and the imidic acid forms of the ligand at low temperature and at room temperature, respectively. The ligands and their organosilicon
complexes have been evaluated for the antifungal activity against Alternaria alternata, Fusarium oxysporum and Rhizoctonia solani, as well as antibacterial activity against gram negative, Escherichia coli and gram positive, Bacillus subtilis, at 28 °C. Organosilicon complexes of ferrocenyl aroylhydrazone were found to be more potent than the parent ligands.
相似文献
997.
In this Letter, we report the confinement of a uniform beam of light (lambda(1) = 400 nm) at the nodes of a standing wave (lambda(2) = 532 nm) via absorbance modulation. In the present implementation of absorbance modulation, a thin polymer film containing a photochromic azobenzene side chain is exposed to a standing wave at lambda(2) and a uniform beam at lambda(1), resulting in alternate regions of high and low absorbance. Light at lambda(1) is localized around the low-absorbance regions. Using photoresist exposures, we mapped out the localized light intensity distribution, which agrees well with our theoretical model. Since the width of this distribution is primarily determined by the ratio of the intensities at the two wavelengths, this technique opens up the possibility of localizing light fields below the diffraction limit using far-field optics. 相似文献
998.
Leys J Wübbenhorst M Preethy Menon C Rajesh R Thoen J Glorieux C Nockemann P Thijs B Binnemans K Longuemart S 《The Journal of chemical physics》2008,128(6):064509
The electrical conductivities of 1-alkyl-3-methylimidazolium tetrafluoroborate ionic liquids and of 1-hexyl-3-methylimidazolium ionic liquids with different anions were determined in the temperature range between 123 and 393 K on the basis of dielectric measurements in the frequency range from 1 to 10(7) Hz. Most of the ionic liquids form a glass and the conductivity values obey the Vogel-Fulcher-Tammann equation. The glass transition temperatures are increasing with increasing length of the alkyl chain. The fragility is weakly dependent on the alkyl chain length but is highly sensitive to the structure of the anion. 相似文献
999.
Andhariya N Chudasama B Patel R Upadhyay RV Mehta RV 《Journal of colloid and interface science》2008,323(1):153-157
In the present investigation we report the effect of capillary diameter and the direction of applied magnetic field on the rotational viscosity of water and kerosene based ferrofluids. We found that changes in the field induced rotational viscosity are larger in the case of water based magnetic fluid than that of kerosene based fluid. The field induced rotational viscosity is found to be inversely proportional to the capillary diameter and it falls exponentially as a function of the angle between the direction of field and vorticity of flow. Magnetophoretic mobility and hydrodynamic volume fraction of nanomagnetic particles are determined for above cases. 相似文献
1000.
Uday C. Mashelkar Deepak M. Rane Rajesh S. Kenny 《Journal of heterocyclic chemistry》2008,45(3):865-872