全文获取类型
收费全文 | 174篇 |
免费 | 9篇 |
专业分类
化学 | 91篇 |
力学 | 4篇 |
数学 | 27篇 |
物理学 | 61篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 3篇 |
2020年 | 1篇 |
2019年 | 7篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 11篇 |
2015年 | 5篇 |
2014年 | 4篇 |
2013年 | 9篇 |
2012年 | 12篇 |
2011年 | 12篇 |
2010年 | 11篇 |
2009年 | 12篇 |
2008年 | 8篇 |
2007年 | 7篇 |
2006年 | 8篇 |
2005年 | 5篇 |
2004年 | 5篇 |
2003年 | 2篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1994年 | 1篇 |
1993年 | 7篇 |
1992年 | 1篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 6篇 |
1979年 | 1篇 |
1974年 | 2篇 |
排序方式: 共有183条查询结果,搜索用时 62 毫秒
121.
Joaquín Barrera Alfonso Carriazo Luis M. Fernández Alicia Prieto-Martín 《Annali di Matematica Pura ed Applicata》2012,191(4):803-818
We present a characterization theorem for the Maslov form in certain non-invariant slant submanifolds of S-space-forms to be closed and, from it, we deduce a topological obstruction for these types of non-invariant slant immersions. Moreover, we also give conditions for an anti-invariant submanifolds of an S-manifold, tangent to the structure vector fields, to have closed and conformal Maslov form. 相似文献
122.
José Pablo Arias‐Nicolás Félix Belzunce Olga Núñez‐Barrera Alfonso Suárez‐Llorens 《商业与工业应用随机模型》2009,25(3):339-358
In this paper we present a definition of multivariate increasing failure rate based on the concept of multivariate dispersion. This new definition is an extension of the univariate characterization of increasing failure rate distributions under dispersive ordering of the residual lives. We study this definition in the Clayton–Oakes model and the family of generalized order statistics. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
123.
Exequiel E. Barrera Guisasola Marcelo F. Masman Ricardo D. Enriz Ana M. Rodríguez 《Central European Journal of Chemistry》2010,8(3):566-575
The potential energy surface (PES) of tyrosyl-glycyl-glycine (YGG) tripeptide in solution was explored using EDMC (Electrostatically
Driven Monte Carlo) and in the gas-phase by means of ab initio quantum chemical calculations. The theoretical computational
analysis revealed that this tripeptide possesses a significant molecular flexibility. A C7 backbone conformation was the most energetically preferred for the central Gly residue, using both methodologies. Some new
stable conformers that have not been previously reported were identified in the gas phase as well. This study points out the
interplay of backbone and side-chain contributions in determining the relative stabilities of energy minima. In addition,
the peptide backbone of YGG was compared with other small peptides containing aromatic side-chains (Phe-Gly-Gly and Trp-Gly-Gly).
The comparison with experimental X-ray results was also satisfactory.
相似文献
124.
Wang SC Politis A Di Bartolo N Bavro VN Tucker SJ Booth PJ Barrera NP Robinson CV 《Journal of the American Chemical Society》2010,132(44):15468-15470
Here we examined the gas-phase structures of two tetrameric membrane protein complexes by ion mobility mass spectrometry. The collision cross sections measured for the ion channel are in accord with a compact configuration of subunits, suggesting that the native-like structure can be preserved under the harsh activation conditions required to release it from the detergent micelle into the gas phase. We also found that the quaternary structure of the transporter, which has fewer transmembrane subunits than the ion channel, is less stable once stripped of detergents and bulk water. These results highlight the potential of ion mobility mass spectrometry for characterizing the overall topologies of membrane protein complexes and the structural changes associated with nucleotide, lipid, and drug binding. 相似文献
125.
We introduce the technique to get the undercover multiplexing of a set of encrypted data. We base the general encryption approach on the double-random phase encoding method. We made the encoding phase masks with scaled versions of a master speckle pattern. A fake object is encrypted using a master mask made with the master speckle pattern. Each subsequent object to be hidden is associated to a suitable different scaled version of the original master mask. We apply the term suitable referring to avoid a possible cross-talk in the final decrypted images. All encrypted data are multiplexed to form a single message. This operation enables the true information undercover. We openly send this undercover message along with the master mask. Via separated private channels, we send the information on the actual scaling for each encrypting mask to the authorized users. Unauthorized users attempting to recover the information by using the master mask alone, get the fake object. During decryption of the multiplexed message, we only reconstruct the object that matches the predetermined scaled version of the master mask used to encode it. We show results that confirm our approach. 相似文献
126.
Andrs E. Ciolino Griselda Barrera Galland María Lujn Ferreira Marcelo A. Villar 《Journal of polymer science. Part A, Polymer chemistry》2004,42(10):2462-2473
Polyethylene–poly(dimethylsiloxane) copolymers were synthesized in solution from an ethylene monomer and an ω‐vinyl poly(dimethylsiloxane) (PDMS) macromonomer at 363 and 383 K with EtInd2ZrCl2/methylaluminoxane as a catalyst. The copolymers obtained were characterized with Fourier transform infrared spectroscopy, 1H and 13C NMR, size exclusion chromatography, and differential scanning calorimetry. The rheological properties of the molten polymers were determined under dynamic shear flow tests at small‐amplitude oscillations, whereas the physical arrangement of the phase domains was analyzed with scanning electron microscopy (SEM)/energy dispersive X‐ray (EDX). The analysis of the catalyst activity and the resulting polymers supported the idea of PDMS blocks or chains grafted to polyethylene. The changes in the rheological behavior and the changes in the Fourier transform infrared and NMR spectra were in agreement with this proposal. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2462–2473, 2004 相似文献
127.
Teresa Velilla Katherine Delgado Raúl Quijada Daniela Bianchini Griselda Barrera Galland João Henrique Z. Dos Santos Diana P. Fasce Roberto J. J. Williams 《Journal of polymer science. Part A, Polymer chemistry》2007,45(23):5480-5486
We report the synthesis of a supported metallocene catalyst that exhibits the same activity as a homogeneous catalyst for ethylene polymerization reactions. The key to this new catalytic system is a hybrid organic–inorganic polymer obtained by the cocondensation of an organotrialkoxysilane (OTAS; 40 mol %) with tetraethoxysilane (TEOS; 60 mol %). The particular organic group of OTAS enabled us to avoid gelation when the hydrolytic condensation was performed with a thermal cycle attaining 150 °C. The resulting product [soluble functionalized silica (SFS)] was a glass at room temperature that was soluble in several organic solvents such as tetrahydrofuran and toluene. The 29Si NMR spectrum of SFS showed that the OTAS units were fully condensed (T3 species), whereas the TEOS units were mainly present as tricondensed (Q3) and tetracondensed (Q4) units. SFS was grafted onto activated silica through a reaction of silanol groups. The metallocene [(nBuCp)2ZrCl2] was covalently bonded to the SFS‐modified support. The polymerization of ethylene was carried out in toluene in the presence of methylaluminoxane. The activity of the supported catalyst was similar to that of the metallocene catalyst in solution. The simplest explanation accounting for this fact is that most of the metallocene was grafted to SFS species issuing from the surface of the support through a reaction with their silanol groups. This improved the accessibility of the monomer to the reaction sites. Specific interactions of the metallocene species with neighboring organic branches of SFS might also affect the catalytic activity. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5480–5486, 2007 相似文献
128.
Marco Antnio da Silva Griselda Barrera Galland 《Journal of polymer science. Part A, Polymer chemistry》2008,46(3):947-957
Ethylene (E), propylene (P), and 1‐pentene (A) terpolymers differing in monomer composition ratio were produced, using the metallocenes rac‐ethylene bis(indenyl) zirconium dichloride/methylaluminoxane (rac‐Et(Ind)2ZrCl2/MAO), isopropyl bis(cyclopentadienyl)fluorenyl zirconium dichloride/methylaluminoxane (Me2C(Cp)(Flu)ZrCl2/MAO, and bis(cyclopentadienyl)zirconium dichloride, supported on silica impregnated with MAO (Cp2ZrCl2/MAO/SiO2/MAO) as catalytic systems. The catalytic activities at 25 °C and normal pressure were compared. The best result was obtained with the first catalyst. A detailed study of 13C NMR chemical shifts, triad sequences distributions, monomer‐average sequence lengths, and reactivity ratios for the terpolymers is presented. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 947–957, 2008 相似文献
129.
Jean-Claude Auger Brian Stout Rub n G. Barrera Fernando Curiel 《Journal of Quantitative Spectroscopy & Radiative Transfer》2001,70(4-6):675-695
We study the optical properties of opaque polymer pigmented coatings. The system consists of spherical rutile particles encapsulated in spherical microvoids embedded in a transparent polymer resin. The single-scattering properties of this system have been analyzed already, in case the rutile particle is located at the center of the microvoid . Here, we use a T-matrix approach to generalize and extend this analysis to the more realistic case when the rutile particles is located off-center within the microvoid. We also consider the multiple-scattering effects of a cluster composed by a collection of air bubbles with off-center rutile inclusions. Our calculations take into account the multiple scattering and the dependent-scattering processes of each pigment particle of the aggregate, using a new recursive T-matrix algorithm. 相似文献
130.