全文获取类型
收费全文 | 2120篇 |
免费 | 66篇 |
国内免费 | 14篇 |
专业分类
化学 | 1522篇 |
晶体学 | 12篇 |
力学 | 60篇 |
数学 | 355篇 |
物理学 | 251篇 |
出版年
2021年 | 34篇 |
2020年 | 22篇 |
2019年 | 25篇 |
2018年 | 25篇 |
2017年 | 16篇 |
2016年 | 32篇 |
2015年 | 55篇 |
2014年 | 42篇 |
2013年 | 110篇 |
2012年 | 119篇 |
2011年 | 137篇 |
2010年 | 76篇 |
2009年 | 61篇 |
2008年 | 107篇 |
2007年 | 111篇 |
2006年 | 126篇 |
2005年 | 89篇 |
2004年 | 90篇 |
2003年 | 80篇 |
2002年 | 65篇 |
2001年 | 39篇 |
2000年 | 20篇 |
1999年 | 13篇 |
1998年 | 20篇 |
1997年 | 17篇 |
1996年 | 35篇 |
1995年 | 19篇 |
1994年 | 18篇 |
1993年 | 28篇 |
1992年 | 14篇 |
1991年 | 23篇 |
1990年 | 19篇 |
1989年 | 19篇 |
1988年 | 21篇 |
1986年 | 13篇 |
1985年 | 28篇 |
1984年 | 24篇 |
1983年 | 14篇 |
1982年 | 27篇 |
1981年 | 26篇 |
1980年 | 15篇 |
1979年 | 32篇 |
1978年 | 20篇 |
1977年 | 28篇 |
1976年 | 22篇 |
1975年 | 23篇 |
1974年 | 24篇 |
1973年 | 18篇 |
1971年 | 12篇 |
1968年 | 12篇 |
排序方式: 共有2200条查询结果,搜索用时 421 毫秒
991.
Pichon C Dolbecq A Mialane P Marrot J Rivière E Goral M Zynek M McCormac T Borshch SA Zueva E Sécheresse F 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(10):3189-3199
While the reaction of [PW(11)O(39)](7-) with first row transition-metal ions M(n+) under usual bench conditions only leads to monosubstituted {PW(11)O(39)M(H(2)O)} anions, we have shown that the use of this precursor under hydrothermal conditions allows the isolation of a family of novel polynuclear discrete magnetic polyoxometalates (POMs). The hybrid asymmetric [Fe(II)(bpy)(3)][PW(11)O(39)Fe(2) (III)(OH)(bpy)(2)]12 H(2)O (bpy=bipyridine) complex (1) contains the dinuclear {Fe(micro-O(W))(micro-OH)Fe} core in which one iron atom is coordinated to a monovacant POM, while the other is coordinated to two bipyridine ligands. Magnetic measurements indicate that the Fe(III) centers in complex 1 are weakly antiferromagnetically coupled (J=-11.2 cm(-1), H=-JS(1)S(2)) compared to other {Fe(micro-O)(micro-OH)Fe} systems. This is due to the long distances between the iron center embedded in the POM and the oxygen atom of the POM bridging the two magnetic centers, but also, as shown by DFT calculations, to the important mixing of bridging oxygen orbitals with orbitals of the POM tungsten atoms. The complexes [Hdmbpy](2)[Fe(II)(dmbpy)(3)](2)[(PW(11)O(39))(2)Fe(4) (III)O(2)(dmbpy)(4)]14 H(2)O (2) (dmbpy=5,5'-dimethyl-2,2'-bipyridine) and H(2)[Fe(II)(dmbpy)(3)](2)[(PW(11)O(39))(2)Fe(4) (III)O(2)(dmbpy)(4)]10 H(2)O (3) represent the first butterfly-like POM complexes. In these species, a tetranuclear Fe(III) complex is sandwiched between two lacunary polyoxotungstates that are pentacoordinated to two Fe(III) cations, the remaining paramagnetic centers each being coordinated to two dmbpy ligands. The best fit of the chi(M)T=f(T) curve leads to J(wb)=-59.6 cm(-1) and J(bb)=-10.2 cm(-1) (H=-J(wb)(S(1)S(2)+S(1)S(2*)+S(1*)S(2)+S(1*)S(2*))-J(bb)(S(2)S(2*))). While the J(bb) value is within the range of related exchange parameters previously reported for non-POM butterfly systems, the J(wb) constant is significantly lower. As for complex 1, this can be justified considering Fe(w)--O distances. Finally, in the absence of a coordinating ligand, the dimeric complex [N(CH(3))(4)](10)[(PW(11)O(39)Fe(III))(2)O]12 H(2)O (4) has been isolated. In this complex, the two single oxo-bridged Fe(III) centers are very strongly antiferromagnetically coupled (J=-211.7 cm(-1), H=-JS(1)S(2)). The electrochemical behavior of compound 1 both in dimethyl sulfoxide (DMSO) and in the solid state is also presented, while the electrochemical properties of complex 2, which is insoluble in common solvents, have been studied in the solid state. 相似文献
992.
993.
Murielle Rivenet Pascal Roussel Francis Abraham 《Journal of solid state chemistry》2008,181(10):2586-2590
Single crystals of Bi(C2O4)OH were obtained by the slow diffusion of Bi3+ cations through silica gel impregnated with oxalic acid. The structure was solved in the Pnma space group with a=6.0853(2) Å, b=11.4479(3) Å, c=5.9722(2) Å, leading to R=0.0188 and wR=0.0190 from 513 unique reflections. The bismuth coordination polyhedron is a BiO6E pentagonal bipyramid with the lone pair E sitting at an axial vertex. The opposite axial vertex is occupied by a hydroxyl oxygen atom, which is also an equatorial corner of a neighboring BiO6E bipyramid. The sharing of the hydroxyl oxygen atoms build zig-zag chains running down the [100] direction. These chains are aligned in a sheet parallel to the (010) plane and are further connected through oxalate ions to form a three-dimensional arrangement. On heating, Bi(C2O4)OH decomposes to the meta-stable quadratic β-Bi2O3 phase. 相似文献
994.
Nanocomposites based on chloroprene rubber: Effect of chemical nature and organic modification of nanoclay on the vulcanizate properties 总被引:2,自引:0,他引:2
Amit Das Francis Reny Costa Udo Wagenknecht Gert Heinrich 《European Polymer Journal》2008,44(11):3456-3465
The effect of two chemically opposite type of nanofillers, namely montmorillonite (MMT) and layered double hydroxide (LDH), both in pristine and organically modified forms (OLDH and OMMT) on the mechanical properties and crystallization behavior of chloroprene rubber (CR) vulcanizates have been investigated. While the addition of very small amount of pristine clays shows a significant improvement of the physical properties of the CR based nanocomposites, the organic modification improves the reinforcing efficiency of MMT more than that of LDH. MMT is found to enhance the crystallization tendency of CR chains, whereas LDH has a role to resist it as observed from the dynamic mechanical analysis (DMA). The DMA results also show that the presence small amount of nanoclay enhances the storage modulus of CR based vulcanizates, which becomes more pronounced in case of organically modified clays, especially with OMMT. Finally, we report the ‘house of cards’ structure of exfoliated platelets of montmorillonite in the CR matrix which are produced by mechanical shear mixing. 相似文献
995.
996.
Back Cover: Engaging Copper(III) Corrole as an Electron Acceptor: Photoinduced Charge Separation in Zinc Porphyrin–Copper Corrole Donor–Acceptor Conjugates (Chem. Eur. J. 4/2016)
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
997.
998.
999.