全文获取类型
收费全文 | 1412篇 |
免费 | 37篇 |
国内免费 | 6篇 |
专业分类
化学 | 1017篇 |
晶体学 | 7篇 |
力学 | 53篇 |
数学 | 192篇 |
物理学 | 186篇 |
出版年
2023年 | 8篇 |
2022年 | 21篇 |
2021年 | 22篇 |
2020年 | 15篇 |
2019年 | 23篇 |
2018年 | 19篇 |
2017年 | 19篇 |
2016年 | 24篇 |
2015年 | 32篇 |
2014年 | 36篇 |
2013年 | 65篇 |
2012年 | 101篇 |
2011年 | 90篇 |
2010年 | 59篇 |
2009年 | 59篇 |
2008年 | 106篇 |
2007年 | 94篇 |
2006年 | 78篇 |
2005年 | 99篇 |
2004年 | 72篇 |
2003年 | 53篇 |
2002年 | 60篇 |
2001年 | 23篇 |
2000年 | 28篇 |
1999年 | 13篇 |
1998年 | 18篇 |
1997年 | 10篇 |
1996年 | 9篇 |
1995年 | 11篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1985年 | 5篇 |
1984年 | 14篇 |
1983年 | 10篇 |
1982年 | 8篇 |
1981年 | 11篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1974年 | 4篇 |
1915年 | 4篇 |
1913年 | 5篇 |
排序方式: 共有1455条查询结果,搜索用时 15 毫秒
961.
Ranking problems arise from the knowledge of several binary relations defined on a set of alternatives, which we intend to
rank. In a previous work, the authors introduced a tool to confirm the solutions of multi-attribute ranking problems as linear
extensions of a weighted sum of preference relations. An extension of this technique allows the recognition of critical preference
pairs of alternatives, which are often caused by inconsistencies. Herein, a confirmation procedure is introduced and applied
to confirm the results obtained by a multi-attribute decision methodology on a tender for the supply of buses to the Porto
Public Transport Operator. 相似文献
962.
Y. Zhang I. Matos M. A. N. D. A. Lemos Filipe Freire Teresa G. Nunes A. M. Botelho do Rego R. T. Henriques I. F. Fonseca M. M. Marques F. Lemos 《Journal of polymer science. Part A, Polymer chemistry》2003,41(23):3768-3780
Cr catalysts supported on silica, zeolite NaY, and charcoal were prepared with two different methods. They were characterized and examined in the polymerization of ethene. Cyclic voltammetry, electron spin resonance, X‐ray photoelectron spectroscopy and silicon‐29 magic‐angle spinning nuclear magnetic resonance spectroscopy were used to characterize them, demonstrating that Cr is not in a single oxidation state, that the distribution among the various oxidation states depends on the history of the sample, and that even for a single oxidation state a variety of different environments can occur. In the polymerization of ethene, the supported Cr catalysts exhibited activity values varying from 103 to 105 gPE · molCr?1 · [M]?1 · h?1, depending on the choice of the support and on the method by which the Cr is placed on it. Silica seemed to be the most efficient support for Cr for this reaction. However, the zeolite‐supported catalysts also showed reasonable activity values (Ap ? 104 units) and presented the advantage of having a strong interaction between the Cr and the support, which may prevent leaching of the cation into the surrounding environment. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3768–3780, 2003 相似文献
963.
964.
965.
966.
Freire F Cuesta I Corzana F Revuelta J González C Hricovini M Bastida A Jiménez-Barbero J Asensio JL 《Chemical communications (Cambridge, England)》2007,(2):174-176
A complete characterisation of the protonation equilibrium that accompanies the molecular recognition of neomycin-B by a specific RNA receptor has been achieved by employing simple NMR measurements. 相似文献
967.
Grirrane A Resa I Rodriguez A Carmona E Alvarez E Gutierrez-Puebla E Monge A Galindo A del Río D Andersen RA 《Journal of the American Chemical Society》2007,129(3):693-703
While, in general, decamethylzincocene, Zn(C5Me5)2, and other zincocenes, Zn(C5Me4R)2 (R = H, But, SiMe3), react with dialkyl and diaryl derivatives, ZnR'2, to give the half-sandwich compounds (eta5-C5Me4R)ZnR', under certain conditions the reactions of Zn(C5Me5)2 with ZnEt2 or ZnPh2 produce unexpectedly the dizincocene Zn2(eta5-C5Me5)2 (1) in low yields, most likely as a result of the coupling of two (eta5-C5Me5)Zn* radicals. An improved, large scale (ca. 2 g) synthesis of 1 has been achieved by reduction of equimolar mixtures of Zn(C5Me5)2 and ZnCl2 with KH in tetrahydrofuran. The analogous reduction of Zn(C5Me4R)2 (R = H, SiMe3, But) yields only decomposition products, but the isotopically labeled dimetallocene 68Zn2(eta5-C5Me5)2 and the related compound Zn2(eta5-C5Me4Et)2 (2) have been obtained by this procedure. Compound 2 has lower thermal stability than 1, but it has been unequivocally characterized by low-temperature X-ray diffraction studies. As for 1 a combination of structural characterization techniques has provided unambiguous evidence for its formulation as the Zn-Zn bonded dimer Zn2(eta5-C5Me4Et)2, with a short Zn-Zn bond of 2.295(3) A indicative of a strong Zn-Zn bonding interaction. The electronic structure and the bonding properties of 1 and those of related dizincocenes Zn2(eta5-Cp')2 have been studied by DFT methods (B3LYP level), with computed bond distances and angles for dizincocene 1 very similar to the experimental values. The Zn-Zn bond is strong (ca. 62 kcal.mol-1 for 1) and resides in the HOMO-4, that has a contribution of Zn orbitals close to 60%, consisting mostly of the Zn 4s orbitals (more than 96%). 相似文献
968.
969.
Novel palladium(II) complexes with bis(pyrazol-1-yl)methane ligands at the focal point of G0-G3 poly(aryl ether) Fréchet-type dendrons are reported. The molecular structures of the metallodendrimer series G0, G1, and G2 [(dend)CH(3,5-Me2pz)2(PdCl2)] have been determined by X-ray diffraction methods. The three structures show a similar three-dimensional organization of the metal complex, which is progressively engulfed by the branches with increasing dendrimer generation. 相似文献
970.
A new approach is developed for identifying suitable reaction coordinates to describe the progression of rare events in complex systems. The method is based on the forward flux sampling (FFS) technique and standard least-square estimation (LSE) and it is denoted as FFS-LSE. The FFS algorithm generates trajectories for the transition between stable states as chains of partially connected paths, which can then be used to obtain "on-the-fly" estimates for the committor probability to the final region, p(B). These p(B) data are then used to screen a set of candidate collective properties for an optimal order parameter (i.e., reaction coordinate) that depends on a few relevant variables. LSE is used to find the coefficients of the proposed reaction coordinate model and an analysis of variance is used to determine the significant terms in the model. The method is demonstrated for several test systems, including the folding of a lattice protein. It is shown that a simple approximation to p(B) via a model linear on energy and number of native contacts is sufficient to describe the intrinsic dynamics of the protein system and to ensure an efficient sampling of pathways. In addition, since the p(B) surface found from the FFS-LSE approach leads to the identification of the transition state ensemble, mechanistic details of the dynamics of the system can be readily obtained during a single FFS-type simulation without the need to perform additional committor simulations. 相似文献