全文获取类型
收费全文 | 141篇 |
免费 | 1篇 |
国内免费 | 3篇 |
专业分类
化学 | 103篇 |
力学 | 4篇 |
数学 | 20篇 |
物理学 | 18篇 |
出版年
2022年 | 1篇 |
2021年 | 3篇 |
2020年 | 5篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 3篇 |
2015年 | 1篇 |
2014年 | 4篇 |
2013年 | 5篇 |
2012年 | 7篇 |
2011年 | 10篇 |
2010年 | 10篇 |
2009年 | 8篇 |
2008年 | 13篇 |
2007年 | 16篇 |
2006年 | 12篇 |
2005年 | 7篇 |
2004年 | 7篇 |
2003年 | 2篇 |
2002年 | 6篇 |
2001年 | 2篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1994年 | 1篇 |
1992年 | 2篇 |
1990年 | 2篇 |
1986年 | 3篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有145条查询结果,搜索用时 15 毫秒
71.
Athanasios B. Bourlinos Panagiotis Dallas Yiannis Sanakis Dimosthenis Stamopoulos Christos Trapalis Dimitrios Niarchos 《European Polymer Journal》2006,42(11):2940-2948
Nucleophilic substitutions of the reactive chlorine atoms in cyanuric chloride by the bridging 4,4′-bipyridine in refluxing toluene lead to quaternarization of the latter and the subsequent formation of a π-conjugate, covalent layered network. The network is composed of central 1,3,5-triazine units with 4,4′-bipyridinium rings covalently attached and balanced by the released chloride ions. Due to the extremely high electron deficiency of the triazine rings, the material undergoes partial reduction by its compensated chloride ions resulting in a radical concentration of 1 × 1020 spin g−1, according to EPR quantitative analysis. In this instance, the radicals provide stability to the organic network by minimizing its electron deficiency. The material exhibits thermal and electrochemical stability, as evidenced by thermal gravimetric analysis (TGA) and cyclic voltammetry techniques. As such, the π-conjugate organic material displays low band gaps and electrical conductivity in the range of 10−4-10−5 S cm−1 at room temperature. 相似文献
72.
M. Sc. Hendrik Naatz Dr. Bella B. Manshian Dr. Carla Rios Luci Dr. Vasiliki Tsikourkitoudi Prof. Dr. Yiannis Deligiannakis Dr. Johannes Birkenstock Dr. Suman Pokhrel Prof. Dr. Lutz Mädler Dr. Stefaan J. Soenen 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(5):1844-1852
The progress in nanomedicine (NM) using nanoparticles (NPs) is mainly based on drug carriers for the delivery of classical chemotherapeutics. As low NM delivery rates limit therapeutic efficacy, an entirely different approach was investigated. A homologous series of engineered CuO NPs was designed for dual purposes (carrier and drug) with a direct chemical composition–biological functionality relationship. Model-based dissolution kinetics of CuO NPs in the cellular interior at post-exposure conditions were controlled through Fe-doping for intra/extra cellular Cu2+ and biological outcome. Through controlled ion release and reactions taking place in the cellular interior, tumors could be treated selectively, in vitro and in vivo. Locally administered NPs enabled tumor cells apoptosis and stimulated systemic anti-cancer immune responses. We clearly show therapeutic effects without tumor cells relapse post-treatment with 6 % Fe-doped CuO NPs combined with myeloid-derived suppressor cell silencing. 相似文献
73.
74.
Georgopoulou AN Sanakis Y Boudalis AK 《Dalton transactions (Cambridge, England : 2003)》2011,40(24):6371-6374
The magnetic properties of the antiferromagnetic basic iron(III) carboxylate [Fe(3)O(O(2)CPh)(6)(H(2)O)(3)]ClO(4)·py are studied by magnetic susceptometry and electron paramagnetic resonance spectrocopy. Ac susceptometry under moderate external magnetic fields reveals magnetic relaxation at liquid helium temperatures. 相似文献
75.
Kioussi MK Angelis YS Cawley AT Koupparis M Kazlauskas R Brenna JT Georgakopoulos CG 《Journal of chromatography. A》2011,1218(33):5675-5682
An alternative calibration procedure for the Gas Chromatography–Combustion–Isotope Ratio Mass Spectrometry (GC–C–IRMS) measurements of the World Antidoping Agency (WADA) Accredited Laboratories is presented. To alleviate the need for externally calibrated CO2 gas for GC–C–IRMS analysis of urinary steroid metabolites, calibration using an external standard mixture solution of steroids with certified isotopic composition was investigated. The reference steroids of the calibration mixture and routine samples underwent identical instrumental processes. The calibration standards bracketed the entire range of the relevant δ13C values for the endogenous and exogenous steroids as well as their chromatographic retention times. The certified δ13C values of the reference calibrators were plotted in relation to measured m/z13CO2/12CO2 (i.e. R(45/44)) mass spectrometric signals of each calibrator. δ13C values of the sample steroids were calculated from the least squares fit through the calibration curve. The effect of the external calibration on δ13C values, using the same calibration standards and set of urine samples but different brands of GC–C–IRMS instruments, was assessed by an interlaboratory study in the WADA Accredited Laboratories of Sydney, Australia and Athens, Greece. Relative correspondence between the laboratories for determination of androsterone, etiocholanolone, 5β-androstane-3α,17β-diacetate, and pregnanediacetate means were SD(δ13C) = 0.12‰, 0.58‰, −0.34‰, and −0.40‰, respectively. These data demonstrate that accurate intralaboratory external calibration with certified steroids provided by United States Antidoping Agency (USADA) and without external CO2 calibration is feasible and directly applicable to the WADA Accredited Laboratories for the harmonization of the GC–C–IRMS measurements. 相似文献
76.
Zueva EM Sameera WM Piñero DM Chakraborty I Devlin E Baran P Lebruskova K Sanakis Y McGrady JE Raptis RG 《Inorganic chemistry》2011,50(3):1021-1029
Six [Fe(8)(μ(4)-O)(4)(μ-4-R-pyrazolato)(12)X(4)] complexes containing an identical Fe(8)(μ(4)-O)(4) core have been structurally characterized and studied by M?ssbauer spectroscopy. In each case, an inner μ(4)-O bridged Fe(III) cubane core is surrounded by four trigonal bipyramidal iron centers, the two distinct sites occurring in a 1:1 ratio. The M?ssbauer spectrum of each of the clusters consists of two quadrupole doublets, which, with one exception (X = NCS, R = H), overlap to give three absorption lines. The systematic variation of X and R causes significant changes in the M?ssbauer spectra. A comparison with values for the same clusters computed using density functional theory allows us to establish an unequivocal assignment of these peaks in terms of a nested model for the overlapping doublets. The changes in M?ssbauer parameters (both experimental and computed) for the 1-electron reduced species [Fe(8)(μ(4)-O)(4)(μ-4-Cl-pyrazolato)(12)Cl(4)](-) are consistent with a redox event that is localized within the cubane core. 相似文献
77.
In this work, a revisit to the retention mechanism of HILIC was attempted to point out critical factors that contribute to the chromatographic regime as well as to bring out subtle details of the relative contribution of partitioning and surface adsorption. In this vein, the retention behaviour of a set of water-soluble vitamins (WSVs) and toluene on three silica based columns was evaluated under varying chromatographic conditions. The data obtained were associated with the hydration degree of the stationary phases and the ability of the organic solvents to disrupt the formation of the water-enriched layer. Moreover, the elution behaviour of toluene at different buffer salt concentrations in the mobile phase, confirmed the preferential partition of salt ions into the stagnant layer, as ACN content was increased. The results from the fitting of partitioning and surface adsorption models indicated differences in the contribution of the two retention mechanisms to both neutral and charged compounds. The occurrence of surface adsorption and the retentivity differences for neutral WSVs depend on the hydration degree and the hydrogen bonding properties of the solutes and the column surface, respectively. For charged solutes experiencing electrostatic repulsion, the contribution of the adsorption mechanism at highly organic mobile phases, emanates from both the weak effect of buffer salt ions on the electrostatic interaction and the strong effect of hydrophilic interactions. On the other hand, the chromatographic retention of electrostatically attracted solutes indicates that the surface adsorption dominates, even at mobile phases rich in water. 相似文献
78.
Chrysina M Zahariou G Sanakis Y Ioannidis N Petrouleas V 《Journal of photochemistry and photobiology. B, Biology》2011,104(1-2):72-79
The paper extends earlier studies on the S(2)Y(Z)* intermediate that is trapped by illumination in the temperature range 77 K to 190 K of untreated samples poised in the S(2)...Q(A) state. X-band EPR experiments on untreated and glycerol (50% v/v) treated samples at 10 K indicate that the intermediate consists of two components. A wide one with a splitting of ca 170 G, and a narrow one characterized by a splitting of ca 120 G (untreated), or 124 G (glycerol-treated samples). Lower temperatures of illumination in the above temperature range favor the wide component, which at 10 K decays faster than the narrow one. Re-illumination at 10 K after decay of the signal trapped at 77-190 K induces only the narrow component. Rapid scan experiments in the temperature range 77-190 K reveal high resolution spectra of the isolated tyz Z* radical and no evidence of alternative radicals. The two split signals are accordingly assigned to different conformations of the S(2)Y(Z)* intermediate A point-dipole simulation of the spectra yields "effective distances" between the spin densities of Y(Z)* and the Mn(4)Ca center of 5.7 ? for the wide and 6.4 ? for the narrow component. The results are discussed on the basis of a molecular model assuming two sequential proton transfers during oxidation of tyr Z. The wide component is assigned to a transient S(2)Y(Z)* conformation, that forms during the primary proton transfer. 相似文献
79.
An unstructured adaptive mesh flow solver, a finite element structure solver and a moving mesh algorithm were implemented in the numerical simulation of the interaction between a shock wave and a structure. In the past, this interaction is mostly considered as one-way in the sense that the shock causes a transient load on the structure while it is reflected uneffected by the impact. A fully coupled approach was implemented in the present work which can account for the effects associated with a mutual interaction. This approach included a compressible flow Eulerian solver of second order accuracy in finite volume formulation for the fluid and a Langargian solver in finite element formulation for the solid structure. A novel implementation of advancing front moving mesh algorithm was made possible with the introduction of a flexible and efficient quad-edge data structure. Adaptive mesh refinement was introduced into the flow solver for improved accuracy as well. Numerical results are further validated by theoretical analysis, experimental data and results from other numerical simulations. Grid dependency study was performed and results showed that the physical phenomena and quantities were independent of the numerical grid chosen in the simulations. The results illuminated complicated flow phenomena and structure vibration patterns, which in order to be detected experimentally require capabilities beyond those of the current experimental techniques. The numerical simulations also successfully modelled the aero-acoustic damping effects on the structure, which do not exist in previous numerical models. Further analysis of the results showed that the mutual interaction is not linear and that the non-linearity arises because the wave propagation in the fluid is not linear and it cascades a non-linear and non-uniform loading on the plate. Non-linearity intensifies when the plate is vibrating at high frequency while the wave propagation speed is low. 相似文献
80.
Apostolos Hadjidimos Theodore S. Papatheodorou Yiannis G. Saridikis 《Linear algebra and its applications》1983
The problem of determining fast iterative solutions of certain large, sparse, and nonsymmetric linear systems, arising in applications, is addressed here. Several iterative schemes, from the accelerated overrelaxation family, are considered. Different geometrical algorithms are used for the explicit determination of the optimal factors. Direct comparisons of the spectral radii of the resulting optimal schemes reveal that the optimal extrapolated accelerated Gauss-Seidel (EAGS) is always asymptotically faster than the optimal successive overrelaxation, while the optimal EAGS and extrapolated Gauss-Seidel strongly compete. Application of the collocation method on simple boundary-value problems is used to demonstrate our results numerically. 相似文献