全文获取类型
收费全文 | 77篇 |
免费 | 4篇 |
国内免费 | 1篇 |
专业分类
化学 | 30篇 |
力学 | 6篇 |
数学 | 29篇 |
物理学 | 17篇 |
出版年
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 8篇 |
2020年 | 7篇 |
2019年 | 3篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 5篇 |
2015年 | 3篇 |
2014年 | 2篇 |
2013年 | 4篇 |
2012年 | 2篇 |
2011年 | 5篇 |
2009年 | 2篇 |
2008年 | 4篇 |
2007年 | 5篇 |
2006年 | 1篇 |
2005年 | 2篇 |
2004年 | 3篇 |
2003年 | 2篇 |
2002年 | 1篇 |
2001年 | 2篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1983年 | 1篇 |
排序方式: 共有82条查询结果,搜索用时 0 毫秒
21.
Lyle W. Castle Milton D. Johnston Charalampos L. Camoutsis Raymond N. Castle 《Journal of heterocyclic chemistry》1992,29(7):1805-1815
The 1H nmr spectra of phenanthro[9′,10′:4,5]thieno[2,3-c]quinoline, benzo[f]phenanthro-[9′,10′:4,5]thieno[2,3-c]quinoline and benzo[h]phenanthro[9′,10′:4,5]thieno[2,3-c]quinoline are highly congested. For each compound, all protons abide in an aromatic environment complicated by pseudo-symmetric regions which result in multiple overlap of the different spin systems these molecules contain. We illustrate here the utility of the HMQC-TOCSY experiment to identify spin systems when the proton spectrum is highly congested. To complete the assignment of the 1H and 13C nmr spectra of each compound the HMBC experiment is used to assign the quaternary carbons. 相似文献
22.
23.
A direct comparison between volume and surface tracking methods with a boundary-fitted coordinate transformation and third-order upwinding 总被引:1,自引:0,他引:1
Maria Zacharioudaki Charalampos Kouris Yannis Dimakopoulos John Tsamopoulos 《Journal of computational physics》2007,227(2):1428-1469
A Volume Tracking (VT) and a Front Tracking (FT) algorithm are implemented and compared for locating the interface between two immiscible, incompressible, Newtonian fluids in a tube with a periodically varying, circular cross-section. Initially, the fluids are stationary and stratified in an axisymmetric arrangement so that one is around the axis of the tube (core fluid) and the other one surrounds it (annular fluid). A constant pressure gradient sets them in motion. With both VT and FT, a boundary-fitted coordinate transformation is applied and appropriate modifications are made to adopt either method in this geometry. The surface tension force is approximated using the continuous surface force method. All terms appearing in the continuity and momentum equations are approximated using centered finite differences in space and one-sided forward finite differences in time. In each time step, the incompressibility condition is enforced by a transformed Poisson equation, which is linear in pressure. This equation is solved by either direct LU decomposition or a Multigrid iterative solver. When the two fluids have the same density, the former method is about 3.5 times faster, but when they do not, the Multigrid solver is as much as 10 times faster than the LU decomposition. When the interface does not break and the Reynolds number remains small, the accuracy and rates of convergence of VT and FT are comparable. The well-known failure of centered finite differences arises as the Reynolds number increases and leads to non-physical oscillations in the interface and failure of both methods to converge with mesh refinement. These problems are resolved and computations with Reynolds as large as 500 converged by approximating the convective terms in the momentum equations by third-order upwind differences using Lagrangian Polynomials. When the volume of the core fluid or the Weber number decrease, increasing the importance of interfacial tension and leading to breakup of the interface forming a drop of core fluid, the FT method converges faster with mesh refinement than the VT method and upwinding may be required. Finally, examining the generation of spurious currents around a stationary “bubble” in the tube for Ohnesorge numbers between 0.1 and 10 it is found that the maximum velocity remains approximately the same in spite mesh refinements when VT is applied, whereas it is of the same order of magnitude for the coarsest mesh and monotonically decreases with mesh refinement when FT is applied. 相似文献
24.
Petros Karalis Anastasia Elektra Poutouki Theodora Nikou Maria Halabalaki Charalampos Proestos Effie Tsakalidou Sofia Gougoura George Diamantopoulos Maria Tassi Elissavet Dotsika 《Molecules (Basel, Switzerland)》2020,25(24)
In recent years, isotopic analysis has been proven a valuable tool for the determination of the origin of various materials. In this article, we studied the 18O and 13C isotopic values of 210 olive oil samples that were originated from different regions in Greece in order to verify how these values are affected by the climate regime. We observed that the δ18O isotopic values range from 19.2 ‰ to 25.2 ‰ and the δ13C values range from −32.7 ‰ to −28.3 ‰. These differences between the olive oils’ isotopic values depended on the regional temperature, the meteoric water, and the distance from the sea. Furthermore, we studied the 13C isotopic values of biophenolic extracts, and we observed that they have same capability to differentiate the geographic origin. Finally, we compared the isotopic values of Greek olive oils with samples from Italy, and we concluded that there is a great dependence of oxygen isotopes on the climatic characteristics of the different geographical areas. 相似文献
25.
26.
Hossein Goudarzi Loukas Koutsokeras Ahmed H. Balawi Chen Sun Giorgos K. Manolis Nicola Gasparini Yuan Peisen Giannis Antoniou Stavros Athanasopoulos Charalampos C. Tselios Polycarpos Falaras Constantinos Varotsis Frdric Laquai Juan Cabanillas-Gonzlez Panagiotis E. Keivanidis 《Chemical science》2023,14(8):2009
Bimolecular processes involving exciton spin-state interactions gain attention for their deployment as wavelength-shifting tools. Particularly triplet–triplet annihilation induced photon energy up-conversion (TTA-UC) holds promise to enhance the performance of solar cell and photodetection technologies. Despite the progress noted, a correlation between the solid-state microstructure of photoactuating TTA-UC organic composites and their photophysical properties is missing. This lack of knowledge impedes the effective integration of functional TTA-UC interlayers as ancillary components in operating devices. We here investigate a solution-processed model green-to-blue TTA-UC binary composite. Solid-state films of a 9,10 diphenyl anthracene (DPA) blue-emitting activator blended with a (2,3,7,8,12,13,17,18-octaethyl-porphyrinato) PtII (PtOEP) green-absorbing sensitizer are prepared with a range of compositions and examined by a set of complementary characterization techniques. Grazing incidence X-ray diffractometry (GIXRD) measurements identify three PtOEP composition regions wherein the DPA:PtOEP composite microstructure varies due to changes in the packing motifs of the DPA and PtOEP phases. In Region 1 (≤2 wt%) DPA is semicrystalline and PtOEP is amorphous, in Region 2 (between 2 and 10 wt%) both DPA and PtOEP phases are amorphous, and in Region 3 (≥10 wt%) DPA remains amorphous and PtOEP is semicrystalline. GIXRD further reveals the metastable DPA-β polymorph species as the dominant DPA phase in Region 1. Composition dependent UV-vis and FT-IR measurements identify physical PtOEP dimers, irrespective of the structural order in the PtOEP phase. Time-gated photoluminescence (PL) spectroscopy and scanning electron microscopy imaging confirm the presence of PtOEP aggregates, even after dispersing DPA:PtOEP in amorphous poly(styrene). When arrested in Regions 1 and 2, DPA:PtOEP exhibits delayed PtOEP fluorescence at 580 nm that follows a power-law decay on the ns time scale. The origin of PtOEP delayed fluorescence is unraveled by temperature- and fluence-dependent PL experiments. Triplet PtOEP excitations undergo dispersive diffusion and enable TTA reactions that activate the first singlet-excited (S1) PtOEP state. The effect is reproduced when PtOEP is mixed with a poly(fluorene-2-octyl) (PFO) derivative. Transient absorption measurements on PFO:PtOEP films find that selective PtOEP photoexcitation activates the S1 of PFO within ∼100 fs through an up-converted 3(d, d*) PtII-centered state.Dispersive diffusion and annihilation of excitations in the amorphous aggregate phase of a square-planar PtOEP sensitizer in the solid state result in the activation of delayed PtOEP fluorescence through an up-converted PtII-centered state. 相似文献
27.
In an attempt to reduce the emission of hazardous VOCs, SCFs have been intensively investigated as alternative solvents during the last two decades. In this study, the application of reaction calorimetry, an efficient tool to obtain kinetic and safety data, is presented on the free radical dispersion polymerization of MMA in scCO2. The effect of three major parameters with respect to the reaction evolution are studied, namely of stirrer type and stirring speed, the monomer and CO2 concentration and the stabilizer concentration. The effective formation of the dispersion as well as the balance between the polymer formed in the continuous phase or inside the particles are key features of this analysis.
28.
Magnetic octadecyl‐based matrix solid‐phase dispersion coupled with gas chromatography with mass spectrometry in a proof‐of‐concept determination of multi‐class pesticide residues in carrots 下载免费PDF全文
Charalampos S. Binellas Constantine D. Stalikas 《Journal of separation science》2015,38(20):3575-3581
A novel procedure is put forward based on the combination of the well‐established matrix solid‐phase dispersion and the magnetic and sorption properties of magnetic octadecyl in the presence of n‐octanol and was employed in a proof‐of‐concept sample preparation and determination of several classes of pesticide residues in carrots. The procedure does not require the transfer of blend to cartridge and subsequent packing, nor any co‐sorbent for extract clean up. The hydrophobic magnetic nanoparticles utilized as a sorbent, can be retrieved by n‐octanol under the application of a magnetic field due to hydrophobic interactions. Elution of pesticide residues is then carried out with an organic solvent. A total of 26 pesticides were included in this procedure and the target compounds were analyzed using gas chromatography with mass spectrometry in the selective ion monitoring mode. The average extraction recoveries obtained from carrot samples fortified at three different concentrations (20, 50, and 500 μg/kg) were 77–107%. The estimated limits of quantitation for most target analytes were in the low μg/kg level. The study demonstrates that the proposed extraction procedure is simple and effective, avoiding a clean‐up step for the sample preparation of vegetable. 相似文献
29.
30.
Charalampos CharitosIoannis Papadoperakis Georgios Tsapogas 《Topology and its Applications》2011,158(8):978-995
A complex of incompressible surfaces in a handlebody is constructed so that it contains, as a subcomplex, the complex of curves of the boundary of the handlebody. For genus 2 handlebodies, the group of automorphisms of this complex is used to characterize the mapping class group of the handlebody. In particular, it is shown that all automorphisms of the complex of incompressible surfaces are geometric, that is, induced by a homeomorphism of the handlebody. 相似文献