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91.
92.
Pengou Martin Ngassa Guy Bertrand Piegang Boutianala Michèle Tchakouté Hervé Kouamo Nanseu-Njiki Charles Péguy Ngameni Emmanuel 《Journal of Solid State Electrochemistry》2021,25(4):1183-1195
Journal of Solid State Electrochemistry - Pb2+ ions were detected on a carbon paste electrode modified with a geopolymer cement. The X-ray pattern and the infrared spectrum of the geopolymer... 相似文献
93.
We have written this article in the honor of our friend Vladilen Lethokov, who has produced so many brilliant ideas and results
in the field of atomic and molecular physics and with whom we have had frequent unlightening discussions. We hope that the
work described here will contribute to illustrate the richness of the field. 相似文献
94.
The basic salt-initiated polymerization of α-aminoisobutyric acid NCA in acetonitrile was studied using various alkaline alcoholates and in the presence or absence of various protic (very weak acid) additives. The cation effect observed was the one expected from either the N-carboxy-α-amino acid anhydride (NCA) anion mechanism (activated monomer mechanism) or the alcoholate anion mechanism (Blout's mechanism). The anion effect appeared to be abnormal for the former mechanism, but did not agree nor disagree substantially with the latter. Furthermore, such additives as methanol (conjugate acid of the initiator), 3-methylhydantoin, 2-oxazolidone, and N-acetylglycine NCA (prototype of the chain growing through the NCA anion mechanism) considerably enhanced the rate of initiation. A still higher rate of initiation could be obtained by the combined use of two additives. IR and DTA analyses of the polymerization products showed the formation of 5,5-dimethylhydan-toin-3-isobutyric acid in the sample using the alcohol-free initiator, hence the NCA anion mechanism is operative. This acid was absent in the low DP polymer obtained in the presence of added methanol, and this agrees with the alcoholate anion mechanism without, however, proving it. Thus, while only part of the results could be explained by one or the other of the previous interpretations, all the experimental facts were accounted for, without noticeable contradiction, by the hypothesis of a multiple mechanism which contains both interpretations among its elements. 相似文献
95.
96.
Dr. Mohand Melaimi Dr. Michèle Soleilhavoup Prof. Guy Bertrand 《Angewandte Chemie (International ed. in English)》2010,49(47):8810-8849
The success of homogeneous catalysis can be attributed largely to the development of a diverse range of ligand frameworks that have been used to tune the behavior of various systems. Spectacular results in this area have been achieved using cyclic diaminocarbenes (NHCs) as a result of their strong σ‐donor properties. Although it is possible to cursorily tune the structure of NHCs, any diversity is still far from matching their phosphorus‐based counterparts, which is one of the great strengths of the latter. A variety of stable acyclic carbenes are known, but they are either reluctant to bind metals or they give rise to fragile metal complexes. During the last five years, new types of stable cyclic carbenes, as well as related carbon‐based ligands (which are not NHCs), and which feature even stronger σ‐donor properties have been developed. Their synthesis and characterization as well as the stability, electronic properties, coordination behavior, and catalytic activity of the ensuing complexes are discussed, and comparisons with their NHC cousins are made. 相似文献
97.
Michèle Artigue Michele Cerulli Mariam Haspekian Mirko Maracci 《International Journal of Computers for Mathematical Learning》2009,14(3):217-240
This paper presents the methodology developed within TELMA for connecting and integrating the theoretical frames used by the
different teams for studying the design and use of interactive learning environments in mathematics education. Two case studies
are then analysed and compared in order to illustrate the methodology and the results it can lead to. The papers ends by a
more general discussion about the outcomes of the experimental work developed within TELMA and the perspectives it offers
for approaching theoretical fragmentation. 相似文献
98.
Under aqueous conditions, 4-azidouracil/tetrazolo[1,5-c]pyrimidin-5(6H)-one nucleosides undergo a very efficient photochemical nitrogen elimination and ring expansion to 1,3,5-triazepin-2,4-dione nucleosides whose structure has been confirmed by X-ray crystallography. In contrast, when the photolysis was attempted under anhydrous conditions in the presence of a nucleophile, a ring contraction reaction occurred, affording 2-oxoimidazolone nucleosides. A mechanism to account for the formation of ring expansion and contraction reactions and involving a carbodiimide intermediate is proposed which is reminiscent of the known photochemical behavior of 2-azidopyridines/tetrazolo[1,5-a]pyridines. 相似文献
99.
100.