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101.
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
102.
103.
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
104.
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.
105.
Chronis Kynigos Giorgos Psycharis 《International Journal of Computers for Mathematical Learning》2009,14(3):265-298
The paper describes a study of the contexts of six teams, expert in research and development of digital media for learning
mathematics, who cross-experimented in classrooms with the use of each other’s artefacts. Contextual issues regarding the
designed tasks and technologies, the socio-systemic milieu and the ways in which the researchers worked with the teachers
were in focus. We analysed the ways in which a set of mutually constructed and negotiated questions aiming to illuminate otherwise
tacit contextual issues operated as boundary objects amongst the teams. We discuss the need to develop special tools such
as these boundary objects in order to elicit issues of context and the ways they may affect the production of theory. 相似文献
106.
Michael A. Terzidis Constantinos A. Tsoleridis Aristides Terzis Vassilis Psycharis 《Tetrahedron》2010,66(4):947-9014
The 1,4-zwitterion derived from 4,5-dimethylthiazole and acetylenedicarboxylates has been shown to react at low temperature readily with 3-formylchromones (chromone-3-carboxaldehydes) resulting, after an unusual rearrangement, in the facile synthesis of thiazolo[3,2-a]pyridine derivatives; in the case of electron-donating substituents in the chromone ring tetracyclic chromenothiazolopyridines are isolated as the main reaction products. However, at higher temperature after an unexpected 1,2-aroyl migration 8-formyl-5H-[1,3]thiazolo[3,2-a]pyridines are formed as a mixture of two rotamers. Structural assignments of the new compounds as well as complete assignment of 1H and 13C NMR signals were based on the analysis of their 1H and 13C NMR (1D and 2D), IR, MS and elemental analysis data. Plausible mechanisms are proposed. 相似文献
107.
Figuerola A Tangoulis V Ribas J Hartl H Brüdgam I Maestro M Diaz C 《Inorganic chemistry》2007,46(26):11017-11024
The synthesis, crystal structure, and magnetic properties of two trinuclear oxo-centered carboxylate complexes are reported and discussed: [Cr3(mu3-O)(mu2-PhCOO)6(H2O)3]NO3.4H2O.2CH3OH (1) and [Cr3(mu3-O)(mu2-PhCOO)2(mu2-OCH2CH3)2(bpy)2(NCS)3] (2). For both complexes the crystal system is monoclinic, with space group C2/c for 1 and P1/n for 2. The structure of complex 1 consists of discrete trinuclear cations, associated NO3- anions, and lattice methanol and water molecules. The structure of complex 2 is built only by neutral discrete trinuclear entities. The most important feature of 2 is the unusual skeleton of the [Cr3O] core due to the lack of peripheral bridging ligands along one side of the triangular core, which is unique among the structurally characterized (mu3-oxo)trichromium(III) complexes. Magnetic measurements were performed in the 2-300 K temperature range. For complex 1, in the high-temperature region (T > 8 K), experimental data could be satisfactorily reproduced by using an isotropic exchange model, H = -2J12S1S2 - 2J13S1S3 - 2J23S2S3 (J12 = J13 = J23) with Jij = -10.1 cm(-1), g = 1.97, and TIP = 550 x 10(-6) emu mol(-1). The antisymmetric exchange interaction plays an important role in the magnetic behavior of the system, so in order to fit the experimental magnetic data at low temperature, a new magnetic model was used where this kind of interaction was also considered. The resulting fitting parameters are the following: Gzz = 0.25 cm(-1), delta = 2.5 cm(-1), and TIP = 550 x 10(-6) emu mol(-1). For complex 2, the experimental data could be satisfactorily reproduced by using an isotropic exchange model, H = -2J1(S1S2 + S1S3) - 2J2(S2S3) with J1 = -7.44 cm(-1), J2 = -51.98 cm(-1), and g = 1.99. The magnetization data allows us to deduce the ground term of S = 1/2, characteristic of equilateral triangular chromium(III) for complex 1 and S = 3/2 for complex 2, which is confirmed by EPR measurements. 相似文献
108.
Theocharis C. StamatatosSpyros P. Perlepes Catherine P. RaptopoulouVassilis Psycharis Nikolaos Klouras 《Polyhedron》2011,30(3):451-457
The reactivity pattern of the 16-electron species [M(Cp)2Cl2] (M = Zr, Hf; Cp− = η5-C5H5−) and [Ti(MeCp)2Cl2] (MeCp− = η5-C5H4CH3−) towards the dipicolinate(−2) (dipic2−) ligand under mild (ambient temperature) and convenient (aerobic reactions, aqueous media) conditions have been investigated. The syntheses, molecular structures and spectroscopic (IR, 1H NMR) characterization are reported for the 18-electron products [Zr(Cp)2(dipic)] (1), [Hf(Cp)2(dipic)] (2) and [Ti(MeCp)2(dipic)] (3). The dipic2− ion behaves as N,O,O′-chelating ligand in the three complexes, while the centroids of the Cp− (1, 2) and MeCp− (3) rings formally occupy the fourth and fifth coordination sites about the central metal. The two identical/very similar bite angles of only ∼70° make the dipic2− ligand particularly suited to form stable metallocene derivatives with 5-coordinate geometry. IR and 1H NMR data are discussed in terms of the known structures and the tridentate chelating mode of the dipic2− ligand. 相似文献
109.
110.
Nikolaos Lemonakis Vassilis Mougios Maria Halabalaki Alexios– Leandros Skaltsounis Evagelos Gikas 《Biomedical chromatography : BMC》2016,30(12):2016-2023
A highly sensitive, rapid and specific ultrahigh‐performance liquid chromatography, coupled to negative electrospray ionization high‐resolution tandem mass spectrometry, method was developed and validated in order to investigate the absorption of dietary oleuropein (OE) in human subjects. Serum samples were collected at predefined time points, after oral administration of an olive leaf extract enriched in OE (204.4 mg OE per capsule) to two subjects. Subsequently, samples were analyzed by the developed method after a simple solid‐phase extraction step. Chromatographic separation was operated with aqueous formic acid, 0.1% (v/v), and acetonitrile following a gradient program at a flow rate of 0.45 mL/min in an RP‐C18 (50 × 2.1 mm, 1.9 μm) column with a total run time of 2.7 min. The method was validated and successfully applied to the determination of OE in human serum, with the pharmacokinetic analysis of the data revealing a biphasic response. 相似文献