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排序方式: 共有265条查询结果,搜索用时 31 毫秒
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Nonlinear Dynamics - This paper deals with a discrete-time two prey–one predator system with Holling Type-III functional response, along with inter-specific competition between the prey and... 相似文献
143.
Sabyasachi Ta Milan Ghosh Noor Salam Jayanta Das Manirul Islam Paula Brandão Vítor Félix Jesus Sanmartin Debasis Das 《应用有机金属化学》2020,34(10):e5823
An amide-imine conjugate, (E)-N′-((2-hydroxybenzen-1-yl) methylene)-4-methylbenzohydrazide (H2LPTASAL), derived from 4-methyl-benzoic acid hydrazide (PTA) and 2-hydroxybenzaldehyde is used to prepare Mo (VI), Cu (II) and Fe (III) complexes. The X-ray structurally characterized complexes have been explored as catalyst for amine assisted asymmetric ring opening (ARO) of epoxide, carbon-heteroatom cross-coupling and ethyl benzene oxidation. In addition, their catecholase like activities have thoroughly been investigated. Moreover, the Cu (II) complex selectively recognizes histidine by fluorescence spectroscopy. 相似文献
144.
Exploring the Oxidative‐Addition Pathways of Phenyl Chloride in the Presence of PdII Abnormal N‐Heterocyclic Carbene Complexes: A DFT Study
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Totan Mondal Sriman De Bholanath Maity Dr. Debasis Koley 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(44):15778-15790
DFT calculations were performed to elucidate the oxidative addition mechanism of the dimeric palladium(II) abnormal N‐heterocyclic carbene complex 2 in the presence of phenyl chloride and NaOMe base under the framework of a Suzuki–Miyaura cross‐coupling reaction. Pre‐catalyst 2 undergoes facile, NaOMe‐assisted dissociation, which led to monomeric palladium(II) species 5 , 6 , and 7 , each of them independently capable of initiating oxidative addition reactions with PhCl. Thereafter, three different mechanistic routes, path a, path b, and path c, which originate from the catalytic species 5 , 7 , and 6 , were calculated at M06‐L ‐D3(SMD)/LANL2TZ(f)(Pd)/6–311++G**//M06‐L/LANL2DZ(Pd)/6–31+G* level of theory. All studied routes suggested the rather uncommon PdII/PdIV oxidative addition mechanism to be favourable under the ambient reaction conditions. Although the Pd0/PdII routes are generally facile, the final reductive elimination step from the catalytic complexes were energetically formidable. The PdII/PdIV activation barriers were calculated to be 11.3, 9.0, 26.7 kcal mol?1 (ΔΔ≠GLS‐D3) more favourable than the PdII/Pd0 reductive elimination routes for path a, path b, and path c, respectively. Out of all the studied pathways, path a was the most feasible as it comprised of a PdII/PdIV activation barrier of 24.5 kcal mol?1 (ΔGLS‐D3). To further elucidate the origin of transition‐state barriers, EDA calculations were performed for some key saddle points populating the energy profiles. 相似文献
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Meenakshi Dowlut Dr. Debasis Mallik Dr. Michael G. Organ Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(14):4279-4283
The reactivity of Pd–PEPPSI (Pyridine, Enhanced, Precatalyst, Preparation, Stabilization, and Initiation) precatalysts in the Stille–Migita cross‐coupling reaction between heteroaryl stannanes and aryl or heteroaryl halides was evaluated. In general, Pd–PEPPSI–IPent (IPent=diisopentylphenylimidazolium derivative) demonstrated high efficiency over a variety of challenging aryl or heteroaryl halides with thiophene‐, furan‐, pyrrole‐, and thiazole‐based organostannanes when compared with Pd–PEPPSI–IPr (IPr=diisopropylphenylimidazolium derivative). The transformations proceeded at appreciably lower temperatures (30–80 °C) than triarylphosphine‐based Pd catalysts, improving the scope of this useful carbon–carbon bond‐forming process. 相似文献
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Xu X Maresca KJ Das D Zahn S Zubieta J Canary JW 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(24):5679-5683
The ligand in [Cu(6)CH3CN]-(ClO4)2 adopts two conformations that may be described as "pseudo-enantiomers" in that they possess approximately mirror-image molecular helicity, although they differ in the orientation of a single methyl substituent. The two conformations differ in energy as judged by analogy to other compounds studied previously, computation of the relative free energies of formation of the isomers, and measurement of solution circular dichroism spectra. The solid-state structures of both single enantiomer and racemic forms of the complex were determined by X-ray crystallography. In the chiral complex, a quasi-racemate was observed with both pseudo-enantiomeric conformers present in the asymmetric unit. Packing forces induce a higher energy conformation in order to achieve higher apparent symmetry in the solid state. In contrast, the racemic complex only displayed a single conformation corresponding to the lower energy one of the two observed in the single enantiomer structure. 相似文献
150.
At the access to networks, in contrast to the core, distances and feedback delays, as well as link capacities are small, which has network engineering implications that are investigated in this paper. We consider a single point in the access network which multiplexes several bursty users. The users adapt their sending rates based on feedback from the access multiplexer. Important parameters are the user's peak transmission rate p, which is the access line speed, the user's guaranteed minimum rate r, and the bound on the fraction of lost data. Two feedback schemes are proposed. In both schemes the users are allowed to send at rate p if the system is relatively lightly loaded, at rate r during periods of congestion, and at a rate between r and p, in an intermediate region. For both feedback schemes we present an exact analysis, under the assumption that the users' file sizes and think times have exponential distributions. We use our techniques to design the schemes jointly with admission control, i.e., the selection of the number of admissible users, to maximize throughput for given p, r and . Next we consider the case in which the number of users is large. Under a specific scaling, we derive explicit large deviations asymptotics for both models. We discuss the extension to general distributions of user data and think times. 相似文献