全文获取类型
收费全文 | 212篇 |
免费 | 4篇 |
国内免费 | 1篇 |
专业分类
化学 | 154篇 |
力学 | 6篇 |
数学 | 43篇 |
物理学 | 14篇 |
出版年
2023年 | 4篇 |
2022年 | 17篇 |
2021年 | 17篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 8篇 |
2017年 | 4篇 |
2016年 | 11篇 |
2015年 | 6篇 |
2014年 | 7篇 |
2013年 | 9篇 |
2012年 | 25篇 |
2011年 | 15篇 |
2010年 | 12篇 |
2009年 | 9篇 |
2008年 | 15篇 |
2007年 | 15篇 |
2006年 | 7篇 |
2005年 | 7篇 |
2004年 | 6篇 |
2003年 | 2篇 |
2002年 | 1篇 |
1998年 | 5篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1992年 | 1篇 |
1987年 | 1篇 |
排序方式: 共有217条查询结果,搜索用时 15 毫秒
41.
The efficiency, reproducibility and sensitivity ofn-hexane and iso-octane extraction and of C18 reversed-phase adsorption for accumulation of 4-chloro-, 2,4-dichloro-, 2,4,5- and 2,4,6-trichloro-, 2,3,4,6-tetrachloro- and pentachlorophenol from aqueous solutions were compared. In extraction procedures the acetyl and pentafluorobenzoyl derivatives of chlorophenols were extracted from water. In adsorption procedure chlorophenols adsorbed on a Sep-Pak C18 cartridge were eluted with acetone and after that derivatized analogously.All three procedures were found to be applicable for an efficient trace enrichment of chlorophenols in water, the proper choice being dependent on the required sensitivity of the analysis. Lower detection limits of single compounds at 10 ng·1–1 levels were achieved by adsorption procedure owing to the more uniform and for most chlorophenols higher adsorption than extraction recoveries as well as owing to the possibility of treating larger volumes of water samples. The extraction procedure could be successfully applied to the concentrations of chlorophenols in water 1g·1–1.Owing to its higher efficiency and better sensitivity the C18 reversed-phase adsorption procedure was chosen as the more suitable one for the determination of chlorophenol levels in surface, ground and drinking waters. The conversion of chlorophenols accumulated from a water sample parallel to both acetyl and pentafluorobenzoyl derivatives and the analysis of both types of derivatives on two basically different gas Chromatographic columns were recommended for a more reliable identification and quantitation of the compounds analyzed. 相似文献
42.
Dr. Milan Sencanski Dr. Vladimir Perovic Dr. Jelena Milicevic Dr. Tamara Todorovic Dr. Radivoje Prodanovic Dr. Veljko Veljkovic Dr. Slobodan Paessler Dr. Sanja Glisic 《ChemistryOpen》2022,11(2):e202100248
In the current pandemic, finding an effective drug to prevent or treat the infection is the highest priority. A rapid and safe approach to counteract COVID-19 is in silico drug repurposing. The SARS-CoV-2 PLpro promotes viral replication and modulates the host immune system, resulting in inhibition of the host antiviral innate immune response, and therefore is an attractive drug target. In this study, we used a combined in silico virtual screening for candidates for SARS-CoV-2 PLpro protease inhibitors. We used the Informational spectrum method applied for Small Molecules for searching the Drugbank database followed by molecular docking. After in silico screening of drug space, we identified 44 drugs as potential SARS-CoV-2 PLpro inhibitors that we propose for further experimental testing. 相似文献
43.
In this paper, we aim to investigate the role of cooperation between low level heuristics within a hyper-heuristic framework.
Since different low level heuristics have different strengths and weaknesses, we believe that cooperation can allow the strengths
of one low level heuristic to compensate for the weaknesses of another. We propose an agent-based cooperative hyper-heuristic
framework composed of a population of heuristic agents and a cooperative hyper-heuristic agent. The heuristic agents perform
a local search through the same solution space starting from the same or different initial solution, and using different low
level heuristics. The heuristic agents cooperate synchronously or asynchronously through the cooperative hyper-heuristic agent
by exchanging the solutions of the low level heuristics. The cooperative hyper-heuristic agent makes use of a pool of the
solutions of the low level heuristics for the overall selection of the low level heuristics and the exchange of solutions.
Computational experiments carried out on a set of permutation flow shop benchmark instances illustrated the superior performance
of the cooperative hyper-heuristic framework over sequential hyper-heuristics. Also, the comparative study of synchronous
and asynchronous cooperative hyper-heuristics showed that asynchronous cooperative hyper-heuristics outperformed the synchronous
ones. 相似文献
44.
45.
Sanja Friganović 《Annali dell'Universita di Ferrara》2018,64(2):361-370
In this note we improve the standard regularity of the dynamic part of the pressure in the Navier–Stokes system. Using the theory of elliptic equations with \(L^1\) right-hand side we prove that, in addition to be in \(L^2\), the dynamic pressure belongs to \(W^{1,\alpha }_{loc} \) with \(1<\alpha <\frac{n}{n-1}\), in case of Dirichlet boundary condition. For pressure boundary condition the dynamic pressure is proved to be in \(W^{1,\alpha } \). As a consequence, for the force \(\mathbf{f} \in L^q (\Omega )^n \) and \(q>n /2 \) the pressure turns out to be continuous. 相似文献
46.
Ab initio calculations on fluoroethane reactions with the hydroxyl radical have been carried out at different levels of theory. The convergence of reaction barriers and reaction enthalpies has been systematically investigated with respect to the size and quality of the basis set and the treatment of correlation energy. The G2 and MP2 barrier heights and reaction enthalpies show the best agreement with the experimental data. The split valence basis sets of triple-zeta quality supplemented by diffuse and polarization functions are necessary to reproduce experimental values for barrier heights and reaction enthalpies at the MP2 level of theory. The full counterpoise correction was used to calculate the basis set superposition error for several standard basis sets, including polarization and diffuse functions. The smallest counterpoise corrections are associated with basis sets that contain polarization and diffuse functions, the diffuse functions being the most effective in reducing BSSE. However, in our case, the uncorrected barrier heights are in better agreement with experimental results than the counterpoise-corrected data. Thus, at the MP2 level of theory, which seems to be dictated for larger electronic systems of chemical interest, the optimal approach is to increase the basis set to the maximum size affordable and to use results without counterpoise corrections for the calculation of reaction barriers. A viable alternative is the use of G2 theory because its results for the barrier heights and reaction enthalpies are in excellent agreement with the experimental data. © 1997 John Wiley & Sons, Inc. J Comput Chem 18: 1190–1199 相似文献
47.
Nayan K. Solanki Eric J. L. McInnes Frank E. Mabbs Sanja Radojevic Mary McPartlin Neil Feeder John E. Davies Malcolm A. Halcrow 《Angewandte Chemie (International ed. in English)》1998,37(16):2221-2223
Replacing the 3- and 3′′-protons of the ligand 2,6-di(pyrazol-1-yl)pyridine L by mesityl groups changes the electronic ground state of [Cu(L)2]2+ complexes from {d}1 to {d}1. This is the best example so far for a “homoleptic” Jahn–Teller-compressed six-coordinate CuII complex. 相似文献
48.
RHF/6-31G* investigations of 4-, 5-, and 6-ethyl(Et)–indole-3-acetic acid (IAA) yielded 11 symmetry-unique local minima with syn-periplanar orientation of the COOH group for each of these compounds. The global minima are of C1 symmetry in all cases. Comparison with earlier results shows that ethylation or chlorination in position 5 or 6 introduces only minor changes on the orientation of the acetic acid side group, with no effect on the reaction paths related to this group. For 4-Et–IAA, the deviations from unsubstituted IAA are larger but preserve the pattern of reaction paths that is present in unsubstituted IAA, which is in contrast to 4-Cl–IAA, where local minima and reaction paths are completely different. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 1169–1175, 1998 相似文献
49.
The kinetic study of the efficient regioselective oxidation of the C? C double bond of 4‐methylcoumarins with isolated dimethyldioxirane was investigated using UV–vis spectroscopy methods. In the excess of dimethyldioxirane, the pyrone ring of a coumarin skeleton is selectively epoxidated and hydroxylated in neutral media, in high yields. Kinetic analyses demonstrate two independent reaction pathways, epoxidation and hydroxylation, respectively, which was also confirmed using kinetic isotope effect methods. Both reaction products were isolated, and their structures were determined by NMR and mass spectra. The position of methyl groups attached at the aromatic part of coumarin molecule shows significant influence on kinetic rate constants and activation parameters. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 414–420, 2009 相似文献
50.
Sanja Frka Zlatica Kozarac 《International journal of environmental analytical chemistry》2013,93(5):325-335
The objective of this work was to develop electrochemical impedance spectroscopy (EIS) to characterise the physical properties of the sea surface microlayer ( ssm ). Samples from Lake Rogoznica in Croatia were extracted by n-hexane and dichloromethane (dcm) respectively and transferred to mercury electrodes. The EIS results were compared with those of a model phospholipid, dioleoyl phosphatidylcholine (DOPC) which forms near defect-free monolayers on a mercury surface. The ssm extracts formed inhomogeneous monolayers on the mercury surface and the dcm ssm extract monolayer showed greater surface roughness than the hexane ssm extract. The hexane ssm extract introduced defects and a greater surface roughness into mixed DOPC- ssm extract monolayers than the dcm ssm extract due to the lower compatibility of the non-polar hexane extract with the DOPC than that of the polar ssm extract. In addition, the dcm ssm component in the mixed DOPC- ssm monolayer showed an association with pyrene added to the solution. 相似文献