全文获取类型
收费全文 | 219篇 |
免费 | 8篇 |
专业分类
化学 | 139篇 |
力学 | 14篇 |
数学 | 39篇 |
物理学 | 35篇 |
出版年
2023年 | 6篇 |
2022年 | 10篇 |
2021年 | 8篇 |
2020年 | 8篇 |
2019年 | 9篇 |
2018年 | 9篇 |
2017年 | 7篇 |
2016年 | 12篇 |
2015年 | 11篇 |
2014年 | 17篇 |
2013年 | 15篇 |
2012年 | 21篇 |
2011年 | 11篇 |
2010年 | 14篇 |
2009年 | 11篇 |
2008年 | 12篇 |
2007年 | 12篇 |
2006年 | 7篇 |
2005年 | 8篇 |
2004年 | 2篇 |
2003年 | 7篇 |
2002年 | 6篇 |
2001年 | 1篇 |
1999年 | 1篇 |
1996年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有227条查询结果,搜索用时 15 毫秒
51.
52.
53.
[reaction: see text] A set of chiral aliphatic amino diselenides have been synthesized from readily available starting materials in a straightforward synthetic route via the ring-opening reaction of the parent aziridines. These ligands have been tested as catalysts for the enantioselective addition of diethylzinc to aldehydes. The influence of the alkyl group substituents on the stereoselectivity has been studied, and in the best case, an enantiomeric excess up to 99% could be obtained by using only 0.5 mol % of the chiral diselenide 3a. 相似文献
54.
Braga AL Lüdtke DS Vargas F Paixão MW 《Chemical communications (Cambridge, England)》2005,(19):2512-2514
The catalytic enantioselective arylation of several aldehydes using boronic acids as the source of transferable aryl groups is described; the reaction is found to proceed in excellent yields and high enantioselectivities (up to 97% ee) in the presence of a chiral amino alcohol. 相似文献
55.
Halio A. Stefani Diogo O. Silva Iguatemi M. Costa Nicola Petragnani 《Journal of heterocyclic chemistry》2003,40(1):163-165
In this paper is described an unreported method employing α‐alkenyl β‐ketoamides as starting material to give 2,3‐dihydrofurans, precursors of substituted furans. 相似文献
56.
Interfacial properties and thermal stability of modified poly(m‐phenylene isophthalamide) thin films
Sandra Cruz dos Santos Lara Fernandes Loguercio Diogo Silva Corrêa Michael Ramos Nunes Marcos Antônio Villetti Irene Teresinha Santos Garcia 《Surface and interface analysis : SIA》2013,45(4):837-843
Poly(m‐phenylene isophthalamide) (PMIA) is a resistant to high temperatures and chemically stable engineering material. The application as coatings and membranes, however, is limited by its poor interaction with other materials. In this report, we describe the molecular modification of PMIA through reaction with dimsyl sodium and 2‐iodine‐1‐ethanol. The substitution of 58% of amide hydrogen by ethanol (etOH) groups produces a material (MPMIA) able to develop regularly structured films on silicon substrate. The morphology of the films is dependent on the ionic strength of the precursory solution. MPMIA starts a degradation process by losing the etOH group. MPMIA has a better affinity with poly(p‐cresolformaldehyde) than with a pristine one, increasing the range of composition in which thermal stability and miscibility are observed. Thin films of these blends have different morphologies that vary from nanometric porous to two‐phase microstructured grains, according to the composition. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
57.
Dobies Návia Marcos Vinícius Alves Gálico Diogo Junior Caires Flávio Marques Luiz José Spezia Nunes Ronaldo 《Journal of Thermal Analysis and Calorimetry》2018,132(3):1717-1727
Journal of Thermal Analysis and Calorimetry - Solid-state [Ln(nal)3]·nH2O compounds, where Ln represents light trivalent lanthanide (La to Sm, except Pm), nal is nalidixate (C12H11N2O3), and n... 相似文献
58.
Antonio L. Braga Wolmar A. Severo Filho Ricardo S. Schwab Luciano Dornelles Diogo S. Lüdtke 《Tetrahedron letters》2009,50(25):3005-4730
The synthesis of selenium- and tellurium-containing nucleosides, derived from uridine is described herein. These compounds were prepared in a concise and short synthetic route in good yields, by nucleophilic substitution of a tosylate group by organoselenium nucleophiles. 相似文献
59.
HPLC‐DAD for the determination of three different classes of antifungals: method characterization,statistical approach,and application to a permeation study 下载免费PDF全文
Diogo Miron Alini Lange Aline R. Zimmer Paulo Mayorga Elfrides E. S. Schapoval 《Biomedical chromatography : BMC》2014,28(12):1728-1737
This study describes and characterizes methods for high‐performance liquid chromatography diode array detection (HPLC‐DAD) analysis of formulations containing molecules with antifungal activity of three different classes: terbinafine and butenafine (allylamines), miconazole and fluconazole (azoles), and geraniol, neral and geranial (monoterpenes). All methods used the same chromatographic column (RP18), enabling the analysis to be performed in a single batch. The specificity was extensively discussed through the establishment of purity peak methods. The analytical parameters (linearity, precision and accuracy) were calculated and discussed in detail using specific statistical approaches. All substances showed satisfactory results for chromatographic and analytical parameters. Limits of 1.3% to mean repeatability and 2.0% for intermediate precision are suggested as acceptance criteria in validation of methods by HPLC‐DAD, in situations where there is no extensive pretreatment of the samples. The methods proved to be robust and significant factors were discussed regarding their influence on chromatographic parameters (retention time, resolution, tailing factor and column efficiency). Finally, the application of the developed methods was demonstrated by the results of a permeation study of the antifungal agents through bovine hoof membranes. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
60.
In this paper we consider time-dependent mean-field games with subquadratic Hamiltonians and power-like local dependence on the measure. We establish existence of classical solutions under a certain set of conditions depending on both the growth of the Hamiltonian and the dimension. This is done by combining regularity estimates for the Hamilton-Jacobi equation based on the Gagliardo-Nirenberg interpolation inequality with polynomial estimates for the Fokker-Planck equation. This technique improves substantially the previous results on the regularity of time-dependent mean-field games. 相似文献