全文获取类型
收费全文 | 600篇 |
免费 | 6篇 |
国内免费 | 2篇 |
专业分类
化学 | 371篇 |
晶体学 | 3篇 |
力学 | 15篇 |
数学 | 130篇 |
物理学 | 89篇 |
出版年
2023年 | 2篇 |
2022年 | 1篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 36篇 |
2017年 | 36篇 |
2016年 | 28篇 |
2015年 | 26篇 |
2014年 | 9篇 |
2013年 | 37篇 |
2012年 | 39篇 |
2011年 | 54篇 |
2010年 | 42篇 |
2009年 | 30篇 |
2008年 | 44篇 |
2007年 | 38篇 |
2006年 | 27篇 |
2005年 | 16篇 |
2004年 | 19篇 |
2003年 | 12篇 |
2002年 | 10篇 |
2001年 | 9篇 |
2000年 | 5篇 |
1999年 | 4篇 |
1998年 | 1篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 9篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 1篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 4篇 |
1974年 | 5篇 |
1973年 | 2篇 |
1971年 | 1篇 |
排序方式: 共有608条查询结果,搜索用时 15 毫秒
141.
Peter Segľa Vladimír Kuchtanin Miroslav Tatarko Jozef Švorec Ján Moncol Marian Valko 《Chemical Papers》2018,72(4):863-876
The synthesis and characterization of [Cu(5-Me-2-tpc)2(4-pyme)2] (I), [Cu(3-Me-2-tpc)2(4-pyme)2] (II), [Cu(2-tpc)2(4-pyme)2] (III), [Cu(2-tpc)2(isonia)2(2-tpcH)] (IV), [Cu(5-Me-2-tpc)2(isonia)2(5-Me-2-tpcH)] (V), [Cu2(2-tpc)4(4-pyme)2] (VI), [Cu2(3-Me-2-tpc)4(isonia)2] (VII) (where 2-tpc is 2-thiophenecarboxylate, 3-Me-2-tpc is 3-methyl-2-thiophenecarboxylate, 5-Me-2-tpc is 5-methyl-2-thiophenecarboxylate and 4-pyme is 4-pyridinemethanol and isonia is isonicotinamide) are reported. The complexes under study were characterized by electronic, IR and EPR spectroscopy, magnetic susceptibility over the temperature range and X-ray structure analysis. Structural studies revealed a distorted tetragonal-bipyramidal environment around the copper ion for monomeric complexes I–V. The structure of dimeric complexes VI and VII consists of units of the known paddle-wheel dicopper(II) tetracarboxylates, which are made up of four thiophene-2-carboxylate ions thus bridging the two copper atoms. The complex molecules of all compounds are connected through H-bonds into supramolecular chains or frameworks. The spectral and magnetic properties are discussed with regard to X-ray data. 相似文献
142.
Tomislav Došlić Ivica Martinjak Riste Škrekovski Sanja Tipurić Spužević Ivana Zubac 《Journal of mathematical chemistry》2018,56(10):2995-3013
We propose and investigate a new bond-additive structural invariant as a measure of peripherality in graphs. We first determine its extremal values and characterize extremal trees and unicyclic graphs. Then we show how it can be efficiently computed for large classes of chemically interesting graphs using a variant of the cut method introduced by Klav?ar, Gutman and Mohar. Explicit formulas are presented for several classes of benzenoid graphs and Cartesian products. At the end we state several conjectures and list some open problems. 相似文献
143.
144.
Dijana Jelić Saša Zeljković Branko Škundrić Slavko Mentus 《Journal of Thermal Analysis and Calorimetry》2018,133(1):77-86
The present study reports the results of investigation on the role of metakaolin in the formation of ettringite in a model relevant to Portland cement. The model consists of ternary system (Trio) metakaolin–lime–gypsum. Five samples of defined ternary system were cured at different temperatures 20, 30, 40, 50 and 60 °C. Conduction calorimeter TAM AIR was mainly used to capture heat evolution at different temperatures. Thermoanalytical (simultaneous TGA/DSC) and X-ray diffraction methods were used to identify different products after curing. It results that ettringite is the main hydration product supplemented by calcium silicate and calcium aluminosilicate hydrates according to sample composition. The mechanism and kinetics of hydration, as displayed by calorimetric curves, depend on composition of samples and curing temperatures. Two main types of processes have been elucidated: reaction of aluminum ions with sulfate ones in the presence of calcium ions in aqueous solution to form ettringite supplemented by pozzolanic activity leading to the formation of calcium silicate and calcium aluminosilicate hydrates. Concomitant condensation of alumina and silica species and carbonation have influenced the course of hydration. Activation energy E a depends slightly on composition of ternary system. 相似文献
145.
New types of combined chromophore-HAS (Hindered Amine Stabilizer) fluorescence probes were prepared and their photo-stability as well as their photo-stabilizing efficiency was tested in polypropylene film. The chromophore was benzothioxanthene and HAS was 2,2,6,6-tetramethylpiperidine. They were prepared by a one-step synthesis from benzothioxanthene-3,4-dicarboxylic anhydride (BTXA) by condensation with 4-amino-2,2,6,6-tetramethylpiperidine to obtain the probe in the form of parent amine (BTXI-NH) and 4-amino-1-oxy-2,2,6,6-tetramethylpiperidine in the case of stable nitroxyl radical form (BTXI-NO). Kinetics of BTXA photo-decomposition followed by UV spectroscopy were similar to kinetics of photo-decomposition for derivatives with covalently linked HAS i.e. BTXI-NH and BTXI-NO. It consists of two parts, slower in the beginning and very fast at the end of the process. Better stability of BTXI-NO in comparison with BTXI-NH can be explained by the presence of stable nitroxyl radical in its structure. The rate of decomposition of the fast part is similar for both additives. As soon as the decomposition starts there is no influence of NO or NH on this process. Times represented the start of the fast decomposition of probes correspond to the induction period of photo-oxidation of PP films. Possible effect of mutual interaction of chromophore and HAS coupled in one molecule (BTXI-NH or BTXI-NO) during photo-oxidation was followed by comparison with the course of photo-oxidation of PP film containing physical mixture of chromophore in the form of BTXA and HAS in the form of parent amine (4-hydroxy-2,2,6,6-tetramethylpiperidine) and stable nitroxyl radical (4-hydroxy-2,2,6,6-tetramethylpiperidin-N-oxyl). 相似文献
146.
Michal Svr
ek Pavol Baacký Anton Zajac 《International journal of quantum chemistry》1992,43(3):393-414
A systematic procedure has been developed to construct an electronic energy matrix for diatomics in the basis of antisymmetrized products of atomic wave functions represented as linear combinations of coupled momenta eigenfunctions. The exchange matrix element is expanded in powers of electronic interchange between atoms. General expressions of many-electron angular coefficients have been obtained for all types of products of one- and two-electron and overlap integrals in energy matrix elements. © 1992 John Wiley & Sons, Inc. 相似文献
147.
Pavol Farkašovský 《Czechoslovak Journal of Physics》1993,43(2):159-168
We present the exact solution of the simplified Hubbard model in which only one kind of electrons can hop and this quantum mechanical hopping of electrons is assumed to be unconstrained. It is shown that the model still behaves nontrivially, although it no longer depends on the lattice structure and the dimensionality of the system. For this case we find: (i) a gap in the ground state energy always exists at the half-filled band point (n=1), (ii) a preferred magnetic state atn=1 and largeU is a total spin singlet, (iii)U-dependence of the ground state energy has qualitatively the same form as one of the conventional Hubbard model with the (t
2/U)-behavior at largeU. A phase diagram of the model is discussed. 相似文献
148.
The hydrogenolysis of methyl 3,5-0-benzylidene-α- and -β-D-xylofuranoside derivatives with the LiAlH4-AlCl3 reagent gave 5-benzyl ethers as main products. In some cases the attack of the reagent occured at the ring oxygen of the furenoside skeleton to yield 5-0-benzyl-1-0-methylxylitol derivatives. The structure of the synthesized compounds was proved by 13C-NMR spectroscopy. Unambiguous assignment of lines in the 13C-NMR spectra of numerous partially methylated methyl α-and β-d-xylofuranoside derivatives has been made. 相似文献
149.
Reaction of phenylsulfonyl formamides, readily available in a single step from an aromatic aldehyde and sodium phenylsulfinate, with ketene diethyl acetal under basic conditions gives N-formyl β-amino acid esters in good yield, which can be kinetically resolved with a lipase. 相似文献
150.
Ján Labuda Pavol Tarapčík Adela Kotočová Jozef Šima 《Monatshefte für Chemie / Chemical Monthly》1992,123(8-9):693-699
Summary Half-wave potentials for a one-electron reduction of copper(II) complexes containing polydentate ligands can be calculated using the equationE
1/2=E
0(Cu2+/+)+
i
j
E
i where E
i are contributions related to the electronic and steric properties of the ligands. The values of 18 E
i contributions are presented and explained, and the effect of the solvents on the half-wave potentials is exemplified.Dedicated to Prof. Dr. Viktor Gutmann to his 70th birthday 相似文献