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Summary. A formalism has been developed that describes spin crossover equilibrium in the solid state by taking into account the effects
of n nearest neighbours of a given molecule on its partition function. In this way binary and many-body interactions of the order
n + 1 are included into the theoretical model and represented by non-ideality parameters connected with the splitting of free
energy levels. Binary interactions are characterised by the main splittings whereas higher order interactions manifest themselves
in asymmetries of splittings within multiplets. The contribution of molecular interactions can also be written in terms of
formal excess free energies of the second, third, fourth and higher orders. Simple relationships between excess free energies
and parameters of multiplets have been found for binary, ternary and quaternary interactions. This formalism is reduced to
that of the model of binary interactions when effects of surroundings are additive leading to equidistant free energy multiplets.
Higher order interactions may cause an abrupt spin crossover but in a limited range of compositions around the transition
point. The regression of experimental transition curves of one-step spin crossover may yield estimates of excess energies
up to the fifth order. 相似文献
4.
Gutman I Linert W Lukovits I Tomovic Z 《Journal of chemical information and computer sciences》2000,40(1):113-116
The classical Wiener index, W(G), is equal to the sum of the distances between all pairs of vertexes of a (molecular) graph, G. We now consider a related topological index, pi(G), equal to the product of distances between all pairs of vertexes of G. The basic properties of the pi index are established and its possible physicochemical applications examined. In the case of alkanes, pi and W are highly correlated; a slightly curvilinear correlation exists between In pi and W. 相似文献
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N. T. Madhu P. K. Radhakrishnan W. Linert 《Journal of Thermal Analysis and Calorimetry》2006,84(3):607-611
The
phenomenological, kinetic and mechanistic aspects of the nitrate, chloride,
bromide and iodide complexes of nickel(II) with1,2-(diimino-4’-antipyrinyl)ethane
(GA) have been studied by TG and DTG techniques. The kinetic parameters like
activation energy, pre-exponential factor and entropy of activation were computed.
The rate controlling process in all stages of decomposition is random nucleation
with one nucleus on each particle (Mampel model). 相似文献
7.
M. Enamullah W. Linert V. Gutmann R. F. Jameson 《Monatshefte für Chemie / Chemical Monthly》1994,125(12):1301-1309
Summary 2,6-bis-(Benzimidazol-2-yl)-pyridine (bzimpy = H2
L) acts as a bidentate ligand when combining with transition metal ions. The complexes [M(bzimpy)2](ClO4)2 (M = Fe2+, Mn2+, Zn2+, Co2+, and Ni2+) were obtained as solids. The protonation constants (logK) for the ligand and the complexes were evaluated in 30:70 (v/v) H2O:EtOH at 293 K and at constant ionic strength of 0.12M KCl. Coordination of the ligand to the metal ions leads to an increase of acidity of the imino-hydrogen of the benzimidazole group of the ligand as a function of the complex stability. Deprotonation leads to a spin-state transition (intermediate spin-state low-spin) of the iron(II)-complex, followed by a shift of the metal-to-ligandcharge transfer band (MLCT) to lower energies (max=563 to 580 nm). The d-d absorption bands are found to shift to higher energies and the low-spin isomer is favoured at room temperature. An opposite shift of theMLCT band (max=563 to 557 nm) is observed when HClO4 is added to the complex solution, rendering the high-spin state of the complex more favourable.On leave from the Chemistry Department, Jahangirnagar University, Dhaka, Bangladesh 相似文献
8.
Chiral resolution of arginine (Arg) and Arg derivatives is demonstrated using electrospray ionization-tandem mass spectrometry (ESI-MS). Calcium ion (Ca(II))-mediated trimeric clusters are generated, which incorporate the analyte of interest and an enantiomerically pure reference molecule of similar metal ion affinity. Two methods, one based on the measurement of a competitive-dissociation-based branching ratio (R(chir)) by the kinetic method (KM) and one based on the measurement of a chiral recognition ratio (CR) by a similar method, are compared. Incorporating N-blocked Arg derivatives (Z-Arg and Boc-Arg) as chiral references provides chiral resolution greater than that previously reported for Arg enantiomers. In a reciprocal manner, pure Arg enantiomers can be used as references for discriminating enantiomers of these N-blocked Arg derivatives. Condensed-phase and gas-phase Ca(II) ion affinity relative to Arg is also addressed qualitatively for other acidic, basic, and neutral amino acids. In some cases, when only one offspring ion is observed (insufficient for KM analysis), the CR method can be applied as an alternative to obtain a measurable stereoselectivity value for the system. The results of these experiments demonstrate the applicability of, and the difference between, the KM and the CR method for improved quantitative analysis of enantiomeric excess for Arg. 相似文献
9.
Svitlana R. Petrusenko Wolfgang Linert Viktoria V. Dyakonenko Oksana V. Nesterova Oleg V. Shishkin 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(7):m281-m283
The title salt, [Zn(C2N2H8)3]2[CdI4]I2, conventionally abbreviated [Zn(en)3]2[CdI4]I2, where en is ethylenediamine, contains discrete [Zn(en)3]2+ cations and [CdI4]2− anions with distorted octahedral and nearly tetrahedral geometries, respectively, as well as uncoordinated I− ions. The cation and the free I− anion lie on twofold rotation axes and the [CdI4]2− anion lies on a axis in the space group I2d. The structure exhibits numerous weak inter‐ionic hydrogen bonds of two types, viz. N—H⋯I−(free ion) and N—H⋯I([CdI4]2−), which support the resulting three‐dimensional framework. 相似文献
10.
Summary. Parameters of the formalism [1–6] describing spin crossover in the solid state have been defined via molecular potentials in model systems of neutral and ionic complexes. In the first instance Lennard-Jones and electric dipole–dipole potentials have been used whereas in ionic systems Lennard-Jones and electric point-charge potentials have been used. Electric dipole–dipole interaction of neutral complexes brings about
a positive excess energy controlled by the difference of electric dipole moments of HS and LS molecules. Differences of the
order of Δμ = 1–2 D cause an abrupt spin crossover in systems with T1/2 = 100–150 K. Magnetic coupling contributes both to the excess energy and excess entropy, however the overall effect is equivalent
to a modest positive excess energy. Ionic systems in the absence of specific interactions are characterised by very small
excess energies corresponding to practically linear van’t Hoff plots. Detectable positive and negative excess energies in these systems may arise from interactions of ligands belonging
to neighbouring complexes. The HOMO–LUMO overlap in HS–LS pairs can bring about a nontrivial variation of the shape of transition
curves. Examples of regression analysis of experimental transition curves in terms of molecular potentials are given. 相似文献