全文获取类型
收费全文 | 3445篇 |
免费 | 136篇 |
国内免费 | 24篇 |
专业分类
化学 | 2173篇 |
晶体学 | 13篇 |
力学 | 91篇 |
数学 | 774篇 |
物理学 | 554篇 |
出版年
2023年 | 35篇 |
2022年 | 80篇 |
2021年 | 90篇 |
2020年 | 63篇 |
2019年 | 85篇 |
2018年 | 64篇 |
2017年 | 67篇 |
2016年 | 139篇 |
2015年 | 105篇 |
2014年 | 121篇 |
2013年 | 199篇 |
2012年 | 250篇 |
2011年 | 286篇 |
2010年 | 158篇 |
2009年 | 173篇 |
2008年 | 232篇 |
2007年 | 222篇 |
2006年 | 201篇 |
2005年 | 162篇 |
2004年 | 159篇 |
2003年 | 100篇 |
2002年 | 95篇 |
2001年 | 40篇 |
2000年 | 42篇 |
1999年 | 29篇 |
1998年 | 27篇 |
1997年 | 24篇 |
1996年 | 32篇 |
1995年 | 15篇 |
1994年 | 19篇 |
1993年 | 16篇 |
1992年 | 27篇 |
1991年 | 14篇 |
1990年 | 28篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 11篇 |
1986年 | 16篇 |
1985年 | 21篇 |
1984年 | 23篇 |
1983年 | 10篇 |
1982年 | 7篇 |
1981年 | 14篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1974年 | 8篇 |
1973年 | 5篇 |
1971年 | 6篇 |
1963年 | 5篇 |
排序方式: 共有3605条查询结果,搜索用时 15 毫秒
111.
Mixtures of La(III) and Mg(II) form with purpurin (P; 1,2,4-trihydroxyanthraquinone) the mixed-metal complex LaMg2P5, which is extracted with methyl isobutyl ketone at pH 7.5. The molar absorptivity of the complex is 6.1 × 104 l.mole−1.cm−1 at 570 nm and its conditional extraction constant 5 × 1013 l4.mole−4. Similar complexes have been found to be formed with yttrium, cerium, praseodymium, neodymium and samarium. The use of these complexes for the spectrophotometric determination of yttrium and lanthanides up to 15 μg has been investigated. 相似文献
112.
Jorge Angulo Cornejo Ketty Ayala Rainer Richter Heinz Bhlig Lothar Hennig Lothar Beyer 《无机化学与普通化学杂志》2005,631(15):3040-3045
Hydrogen Bonds in 1,1‐Bis(2‐hydroxyethyl)‐3‐benzoylthiourea and its Nickel(II)‐ and Copper(II)‐Chelate Complexes The ligand 1,1‐bis(2‐hydroxyethyl)‐3‐benzoylthiourea HL, ( 1 ), yields with nickel(II) and copper(II) ions neutral complexes [NiL2], ( 2 ), and [CuL2], ( 3 ). By X‐ray structure analysis and IR spectroscopy different intramolecular hydrogen bonds (OH…O) and (OH…N) could be identified in both equally coordinated ligands of the [NiL2] molecule. For comparison X‐ray and IR data were also estimated for 1 and 3 . 相似文献
113.
114.
115.
116.
Daniela P. Mesquita Cristiano Leal Jorge R. Cunha Adrian Oehmen A. Luís Amaral Maria A.M. Reis Eugénio C. Ferreira 《Analytica chimica acta》2013
The present study focuses on predicting the concentration of intracellular storage polymers in enhanced biological phosphorus removal (EBPR) systems. For that purpose, quantitative image analysis techniques were developed for determining the intracellular concentrations of PHA (PHB and PHV) with Nile blue and glycogen with aniline blue staining. Partial least squares (PLS) were used to predict the standard analytical values of these polymers by the proposed methodology. Identification of the aerobic and anaerobic stages proved to be crucial for improving the assessment of PHA, PHB and PHV intracellular concentrations. Current Nile blue based methodology can be seen as a feasible starting point for further enhancement. Glycogen detection based on the developed aniline blue staining methodology combined with the image analysis data proved to be a promising technique, toward the elimination of the need for analytical off-line measurements. 相似文献
117.
γ-Carboxylation of β-diketones, 1, can be improved using samples containing 100% of ketoenol tautomers, 3, prepared by mild hydrolysis of the corresponding copper(II) complexes 2. Cyclization of the so formed 4-alkyl-3,5-dioxohexanoic acids, 4, affords 5-alkyl-4-hydroxy-6-methyl-2-pyrones, 5. 相似文献
118.
Nicolás D. Gómez Violeta D'Accurso V. Mariana Freytes Francisco A. Manzano Jorge Codnia M. Laura Azcárate 《国际化学动力学杂志》2013,45(5):306-313
An experimental setup that coupled IR multiple‐photon dissociation (IRMPD) and laser‐induced fluorescence (LIF) techniques was implemented to study the kinetics of the recombination reaction of dichlorocarbene radicals, CCl2, in an Ar bath. The CCl2 radicals were generated by IRMPD of CDCl3. The time dependence of the CCl2 radicals’ concentration in the presence of Ar was determined by LIF. The experimental conditions achieved allowed us to associate the decrease in the concentration of radicals to the self‐recombination reaction to form C2Cl4. The rate constant for this reaction was determined in both the falloff and the high‐pressure regimes at room temperature. The values obtained were k0 = (2.23 ± 0.89) × 10?29 cm6 molecules?2 s?1 and k∞ = (6.73 ± 0.23) × 10?13 cm3 molecules?1 s?1, respectively. 相似文献
119.
Silica obtained by acid treatment of sepiolite was used as a support for catalysts consisting of palladium complexes of 2‐ and 3‐thiophenecarbaldehyde. The support and the catalysts were characterized by X‐ray diffraction, and solid‐state 29Si and 13C nuclear magnetic resonance spectroscopies. The supported palladium catalysts were used in the Suzuki reaction of bromobenzene with phenylboronic acid. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
120.
Sonia Dopico‐García Ana Ares‐Pernas Jorge Otero‐Canabal Mar Castro‐López José M. López‐Vilariño Victoria González‐Rodríguez María J. Abad‐López 《先进技术聚合物》2013,24(8):723-731
Nowadays, there is a growing availability of biodegradable industrial materials intended to food contact applications whose service life behavior needs to be further investigated. This article is focused on the degradation of two materials based on polylactic acid. The correlation between the rate of degradation and the amount of trapped degradation products was investigated applying three characterization techniques in parallel, namely rheology, high‐performance liquid chromatography (HPLC), and matrix‐assisted laser desorption/ionization (MALDI). The rate of degradation was studied through the evaluation of their rheological properties and calculation of the number of average molecular weights, and weight‐average molecular weights. Water‐soluble oligomers and lactic acid were quantified by HPLC‐ultraviolet. Changes in cyclic and linear oligomers were monitored by MALDI‐time‐of‐flight mass spectrometry. Specimens of 4‐mm thickness of each biopolymer were subjected to hydrolysis in deionized water up to 6 months at two temperatures, simulating service conditions of food packaging. The diminution in viscosity and consequently in molecular weight distribution (20–60%) showed the degradation of the molecular structure of both polylactic acids. The chain scission was followed through the increasing values of lactic acid and hydrolyzed oligomers (twofold to eightfold), and the predominant signal of the linear oligomers over the cyclic ones with aging. Rheology, HPLC, and MALDI showed to be complementary tools to better understand the changes in the molecular structure. The obtained results showed the necessity of adding suitable stabilizers for each particular food packaging application. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献