全文获取类型
收费全文 | 276篇 |
免费 | 4篇 |
国内免费 | 1篇 |
专业分类
化学 | 171篇 |
晶体学 | 2篇 |
力学 | 5篇 |
数学 | 44篇 |
物理学 | 59篇 |
出版年
2023年 | 3篇 |
2022年 | 2篇 |
2021年 | 10篇 |
2020年 | 5篇 |
2019年 | 9篇 |
2018年 | 5篇 |
2017年 | 8篇 |
2016年 | 16篇 |
2015年 | 7篇 |
2014年 | 14篇 |
2013年 | 21篇 |
2012年 | 10篇 |
2011年 | 16篇 |
2010年 | 15篇 |
2009年 | 15篇 |
2008年 | 14篇 |
2007年 | 16篇 |
2006年 | 7篇 |
2005年 | 13篇 |
2004年 | 7篇 |
2003年 | 8篇 |
2002年 | 10篇 |
2001年 | 7篇 |
2000年 | 6篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1991年 | 2篇 |
1988年 | 1篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有281条查询结果,搜索用时 31 毫秒
101.
Gerson F. Duarte‐Junior Eulício O. Lobo‐Júnior Íris Medeiros Junior Jos A. Fracassi da Silva Claudimir L. do Lago Wendell K. T. Coltro 《Electrophoresis》2019,40(5):693-698
This study reports the separation of fructose, galactose, glucose, lactose and sucrose on glass microchip electrophoresis (ME) devices using a microfluidic platform adapted with external reservoirs for controlling the electrolysis phenomenon. The connections between external reservoirs and microfluidic platform were performed by saline bridges created using silicone tubing filled with BGE. The separation conditions were optimized and the best results were achieved using a BGE containing 75 mmol/L NaOH and 15 mmol/L trisodium phosphate. Electrophoretic separations were monitored using a capacitively coupled contactless conductivity detection system. The controlled electrolysis has successfully allowed the application of a higher voltage on the separation channel promoting the baseline separation of five carbohydrates within 180 s with great run‐to‐run repeatability (RSD < 1%). The achieved efficiencies ranged from 45 000 ± 6000 to 70 000 ± 3000 plates/m demonstrating a performance better than ME devices without controlled electrolysis. The proposed system offered good linearity from 1 to 10 mmol/L and LODs between 150 and 740 μmol/L. The use of external tubes for controlling the electrolysis phenomenon on ME devices has solved common problems associated to run‐to‐run repeatability and analytical reliability required for routine and quantitative analysis. 相似文献
102.
An electroanalytical method for the determination of morpholine, a corrosion inhibitor, was developed at a cathodically pretreated boron-doped diamond electrode (BDDE). The voltammetric response of morpholine at the BDDE in 0.1?mol L?1 KCl (pH 10) shows an irreversible oxidation process at approximately 1.3?V vs. Ag/AgCl in 3.0?mol L?1 KCl. Using cyclic voltammetry, the number of electrons involved in the morpholine electroxidation mechanism was found to be 1. The application of chronoamperometry showed that the apparent diffusion coefficient (D0) was 2.99?×?10?6 cm2 s?1. Using square wave voltammetry under the optimized conditions (frequency of 30.0?Hz, pulse amplitude of 100?mV and step potential of 20?mV at pH 10.0), the developed method provided limits of detection and quantification of 2.1 and 6.9?mg L?1, respectively, with a linear range from 5.0 to 100.0?mg L?1 (r?=?0.991). Intraday (n?=?10) and interday (two consecutive day) precision values assessed as the relative standard deviation for solutions containing 30.0, 60.0, and 90.0?mg L?1 of morpholine were from 0.41 to 5.86% and 0.92 to 3.19%, respectively. The feasibility of the method for the interference-free determination of morpholine was verified by the analysis of synthetic boiler water samples containing CaCO3, Na2SO3, Na3PO4, FeCl3, and humic acid as organic matter. In addition, hydrazine was added as a possible interfering compound because of its widespread use in corrosion inhibition. Recovery values from 90.9 to 109.4% were obtained in the synthetic boiler water, thereby attesting to the accuracy of the method. 相似文献
103.
Vanessa Cristina de Medeiros Railton Barbosa de Andrade Glauco Favilla Bauerfeldt 《Molecular physics》2018,116(17):2187-2195
Highly correlated calculations at the multi-reference configuration interaction levels including singles and doubles excitations (MR-CISD) and extensivity corrections (MR-CISD?+?Q) have been performed to study some low-lying valence and Rydberg states of the CF3 radical. Our highest level results (at the MR-CISD?+?Q level) yield the following energy ordering: 3s (7.90?eV)?12A2 (8.61?eV)?3pπ (8.72?eV)?3pz (8.73?eV). MR-CISD results indicate transitions of similar intensities from the ground to the following three final states, in the following order: 3pπ?>?3pz?>?3s. It has also been found that the aforementioned Rydberg states should be responsible for visible emissions and correspond to transitions between bound states. Therefore, it is suggested that the lack of vibrational structure in the visible band of parent systems (e.g. CF3Cl) may be due to a transition from a bound to an unbound state of the parent molecule. 相似文献
104.
Giovanna?Medeiros?Tavares?de?OliveiraEmail authorView authors OrcID profile Elisa?Magno?Nunes?de?Oliveira Talita?Carneiro?Brand?o?Pereira Ricardo?Meurer?Papaléo Maurício?Reis?Bogo 《Journal of nanoparticle research》2017,19(12):389
Iron oxide nanoparticles (IONPS) have been widely investigated as a platform for a new class of multifunctional theranostic agents. They are considered biocompatible, and some formulations are already available in the market for clinical use. However, contradictory results regarding toxicity of IONPs raise a concern about the potential harm of these nanoparticles. Changes in the nanoparticle (NP) physicochemical properties or exposure media can significantly alter their behavior and, as a consequence, their toxic effects. Here, behavior and two-step RT-qPCR were employed to access the potential toxicological effects of dextran-coated IONPs (CLIO-NH2) and uncoated IONPs (UCIO) in zebrafish larvae. Animals were exposed for 7 days to NP solutions ranging from 0.1–100 μg/mL directly mixed to the system water. UCIO showed high decantation and instability in solution, altering zebrafish mortality but showing no alterations in behavior and molecular expression analysis. CLIO-NH2 exposure did not cause significant mortality or changes in hatching rate of zebrafish larvae; however, behavior and expression profiles of the group exposed to lower concentration (1 μg/mL) presented a tendency to decrease the locomotor activity and apoptotic pathway activation. 相似文献
105.
R. Aldrovandi R. R. Cuzinatto L. G. Medeiros 《The European Physical Journal C - Particles and Fields》2008,58(3):483-497
Equations of state for the early universe including realistic interactions between constituents are formulated. Under certain
hypotheses, these equations are able to generate an inflationary regime prior to the period of the nucleosynthesis. The resulting
accelerated expansion is intense enough to solve the flatness and horizon problems. In the cases of a curvature parameter
κ equal to 0 or +1, the model is able to avoid the initial singularity and offers a natural explanation for why the universe
is in expansion. All the results are valid only for a matter–antimatter symmetric universe. 相似文献
106.
107.
A. C. D. de Medeiros N. A. B. de Cervantes A. P. B. Gomes R. O. Macêdo 《Journal of Thermal Analysis and Calorimetry》2001,64(2):745-750
TG and DSC data were used to determine the thermal parameters of prednisone drug and tablets. Two formulations of prednisone
20 mg were analysed in the form of tablets. The TG curves of prednisone drug and tablets A and B displayed six, eight and
seven thermal decomposition processes, respectively. Analysis of the DSC data pointed to chemical interactions between prednisone
drug and the excipients of tablets A and B, suggested by alterations in the melting temperature of prednisone. The analysis
revealed that prednisone drug is more stable than tablets A and B.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
108.
L. A. Medeiros J. Limaco S. B. Menezes 《Journal of Computational Analysis and Applications》2002,4(2):91-127
This paper is divided into two parts. Part One Chapter 1 contains the deduction of the model for vertical vibrations of elastic strings with moving ends and its relations to the models of d'Alembert and Kirchhoff-Carrier. Chapter 2 contains the results of investigations related to Kirchhoff-Carrier model during the last twenty years and an almost complete bibliography.Part Two Chapter 3 of the paper is dedicated to the model with moving ends. It contains new results obtained by the authors during the last five years. 相似文献
109.
The organic-inorganic hybrid [(CH(3))(3)NCH(2)CH(2)NH(3)]SnI(4) presents a layered perovskite structure, templated by an organic dication containing both a primary and a quaternary ammonium group. Due to the high charge density and small size of the organic cation, the separation of the perovskite layers is small and short iodine-iodine contacts of 4.19 A are formed between the layers. Optical thin-film measurements on this compound indicate a significant red shift of the exciton peak (630 nm) associated with the band gap, as compared with other SnI(4)(2)(-)-based layered perovskite structures. 相似文献
110.
Ana P Esteves Danielle M Goken Lee J Klein Maria J Medeiros Dennis G Peters 《Journal of Electroanalytical Chemistry》2003,560(2):F167
Cyclic voltammograms for the reduction of ethyl 2-bromo-3-(3′,4′-dimethoxyphenyl)-3-(propargyloxy)propanoate (1) at glassy carbon electrodes in dimethylformamide containing tetraalkylammonium salts exhibit three prominent waves corresponding to cleavage of the carbon–bromine bond and to subsequent reduction of ethyl trans-3-(3′,4′-dimethoxyphenyl)-prop-2-enoate (4). Controlled-potential electrolyses of 1 at potentials corresponding to reduction of the carbon–bromine bond afford 4 as the major product with an average yield of 56%. In the presence of a proton donor (1,1,1,3,3,3-hexafluoro-2-propanol), the quantity of 4 decreases slightly, and 2-(3′,4′-dimethoxyphenyl)-3-(ethoxycarbonyl)-4-methyl-2,5-dihydrofuran (3) is obtained in moderate amount (26%). We propose a mechanistic scheme whereby the major products are formed via a combination of one- and two-electron processes. 相似文献