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排序方式: 共有416条查询结果,搜索用时 93 毫秒
101.
Piotr Cmoch Rafał Głaszczka Jarosław Jaźwiński Bohdan Kamieński Elżbieta Senkara 《Magnetic resonance in chemistry : MRC》2014,52(3):61-68
Complexation of tetrakis(μ2‐N,N'‐diphenylformamidinato‐N,N')‐di‐rhodium(II) with ligands containing nitrile, isonitrile, amine, hydroxyl, sulfhydryl, isocyanate, and isothiocyanate functional groups has been studied in liquid and solid phases using 1H, 13C and 15N NMR, 13C and 15N cross polarisation–magic angle spinning NMR, and absorption spectroscopy in the visible range. The complexation was monitored using various NMR physicochemical parameters, such as chemical shifts, longitudinal relaxation times T1, and NOE enhancements. Rhodium(II) tetraformamidinate selectively bonded only unbranched amine (propan‐1‐amine), pentanenitrile, and (1‐isocyanoethyl)benzene. No complexation occurred in the case of ligands having hydroxyl, sulfhydryl, isocyanate, and isothiocyanate functional groups, and more expanded amine molecules such as butan‐2‐amine and 1‐azabicyclo[2.2.2]octane. Such features were opposite to those observed in rhodium(II) tetracarboxylates, forming adducts with all kind of ligands. Special attention was focused on the analysis of Δδ parameters, defined as a chemical shift difference between signal in adduct and corresponding signal in free ligand. In the case of 1H NMR, Δδ values were either negative in adducts of rhodium(II) tetraformamidinate or positive in adducts of rhodium(II) tetracarboxylates. Experimental findings were supported by density functional theory molecular modelling and gauge independent atomic orbitals chemical shift calculations. The calculation of chemical shifts combined with scaling procedure allowed to reproduce qualitatively Δδ parameters. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
102.
Rafał Pelka Karolina Kiełbasa Walerian Arabczyk 《Central European Journal of Chemistry》2011,9(2):240-244
Iron catalyst for ammonia synthesis of various mean sizes of iron nanocrystallites were nitrided with ammonia in a differential
reactor equipped with systems that made it possible to conduct both thermogravimetric measurements and hydrogen concentration
analyses in the reacting gas mixture. The nitriding process was investigated under atmospheric pressure at the temperature
of 475°C. It was found that along with an increase of mean size of iron nanocrystallites, with a decrease of specific surface
area of the samples, nitriding degree of solid samples increased. At the same time the rate of surface reaction of catalytic
ammonia decomposition decreased. Along with an increase of the samples’ specific surface area an increase of the catalyst’s
activity was observed. However, it was also observed that the concentration of active sites on the catalysts’ surface decreased
along with an increase of specific surface area. 相似文献
103.
Aequationes mathematicae - Using the Banach fixed-point theorem we provide a simple criterion of the geometric rate of convergence and of asymptotic stability of Markov operators in the Hutchinson... 相似文献
104.
Rafał Orłowski Grzegorz Cichowicz Dr. Olga Staszewska-Krajewska Dr. Wojciech Schilf Prof. Michał K. Cyrański Prof. Dr. Daniel T. Gryko 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(41):9658-9664
Four bis-corroles linked by diamide bridges were synthesized through peptide-type coupling of a trans-A2B-corrole acid with aliphatic and aromatic diamines. In the solid state, the hydrogen-bond pattern in these bis-corroles is strongly affected by the type of solvent used in the crystallization process. Although intramolecular hydrogen bonds play a decisive role, they are supported by intermolecular hydrogen bonds and weak N−H⋅⋅⋅π interactions between molecules of toluene and the corrole cores. In an analogy to mono(amido-corroles), both in crystalline state and in solutions, the aliphatic or aromatic bridge is located directly above the corrole ring. When either ethylenediamine or 2,3-diaminonaphthalene are used as linkers, incorporation of polar solvents into the crystalline lattice causes a roughly parallel orientation of the corrole rings. At the same time, both NHCO⋅⋅⋅NH corrole hydrogen bonds are intramolecular. In contrast, solvation in toluene causes a distortion with one of the hydrogen bonds being intermolecular. Interestingly, intramolecular hydrogen bonds are always formed between the –NHCO– functionality located further from the benzene ring present at the position 10-meso. In solution, the hydrogen-bonds pattern of the bis(amido-corroles) is strongly affected by the type of the solvent. Compared with toluene (strongly high-field shifted signals), DMSO and pyridine disrupt self-assembly, whereas hexafluoroisopropanol strengthens intramolecular hydrogen bonds. 相似文献
105.
106.
Dr. Rafał Wysokiński Wiktor Zierkiewicz Mariusz Michalczyk Steve Scheiner 《Chemphyschem》2022,23(11):e202200173
The PnF2 (Pn=P,As,Sb,Bi) on a naphthalene scaffold can engage in an internal pnicogen Pn⋅⋅⋅N bond (PnB) with an NH2 group placed close to it on the adjoining ring. An approaching neutral NH3 molecule can engage in a second PnB with the central Pn, which tends to weaken the intramolecular bond. The presence of the latter in turn weakens the intermolecular PnB with respect to that formed in its absence. Replacement of the external NH3 by a CN− anion causes a fundamental change in the bonding pattern, producing a fourth covalent bond with Pn, which rearranges into a trigonal bipyramidal motif. This addition disrupts the internal Pn⋅⋅⋅N pnicogen bond, recasting the PnF2⋅⋅⋅NH2 interaction into an NH⋅⋅⋅F H-bond. 相似文献
107.
108.
A Remez-type inequality is proved for a large family of sets with cusps in RN, including compact, fat and semialgebraic (or subanalytic) sets. 相似文献
109.
Joachim Stasiek Rafał Malinowski Tomasz Ligor Bogusław Buszewski 《Chemical Papers》2010,64(5):579-583
Results of the investigation of volatile organic compounds emission during polyethylene extrusion are presented. Two polymers
of different processing properties were tested, namely linear low density polyethylene (ExxonMobil) and high density polyethylene
(Liten FB 29). Blowing film extrusion in experimental technological line using a single screw extruder as the imported element
was done. VOCs were collected on sorbent tubes containing Tenax. Gas chromatography coupled with mass spectrometry (GC/MS)
was applied for the identification of volatile degradation products. PE LLD material emits a significantly larger amount of
hydrocarbons than PE-HD. Its emission contains mainly C18 and C20 hydrocarbons (alkanes, 1-alkenes, and α,ω-alkadienes). In case of the PE-HD polymer, lower degradation was observed and C18 and C23 hydrocarbons were emitted. 相似文献
110.
Rafał Bogel-Łukasik Dobrochna Matkowska Małgorzata E. Zakrzewska Ewa Bogel-Łukasik Tadeusz Hofman 《Fluid Phase Equilibria》2010
Solid–liquid, liquid–liquid and vapour–liquid equilibrium measurements for binary and ternary systems containing building blocks of biomass origin such as propionic acid, lactic acid and alternative solvents like carbon dioxide and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid have been carried out at 313.15 K. The binary solid–liquid and liquid–liquid equilibrium measurements were performed at ambient pressure. The vapour–liquid equilibrium was studied in the range of pressure from 3.54 to 12 MPa while ternary systems were examined at 9, 10 and 12 MPa. The samples from the coexisting phases were taken and the compositions of both liquid and vapour phases were determined experimentally. The three-phase system was observed for lactic acid + ionic liquid + CO2 as well. The achieved results were correlated using the Peng–Robinson equation of state with the Mathias–Klotz–Prausnitz mixing rule. The set of interaction parameters for the employed equations of state and the mixing rule for the investigated systems were obtained. 相似文献