全文获取类型
收费全文 | 874篇 |
免费 | 24篇 |
专业分类
化学 | 700篇 |
晶体学 | 6篇 |
力学 | 9篇 |
数学 | 114篇 |
物理学 | 69篇 |
出版年
2023年 | 3篇 |
2022年 | 12篇 |
2021年 | 7篇 |
2020年 | 8篇 |
2019年 | 17篇 |
2018年 | 3篇 |
2017年 | 9篇 |
2016年 | 14篇 |
2015年 | 17篇 |
2014年 | 13篇 |
2013年 | 40篇 |
2012年 | 57篇 |
2011年 | 53篇 |
2010年 | 29篇 |
2009年 | 23篇 |
2008年 | 45篇 |
2007年 | 52篇 |
2006年 | 47篇 |
2005年 | 50篇 |
2004年 | 43篇 |
2003年 | 45篇 |
2002年 | 47篇 |
2001年 | 11篇 |
2000年 | 12篇 |
1999年 | 16篇 |
1998年 | 7篇 |
1997年 | 16篇 |
1996年 | 23篇 |
1995年 | 8篇 |
1994年 | 10篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 9篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1982年 | 12篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1977年 | 14篇 |
1976年 | 15篇 |
1975年 | 10篇 |
1974年 | 9篇 |
1973年 | 8篇 |
1972年 | 3篇 |
1971年 | 3篇 |
排序方式: 共有898条查询结果,搜索用时 31 毫秒
21.
The synthesis and crystal structure of Cu(6)(4,7-phenanthroline)(8)(MeCN)(4)(6+) a novel Cu(i)-molecular hexamer is described in which the metal cations and phenanthroline molecules self-assemble into a dimer of shallow triangular-shaped bowls, within which are located large spherical polyoxometalate anions PM(12)O(40)(3-)(M = Mo or W). 相似文献
22.
Jacqueline Forcada Jos M. Asua 《Journal of polymer science. Part A, Polymer chemistry》1991,29(9):1231-1242
A mathematical model for the time evolution of both number-average molecular weight and weight-average molecular weight is described. The model results in a set of ordinary differential equations and its application is not limited by the maximum number of radicals per particle. The model was used to analyze the effect of the monomer molar ratio in the initial charge on the weight-average molecular weight during the emulsion copolymerization of styrene and methyl methacrylate in a batch reactor. 相似文献
23.
24.
Jacqueline Ferrand 《Geometriae Dedicata》1996,61(1):103-120
This paper develops the theory of conformal invariants initiated inJ. Differential Geom
8 (1973), 487–510 for a Riemannian manifoldM with dimensionn2. We construct and study four conformally invariant functions M, M, M, M resp. depending on 4, 3 or 2 points onM, defined as extremal capacities for condensers associated with those points. These functions have similarities with the classical invariants onS
n
,R
n
orH
n
. Their properties, and especially their continuity, are efficient tools for solving some problems of conformal geometry in the large. 相似文献
25.
The reaction of tungstate ions with the gamma-10-tungstosilicate in mixed water-ethanol (v/v) yields the corresponding isomer of the 12-tungstosilicate isolated as its tetrabutylammonium salt. It was characterized by means of (183)W NMR, infrared, Raman, and UV spectroscopies and was identified with the isomer resulting from the Keggin structure (alpha-isomer) by rotation of two tritungstic groups by pi/3. Cyclic voltammetry shows that the reducibility increases in the sequence alpha-beta-gamma as the number of rotated tritungstic groups. Whereas the gamma-12-tungstosilicate anion is unstable in pure aqueous solution whatever the pH value, it is stable in mixed aqueous-organic or pure organic solvents, even at boiling temperatures. In contrast, the two- and four-electron-reduced blue species are stable in aqueous media but not the one-electron-reduced blue. Study of the (183)W NMR spectrum of the two-electron-reduced species showed that the two spin-paired electrons are delocalized on all the W atoms on the NMR time scale but have a larger residency time on one group of four atoms. 相似文献
26.
The synthesis of 3-acetylcyclohexanones , , has been realized by conjugate addition of lithiated cyanohydrin ether to 2-cyclohexenones , , in THF-HMPA, even if 3-substituted. 3-benzoylcyclohexanones , , are obtained from and , , in THF with excellent yields. 相似文献
27.
Céline Jousse-KarinthiFatima Zouhiri Jacqueline MahuteauDidier Desmaële 《Tetrahedron》2003,59(12):2093-2099
The palladium-catalyzed condensation of a variety of active methylene compounds with methyl 6-acetoxymethyl-hepta-2,6-dienoate was investigated. The six-membered adducts resulting from a η3 palladium complex alkylation-Michael addition sequence were obtained with moderate to good yields. In some cases, further evolution of the primary adduct was observed. The process has been expanded to access nitrogen heterocycles by using sodium p-toluenesulfonamide as the nucleophilic partner. 相似文献
28.
Jacqueline Ficini Jean dAngelo Arnaud Eman Anne Marie Touzin 《Tetrahedron letters》1976,17(9):683-686
29.
Bernard Gordon Jacqueline S. Butler Ian R. Harrison 《Journal of polymer science. Part A, Polymer chemistry》1987,25(8):2139-2142
Catalysts bound to polymers in the form of crosslinked beads have been demonstrated to have a number of advantages over homogeneous catalysts. However, there are several problems that exist due to the polymer support being in the form of a bead. The rate of reaction depends on the presence of solvents that adequately swell the bead in order to allow access to the catalytic sites. Differences in polarity and reactant size can inhibit diffusion into the bead. Recently a new system has been developed whereby tris(triphenyl phosphine) chlororhodium (I) (Wilkinson's catalyst) is bound to the surface of polyethylene single crystals. Polyethylene single crystals have a very high surface to volume ratio allowing for greater ease of reaction compared to a bead system. In a previous paper we showed that there is a dramatic increase in catalytic activity and that the reaction rate increased as the polarity of solvent was increased, even in ethanol where the homogeneous catalyst is not soluble and the polystyrene bead support would not swell. In this letter we are describing the activity of hydrogenation of olefins contained in both large and/or polar molecules. The results demonstrate the advantages of supported catalysts on polyethylene single crystals rather than on polymer beads. 相似文献
30.
Ruhlmann L Canny J Vaissermann J Thouvenot R 《Dalton transactions (Cambridge, England : 2003)》2004,(5):794-800
Two new mixed-metal sandwich complexes [M(II)2(H2O)2Fe(III)2(P2W15O56)2]14- (abbreviated [M2Fe2P4W30], M(II) = Co(II), Mn(II)) were obtained at pH 3 by addition of M2+ to [Na2(H2O)2Fe(III)2(P2W15O56)2]16- (abbreviated [Na2Fe2P4W30]) without substitution in the alpha-[P2W15O56]12- (abbreviated [P2W15]) units. Their X-ray structures are reported. At lower pH, back conversion to [Na2Fe2P4W30] was followed by 31P NMR, electrochemistry and UV-visible spectroscopy. The preparation and the characterization in solution of the lacunary intermediate [NaCo(II)(H2O)2Fe(III)2(P2W15O56)2]15- (abbreviated [NaCoFe2P4W30]) is also described. 相似文献