全文获取类型
收费全文 | 161篇 |
免费 | 3篇 |
国内免费 | 4篇 |
专业分类
化学 | 112篇 |
力学 | 10篇 |
数学 | 33篇 |
物理学 | 13篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 4篇 |
2020年 | 1篇 |
2018年 | 1篇 |
2017年 | 6篇 |
2016年 | 6篇 |
2014年 | 2篇 |
2013年 | 7篇 |
2012年 | 10篇 |
2011年 | 9篇 |
2010年 | 7篇 |
2009年 | 16篇 |
2008年 | 18篇 |
2007年 | 9篇 |
2006年 | 10篇 |
2005年 | 5篇 |
2004年 | 4篇 |
2003年 | 8篇 |
2002年 | 8篇 |
2001年 | 8篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有168条查询结果,搜索用时 31 毫秒
91.
Katerina D. Papoulia Vassilis P. Panoskaltsis Nishu V. Kurup Igor Korovajchuk 《Rheologica Acta》2010,49(4):381-400
We develop rheological representations, i.e., discrete spectrum models, for the fractional derivative viscoelastic element
(fractional dashpot or springpot). Our representations are generalized Maxwell models or series of Kelvin-Voigt units, which,
however, maintain the number of parameters of the corresponding fractional order model. Accordingly, the number of parameters
of the rheological representation is independent of the number of rheological units. We prove that the representations converge
to the corresponding fractional model in the limit as the number of units tends to infinity. The representations extend to
compound fractional derivative models such as the fractional Maxwell model, fractional Kelvin-Voigt model, and fractional
standard linear solid. Computational experiments show that the rheological representations are accurate approximations of
the fractional order models even for a small number of units. 相似文献
92.
H. Winkler A. Kostikas V. Petrouleas A. Simopoulos A. X. Trautwein 《Hyperfine Interactions》1986,29(1-4):1347-1350
Measurements of three high-spin FeIIS4 complexes at various temperatures and applied magnetic fields are reported and the results are compared with those of reduced
rubredoxin. Simulations of the measured spectra by means of the fully developed stochastic theory of lineshape prove that
intermediate relaxation behavior is present and is determined essentially by the phonon energy distribution and by one single
parameter W0, the scaling factor, which contains the strength of spin-lattice coupling. 相似文献
93.
94.
Christina D. Polyzou Helen Nikolaou Catherine P. Raptopoulou Konstantis F. Konidaris Vlasoula Bekiari Vassilis Psycharis Spyros P. Perlepes 《Molecules (Basel, Switzerland)》2021,26(6)
The first use of methyl 2-pyridyl ketoxime (mepaoH) in homometallic lanthanide(III) [Ln(III)] chemistry is described. The 1:2 reactions of Ln(NO3)3·nH2O (Ln = Nd, Eu, Gd, Tb, Dy; n = 5, 6) and mepaoH in MeCN have provided access to complexes [Ln2(O2CMe)4(NO3)2(mepaoH)2] (Ln = Nd, 1; Ln = Eu, 2; Ln = Gd, 3; Ln = Tb, 4; Ln = Dy, 5); the acetato ligands derive from the LnIII—mediated hydrolysis of MeCN. The 1:1 and 1:2 reactions between Dy(O2CMe)3·4H2O and mepaoH in MeOH/MeCN led to the all-acetato complex [Dy2(O2CMe)6(mepaoH)2] (6). Treatment of 6 with one equivalent of HNO3 gave 5. The structures of 1, 5, and 6 were solved by single-crystal X-ray crystallography. Elemental analyses and IR spectroscopy provide strong evidence that 2–4 display similar structural characteristics with 1 and 5. The structures of 1–5 consist of dinuclear molecules in which the two LnIII centers are bridged by two bidentate bridging (η1:η1:μ2) and two chelating-bridging (η1:η2:μ2) acetate groups. The LnIII atoms are each chelated by a N,N’-bidentate mepaoH ligand and a near-symmetrical bidentate nitrato group. The molecular structure of 6 is similar to that of 5, the main difference being the presence of two chelating acetato groups in the former instead of the two chelating nitrato groups in the latter. The geometry of the 9-coordinate LnIII centers in 1, 5 and 6 can be best described as a muffin-type (MFF-9). The 3D lattices of the isomorphous 1 and 5 are built through H-bonding, π⋯π stacking and C-H⋯π interactions, while the 3D architecture of 6 is stabilized by H bonds. The IR spectra of the complexes are discussed in terms of the coordination modes of the organic and inorganic ligands involved. The Eu(III) complex 2 displays a red, metal-ion centered emission in the solid state; the TbIII atom in solid 4 emits light in the same region with the ligand. Magnetic susceptibility studies in the 2.0–300 K range reveal weak antiferromagnetic intramolecular GdIII…GdIII exchange interactions in 3; the J value is −0.09(1) cm−1 based on the spin Hamiltonian Ĥ = −J(ŜGd1·ŜGd2). 相似文献
95.
Vassilis Saliakas Christos Chatzidoukas Apostolos Krallis Dimitris Meimaroglou Costas Kiparissides 《大分子反应工程》2007,1(1):119-136
In the present study, two numerical methods, namely the orthogonal collocation on finite elements and the fixed pivot technique, are employed to calculate the MWD in an MMA free‐radical batch suspension polymerization reactor operating up to very high conversions (e.g., ≥95%). The theoretical MWD predictions are directly compared with experimentally measured MWDs, obtained from a pilot‐scale batch MMA suspension polymerization reactor. It is shown that there is a very good agreement between model predictions and experimental measurements on both monomer conversion and MWD. Subsequently, two different time‐optimal temperature trajectories are calculated to obtain a polymer having either a narrow or a bimodal MWD in minimum batch time. The calculated time optimal trajectories are then applied, as set point temperature changes, to a pilot plant batch polymerization reactor. It is shown that the measured MWDs are in very good agreement with the off‐line calculated optimal MWDs.
96.
A recently developed experimental and theoretical procedure is used in order to calculate the magnitude and anisotropy of interaction between a lanthanide and a 3d-metal ion. The general formula of the molecular compounds is [Ln(H2O)3(dmf)4(μ-CN)Fe–(CN)5] · nH2O where 1 n 1,5 and dmf = N,N′-dimethylformamide, abbreviated as [LnFe] from now on. The main parts of this procedure are (a) the evaluation of the effective g-parameters of the lanthanide ion with the help of EPR measurements. (b) The use of dual mode EPR spectroscopy to define the anisotropic exchange interactions with the help of an anisotropic Hamiltonian model. (c) Use of the same magnetic model to fit magnetization and susceptibility data in order to verify the EPR findings.It was possible to define some trends concerning the exchange components of the [DyFe] dimer according to which the antiferromagnetic isotropic exchange constant is smaller than 4 cm−1 and the anisotropic components are [Dexc, Eexc] = [6(1), 0.0] cm−1. Also for the case of [TmFe] and [YbFe] dimers the antiferromagnetic isotropic exchange constant is smaller than 0.3 cm−1 while the anisotropic components are [Dexc, Eexc] = [12.0, 0.0] cm−1 and [Dexc, Eexc] = [0.4(1), 0.0] cm−1, respectively. 相似文献
97.
This paper presents a review of and refinements to a class of discrete-event models for the analysis of unreliable queueing systems. In contrast to conventional piece-by-piece simulators, these models observe a number of rare events that affect the inflow and outflow rates at each queue. Between events, the evolution of the system is approximated by a linear function. Several experiments confirm the accuracy of this approximation and its computational efficiency over conventional simulation. © 1997 by John Wiley & Sons, Ltd. 相似文献
98.
99.
Inglezakis VJ Loizidou MD Grigoropoulou HP 《Journal of colloid and interface science》2003,261(1):49-54
In the present study ion exchange of Pb(2+), Cu(2+), Fe(3+), and Cr(3+) on natural Greek clinoptilolite was examined in terms of selectivity toward the above heavy metals in single- and multicomponent solutions in batch systems. Also examined are the influence of clinoptilolite on solution acidity and the effect of acidity on the ion exchange process. Clinoptilolite increases solution acidity due to the exchange of H(+) cations with the cations initially present in its structure. H(+) cations should be considered as competitive ones in ion exchange processes, and consequently ion exchange of metals is favored at high acidity values. Cu(2+) and Cr(3+) are the most sensitive cations with respect to acidity. Selectivity determination demonstrates that the selectivity at total concentration 0.01 N and acidity 2 in both single- and multicomponent solutions is following the order Pb(2+)>Fe(3+)>Cr(3+) > or =Cu(2+). This order is set since the first days of equilibration. However, Cu(2+) shows remarkable changes in selectivity and generally its uptake and selectivity are increasing with time. On the other hand selectivity in single metal solutions where acidity is not adjusted is following the order Pb(2+)>Cr(3+)>Fe(3+) congruent with Cu(2+). 相似文献
100.
Vassilis Kanellopoulos 《Proceedings of the American Mathematical Society》2000,128(9):2725-2733
In this paper two convexity criteria are proven. The first one characterizes compact convex sets in a locally convex space and extends a previous result by G. Aumann, while the second one characterizes closed bounded convex sets with the Radon-Nikodým property in a Banach space.