全文获取类型
收费全文 | 588篇 |
免费 | 8篇 |
专业分类
化学 | 333篇 |
晶体学 | 9篇 |
力学 | 49篇 |
数学 | 75篇 |
物理学 | 130篇 |
出版年
2022年 | 3篇 |
2021年 | 7篇 |
2020年 | 10篇 |
2019年 | 5篇 |
2018年 | 15篇 |
2017年 | 16篇 |
2016年 | 18篇 |
2015年 | 11篇 |
2014年 | 17篇 |
2013年 | 26篇 |
2012年 | 13篇 |
2011年 | 18篇 |
2010年 | 18篇 |
2009年 | 22篇 |
2008年 | 23篇 |
2007年 | 17篇 |
2006年 | 24篇 |
2005年 | 21篇 |
2004年 | 23篇 |
2003年 | 15篇 |
2002年 | 12篇 |
2001年 | 16篇 |
2000年 | 17篇 |
1999年 | 10篇 |
1998年 | 20篇 |
1997年 | 18篇 |
1996年 | 19篇 |
1995年 | 15篇 |
1993年 | 7篇 |
1992年 | 4篇 |
1991年 | 15篇 |
1990年 | 3篇 |
1989年 | 9篇 |
1988年 | 10篇 |
1987年 | 7篇 |
1986年 | 10篇 |
1985年 | 6篇 |
1984年 | 11篇 |
1983年 | 3篇 |
1982年 | 9篇 |
1981年 | 5篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1973年 | 3篇 |
1972年 | 4篇 |
1971年 | 4篇 |
1968年 | 2篇 |
排序方式: 共有596条查询结果,搜索用时 305 毫秒
591.
A complete asymptotic expansion of the solution to an initial value problem for a singularly perturbed hyperbolic system of equations in several spatial variables is constructed and justified. A specific feature of the problem is that its solution has a spike zone in a neighborhood of which the asymptotics is described by a parabolic equation. 相似文献
592.
The local length-dependence of the natural frequencies and forms of plane transverse oscillations of a thin inhomogeneous rod in an elastic medium with a variable stiffness and arbitrary elastic-fastening boundary conditions is investigated. It is established that the presence of an external elastic medium, described by the Winkler model, can lead to an anomalous effect – an increase in the natural frequencies of lower oscillation modes as the length of the rod increases continuously. The extremely fine properties of this change as a function of the length, the mode number and the method of fastening are revealed. The oscillations in the case of standard methods of fastening are investigated separately. Simple examples, which illustrate the anomalous dependence of the natural oscillation frequencies of the rod in an extremely inhomogeneous elastic medium with different boundary conditions are calculated. 相似文献
593.
DS Nesterov EN Chygorin VN Kokozay VV Bon R Boča YN Kozlov LS Shul'pina J Jezierska A Ozarowski AJ Pombeiro GB Shul'pin 《Inorganic chemistry》2012,51(16):9110-9122
The heterometallic complex [Co(4)Fe(2)OSae(8)]·4DMF·H(2)O (1) was synthesized by one-pot reaction of cobalt powder with iron chloride in a dimethylformamide solution of salicylidene-2-ethanolamine (H(2)Sae) and characterized by single crystal X-ray diffraction analysis, magnetic measurements, high frequency electron paramagnetic resonance (HF-EPR), and M?ssbauer spectroscopies. The exchange coupling in the Fe(III)-Fe(III) pair is of antiferromagnetic behavior with J/hc = -190 cm(-1). The HF-EPR spectra reveal an unusual pattern with a hardly detectable triplet signal of the Fe(III) dimer. The magnitude of D (ca. 13.9 cm(-1)) was found to be much larger than in related dimers. The catalytic investigations disclosed an outstanding activity of 1 toward oxidation of cycloalkanes with hydrogen peroxide, under mild conditions. The most efficient system showed a turnover number (TON) of 3.57 × 10(3) with the concomitant overall yield of 26% for cyclohexane, and 2.28 × 10(3)/46%, respectively, for cyclooctane. A remarkable turnover frequency (TOF) of 1.12 × 10(4) h(-1) (the highest initial rate W(0) = 3.5 × 10(-4) M s(-1)) was achieved in oxidation of cyclohexane. Kinetic experiments and selectivity parameters led to the conclusion that hydroxyl radicals are active (attacking C-H bonds) species. Kinetic and electrospray ionization mass spectrometry (ESI-MS) data allowed us to assume that the trinuclear heterometallic particle [Co(2)Fe(Sae)(4)](+), originated from 1 in solution, could be responsible for efficient generation of hydroxyl radicals from hydrogen peroxide. 相似文献
594.
Nesterov DS Kokozay VN Dyakonenko VV Shishkin OV Jezierska J Ozarowski A Kirillov AM Kopylovich MN Pombeiro AJ 《Chemical communications (Cambridge, England)》2006,(44):4605-4607
An unprecedented hexanuclear heterotrimetallic Fe/Cu/Co complex bearing two Cu(mu-O)2Co(mu-O)2Fe cores is easily prepared by self-assembly and acts as a remarkable catalyst for the peroxidative oxidation of cycloalkanes under mild conditions. 相似文献
595.
Using the HF, B3LYP, and MP2 methods in the 6−31+G(d) basis with zero-point energy corrections, quantum chemical calculations
of energy characteristics were carried out for the model molecules CH2=XH+ (X = NH, O, S, Se) formed from the molecules YCH2XH (Y = NH2, OH, SH, SeH, Cl) either through the elimination of Y-anions or as a result of the abstraction of neutral species YH from
these molecules upon their interaction with a proton. Stabilities of the onium states of nitrogen atom were shown to be considerably
higher than those of the onium states of chalcogen derivatives, with the lowest stability shown by the models with the Cl
atom being in the onium state. The results have been formulated in the form of stability series of the onium compounds and
allowed one to interpret certain features of the aminomethylation reaction (the Mannich reaction), hydroxy- and alkoxymethylation,
thio- and selenomethylation, and chloromethylation (the Blanc reaction). 相似文献
596.
Anatolij M. Shestopalov Olga P. Bogomolova Ludmila A. Rodinovskaja Victor P. Litvinov Bogdan Bujnicki Marian Mikolajczyk Vladimir N. Nesterov Yurij T. Struchkov 《Heteroatom Chemistry》1993,4(6):593-602
A series of 2-oxo-4-pyridyl-3-(1-pyridinio)-5-cyano-3,4-trans-1,2,3,4-tetrahydropyridine-6-6-olates were prepared by condensation of pyridinium ylides with α,β-unsaturated carbonyl compounds or more conveniently by a three-component condensation of pyridinium ylides, pyridine aldehydes, and ethyl cyanoacetate 3 and/or 6 . This analogues of the above tetrahydropyridines were prepared in a similar way starting from suitable substrates. Spectroscopic data revealed that the reaction leads to trans-isomers around the C3-C4 bond and is atroposelective. The conformation of and tautomerism in the tetrahydropyridines are discussed in the light of 1H NMR data. The reaction of 5-cyano-3-(3-methyl-1-pyridinio)-2-oxo-4-(3-pyridyl)-1,2,3,4-tetrahydropyridine-6-thiolate 10c with phenacyl bromide was found to give 3-hydroxy-5-oxo-7-(3-pyridyl)-6-(3-methyl-1-pyridinio)-3-phenyl-8-cyano-6,7-trans-2,3,6,7-tetrahydrothiazol[3,2a]pyridine bromide, the crystal and molecular structure of which has been determined by X-ray crystallographic analysis. 相似文献