全文获取类型
收费全文 | 413篇 |
免费 | 4篇 |
国内免费 | 1篇 |
专业分类
化学 | 206篇 |
晶体学 | 12篇 |
力学 | 17篇 |
数学 | 103篇 |
物理学 | 80篇 |
出版年
2021年 | 1篇 |
2020年 | 4篇 |
2019年 | 9篇 |
2018年 | 12篇 |
2017年 | 14篇 |
2016年 | 18篇 |
2015年 | 15篇 |
2014年 | 15篇 |
2013年 | 39篇 |
2012年 | 23篇 |
2011年 | 35篇 |
2010年 | 30篇 |
2009年 | 19篇 |
2008年 | 19篇 |
2007年 | 21篇 |
2006年 | 16篇 |
2005年 | 13篇 |
2004年 | 13篇 |
2003年 | 9篇 |
2002年 | 10篇 |
2001年 | 2篇 |
2000年 | 5篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 5篇 |
1996年 | 5篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 5篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1985年 | 12篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1931年 | 1篇 |
排序方式: 共有418条查询结果,搜索用时 31 毫秒
71.
Stanis?aw Kowalak Aldona Jankowska Andrzej B. Wie¸ckowski 《Journal of solid state chemistry》2007,180(3):1119-1124
The colored (greenish) products analogous to ultramarine obtained from zeolite A, cancrinite and erionite by means of high-temperature (500-800 °C) treatment of zeolites mixed with elemental sulfur and alkalis can maintain the original structure of the parent zeolite under certain preparation conditions. The ESR spectra of samples recorded at room temperature always indicate the presence of radicals S3− (the blue chromophore). The spectra of samples prepared from zeolites recorded at 77 K exhibit additional signals that could be assigned to the yellow chromophore (the radical S2−) encapsulated inside the β or ε-cages. It is remarkable that in the case of products with preserved cancrinite structure, where the S2− radicals are encapsulated inside the ε-cages, the above signals are visible already at room temperature. It may result from retarded mobility of these species in small cancrinite cages. 相似文献
72.
Stanis?aw Lewanowicz 《Journal of Computational and Applied Mathematics》1997,80(2):351-358
Three equivalent forms of the fourth-order difference equation obeyed by the associated Meixner polynomials (with a nonnegative real association parameter) are derived from a refinement of a recent result due to Letessier et al. (1996). 相似文献
73.
Stanis?aw Le?niak Anna Chrostowska Dawid Kuc Saïd Khayar ?ukasz Urbaniak 《Tetrahedron》2009,65(51):10581-6916
The synthesis of [(E)-arylimino]-acetonitriles 3 has been described. It was found that the title compounds can be obtained on the three ways, namely by: (i) dehydrogenation of arylaminoacetonitriles 1, (ii) thermal fragmentation of 1-aryl-4-cyano-β-lactams 4 and (iii) retro-ene reaction of (allyl-p-methoxyphenyl-amino)-acetonitrile (7a) under FVT conditions. 1H and 13C NMR spectra of compounds 3, 5 and 6, and all their precursors 1 and 4, were recorded and analysed in detail using chemical shifts δH and δC [from GIAO DFT B3LYP/6-31(d) calculations] and J-couplings predicted at the DFT B3LYP/IGLO-II level. Also, UV-photoelectron spectra of 4a,d and 3a,d were measured and analysed considering the theoretical evaluation of their ionisation potentials. 相似文献
74.
Mariusz Trytek Jan Fiedurek Agnieszka Lipke Stanisław Radzki 《Journal of Sol-Gel Science and Technology》2009,51(3):272-286
Two types of porphyrins (water-soluble and water-insoluble) were encapsulated in transparent monolithic silica gels. Their
properties in solutions and at various steps of the sol–gel process were studied by absorption and emission electron spectroscopy.
A photocatalytic system containing porphyrins immobilized in powdered silica gel for α-pinene biomimetic oxidation to pinocarveol,
pinocarvone and myrtenol is reported. The impact of several parameters (visible light irradiation time, organic solvent, the
presence of an electron acceptor/donor, and substrate concentration) on this biotransformation process was investigated and
optimized. It was established that photochemical excitation of sol–gel immobilized metal-free porphyrins is crucial for catalyzed
oxidation of monoterpenes. 相似文献
75.
Magdalena A. ZaŁuska–Kotur Filip Krzyżewski StanisŁaw Krukowski 《Journal of Crystal Growth》2012,343(1):138-144
Step meandering during the growth of gallium nitride crystal is studied on using kinetic Monte Carlo method. Cause of instability is identified to be the particle advection caused by the step flow. Growth process is conducted in N-rich conditions and GaN(0001) surface kinetics is modeled by setting jump probabilities for Ga atoms adsorbed at the surface. We show that at low enough temperatures and relatively high external particle fluxes periodic regular pattern of meanders is created with its wavelength inversely proportional to the particle flux. An increase of the meander amplitude saturates after some period and further crystal grow is stationary, creating “finger-like” structure. For medium fluxes regular structure of meanders builds up for low or zero value of Schwoebel barrier. For higher fluxes wavelengths of meanders become shorter than the terrace width and they start to grow independently and finally transfer the surface to a rough structure. For very low fluxes or at relatively high temperatures steps move steadily remaining their initial shapes of straight, parallel lines. 相似文献
76.
The paper presents a method of modeling dynamics of multibody systems with open and closed kinematic chains. The joint coordinates
and homogeneous transformations are applied in order to formulate the equations of motion of a rigid body. In this method,
constraint equations are introduced only in the case when closed subchains are considered or when the joint reactions have
to be calculated. This allows the number of generalized coordinates in the system to be reduced in comparison to the case
when absolute coordinates are applied. It is shown how the method can be applied to modeling of vehicle dynamics. The calculation
results are compared with those obtained when the ADAMS/Car package is used. Experimental verification has been performed
and is reported in the paper, as well. In both cases, a good correspondence of results has been achieved. Final remarks concerning
advantages and disadvantages of the method are formulated at the end of the paper. 相似文献
77.
Andrzej Kaczyński Stanisław J. Matysiak 《Archive of Applied Mechanics (Ingenieur Archiv)》2010,80(3):271-283
The stress fields in an infinite elastic bimaterial layered system with an embedded rigid ribbon-like inclusion oriented in
the normal direction to the layering and subjected to a far-field uniform tension loading are obtained approximately within
the linear static elasticity with microlocal parameters. The solution method is based on the Fourier transform and dual integral
equations. The effects of geometrical and mechanical parameters of the composite structure on the stress singularities near
the inclusion tips are discussed and presented in graphical form. 相似文献
78.
Anna Kultys Stanisław Pikus 《Journal of polymer science. Part A, Polymer chemistry》2001,39(10):1733-1742
Three series of new thermoplastic, high molecular weight, segmented thiopolyurethanes were synthesized by a one-step melt polymerization from newly obtained thiodiols, including bis[4-(2-hydroxyethyl)thiomethylphenyl]methane, bis[4-(3-hydroxypropyl)thiomethylphenyl]methane, and bis[4-(6-hydroxyhexyl)thiomethylphenyl]methane (BHHM), as chain extenders; hexamethylene diisocyanate; and 20–80 mol % poly(oxytetramethylene) glycol (PTMG; number-average molecular weight = 1000) as the soft segment. Solution polymerization with the chain extender BHHM gave considerably lower molecular weight polymers. The structures of all the polyurethanes were determined with Fourier transform infrared and X-ray diffraction analysis. The thermal properties of the polyurethanes were examined with differential scanning calorimetry and thermogravimetric analysis. Shore A/D hardness and tensile properties were also determined. All the polyurethanes showed partially crystalline structures; those obtained with 40–80 mol % PTMG were elastomers. An increase in the PTMG content decreased hardness, modulus of elasticity, and tensile strength, whereas elongation at break increased. BHHM-based polyurethanes obtained in the melt showed the best tensile properties. The polyurethanes exhibited definite glass transitions (−70 to −59 °C) that were nearly independent of the hard-segment content up to about 50 wt % (40–80 mol % PTMG), indicating the existence of mainly microphase-separated soft and hard segments. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1733–1742, 2001 相似文献
79.
JPC – Journal of Planar Chromatography – Modern TLC - The lipophilicity of fifteen anticancer-active propargyl thioquinolines has been determined by reversed-phase thin-layer... 相似文献
80.
We propose an incomplete split plot design where levels of one factor (say A) are applied to the wholeplots and levels of the other (say B) to subplots, and where the number of subplots in each wholeplot may be less than the number of levels of factor B.The t levels of factor A are arranged in a completely randomized design. The s levels of factor B are arranged in a connected and proper incomplete block design within each level of factor A, by considering the wholeplots as blocks. 相似文献