全文获取类型
收费全文 | 109篇 |
免费 | 4篇 |
国内免费 | 4篇 |
专业分类
化学 | 57篇 |
力学 | 5篇 |
数学 | 33篇 |
物理学 | 22篇 |
出版年
2022年 | 2篇 |
2021年 | 1篇 |
2020年 | 5篇 |
2019年 | 2篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 6篇 |
2015年 | 5篇 |
2014年 | 7篇 |
2013年 | 10篇 |
2012年 | 11篇 |
2011年 | 6篇 |
2010年 | 4篇 |
2009年 | 7篇 |
2008年 | 8篇 |
2007年 | 5篇 |
2006年 | 4篇 |
2005年 | 8篇 |
2004年 | 4篇 |
2003年 | 2篇 |
2002年 | 4篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有117条查询结果,搜索用时 171 毫秒
11.
Hormonal treatments which have an androgenic effect have the potential to cause vocal changes. The changes in vocal fold structure and voice quality are considered to be irreversible. To date, studies have documented subjective vocal changes or documented single cases without detailed, baseline voice assessments. The impact on laryngeal function of women taking these androgenic treatments requires further detailed, objective assessment. The need for increased awareness of the actions of androgenic hormones on womns' voices, and the benefits of a thorough voice assessment are discussed. 相似文献
12.
Numerical guided mode solutions of arbitrary cross sectional shaped waveguides are obtained using a finite difference (FD) technique. The standard FD scheme is appropriately modified to capture all discontinuities, due to the change of the refractive index, across the waveguides’ interfaces taking into account the shape of each interface at the same time. The method is applied to the vector Helmholtz equation formulated to describe the electric or magnetic fields in the waveguide (one field is retrieved from the other through Maxwell’s equations). Computational cost is kept to a minimum by exploiting sparse matrix algebra. The waveguides under study have arbitrary cross sectional shape and arbitrary refractive index profile. 相似文献
13.
14.
15.
Theodoros Vlachos 《manuscripta mathematica》2008,126(2):201-230
We deal with minimal surfaces in a sphere and investigate certain invariants of geometric significance, the Hopf differentials,
which are defined in terms of the complex structure and the higher fundamental forms. We discuss the holomorphicity of Hopf
differentials and provide a geometric interpretation for it in terms of the higher curvature ellipses. This motivates the
study of a class of minimal surfaces, which we call exceptional. We show that exceptional minimal surfaces are related to
Lawson’s conjecture regarding the Ricci condition. Indeed, we prove that, under certain conditions, compact minimal surfaces
in spheres which satisfy the Ricci condition are exceptional. Thus, under these conditions, the proof of Lawson’s conjecture
is reduced to its confirmation for exceptional minimal surfaces. In fact, we provide an affirmative answer to Lawson’s conjecture
for exceptional minimal surfaces in odd dimensional spheres or in S
4m
. 相似文献
16.
Schmarr HG Potouridis T Ganss S Sang W Köpp B Bokuz U Fischer U 《Analytica chimica acta》2008,617(1-2):119-131
An improved method for the analysis of carbonyls is described utilizing a headspace solid-phase microextraction (HS-SPME) step and on-fiber derivatization with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) hydrochloride. Thermal desorption of the oxime derivatives formed on the fiber is followed by gas chromatographic separation coupled to an ion trap tandem mass spectrometer (GC-ITMS). Selecting specific fragment ions within the electron ionization (EI(+)) mass spectra of these oxime derivatives as precursor ions for MS-MS fragmentation provides a suitable method for the target analysis of individual carbonyl classes, such as alkanals, (E)-2-alkenals, (E,E)-2,4-alkadienals, and others. Retention indices on polar as well as on apolar stationary phases along with EI(+) mass spectra patterns are presented for a large set of oxime derivatives, giving valuable information needed for unambiguous assignment of substances in complex sample matrices. The fast sample preparation and derivatization step via HS-SPME can be automated and is applicable to a variety of biological samples and foodstuffs, allowing rapid and sensitive screening analyses of important aldehydic biomarkers and aroma active compounds. 相似文献
17.
A finite-difference approach based upon the immersed interface method is used to analyze the mode structure of Bragg fibers with arbitrary index profiles. The method allows general propagation constants and eigenmodes to be calculated to a high degree of accuracy, while computation times are kept to a minimum by exploiting sparse matrix algebra. The method is well suited to handle complicated structures comprised of a large number of thin layers with high-index contrast and simultaneously determines multiple eigenmodes without modification. 相似文献
18.
Alexandros Dimitriadis Nikolaos Kantartzis Theodoros Tsiboukis 《Applied Physics A: Materials Science & Processing》2012,109(4):1065-1070
An enhanced metamaterial absorber based on the circumscribed-cross resonator is introduced in this paper. The new structure is polarization-independent, due to the symmetry of its unit cell, and is proven efficient for the attenuation of obliquely incident waves. The absorption mechanism is thoroughly investigated and is found to be mainly related to the losses of the dielectric substrate. Furthermore, by exploiting the scalability property of metamaterials, the operational bandwidth of our design can be drastically improved by placing unit cells with properly scaled resonators adjacent to each other. In this context, various combinations of three, four, and nine unit cells that can increase the full width at half maximum up to as much as 11.18?%, are developed. The overall performance of the proposed configurations is deemed promising for the realization of microwave metamaterial absorbers for several practical applications. 相似文献
19.
We present results concerning the dynamical behavior of a Ni3+ adsorbate on a NiO(0 0 1) surface obtained by molecular dynamics simulations. In a first place, we examined at low temperature the position of the Ni3+ ion as an adatom on the surface and the corresponding modification of its local environment as reflected on the pair-wise radial distribution function. The calculation of the vibrational properties of the adatom by means of the phonon local density of states (LDOS) shows that there is an anisotropic behavior both in the two principal in-plane directions as well as in the direction normal to the surface in accordance with the structural results. We compare the phonon LDOS of the Ni3+ adatom with the corresponding results for the Ni2+ adatom and the Ni2+ surface cations.Static energetic calculations are indicative that the exchange of the Ni3+ ion with a surface Ni2+ ion could be favorable. Such a behavior is confirmed by results observed at temperatures higher than 700 K where the Ni3+ adsorbate is located on a substitutional position on the surface and not on adatom position. The exchange takes place through simple or double exchange mechanisms. The structural and dynamical behavior of the Ni3+ ion at the substitution position was investigated in the temperature range 700-2000 K through the calculation of the pair distribution function, the relaxed interlayer relative position (RIRP), mean-square displacements (MSDs) and phonon LDOS. Results show that in comparison with the Ni2+ surface ions the Ni3+ ion at substitution position is more tightly bound especially in the direction normal to the surface as is indicated by the local structure and the contraction it presents as well as its phonon LDOS. As temperature increases the binding of the Ni3+ ion becomes less important as reflected on the physical properties mentioned above. 相似文献
20.
Theodoros F. Zafiropoulos Spyros P. Perlepes John Plakatouras 《Monatshefte für Chemie / Chemical Monthly》1989,120(4):357-361
Summary The reaction between cobalt(II) nitrate and 1-methylbenzotriazole (MeBTA) leads to a complex with unusual magnetochemical and ligand field characteristics. The synthesis and the physical and spectroscopic properties of the pseudo-octahedral complex [Co(MeBTA)2(NO3)2] are described.
Bis(1-methylbenzotriazol)dinitratocobalt(II): Ein pseudo-octaedrischer Komplex mit pseudotetraedrischen magnetochemischen und Ligandenfeld-Charakteristika (Kurze Mitt.)
Zusammenfassung Die Reaktion zwischen Kobalt(II)nitrat und 1-Methylbenzotriazol (MeBTA) führt zu einem Komplex mit ungewöhnlichen magnetochemischen und Ligandenfeld-Eigenschaften. Die Synthese und die spektroskopischen Eigenschaften des pseudo-octaedrischen Komplexes [Co(MeBTA)2(NO3)2] werden beschrieben.相似文献