全文获取类型
收费全文 | 619篇 |
免费 | 24篇 |
国内免费 | 1篇 |
专业分类
化学 | 444篇 |
晶体学 | 30篇 |
力学 | 92篇 |
数学 | 49篇 |
物理学 | 29篇 |
出版年
2023年 | 6篇 |
2022年 | 13篇 |
2021年 | 12篇 |
2020年 | 10篇 |
2019年 | 10篇 |
2018年 | 6篇 |
2017年 | 7篇 |
2016年 | 18篇 |
2015年 | 25篇 |
2014年 | 25篇 |
2013年 | 30篇 |
2012年 | 34篇 |
2011年 | 50篇 |
2010年 | 34篇 |
2009年 | 24篇 |
2008年 | 51篇 |
2007年 | 38篇 |
2006年 | 25篇 |
2005年 | 26篇 |
2004年 | 24篇 |
2003年 | 22篇 |
2002年 | 11篇 |
2001年 | 6篇 |
2000年 | 9篇 |
1999年 | 8篇 |
1998年 | 8篇 |
1997年 | 4篇 |
1996年 | 9篇 |
1995年 | 8篇 |
1994年 | 5篇 |
1993年 | 11篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 10篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1972年 | 5篇 |
1971年 | 5篇 |
1921年 | 1篇 |
排序方式: 共有644条查询结果,搜索用时 31 毫秒
11.
Boskovic C Sieber A Chaboussant G Güdel HU Ensling J Wernsdorfer W Neels A Labat G Stoeckli-Evans H Janssen S 《Inorganic chemistry》2004,43(16):5053-5068
Nine members of a new family of polynuclear ferric complexes have been synthesized and characterized. The reaction of Fe(O(2)CMe)(2) with polydentate Schiff base proligands (H(2)L) derived from salicylidene-2-ethanolamine, followed in some cases by reaction with carboxylic acids, has afforded new complexes of general formulas [Fe(2)(pic)(2)(L)(2)] (where pic(-) is the anion of 2-picolinic acid), [Fe(3)(O(2)CMe)(3)(L)(3)], [Fe(4)(OR)(2)(O(2)CMe)(2)(L)(4)], and [Fe(5)O(OH)(O(2)CR)(4)(L)(4)]. The tri-, tetra-, and pentanuclear complexes all possess unusual structures and novel core topologies. M?ssbauer spectroscopy confirms the presence of high-spin ferric centers in the tri- and pentanuclear complexes. Variable-temperature magnetic measurements suggest spin ground states of S = 0, 1/2, 0, and 5/2 for the bi-, tri-, tetra-, and pentanuclear complexes, respectively. Fits of the magnetic susceptibility data have provided the magnitude of the exclusively antiferromagnetic exchange interactions. In addition, an easy-axis-type magnetic anisotropy has been observed for the pentanuclear complexes, with D values of approximately -0.4 cm(-)(1) determined from modeling the low-temperature magnetization data. A low-temperature micro-SQUID study of one of the pentanuclear complexes reveals magnetization hysteresis at nonzero field. This is attributed to an anisotropy-induced energy barrier to magnetization reversal that is of molecular origin. Finally, an inelastic neutron scattering study of one of the trinuclear complexes has revealed that the magnetic behavior arises from two distinct species. 相似文献
12.
Sieber A Boskovic C Bircher R Waldmann O Ochsenbein ST Chaboussant G Güdel HU Kirchner N van Slageren J Wernsdorfer W Neels A Stoeckli-Evans H Janssen S Juranyi F Mutka H 《Inorganic chemistry》2005,44(12):4315-4325
A new family of tetranuclear Ni complexes [Ni(4)(ROH)(4)L(4)] (H(2)L = salicylidene-2-ethanolamine; R = Me (1) or Et (2)) has been synthesized and studied. Complexes 1 and 2 possess a [Ni(4)O(4)] core comprising a distorted cubane arrangement. Magnetic susceptibility and inelastic neutron scattering studies indicate a combination of ferromagnetic and antiferromagnetic pairwise exchange interactions between the four Ni(II) centers, resulting in an S = 4 spin ground state. Magnetization measurements reveal an easy-axis-type magnetic anisotropy with D approximately -0.93 cm(-)(1) for both complexes. Despite the large magnetic anisotropy, no slow relaxation of the magnetization is observed down to 40 mK. To determine the origin of the low-temperature magnetic behavior, the magnetic anisotropy of complex 1 was probed in detail using inelastic neutron scattering and frequency domain magnetic resonance spectroscopy. The spectroscopic studies confirm the easy-axis-type anisotropy and indicate strong transverse interactions. These lead to rapid quantum tunneling of the magnetization, explaining the unexpected absence of slow magnetization relaxation for complex 1. 相似文献
13.
Düggeli M Goujon-Ginglinger C Ducotterd SR Mauron D Bonte C von Zelewsky A Stoeckli-Evans H Neels A 《Organic & biomolecular chemistry》2003,1(11):1894-1899
A series of new tetradentate ligands containing two bipyridine groups or two pyridine moieties carrying amine substituents has been synthesised either from 5'- and 6'-substituted chiral bipyridines, or from chiral pyridine derivatives. These precursors have been prepared from (-)-alpha-pinene or (-)-myrtenal, respectively. The structures of three tetradentate-, and of five chiral bipyridine ligands have been determined by X-ray diffraction. 相似文献
14.
José R. Masaguer María Antonia Mendiola Cristina Molleda 《Transition Metal Chemistry》1985,10(10):387-389
Summary 2-Pyridylphenylacetonitrile (ppa) is oxidized by copper(II) halides in 1,2-dichloroethane to 1,2-dicyano-1,2-diphenyl-1,2-di(2-pyridyl)ethane (dcppe), yielding 41 complexes of dcppe with copper(II) dihalide, [CuX2(dcppe)4] (green). Nickel(II) and zinc(II) chlorides react with ppa giving complexes of a general formula [MCl2(ppa)2].Dcppe reacts with copper(II), zinc(II) chlorides and copper(II) bromide yielding complexes of formulae [CuCl2(dcppe)4] (yellow), [ZnCl2(dcppe)2] and [CuBr2(dcppe)]. No reaction is observed with cobalt(II) and nickel(II) chlorides. 相似文献
15.
A kinetic method is presented for the determination of 0.5–5 μg ml?1 gallium based on its activating effect on the copper(II)-catalyzed oxidation of 4,4′-dihydroxybenzophenone thiosemicarbazone by hydrogen peroxide. The reaction is monitored spectrophotometrically at 415 nm. Two sets of reaction conditions are established; one for the direct determination of gallium, and another, in which indium affects the gallium response, for determination of indium. Mixtures of these cations can be determined at μg ml?1 levels and in gallium/indium ratios from 7.5:1 to 1:1.6, with an accuracy and precision of ca. 4.5%. 相似文献
16.
Andrés G. León Ana I. Olives M. Antonia Martín Benito del Castillo 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):577-583
The use of cyclodextrins (CDs) in HPLC as mobile phase additives provides a flexible alternative for the separation of chemically
related compounds because these separations can be performed on conventional columns and are economically advantageous over
the use of chiral stationary phases. The present paper describes the influence of the presence of β-cyclodextrin (β-CD) and
2-hydroxypropyl-β-cyclodextrin (HPβ-CD) on the separation of the β-carboline alkaloids norharmane, harmane and harmine. The
nature of the stationary phase (reverse phases C1 and C18) affects the chromatographic separations and also the stability of the inclusion complexes that are developed. The changes
in the proportion of the organic solvents at constant concentration of CDs (3 mM for β-CD and 15 mM for HPβ-CD) modify the
retention factors (k′) for all alkaloids studied. The nature of the organic solvent in the mobile phase also changes the chromatographic parameters.
The logarithm of the capacity factor (k′) is linearly increased with the proportion of water in the hydro-organic mobile phase (ethanolic or methanolic) but the
slopes obtained vary depending on the CD added to the mobile phase. The role of competitive equilibria, i.e., chromatographic
distribution and inclusion complexes formation is discussed.
This paper was presented at XIIIth International Cyclodextrin Symposium. Torino, Italy, May, 14–17, 2006 相似文献
17.
Isabel Pizarro Ma Milagros Gomez Carmen Cámara Ma Antonia Palacios 《International journal of environmental analytical chemistry》2013,93(10):879-890
Gradient ion chromatographic separation coupled with ICP-MS was used to resolve and determine the most common arsenic species in environmental and biological samples of carrots, trout, soil, sediment and river water from Region II of Chile. The carrot and trout samples showed a concentration of 49 and 168 µg g?1, respectively, of total As. Both concentrations are high considering the basal level. In the carrots, percentage of 45 and 31% of total As were found for As(III) and As(V) species, respectively. In the trout, the higher concentration related to AsB at 39% of the total As. As(III) and DMA were also present in relatively high concentrations. The River Loa and the soil in which the carrots are growing also present very high As(V) concentrations of 100 and 17 µg g?1, respectively. The ratio between the concentration for the same As species found in the living organisms (carrots and trout) and the environment in which they grow (soil and water) can provide important information about the possible absorption or biotransformation of As species in living beings. As(III) and DMA are the species in which the greatest accumulation occurs with respect to the medium in which they are present, and biotransformation also appears to take place. 相似文献
18.
19.
20.