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101.
102.
《大分子反应工程》2018,12(3)
This work is focused on the development and validation of a model accounting for the impact of the reactor residence time distribution in well‐stirred slurry‐phase catalytic polymerization of ethylene. Particle growth and morphology are described through the Multigrain model, adopting a two‐site model for the catalyst and a conventional kinetic scheme. Particle size distribution and polymer properties (average molecular weights and polydispersity) are computed as a function of particle size through a segregated model, assuming that neither breakage nor aggregation occur. Reactors are modeled by means of fundamental mass conservation equations. The model is applied to a system constituted by a series of two ideal continuous stirred tank reactors, where the synthesis of polyethylene with bimodal molecular weight distribution is performed, employing the initial catalyst size distribution as the only adjustable parameter. The model provides insights at the single particle scale for each specific size, thus highlighting the inhomogeneity which arises from the synergic effects of chemical kinetics and residence time distributions in both reactors. The satisfactory agreement between model results and experimental data, in terms of particle size distribution and average molecular weights, confirmed the suitability of the model and underlying assumptions. 相似文献
103.
The RPPFM is employed to describe the gas‐phase catalytic polymerization of ethylene in the presence of supported or self‐supported Z‐N catalysts. Numerical simulations are carried out to analyze the effect of the catalyst type on the polymerization rate, particle overheating and the average molecular polymer properties of the polyolefin. It is shown that non‐porous, self‐supported Ziegler‐Natta catalysts exhibit higher particle growth rates and lower particle overheating. The average molecular weight of polyethylene produced by both catalysts is almost identical. Depending on particle size and polymer crystallinity, the average monomer solubility and the effective monomer diffusivity can significantly vary.
104.
Jongho Kim Sang Wook Kang Yong Soo Kang 《Colloids and surfaces. A, Physicochemical and engineering aspects》2008,320(1-3):189-192
Partially positively charged silver nanoparticles were successfully prepared by interaction between p-benzoquinone and the surface of the nanoparticles. This result was primarily due to electron affinity of the carbonyl group in p-benzoquinone, as confirmed by FT-IR and X-ray photoelectron spectroscopy (XPS). In this study, p-benzoquinone acted as both a stabilizer and a reducing agent for silver nanoparticles. UV–vis spectra showed the formation of silver nanoparticles. TEM micrographs confirmed that most of silver nanoparticles exist in sizes less than 7 nm, and the average size of particle aggregates is approximately 20 nm. 相似文献
105.
Anderson DR O'Leary DJ Grubbs RH 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(25):7536-7544
The development of a model system to study ruthenium-olefin complexes relevant to the mechanism of olefin metathesis has been reported recently. Upon addition of the ligand precursor 1,2-divinylbenzene to [RuCl(2)(Py)(2)(H(2)IMes)(==CHPh)] (H(2)IMes=1,3-dimesityl-4,5-dihydroimidazol-2-ylidene), two ruthenium-olefin adducts are formed. Based on (1)H NMR spectroscopy experiments and X-ray crystallographic analysis, these complexes are assigned as side-bound isomers in which the olefin and H(2)IMes ligands are coordinated cis to each other. Herein is reported an investigation of the generality of these observations through variation of the N-heterocyclic carbene ligand and the ligand precursor. 相似文献
106.
Clavier H Grela K Kirschning A Mauduit M Nolan SP 《Angewandte Chemie (International ed. in English)》2007,46(36):6786-6801
Ruthenium-catalyzed olefin metathesis reactions represent an attractive and powerful transformation for the formation of new carbon-carbon double bonds. This area is now quite familiar to most chemists as numerous catalysts are available that enable a plethora of olefin metathesis reactions. Nevertheless, with the exception of uses in polymerization reactions, only a limited number of industrial processes use olefin metathesis. This is mainly due to difficulties associated with removing ruthenium from the final products. In this context, a number of studies have been carried out to develop procedures for the removal of the catalyst or the products of catalyst decomposition, however, none are universally attractive so far. This situation has resulted in tremendous activity in the area dealing with supported or tagged versions of homogeneous catalysts. This Review summarizes the numerous studies focused on developing cleaner ruthenium-catalyzed metathesis processes. 相似文献
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109.
Marisol Güizado-Rodríguez Víctor M. Jiménez-Pérez Jesús E. Hernández-Rivera J.M. Domínguez Rosalinda Contreras Raúl Quijada 《Polyhedron》2007
New non-metallocene polymerization catalysts derived from 1,2-bis(3,5-di-tert-butyl-2-hydroxiphenyl)oxamide (L) and transition metals (Ti, Zr, Hf) were synthesized and tested for ethylene polymerization reactions. The syntheses were carried out from various bases and solvents (triethylamine/toluene, NaH/THF and NaOH/methanol). The zirconium compound (5) showed the highest catalytic activity (the polyethylene molecular weight was 98,000 Da) and polydispersity index (1.8–2.0) when n-heptane was used as solvent. In terms of Tm and crystallinity, this catalyst produced the highest density linear polyethylene. 相似文献
110.
Stephen A. Matchett 《Journal of organometallic chemistry》2007,692(22):4978-4984
Nucleophilic, single substitution of with para substituted anilines was used to prepare a series of cis Fp olefin complexes 10-14 of the general formula, , where X = OMe (10), Me (11), Cl, (12), COMe (13), and CN (14). These complexes contain both vinyl oxygen and vinyl nitrogen π donors capable of p-π donation to the olefin. This series allows a comparison of competitive π donor strengths as X is varied across the series. Correlation of the Hammett σpara parameters for X with the 13C NMR shifts of the metal coordinated vinyl carbons demonstrated that as the electron withdrawing character of the para substituent was increased, the aniline (while still the dominant π donor) competed less effectively with the cis ethoxy group, moving the Fp+ moiety toward a more central point along the olefin face. The implication of such control for the nucleophilic substitution chemistry of these complexes is discussed. 相似文献