全文获取类型
收费全文 | 353篇 |
免费 | 7篇 |
国内免费 | 1篇 |
专业分类
化学 | 195篇 |
晶体学 | 8篇 |
力学 | 14篇 |
数学 | 97篇 |
物理学 | 47篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 2篇 |
2020年 | 9篇 |
2019年 | 10篇 |
2018年 | 12篇 |
2017年 | 9篇 |
2016年 | 29篇 |
2015年 | 13篇 |
2014年 | 17篇 |
2013年 | 80篇 |
2012年 | 21篇 |
2011年 | 32篇 |
2010年 | 30篇 |
2009年 | 13篇 |
2008年 | 19篇 |
2007年 | 16篇 |
2006年 | 11篇 |
2005年 | 4篇 |
2004年 | 2篇 |
2003年 | 2篇 |
2002年 | 8篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 2篇 |
排序方式: 共有361条查询结果,搜索用时 10 毫秒
1.
Jennifer S. Forrester Jennifer S. Zobec Erich H. Kisi 《Journal of solid state chemistry》2004,177(10):3553-3559
The pressure-less sintering behavior of PbTiO3 powders synthesized by mechanical alloying TiO2 and PbO was investigated using dilatometry and Rietveld refinements of X-ray diffraction patterns. As-synthesized, the powders are nanocrystalline with a mean particle size of 20 nm. Pressure-less sintering in the range 500-1050°C gives single phase ceramics with densities of 85-90% and crystallite sizes in the range 80-400 nm. Cracking due to the paraelectric-ferroelectric phase transition was not observed in samples sintered below 700°C due to the small crystallite size whereas macroscopic cracks formed in samples sintered above 700°C. Rietveld analysis indicates the formation of Pb vacancies in samples sintered and held for 24 h at intermediate temperatures (600-1000°C) which gives some insight into the mechanism of Pb loss and second phase formation in this system. 相似文献
2.
4,4-Bis(chloroacetyl)diphenylmethane has been prepared from ClCH2COCl and Ph2CH2. 4,4-Methylenebis(phenylglyoxylohydroximoyl chloride has also been obtained. Four new substituted 4,4-bis(alkylaminoisonitrosoacetyl)diphenylmethanes (ligands) have been prepared from 4,4-methylenebis(phenylglyoxylohydroximoyl chloride) and the corresponding amines. The NiII, CuII and CoII complexes of these ligands were prepared and their structures were identified using AAS, i.r., 1H-n.m.r. spectral data, elemental analyses and magnetic susceptibility measurements. 相似文献
3.
Hakki İsmail Erdoğan 《Journal of Geometry》1991,40(1-2):47-59
In this paper, the problem of determining the pencils of circles which form a hexagonal n-web in E2, is completely solved. It is well-known that n pencils of circles orthogonal to a fixed circle form a hexagonal n-web. Therefore, the main problem is the determination of all circle pencils which form a hexagonal n-web and which do not cut a fixed circle orthogonally. In this connection the following results have been obtained: The number of hexagonal 4-webs is six, whereas the number of hexagonal 5-webs is two.Finally, after having proved that the number of hexagonal 6-webs is one, it is shown that, for n7, there exist no circle pencils forming a hexagonal n-web without being orthogonal to a fixed circle. 相似文献
4.
Asım Davulcu Hüseyin Benli Yasin Şen M. İbrahim Bahtiyari 《Cellulose (London, England)》2014,21(6):4671-4680
Application of natural dyes for textiles is increasing due to awareness of environment, ecology, and pollution control. The purpose of this study is to determine the color, antimicrobial, and fastness properties of cotton fabrics dyed with thyme and pomegranate peel without a mordanting process. In this way, it was planned to avoid use of metallic mordants (heavy-metal salts) and prevent heavy-metal pollution for ecological production. Additionally, a variety of the most commonly used mordants, namely potassium aluminum sulfate, copper(II) sulfate, iron(II) sulfate, and tin(II) chloride, were used for mordanting of cotton fabrics in order to compare the differently mordanted and unmordanted dyed fabrics’ color efficiencies (K/S) and CIE L * a * b * color values. It was found that mordant type had an effect on color efficiency and the color coordinates of fabrics dyed with both thyme and pomegranate fruit peel. Moreover, the antimicrobial properties of the fabrics only dyed directly with thyme and pomegranate peel without any mordanting process were determined to demonstrate the usability of these natural dye sources without use of any mordanting agents. The obtained antimicrobial activities were compared with undyed samples. Undyed samples showed no antimicrobial activity, whereas significant antimicrobial activity was obtained after the dyeing procedure using thyme and pomegranate peel on unmordanted fabrics. Washing, rubbing, perspiration, and lightfastness properties of dyed fabrics were also evaluated. Thyme and pomegranate fruit peel as natural dye sources revealed sufficient results even for unmordanted samples. 相似文献
5.
İlyas Gönül Ender Fakı Burak Ay Muhammet Köse Selahattin Serin 《Transition Metal Chemistry》2018,43(1):73-81
A Schiff base ligand (HL), 2,4-dimethoxy-N-(5-chloro-2-hydroxybenzylidene)-benzenamine, derived from 5-chloro-2-hydroxybenzaldehyde and 2,4-dimethoxyaniline, and its metal complexes [Co(L)2]·CH3OH (1), [Ni(L)2] (2), [Cu(L)2] (3) have been synthesized. The compounds were characterized by analytical and spectroscopic methods. In addition, the structures of the Schiff base HL and its Co(II) complex were determined by single-crystal X-ray analysis. The Co(II) center is six-coordinate, being coordinated to two imine nitrogen, two phenolate oxygen and two methoxy oxygen atoms of two crystallographically independent Schiff base ligands. Luminescence properties of HL and its complexes were investigated both in solution and in the solid state. 相似文献
6.
Emine Özge Karaca Mitat Akkoç Muhammad Nawaz Tahir Cengiz Arıcı Fatma İmik Nevin Gürbüz Sedat Yaşar İsmail Özdemir 《Tetrahedron letters》2017,58(36):3529-3532
A series of seven-membered ditopic ring-expanded N-heterocyclic carbene (dre-NHC) precursors, bearing sterically demanding and electron-rich aryl groups, were synthesised in moderate yields via the reaction of 1,2,4,5-tetrakis(bromomethyl)benzene with the corresponding N,N′-diarylformamidines in the presence of K2CO3 in acetonitrile under an air atmosphere. All new compounds were characterised by HRMS, NMR spectroscopy, and microanalysis, as well as X-ray crystallography for compound 1c. The development of an efficient catalytic system for the Suzuki-Miyaura coupling reaction of aryl chlorides with various boronic acids was also investigated using the in situ generated dre-NHC ligands. 相似文献
7.
8.
Two new Schiff base ligands (L1, L2) have been prepared from the reaction of 2,6-diacetylpyridine and 2-pyridinecarboxyaldehyde with 4-amino-2,3-dimethyl-1-phenyl-3-pyrozolin-5-on,
and their Co(II), Cu(II), Ni(II), Mn(II), and Cr(III) metal complexes have also been prepared. The complexes are formed by
coordination of N and O atoms of the ligands. Their structures were characterized by physico-chemical and spectroscopic methods.
The analytical data shows that the metal to ligand ratio in the Schiff base complexes is 1:2. The Schiff base ligands and
all complexes were evaluated for their in vitro antibacterial and antifungal activities by the disc diffusion method. In addition,
the genotoxic properties of the ligands were studied. 相似文献
9.
Hasan Kırmızıbekmez Yiğit İnan Rengin Reis Hande Sipahi Ahmet C. Gören Erdem Yeşilada 《Natural product research》2019,33(17):2541-2544
Phytochemical investigations on the EtOH extract of Clematis viticella led to the isolation of six flavonoid glycosides, isoorientin (1), isoorientin 3′-O-methyl ether (2), quercetin 7-O-α-L-rhamnopyranoside (3), quercetin 3,7-di-O-α-L-rhamnopyranoside (4), manghaslin (5) and chrysoeriol 7-O-β-D-glucopyranoside (6), one phenylethanol derivative, hydroxytyrosol (7), along with three phenolic acids, caffeic acid (8), (E)-p-coumaric acid (9) and p-hydroxybenzoic acid (10). The structures of the isolates were elucidated on the basis of NMR and HR-MS data. All compounds were isolated from C. viticella for the first time. Compounds 7 and 8 showed significant anti-inflammatory activity at 100 μM by reducing the release of NO in LPS-stimulated macrophages comparable to positive control indomethacin. Compounds 3 and 7 exhibited anti-inflammatory activity through lowering the levels of TNF-α while 1, 3 and 5 decreased the levels of neopterin better than the positive controls. 相似文献
10.
New epoxy resins were prepared from hydroxyl substituted Schiff base monomers in two steps. The first step is based on the synthesis of hydroxyl substituted Schiff base monomers via condensation reaction. The second step includes the reaction between Schiff base monomers with epichlorohydrine (EPC) to obtain epoxy resins. The structures of resulting compounds were confirmed by FTIR and 1H-NMR. TG-DTA and DSC measurements were made for thermal characterizations of the compounds. Chemical resistances of the cured epoxy-amine systems in acidic, alkaline and organic solvents were determined for coating applications. HCl (aqueous solution, 10%), NaOH (aqueous solution, 10%), DMSO, DMF, N-methylpyrrolidone, ethanol, THF and acetone were used for corrosion tests. Chemical resistance data show that the synthesized resins have good chemical resistance against various acid, alkaline and common organic solvents. 相似文献