全文获取类型
收费全文 | 445篇 |
免费 | 10篇 |
专业分类
化学 | 300篇 |
晶体学 | 16篇 |
力学 | 29篇 |
数学 | 48篇 |
物理学 | 62篇 |
出版年
2022年 | 5篇 |
2021年 | 6篇 |
2020年 | 5篇 |
2019年 | 5篇 |
2018年 | 8篇 |
2017年 | 7篇 |
2016年 | 10篇 |
2015年 | 9篇 |
2014年 | 12篇 |
2013年 | 19篇 |
2012年 | 26篇 |
2011年 | 23篇 |
2010年 | 18篇 |
2009年 | 11篇 |
2008年 | 22篇 |
2007年 | 23篇 |
2006年 | 12篇 |
2005年 | 24篇 |
2004年 | 17篇 |
2003年 | 15篇 |
2002年 | 16篇 |
2001年 | 6篇 |
2000年 | 7篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 8篇 |
1995年 | 10篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 7篇 |
1990年 | 9篇 |
1989年 | 2篇 |
1987年 | 5篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 5篇 |
1972年 | 5篇 |
1968年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有455条查询结果,搜索用时 0 毫秒
121.
We calculate the oscillations of the dc conductance across a mesoscopic ring, simultaneously tuned by applied magnetic and electric fields orthogonal to the ring. The oscillations depend on the Aharonov-Bohm flux and of the spin-orbit coupling. They result from mixing of the dynamical phase, including the Zeeman spin splitting, and of geometric phases. By changing the applied fields, the geometric phase contribution to the conductance oscillations can be tuned from the adiabatic (Berry) to the nonadiabatic (Ahronov-Anandan) regime. To model a realistic device, we also include nonzero backscattering at the connection between ring and contacts, and a random phase for electron wave function, accounting for dephasing effects. 相似文献
122.
Lepareur N Mévellec F Noiret N Refosco F Tisato F Porchia M Bandoli G 《Dalton transactions (Cambridge, England : 2003)》2005,(17):2866-2875
Reduction-substitution reactions of [M(O)Cl(4)](-)(M=Re, (99)Tc) precursors with an excess of substituted dithiobenzoate ligands (R-PhCS(2))(-) in dichloromethane/methanol mixtures afford a series of six-coordinated neutral mixed-ligand complexes of the type M(III)(R-PhCS(3))(2)(R-PhCS(2))(M=Re; Rel--9; M=99)Tc; Tel--9). The coordination sphere is entirely filled by sulfur donor atoms, and the complexes adopt a distorted trigonal prismatic arrangement, as assessed by the X-ray crystal structure analysis of Re(4-Me-PhCS(3))(2)(4-Me-PhCS(2)), Re 2. These compounds show sharp proton and carbon NMR profiles, in agreement with the diamagnetism typical of low spin d(4) trigonal prismatic configurations. The red-ox processes involve reduction of the metal from Re(v) to Re(iii) and oxidation of dithiobenzoate to trithioperoxybenzoate. M2--9 complexes contain a substitution-inert [M(R-PhCS(3))(2)](+) moiety including the metal and two trithioperoxybenzoate fragments, while the third dithiobenzoate ligand is labile. The latter is efficiently replaced by reaction with better nucleophiles such as diethyldithiocarbamate giving a further class of mixed ligand complexes of the type M(III)(R-PhCS(3))(2)(Et(2)NCS(2))(M=Re; Re 10--18; M=(99)Tc; Tc--18), which retain the trigonal prismatic arrangement, as determined by the X-ray analyses of the representative compounds Re(PhCS(3))(2)(Et(2)NCS(2)), Re 10 and (99)Tc(PhCS(3))(2)(Et(2)NCS(2)), Tc 10. 相似文献
123.
124.
G. Rapisarda B. Ginatempo G. M. Florio A. Stancanelli E. S. Giuliano 《Il Nuovo Cimento D》1990,12(10):1453-1463
Summary We have extended the well-known relativistic KKR-CPA theory up tol≤3 angular momentum, in order to make this framework suitable to deal with rare-earth alloys. However, such an extension has
also relevance in judging the convergence of the KKR-CPA calculations even for those atomic species with empty valencef-states. To do that we worked out the transformation from the usual real spherical harmonics to the cubic double-point group
representatin. We have tested the present theory and corresponding codes by computing the electronic structure of Cu0.75−Au0.25 and by comparing our results with earlierl≤2 R-KKR-CPA calculations. In order to reduce the large amount of computing time required, we have also used a new technique
for the Brillouin zone integration.
Work sponsored also by CRRN/SM. 相似文献
125.
126.
Tafi A Botta B Botta M Delle Monache G Filippi A Speranza M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(17):4126-4135
Molecular recognition of representative amino acids (A) by a chiral amido[4]resorcinarene receptor (1(L)) was investigated in the gas phase by ESI-FT-ICR mass spectrometry. The ligand displacement reaction between noncovalent diastereomeric [1(L).H.A](+) complexes and the 2-aminobutane enantiomers (B) exhibits a distinct enantioselectivity with regard to both the leaving amino acid A and the amine reactant B. The emerging selectivity picture, discussed in the light of molecular mechanics and molecular dynamics calculations, points to chiral recognition by 1(L), as determined by the effects of the host asymmetric frame on the structure, stability, and rearrangement dynamics of the diastereomeric [1(L).H.A](+) complexes and the orientation of the amine reactant B in encounters with [1(L).H.A](+). The results contribute to the development of a dynamic model of chiral recognition of biomolecules by enzyme mimics in the unsolvated state. 相似文献
127.
Femoni C Iapalucci MC Longoni G Svensson PH 《Chemical communications (Cambridge, England)》2004,(20):2274-2275
Condensation between preformed Ni-Pt and Pt carbonyl clusters leads to the new [H(6-n)Ni(24)Pt(17)(CO)(46)](n-)(n= 5, 6) and the substitutionally Ni/Pt disordered [Ni(24)(Ni(12-x)Pt(x))Pt(20)(CO)(56)](6-) (x = 4) carbonyl clusters, the latter of which represents the highest nuclearity homoleptic carbonyl cluster anion so far reported. 相似文献
128.
Fabbrizzi L Licchelli M Mancin F Pizzeghello M Rabaioli G Taglietti A Tecilla P Tonellato U 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(1):94-101
The fluorescence chemosensor ATMCA has been realised by appending an anthrylmethyl group to an amino nitrogen of TMCA (2,4,6-triamino-1,3,5-trimethoxycyclohexane), a tripodal ligand selective for divalent first-row transition metal ions in water. The ATMCA ligand can act as a versatile sensor for ZnII and CuII ions. Its sensing ability can be switched by simply tuning the operating conditions. At pH 5, ATMCA detects copper(II) ions in aqueous solutions by the complexation-induced quenching of the anthracene emission. Metal ion concentrations < 1 microM can be readily detected and very little interference is exerted by other metal ions. At pH 7, ATMCA signals the presence of ZnII ions at concentrations < 1 microM by a complexation-induced enhancement of the fluorescence. Again the sensor is selective for ZnII over several divalent metal ions, with the exception of CuII, CoII and HgII. Most interestingly, the [ZnII(atmca)]2+ complex can act as a fluorescence sensor for specific organic species, notably selected dicarboxylic acids and nucleotides, by the formation of ternary ligand/zinc/substrate complexes. The oxalate anion is detected in concentrations <0.1 mM; however, no effects on the system's fluorescence is observed in the presence of monocarboxylic acids and long-chain dicarboxylic acids. Among the nucleotides, those containing an imide or amide function are readily detected and an unprecedented high sensitivity for guanine derivatives allows the determination of this nucleotide for 0.05-0.5 mM solutions. Moreover, [ZnII(atmca)]2+ is a very effective and selective sensor in the case of vitamin B13 (orotic acid) in sub-micromolar concentrations. The operative features of the systems investigated are also clearly suitable for intracellular analyses. The factors at the source of organic substrate recognition, here briefly discussed, are of paramount importance for further developments in the applicability of these sensing systems. 相似文献
129.
Alessandro Dolmella Giuliano BandoliClaudio Grandi 《Journal of Molecular Structure》2002,607(1):43-58
Muscarone analogues are compounds that have been proposed for the prevention or treatment of senile dementias. ARL-16607 (I), ARL-15467 (II), ARL-14995 (III) and YM-796 (IV) are spiromuscar-3-one derivatives and behave as muscarinic M1 agonists, with different binding selectivity and efficacy at the M1 receptors. In this work, we have elucidated the solid-state structures of I-III and compared the results obtained with the data available in the literature for IV.The solid-state arrangements of I-IV have then been used to input a series of theoretical calculations. For each molecule, eight conformations have been modeled and the obtained structures (1-32) have been submitted to a series of molecular dynamics/simulated annealing and molecular mechanics calculations aimed to explore the conformational freedom of the spiromuscar-3-one moiety. Some hints about the reactivity of I-IV have been obtained by performing Hartree-Fock, density functional theory and semiempirical quantum mechanics calculations. These studies analyzed the properties of the frontier orbitals and of the molecular electrostatic potential of I-IV.The information gained has been used to explain the better efficacy and poorer selectivity shown by III. Our results suggest that the behavior of III is due to its smaller size, the features of its molecular surface, the shape of its electrostatic potential and the orientation of its reactive domains. 相似文献
130.
We derive the representation of the two-spinon wave function for the Haldane-Shastry model in terms of the spinon coordinates. This result allows us to rigorously analyze spinon interaction and its physical effects. We show that spinons attract one another. The attraction gets stronger as the size of the system is increased and, in the thermodynamic limit, determines the power law with which the susceptibility diverges. 相似文献