全文获取类型
收费全文 | 216篇 |
免费 | 9篇 |
国内免费 | 1篇 |
专业分类
化学 | 130篇 |
晶体学 | 4篇 |
力学 | 21篇 |
数学 | 48篇 |
物理学 | 23篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 8篇 |
2021年 | 13篇 |
2020年 | 10篇 |
2019年 | 10篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 8篇 |
2015年 | 6篇 |
2014年 | 10篇 |
2013年 | 20篇 |
2012年 | 10篇 |
2011年 | 20篇 |
2010年 | 13篇 |
2009年 | 16篇 |
2008年 | 6篇 |
2007年 | 10篇 |
2006年 | 5篇 |
2005年 | 11篇 |
2004年 | 7篇 |
2003年 | 8篇 |
2002年 | 4篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1996年 | 1篇 |
1991年 | 1篇 |
1986年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1973年 | 1篇 |
1910年 | 2篇 |
1907年 | 1篇 |
排序方式: 共有226条查询结果,搜索用时 31 毫秒
91.
The unsteady flow of an incompressible fractional Maxwell fluid between two infinite coaxial cylinders is studied by means of integral transforms.The motion of the fluid is due to the inner cylinder that applies a time dependent torsional shear to the fluid.The exact solutions for velocity and shear stress are presented in series form in terms of some generalized functions.They can easily be particularized to give similar solutions for Maxwell and Newtonian fluids.Finally,the influence of pertinent parameters on the fluid motion,as well as a comparison between models,is highlighted by graphical illustrations. 相似文献
92.
Corina Fetecau Muhammad Jamil Constantin Fetecau Dumitru Vieru 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2009,60(5):921-933
The velocity field corresponding to the Rayleigh–Stokes problem for an edge, in an incompressible generalized Oldroyd-B fluid
has been established by means of the double Fourier sine and Laplace transforms. The fractional calculus approach is used
in the constitutive relationship of the fluid model. The obtained solution, written in terms of the generalized G-functions, is presented as a sum of the Newtonian solution and the corresponding non-Newtonian contribution. The solution
for generalized Maxwell fluids, as well as those for ordinary Maxwell and Oldroyd-B fluids, performing the same motion, is
obtained as a limiting case of the present solution. This solution can be also specialized to give the similar solution for
generalized second grade fluids. However, for simplicity, a new and simpler exact solution is established for these fluids.
For β → 1, this last solution reduces to a previous solution obtained by a different technique.
相似文献
93.
The propagation of a heat wave in an incompressible second grade fluid within the context of a potential vortex is studied. The solutions for the Newtonian fluid can be obtained from those for fluids of second grade as a limiting case. 相似文献
94.
Lupu C Downie C Guloy AM Albright TA Mao JG 《Journal of the American Chemical Society》2004,126(13):4386-4397
A new lithium silver stannide, Li17Ag3Sn6, was synthesized from high-temperature reactions of the pure elements in tantalum containers. Its crystal structure, in the space group, P31m, with a = 8.063(3) A, c = 8.509(4) A, Z = 1, features two distinct AgSn-based anionic layers. Defect graphitic layers of Ag2Sn3, with ordered vacancies at one-third of the Ag sites, are alternately stacked with Kagome-like nets of isolated trigonal planar AgSn3 units. Double layers of Li ions are sandwiched between the stacked AgSn-based layers. Theoretical calculations show unusual pi-interactions within both anionic layers, with the trigonal planar [AgSn3]11- units being isoelectronic with CO(3)2-. In addition, the chemical bonding of the layered [Ag2Sn3]6- pi-network features incompletely filled lone-pair Sn states involved in in-plane trefoil aromatic interactions. Transport and magnetic susceptibility measurements on Li17Ag3Sn6 indicate excellent metallic behavior and temperature-independent paramagnetism consistent with results from band structure calculations. The "trefoil" aromaticity, previously postulated for aromatic molecular systems, is finally observed, albeit in a polar intermetallic solid-state structure that lies at the border between metals and nonmetals. 相似文献
95.
Maria-Alexandra Hoaghia Oana Cadar Gheorghe-Gavrila Hognogi Erika Levei Corina Moisa Cecilia Roman 《Analytical letters》2019,52(8):1268-1281
The quality and potential health risk of drinking waters in Medias, a town near a former non-ferrous ore smelter in Romania, was assessed using the drinking water quality index (DWQI), hazard quotient (HQ) and total hazard quotient (THQ). A total of 29 water samples collected from 26 wells and 3 springs used as drinking water sources, located in near proximity to agricultural, industrial or household contamination sources, were characterized. The obtained results indicated high NO2?, NO3?, Cd and Mn levels that exceeded the corresponding maximum allowable concentrations. According to the DWQI values, only 10% of water sources have acceptable quality, while 21% are threatened, and 69% have poor- quality. The health risk assessment suggested a high risk for NO3? for more than 72% of the drinking waters HQNO3??>?1.0 but no risk for metals and NO2? (HQmetals< 1.0; HQNO2?< 1.0). 相似文献
96.
Sabine Dreer Peter Wilhartitz Bernhard Sartory Richard Tessadri Kurt Piplits Karl Emanuel Mayerhofer 《Mikrochimica acta》2006,155(1-2):125-128
Low amounts of oxygen in AlCrN hard coatings have been quantitatively analysed by means of WDS–EPMA. By combination with SIMS
depth profiling, applying a calibration sample produced by ion implantation, the accuracy of the EPMA results was proven.
Values as low as 0.07 at% were measured and the calculated detection limit is in the range of 0.01 at%. 相似文献
97.
Electrochemical and spectroelectrochemical properties of five cobalt(III) acetate complexes [CoIII3(mu3-O)(CH3CO2)5(OR)(py)3][PF6] are described, where py=pyridine and R=OCCH3 (A), H (B), CH3 (C), CH2CH=CH2 (D), and CH2C6H5 (E). Each is reduced irreversibly as observed by cyclic voltammetry at room temperature and at -40 degrees C in acetonitrile at scan rates up to 20 V s(-1), but oxidized reversibly to a mixed-valence Co(III)2Co(IV) species at approximately 1.23 V vs the ferrocenium/ferrocene couple. Controlled potential coulometry confirmed a one-electron-oxidation process. Spectroelectrochemical oxidation of A at 5 degrees C showed isosbestic points in the electronic absorption spectrum that showed the oxidized complex to be stable in solution for at least 1 h. 相似文献
98.
A chemical analysis and detailed structural characterization, using X-ray single crystal and neutron powder diffraction, of the binary lithium-tin compound "Li(4.4)Sn" is presented. Phase analyses and subsequent structural refinements result in the reformulation of "Li(4.4)Sn" as Li(17)Sn(4). The lithium-rich binary phase crystallizes with a complex cubic structure in the space group Ffourmacr;3m, with a = 19.6907(11) A, Z = 20. The improved crystal structure determination indicates well-defined lithium atom positions, some of which differ from those previously reported. The nearly Zintl phase Li(17)Sn(4) exhibits poor metallic behavior similar to that of heavily doped semiconductors. Comparisons of the refined crystal structure with previously reported X-ray crystal structures associated with "Li(4.4)Sn" are discussed. 相似文献
99.
Cristofor I. Simionescu Virgil BÎrboiu Bogdan C. Simionescu Viorica Talmaciu Corina Sava 《Journal of polymer science. Part A, Polymer chemistry》1986,24(5):851-860
Bulk radical copolymerization of methyl acrylate (MeA, M1) with styrene (St, M2) in presence and absence of ZnCl2 as complexing agent was studied. 1H-NMR spectra were used to establish copolymer composition and sequence distribution. The methoxy group signal was observed to be split due to pentads, but the analysis of sequence distribution is possible only at triad level. Both composition and sequence distribution data confirmed that bulk radical copolymerization respects quite well the terminal addition model; the values of r1 = 0.14 ± 0.02 (from composition data) and r1 = 0.25 ± 0.03 (from sequence distribution data) and r2 = 0.83 ± 0.10 (from composition data) were found. The presence of ZnCl2 increases the probability of alternating addition, e.g., for [ZnCl2]/[MeA] = 0.2, r1 = 0.03 ± 0.02 and r2 = 0.17 ± 0.03. The radical copolymer obtained in bulk in the absence of ZnCl2 presents a coisotactic configuration with σ = 0.75 ± 0.03, but the presence of the complexing agent reduces the probability of coisotactic addition, e.g., for [ZnCl2]/[MeA] = 0.2, σ = 0.52 ± 0.03. 相似文献
100.
D. Vieru Corina Fetecău C. Fetecău 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2008,59(5):834-847
The unsteady flow of an Oldroyd-B fluid due to an infinite flat plate, subject to a translation motion of linear time-dependent
velocity in its plane, is studied by means of the Laplace transform. The velocity field and the associated tangential stress
corresponding to the flow induced by the constantly accelerating plate as well as those produced by the impulsive motion of
the plate are obtained as special cases. The solutions that have been determined, in all accordance with the solutions established
using the Fourier transform, reduce to those for a Newtonian fluid as a limiting case. The similar solutions for a Maxwell
fluid are also obtained. 相似文献