全文获取类型
收费全文 | 316篇 |
免费 | 6篇 |
专业分类
化学 | 205篇 |
晶体学 | 3篇 |
力学 | 9篇 |
数学 | 9篇 |
物理学 | 96篇 |
出版年
2023年 | 2篇 |
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 6篇 |
2018年 | 2篇 |
2016年 | 3篇 |
2015年 | 2篇 |
2014年 | 4篇 |
2013年 | 12篇 |
2012年 | 8篇 |
2011年 | 20篇 |
2010年 | 12篇 |
2009年 | 12篇 |
2008年 | 14篇 |
2007年 | 16篇 |
2006年 | 26篇 |
2005年 | 24篇 |
2004年 | 15篇 |
2003年 | 10篇 |
2002年 | 8篇 |
2001年 | 6篇 |
2000年 | 10篇 |
1999年 | 3篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 10篇 |
1993年 | 3篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 8篇 |
1977年 | 6篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1972年 | 4篇 |
1970年 | 2篇 |
1964年 | 2篇 |
1932年 | 3篇 |
1931年 | 2篇 |
1917年 | 2篇 |
1889年 | 1篇 |
排序方式: 共有322条查询结果,搜索用时 15 毫秒
91.
Three new ruthenium(II) complexes have been prepared which contain two 1,10-phenanthroline units and a third sterically hindering chelate. In one case, the hindering ligand is a disubstituted 2,2'-bipyridine (bpy) attached to two very bulky manisyl groups. The two other systems are similar in terms of size of the hindering groups (anisyl substituents) located close to the central metal. The complexes investigated in the Present Report are aimed at providing building blocks of future light-driven molecular machines. The photochemical expulsion of the sterically hindering chelate has thus been studied by UV-vis spectroscopy and 1H NMR. Surprisingly, the manisyl-containing complex turned out to be photochemically inert, indicating that a too bulky group acts as a protecting function versus decomplexation rather than as a destabilizing group. For the two other systems, a pronounced ring effect was observed: whereas the acyclic systems undergo fast photochemical expulsion of the bipy-based ligand, in the cyclic complex, the bipy-incorporating ring is decoordinated about 5 times less efficiently than the acyclic ligand of the previous case. These observations on the strong dependence of the photochemical behavior of the ruthenium(II) complexes on their structural properties are corroborated by X-ray diffraction studies on the three compounds investigated. 相似文献
92.
The transferable potentials for phase equilibria (TraPPE) force fields are extended to amine, nitro, nitrile, and amide functionalities and to pyridine and pyrimidine. In many cases, the same parameters for a functional group are used for both united-atom and explicit-hydrogen representations of alkyl tails. Following the TraPPE philosophy, the nonbonded interaction parameters were fitted to the vapor-liquid coexistence curves for selected one-component systems. Coupled-decoupled configurational-bias Monte Carlo simulations in the Gibbs ensemble were applied to neat (methyl-, dimethyl-, trimethyl-, ethyl-, diethyl-, or triethyl-)amine, nitromethane, nitroethane, nitrobenzene, acetonitrile, propionitrile, acetamide, propanamide, butanamide, pyridine, and pyrimidine. Excellent agreement with experimental results was found, with the mean unsigned errors being less than 1% for both the critical temperature and the normal boiling temperature. Similarly, the liquid densities at low reduced temperatures are reproduced to within 1%, and the deviation for the critical densities is about 4%. Additional simulations were performed for the binary mixtures of methylamine + n-hexane, diethyl ether + acetonitrile, 1-propanol + acetonitrile, and nitroethane + ethanol. With the exception of the methylamine/n-hexane mixture for which the separation factor is substantially overestimated, agreement with experiment for the other three mixtures is very satisfactory. 相似文献
93.
Julien M Feher T Horvatic M Berthier C Bakharev ON Segransan P Collin G Marucco J 《Physical review letters》2000,84(15):3422-3425
Doping the high- T(c) superconductor YBa2Cu3O6.7 with 1.5% of nonmagnetic Zn impurities in CuO2 planes is shown to produce a considerable broadening of 63Cu NMR spectra, as well as an increase of low-energy magnetic fluctuations detected in 63Cu spin-lattice relaxation measurements. A model-independent analysis demonstrates that these effects are due to the development of staggered magnetic moments on many Cu sites around each Zn and that the Zn-induced moment in the bulk susceptibility might be explained by this staggered magnetization. Several implications of these enhanced antiferromagnetic correlations are discussed. 相似文献
94.
Single crystals of Na5Zr(PO4)3 have been prepared using a flux method. At high temperature (200|MoC), the crystal structure can be described as a 3D network of PO4 tetrahedra corner shared with ZrO6 and NaO6 octahedra. In fact, this compound belongs to the Nasicon-type class which exhibits a large nonstoichiometry range by zirconium deficiency. 相似文献
95.
Silver β alumina is studied by X-ray diffuse scattering. A very short coherence length is observed within the conduction slab (~ 10Å), but in contrast with other β alumina compounds a clear interplanar correlation is also present. It is this 3-D nature of the ion-ion correlation which can explain the relatively high resistivity of this material in spite of the very short coherence lengths. 相似文献
96.
Sonia Collin Daniel P. Vercauteren Didier Vanderveken Guy Evrard François Durant 《Journal of computer-aided molecular design》1989,3(1):39-53
Summary Molecular graphic design coupled with PCILO and crystallographic results have been used to investigate the three-dimensional structure of Tropapride, Piquindone, Zetidoline, and Metoclopramide, four dopamine D-2 receptor antagonists showing Na+-dependent binding. Three putative pharmacophoric elements, a nitrogen lone pair, a phenyl ring and a carbonyl moiety, are similarly oriented in all the Na+-dependent drugs. Conversely, for Na+-independent analogs, the two latter pharmacophoric elements play a subordinate role, but two -electron regions are systematically localized on the other side of the molecule: the first is a phenyl group while the second is a carbonyl function as in butyrophenones, a cyano group as in R48455, or a phenyl ring as in diphenylbutylpiperidines or tricyclics. The presence of a benzyl ring on this side in Tropapride might explain its weak extrapyramidal effects. 相似文献
97.
98.
In the decay Eu152→Gd152 fiveβ(circularly polarizedγ) correlations have been measured (Table). The Fermi matrix element of the 3?–3? β transition is small or vanishing. The levels of 344 and 755 keV (I=2+ and 4+, respectively) seem to be collective states. 相似文献
99.
K. Kayser W. Collin P. Filss S. Guldbakke G. Nolte H. Reich J. O. Trier W. Witschel 《Zeitschrift für Physik A Hadrons and Nuclei》1970,239(5):447-460
In order to obtain data on the photon absorption process between the giant resonance and the meson threshold the cross sections of the reactions12C(γ,n)11C,12C(γ, 2n)10C,39K(γ,n)38Kg, and40Ca(γ,np)38Kg have been determined by the analysis of yield curves at the 140 MeV electron synchrotron of the PTB. Though the (γ,n) cross sections grow small with increasing photon energy they are different from zero up to energies of 60 MeV and above. The cross section of the reaction12C(γ, 2n) is extremely small; its highest value amounts to 0.15% of the highest value of the12C(γ,n) reaction. The measured40Ca(γ,np) cross section is of the order predicted by the naive quasi-deuteron model. The integrated cross sections of the above reactions up to 140MeV are 85±7,0.90±0.10, 139±16, and 76±7MeVmb respectively. 相似文献
100.
Baranoff E Dixon IM Collin JP Sauvage JP Ventura B Flamigni L 《Inorganic chemistry》2004,43(10):3057-3066
A series of Ir(III)-D dyads based on an iridium(III) bis-terpyridine complex as a photoactive center and tertiary amines as donor groups, as well as their individual components, have been designed to generate photoinduced charge separation. Depending on the donor group, a modular approach or a "chemistry-on-the-complex" approach has been used to prepare three different Ir(III)-D dyads. A detailed photophysical study has been performed on one Ir(III)-D dyad in which a triarylamine is linked to the iridium bis-terpyridine complex with an amido-phenyl group used as a spacer. In acetonitrile at room temperature, steady-state and time-resolved methods gave evidence of a photoinduced charge-separated state Ir(-)-D(+) with a lifetime of 70 ps. This relatively short lifetime could be due to the close proximity between the negative charge, likely localized in the bridging terpyridine, and the oxidized donor group. 相似文献