全文获取类型
收费全文 | 802篇 |
免费 | 41篇 |
国内免费 | 4篇 |
专业分类
化学 | 529篇 |
晶体学 | 6篇 |
力学 | 38篇 |
数学 | 66篇 |
物理学 | 208篇 |
出版年
2024年 | 8篇 |
2023年 | 3篇 |
2022年 | 21篇 |
2021年 | 34篇 |
2020年 | 24篇 |
2019年 | 16篇 |
2018年 | 27篇 |
2017年 | 22篇 |
2016年 | 39篇 |
2015年 | 43篇 |
2014年 | 37篇 |
2013年 | 63篇 |
2012年 | 49篇 |
2011年 | 55篇 |
2010年 | 37篇 |
2009年 | 35篇 |
2008年 | 32篇 |
2007年 | 32篇 |
2006年 | 19篇 |
2005年 | 21篇 |
2004年 | 19篇 |
2003年 | 23篇 |
2002年 | 14篇 |
2001年 | 13篇 |
2000年 | 15篇 |
1998年 | 7篇 |
1996年 | 6篇 |
1995年 | 8篇 |
1994年 | 4篇 |
1993年 | 11篇 |
1992年 | 5篇 |
1991年 | 9篇 |
1990年 | 9篇 |
1989年 | 9篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 8篇 |
1976年 | 6篇 |
1975年 | 5篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1970年 | 3篇 |
1969年 | 2篇 |
排序方式: 共有847条查询结果,搜索用时 140 毫秒
781.
A.M. Ahmed S.A. Saleh E.M.M. Ibrahim E. Bontempi H.F. Mohamed 《Journal of magnetism and magnetic materials》2008
The effect of Na doping and annealing time on the structure, electrical properties, magnetoresistance and thermopower properties has been investigated in perovskite La1−xNaxMnOy (x=0.025, 0.075 and 0.1) systems. La1−xNaxMnOy crystallizes in a single-phase rhombohedral structure. It is observed a simultaneous occurrence of the ferromagnetic to paramagnetic state and metallic to insulating state. In the meanwhile, a large negative magnetoresistance with low applied magnetic field is observed. In addition, ρ(T) curves for Na-doped samples exhibit another broad transition Tms2 below Tms. Such double peak behavior in the ρ(T) curve interpreted by the electronic inhomogeneity in the samples. The sign of S changes from positive to negative depending on composition. The values of Seebeck coefficient are small (in the microvolt range). 相似文献
782.
Polycrystalline cadmium doped gallium selenide thin films were obtained by the thermal co‐evaporation of GaSe crystals and Cd grains onto glass substrates. The structural, compositional and optical properties of these films have been investigated by means of X‐ray diffraction, energy dispersive X‐ray analysis and UV‐visible spectroscopy techniques, respectively. Particularly, the elemental analysis, the crystalline nature, the energy band gap, the refractive index, the dispersion energy and static dielectric constant have been identified. The absorption coefficient spectral analysis in the sharp absorption region revealed a direct forbidden energy band gap of 1.22 eV. The cadmium doping has caused a significant decrease in the values of the energy band gap and in all the dispersive optical parameters, as well. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
783.
To elucidate the reasons underlying the poor penetration of non-viral vectors in tissues, relating transport properties to
physico-chemical parameters of vectors may be crucial. These properties can be influenced by the presence of multiples labels
that are used. Therefore utilizing a vector with minimum of labels preferably not more than one is important to studying penetration
in tissues. The cell impermeant bisintercalating dye YOYO-1 was found suitable to both monitor the formation of complexes
between DNA and an amphipathic peptide LK15 and, to track their penetration in HCT116 spheroids by confocal microscopy. The
results revealed a limited decrease of fluorescence ascribed to the high affinity of YOYO-1 to bind DNA. The residual fluorescence
of complexes can be exploited to monitor penetration into spheroids, after correction for YOYO-1 attenuation, and to revealing
hyaluronidase-induced reduced binding. Hence high affinity dyes such as YOYO-1 with inefficiently quenched fluorescence may
be important to establish a relation between novel medicines characteristics and penetration in tissues. 相似文献
784.
JPC – Journal of Planar Chromatography – Modern TLC - The discovery of new direct-acting antiviral drugs gave rise to a leap forward in the treatment of hepatitis C viral infections.... 相似文献
785.
Biaryl lactones were prepared by novel domino retro-Michael-aldol-lactonization reactions of 2,3-dihydropyrans. 相似文献
786.
S.A. Ahmed E.M.M. Ibrahim S.A. Saleh 《Applied Physics A: Materials Science & Processing》2006,85(2):177-184
Polycrystalline samples of Bi2Se3 and stoichiometric ternary compounds in the quasi-binary system SnSe-Bi2Se3 were characterized by measurements of temperature and field dependence of electrical conductivity. The current density–electric field characteristics were found to be non-linear, especially when the applied electric field exceeds a certain value which is dependent on the temperature T. Furthermore, the electrical conductivity can be enhanced by the applied electric field. The characteristic length a(T) seemed to be enhanced with increasing temperature. Electrical conductivity measurements elucidated the semiconducting behaviour of both compounds, especially when the temperature of measurement exceeds a certain value for SnBi4Se7, and hopping and band type conduction are dominant at low and high ranges of temperature, respectively. Below 200 K, the electrical conductivity of SnBi4Se7 decreases with increasing temperature. Meanwhile, additional scattering and hopping seemed to characterize the behaviour of SnBi4Se7 due to the Sn doping of Bi2Se3 resulting in additional states at the Fermi level. PACS 72.20.-i; 72.15.-v 相似文献
787.
The construction of a laser-based Raman scattering system for identifying major gas species and quantifying their partial pressures is described. The system incorporates a pulsed laser to minimize the background luminescence. The results obtained at room temperature for N2 at (365·80·5) nm and for O2 at (355·80·5) nm are presented. 相似文献
788.
Mitić N Saleh L Schenk G Bollinger JM Solomon EI 《Journal of the American Chemical Society》2003,125(37):11200-11201
To elucidate the electronic structure of intermediate X in the oxygen activation reaction of the R2 subunit of ribonucleotide reductase, a protocol has been developed to perform magnetic circular dichroism (MCD) on a rapid-freeze-quench, strain free optical sample. RFQ-MCD data have been collected on intermediate X in the double mutant of R2, Y122/Y356F. While X has been reported to exhibit a broad absorption band at 365 nm, there are at least 10 electronic transitions observed at low-temperature MCD. From C0/D0 ratios, the transitions of X can be divided into three regions: 16 000-22 000 cm-1 region involving spin-allowed ligand field transitions of the Fe(IV), 23 000-24 000 cm-1 region of spin-forbidden, spin-flip transitions on the Fe(IV), and the charge transfer (CT) region from 26 000 to 32 000 cm-1. The C0/D0 ratios from d --> d and CT transitions strongly support significant Fe(IV) character coupled into the paramagnetic center. Ligand field (spin-allowed d --> d region) analysis allows the bis-mu-oxo and mu-oxo plus other monoanionic bridge possibilities for the structure of intermediate X to be distinguished, providing new insight into the molecular mechanism of the cluster formation in R2. 相似文献
789.
I. I. Bondouk F. Machali Z. A. Saleh 《Zeitschrift für Physik A Hadrons and Nuclei》1970,236(2):170-175
The angular distributions of the polarization of protons from C12(d,p)C13(g.s) reaction were measured at 200 keV intervals for deuteron energies from 1.40 to 2.40 MeV. Elastic scattering on C12 at 45 ° (lab) was used to analyze the polarization. Positive sign of the polarization corresponds to the vector productK d ×K p . The maximum polarization observed is about 30%. The results are not similar to those obtained from the mirror reaction C12(d,n)N13 in the same deuteron energy range. 相似文献
790.