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1.
Christo I. Ivanov Nikolai Tyutyulkov Gottfried Olbrich H. Barentzen Oscar E. Polansky 《Theoretical chemistry accounts》1988,73(1):27-42
Utilizing an extended Hubbard-type Hamiltonian which incorporates both nearest-neighbour Coulomb repulsion and exchange interactions, we have studied the energy dispersion of the lowest elementary excitation from the ferromagnetically aligned state of quasi one-dimensional alternant hydrocarbon networks. It was found that the main effect of the long range Coulomb interaction may be thought of as a renormalization (screening) of the on-site Hubbard integral. This implies an enhancement of the kinetic exchange term and impairs the stability of the ferromagnetic state towards single spin inversions. However, for physically relevant values of the parameters entering the model Hamiltonian, the collective spin excitation represents a magnon, whose energy band lies above the reference value pertaining to the magnetically saturated configuration.Dedicated to Prof. Dr. Adolf Neckel on the occasion of his 60th birthday 相似文献
2.
C. Christov S. Petrenko C. Balarew V. Valyashko 《Monatshefte für Chemie / Chemical Monthly》1994,125(12):1371-1382
Summary The standard method ofPitzer for predicting the solubility isotherms of systems in which solid phases with a constant composition crystallize is applied to cases when mixed crystals are formed. The four-component carnallite type systems RbCl-CsCl-MgCl2-H2O, RbCl-KCl-MgCl2-H2O, and RbCl-RbBr-MgCl2-MgBr2-H2O and the corresponding subsystems are thermodynamically simulated at 25°C. It is established that the solubility diagrams consist of crystallization regions of the simple saltsMX,MX, MgX
2·6H2O, and MgX2·6H2O and of the corresponding carnallite type double salts with the composition 1:1:6. A method of calculation of the integralGibbs energy of mixingG
mix(s) of crystals formed in water-salt systems has been proposed. The results on the systems RbCl-KCl-H2O, RbCl-RbBr-H2O, and MgCl2-MgBr2-H2O are compared with experimental data from the literature and with values calculated using various models.
Thermodynamische Simulation von Vierkomponentensystemen des Carnallit-Types
Zusammenfassung DiePitzer-Methode zur Voraussage der Löslichkeitsisothermen in Mehrstoffsystemen, in welchen feste Phasen mit konstanter Zusammensetzung auskristallisieren, wurde auch für Fälle angewendet, bei denen sich Mischkristalle bilden. Die Vierstoffsysteme RbCl-CsCl-MgCl2-H2O, RbCl-KCl-MgCl2-H2O und RbCl-RbBr-MgCl2-MgBr2-H2O, aus welchen Carnallit-Typ-Mischkristalle auskristallisieren, und die dazugehörigen Dreistoff-Randsysteme wurden bei 25°C simuliert. Man stellt fest, daß die Löslichkeitsdiagramme sowohl Kristallisationsbereiche der einfachen SalzeMX,M'X, MgX 2·6H2O und MgX 2·6H2O als auch der entsprechenden carnallitartigen Doppelsalze mit der Zuzammensetzung 1:1:6 umfassen. Eine Methode zur Berechnung derGibbs-EnergieG mix(s) für die in Wasser-Salz-Systemen gebildeten Mischkristalle wird vorgeschlagen. Die für die Systeme RbCl-KCl-H2O, RbCl-RbBr-H2O und MgCl2-MgBr2-H2O erhaltenen Ergebnisse werden mit experimentellen Literaturdaten und Resultaten von Berechnungen aufgrund verschiedener Modelle verglichen.相似文献
3.
Journal of Thermal Analysis and Calorimetry - Die Acetate Mg(OCOCH3)2 · 4H2O, Ca(OCOCH3)2 · H2O, Mn(OCOCH3)2 · 4H2O, Co(OCOCH3)2 · 4H2O, Ni(OCOCH3)2 · 4H2O,... 相似文献
4.
Chr Balarew D. Trendafelov M. Gerganova 《Monatshefte für Chemie / Chemical Monthly》1971,102(2):465-473
The three component system, zinc sulphate-sulphuric acid—water has been investigated in the region of high sulphuric acid concentrations at 15, 25, 35, 45, 60, and 80°C. In all cases a region of existence of anhydrous zinc sulphate was found. The conditions for obtaining anhydrous zinc sulphate by thermal dehydratation have been studied. The endothermic effect due to the conversion monohydrate—anhydrous salt was observed in the temperature interval from 220 to 290°C. The exact transition temperature depended on the conditions of preparation of the zinc sulphate monohydrate sample. The experimental data obtained by the physico-chemical investigation of the system permitted the determination of the equilibrium pressure of water vapour for the conversion monohydrate—anhydrous salt at 25.0°C. 相似文献
5.
A method based on Pitzer's model has been used for calculation of the solubilities of carnallite type double salts crystallizing in the systems MeX–MgX2–H2O (Me=Li, NH4, K, Rb, Cs; X=Cl, Br). The solubility of congruently soluble double salts was also determined experimentally at 25–75°C. The results from studies of the solubility diagrams of ternary carnallite type water-salt systems over a wide temperature range are summarized. It is found that the width of the crystallization region for each of the salts can be explained by the relative differences in the solubilities of the ternary solution components (MeX, MgX2·6H2O and MeX·MgX2·6H2O) and by a change of temperature, and by the effect of temperature on the solubility. A method is proposed for calculating Pitzer's ternary parameters of interionic interaction (MN and MNX) on the basis of experimental data for the solubility in water of the double salts crystallizing in the corresponding ternary water-salt systems. 相似文献
6.
Christo Ivanov A. Dobrev Tzv. Tcholakova G. Dontchev 《Journal of organometallic chemistry》1975,92(2):125-130
By treating ω-cyanocarboxylic acids with lithium amide in liquid ammonia, salts, of the type [NCCH(CH2)nCOOLi]Li are prepared. The formation of these salts is confirmed by their reaction with N-benzolydiphenylketimine and benzophenone to give ω-diarlylate, ω-benzoylamino- and ω-hydroxy-ψ-cyanocarboxylic acids respectively. 相似文献
7.
The physico-chemical analytical data on the systems ZnSO4(MgSO4)–CuSO4(FeSO4, CoSO4 resp.)–H2O at 25.0°C have shown that due to isodimorphous substitution of Zn2+, Mg2+ resp., in the orthorhombic crystals of ZnSO4 · 7 H2O MgSO4 · 7 H2O, resp. for Cu2+, Fe2+ or Co2+ above a specific degree of ionic substitution, the orthorhombic crystals are converted into monoclinic mixed crystals. The crystal phases are characterized by X-ray diffraction, microscopic and optical studies. The dominant effect of the admixed Cu2+, Fe2+, Co2+ ions is explained in terms of their electronic configurations, for which, owing to the operation of the Jahn-Teller effect, a deformation of the regular octahedral arrangement of the water ligands about the metal ion is found to occur. The strongest deforming effect is that of Cu2+ ions followed by the Fe2+ ions, the weakest deforming effect being that of Co2+ ions. 相似文献
8.
Dobromir D. Enchev Christo M. Angelov Marko Kirilov 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4)
Abstract The reaction of 3,3-disubstituted allenylphosphonic amidoesters with halogenes, sulfenyl and selenenylchlorides proceeds with five-membered heterocyclization and formation of 2-N,N-dialkylamino-2,5-dihydro-1,2-oxaphosphole 2-oxides: 相似文献
9.
10.
The reaction of 3-acylsubstituted 2H-1-benzo-pyran-2-ones 1, 5 and 11a-c with acid anhydrides in the presence of potassium fluoride (KF)/molecular sieves 4A gives the 4-(2-oxoalkyl)-2-oxochromans 2, 6 and 12a-c as the main products. Also the 3-carboxylic acid derivatives, such as esters and N,N-dialkylamides, of 2H-1-benzopyran-2-one (11d-g) react with isobutyric acid anhydride in the presence of KF/molecular sieves 4A to give the corresponding 2-oxochroman-4-acetic acid derivatives. 相似文献