全文获取类型
收费全文 | 584篇 |
免费 | 16篇 |
国内免费 | 2篇 |
专业分类
化学 | 398篇 |
力学 | 16篇 |
数学 | 46篇 |
物理学 | 142篇 |
出版年
2022年 | 10篇 |
2021年 | 19篇 |
2020年 | 10篇 |
2019年 | 15篇 |
2018年 | 23篇 |
2017年 | 10篇 |
2016年 | 24篇 |
2015年 | 12篇 |
2014年 | 10篇 |
2013年 | 28篇 |
2012年 | 30篇 |
2011年 | 31篇 |
2010年 | 22篇 |
2009年 | 20篇 |
2008年 | 27篇 |
2007年 | 24篇 |
2006年 | 20篇 |
2005年 | 23篇 |
2004年 | 14篇 |
2003年 | 13篇 |
2002年 | 14篇 |
2001年 | 8篇 |
2000年 | 8篇 |
1999年 | 8篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1991年 | 6篇 |
1989年 | 3篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 15篇 |
1976年 | 13篇 |
1975年 | 10篇 |
1974年 | 9篇 |
1973年 | 8篇 |
1972年 | 6篇 |
1971年 | 7篇 |
1970年 | 4篇 |
1969年 | 5篇 |
1968年 | 4篇 |
1967年 | 5篇 |
排序方式: 共有602条查询结果,搜索用时 78 毫秒
101.
Tauqir Nasir Natalya A. Vodolazkaya Grgoire Herzog Alain Walcarius 《Electroanalysis》2019,31(2):202-207
Electrogenerated silica thin films exhibiting a regular hexagonal packing of vertically‐aligned mesopore channels are promising for preconcentration electroanalysis. This work demonstrates the critical role of film thickness on their sensing performance using paraquat as a model analyte, based on mesoporous silica films prepared by electrochemically assisted self‐assembly performed for various deposition times. Films prepared with too short synthesis times (<10 s) led to deposits covering partially the electrode surface and suffered from rather poor sensing performance. Then, uniformly deposited films were obtained (between 10 and 15 s), and sensitivity rose up by increasing deposition times, whereas some limitations started to occur with much thicker films (>15 s deposition times) as a result of less electrochemically accessible paraquat accumulated far away from the electrode surface and restricted mass transport through the whole film thickness. These limitations were also confirmed on the basis of multi‐layered mesoporous silica films, suggesting a behavior that might be typical for other types of film‐modified electrodes. 相似文献
102.
A new class of multifunctional nanoparticles that combine properties of polymeric drug carriers, ultrasound imaging contrast agents, and enhancers of ultrasound-mediated drug delivery has been developed. At room temperature, the developed systems comprise perfluorocarbon nanodroplets stabilized by the walls made of biodegradable block copolymers. Upon heating to physiological temperatures, the nanodroplets convert into nano/microbubbles. The phase state of the systems and bubble size may be controlled by the copolymer/perfluorocarbon volume ratio. Upon intravenous injections, a long-lasting, strong and selective ultrasound contrast is observed in the tumor volume indicating nanobubble extravasation through the defective tumor microvasculature, suggesting their coalescence into larger, highly echogenic microbubbles in the tumor tissue. Under the action of tumor-directed ultrasound, microbubbles cavitate and collapse resulting in a release of the encapsulated drug and dramatically enhanced intracellular drug uptake by the tumor cells. This effect is tumor-selective; no accumulation of echogenic microbubbles is observed in other organs. Effective chemotherapy of the MDA MB231 breast cancer tumors has been achieved using this technique. 相似文献
103.
The Study of Nonisothermal Kinetics of Dehydration of Gibbsite in a Mixture with Zinc Oxide
下载免费PDF全文
![点击此处可从《国际化学动力学杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Nonisothermal kinetics of dehydration of gibbsite in a mixture with zinc oxide has been studied by Friedman analysis (differential method) and Flynn‐Wall‐Ozawa analysis (integral method). The values of the activation energy and preexponential factor depending on the decomposition extent of gibbsite to boehmite have been determined. It has been shown that both methods give similar results. It has been established that the activation energy has a maximum value of 150–170 kJ/mol in the start stages of thermolysis (for conversion extent of less than 0.3). During further dehydration, the activation energy is reduced to 100–110 kJ/mol. It has been found that comilling of the mixture results in decreasing activation energy to 40–50 kJ/mol for a conversion extent more than 0.8. This testifies to the transition of the dehydration process out of the kinetic mode to the diffusion mode. It was explained by the accumulation of mechanical energy in the form defects of crystal lattice of gibbsite at the comilling stage. 相似文献
104.
Tobramycin and Nebramine as Pseudo‐oligosaccharide Scaffolds for the Development of Antimicrobial Cationic Amphiphiles
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Yifat Berkov‐Zrihen Ido M. Herzog Raphael I. Benhamou Dr. Mark Feldman Kfir B. Steinbuch Pazit Shaul Dr. Shachar Lerer Dr. Avigdor Eldar Dr. Micha Fridman 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(11):4340-4349
Antimicrobial cationic amphiphiles derived from aminoglycoside pseudo‐oligosaccharide antibiotics interfere with the structure and function of bacterial membranes and offer a promising direction for the development of novel antibiotics. Herein, we report the design and synthesis of cationic amphiphiles derived from the pseudo‐trisaccharide aminoglycoside tobramycin and its pseudo‐disaccharide segment nebramine. Antimicrobial activity, membrane selectivity, mode of action, and structure–activity relationships were studied. Several cationic amphiphiles showed marked antimicrobial activity, and one amphiphilic nebramine derivative proved effective against all of the tested strains of bacteria; furthermore, against several of the tested strains, this compound was well over an order of magnitude more potent than the parent antibiotic tobramycin, the membrane‐targeting antimicrobial peptide mixture gramicidin D, and the cationic lipopeptide polymyxin B, which are in clinical use. 相似文献
105.
Raphael I. Benhamou Kfir B. Steinbuch Dr. Micha Fridman 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(32):11148-11151
Herein we report that an imidazole‐decorated cationic amphiphile derived from the pseudo‐disaccharide nebramine has potent antifungal activity against strains of Candida glabrata pathogens. In combination with the natural bis‐benzylisoquinoline alkaloid tetrandrine the reported antifungal cationic amphiphile demonstrated synergistic antifungal activity against Candida albicans pathogens. This unique membrane disruptor caused no detectible mammalian red blood cell hemolysis at concentrations up to more than two orders of magnitude greater than its minimal inhibitory concentrations against the tested C. glabrata strains. We provide evidence that potency against C. glabrata may be associated with differences between the drug efflux pumps of C. albicans and C. glabrata. Imidazole decorated‐cationic amphiphiles show promise for the development of less toxic membrane‐disrupting antifungal drugs and drug combinations. 相似文献
106.
107.
Roman Bashkurov Dr. Alexander Kaushansky Dr. Boris Tumanskii Dr. Natalia Fridman Dr. Dmitry Bravo-Zhivotovskii Prof. Dr. Yitzhak Apeloig 《Angewandte Chemie (International ed. in English)》2023,62(18):e202300847
Thermolysis of a 1 : 1 mixture of tris(di-tert-butylmethylsilyl)germane 9 and bis(di-tert-butylmethylsilyl)germane 17 at 100 °C produces unexpectedly octagermacubane 18 , having two 3-coordinate Ge0 atoms (40 % yield). 18 was characterized by X-ray crystallography and it is a singlet biradical (according to DFT quantum mechanical calculations and the absence of an EPR signal). Reactions of 18 with CH2Cl2 and H2O yield the novel dichloro-octagermacubane 24 and hydroxy-octagermacubane 25 , respectively. Reduction of 18 with tBuMe2SiNa in THF produces an isolable octagermacubane radical anion 26-Na . Based on X-ray crystallography, EPR spectroscopy and DFT quantum mechanical calculations, 26-Na is classified as a Ge-centered radical anion. 相似文献
108.
McHedlov-Petrossyan NO Bryleva EY Vodolazkaya NA Dissanayake AA Ford WT 《Langmuir : the ACS journal of surfaces and colloids》2008,24(11):5689-5699
Aqueous solutions of four cationic poly(propylenimine) low-generation dendrimers of different architecture and hydrophobicity have been examined as media for acid-base reactions of indicator dyes. The cationic dendrimers in solution can be considered as oligomers of cationic polyelectrolytes, or surfactant-like species, able to form micelles through self-association or sometimes even as unimolecular micelles. The dendrimers influence the ionization constants, tautomeric equilibria, and absorption/emission/excitation spectra of indicator dyes. The p K a values of the majority of the indicator dyes decrease in dendrimer solutions, often by 1-2 p K a units, similar to effects registered in micellar solutions of cationic surfactants. Analogously, the shifts of absorption band maxima indicate that the microenvironments of the dyes bound to the dendrimers are less polar than in water. However, some spectral effects denote the specificity of the dendrimers. The greatest difference between the dendrimers and spherical surfactant micelles is revealed by kinetic processes, especially of bromophenol blue alkaline fading in a dendrimer solution but not in a micellar surfactant solution. Within the dendrimer series, the most significant differences were observed for substances possessing n-dodecyl tails on the one hand and those without such hydrophobic portions on the other. For the last-named, the decrease in p K a's of indicators, band shifts of their anions, and in particular displacement of tautomeric equilibria compared with aqueous solutions are much smaller than for more hydrophobic dendrimers. 相似文献
109.
Natalya P. Yevlampieva Anna V. Kashina Tamara K. Meleshko 《International Journal of Polymer Analysis and Characterization》2016,21(8):749-760
The molecular properties of polymer brushes composed of polyimide with polymerization degree 50 and loosely grafted poly(methyl methacrylate) chains of variable length (PI-graft-PMMA) were studied by viscometry, dynamic light scattering, and equilibrium electro-optical Kerr effect methods in a diluted solution. It was established that the intrinsic viscosity and hydrodynamic dimension of PI-graft-PMMA copolymers increase when the electro-optical Kerr constant decreases with the elongation of PMMA side chains in the range of 40–110 monomer units. The observed difference in the solution properties of the copolymers was explained by their side-chain interactions in spite of a large distance between the neighboring grafting points typical of “loose brushes.” A strong effect of the chain rigidity and dipole structure on solution properties of the studied samples was demonstrated. The Kuhn segment lengths for PI-graft-PMMA copolymers were estimated to vary in the range 3.8–12.1?nm. 相似文献
110.
A. Yu. Tsivadze A. Ya. Fridman A. K. Novikov N. P. Sokolova E. M. Morozova A. M. Voloshchuk I. I. Bardyshev A. M. Gorbunov A. Yu. Chernyadiev A. A. Averin 《Russian Journal of Coordination Chemistry》2016,42(12):775-778
A sorbent was synthesized as a cellulose cloth, the fibers of which have nanopores with walls made of cellulose chains and ethanol cyclams. The formation of (NH4)2[NiL(NH3)2Cl2] complexes where L2– is the CH–(O–)–CH–(O–) glucopyranose group was established by chemical analysis and IR and UV/Vis spectroscopy. Using small-angle X-ray scattering and measurement of the partial free space and adsorption capacity, the complex formation in the [Ni(NH3)6]Cl2 concentration range of up to 0.43 mol/L was found to occur in nanopores with the sorption constant K sorb = 15.8. The limiting content of the complexes is 2.63 mmol/g and their effective radius is 0.45 nm. In the concentration range of 0.43–0.91 mol/L, the complexation occurs on the fiber surface, K sorb = 1.85. The effective radius of the complexes is 0.5 nm. 相似文献