全文获取类型
收费全文 | 266篇 |
免费 | 3篇 |
国内免费 | 2篇 |
专业分类
化学 | 182篇 |
晶体学 | 6篇 |
力学 | 6篇 |
数学 | 40篇 |
物理学 | 37篇 |
出版年
2022年 | 8篇 |
2021年 | 8篇 |
2020年 | 11篇 |
2019年 | 12篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 7篇 |
2015年 | 12篇 |
2014年 | 14篇 |
2013年 | 29篇 |
2012年 | 16篇 |
2011年 | 19篇 |
2010年 | 25篇 |
2009年 | 16篇 |
2008年 | 21篇 |
2007年 | 15篇 |
2006年 | 10篇 |
2005年 | 10篇 |
2004年 | 6篇 |
2003年 | 7篇 |
2002年 | 3篇 |
2001年 | 1篇 |
2000年 | 5篇 |
1999年 | 2篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1993年 | 1篇 |
1989年 | 1篇 |
排序方式: 共有271条查询结果,搜索用时 78 毫秒
91.
Choonkil Park Arslan Hojt Ansari Muaadh Almahalebi 《Journal of Fixed Point Theory and Applications》2017,19(4):2417-2425
In this paper, we introduce an \(m{\text{th}}\) root functional equation. Using the fixed point approach, we prove the Hyers–Ulam stability of the \(m{\text{th}}\) root functional equation in \(C^{*}\)-algebras. 相似文献
92.
Arslan M Masnovi J Krafcik R 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2007,66(4-5):1063-1067
Dimer model compounds of polyvinylcarbazoles (1,n-di(N-carbazolyl)alkanes, when n=1-5) were synthesized to model the effects of distance and orientation between carbazole groups in polymeric systems. Charge-transfer (CT) complexes of carbazole, N-ethylcarbazole and 1,n-di(N-carbazolyl)alkanes with p-chloranil (p-CHL) have been investigated spectrophotometrically in dichloromethane. The colored products are measured spectrophotometrically at different wavelength depending on the electronic transition between donors and acceptor. The formation constants of the CT complexes were determined by the Benesi-Hildebrand equation. The thermodynamic parameters were calculated by Van't Hoff equation. Stochiometries of the complexes formed between donors and acceptor were defined by the Job's method of the continuous variation and found in 1:1 complexation with donor and acceptor at the maximum absorption bands. 相似文献
93.
In this article we investigate Vranceanu rotation surfaces with pointwise 1- type Gauss map in Euclidean 4-space $
\mathbb{E}^4
$
\mathbb{E}^4
. We show that a Vranceanu rotation surface M has harmonic Gauss map if and only if M is a part of a plane. Further, we give necessary and sufficent conditions for Vranceanu rotation surface to have pointwise
1-type Gauss map. 相似文献
94.
A sensitive and efficient method was developed for the determination of atenolol in human urine by gas chromatography-mass spectrometry (GC-MS). Atenolol and metoprolol (internal standard, IS) were extracted from human urine with a mixture of chloroform and butanol at basic pH with liquid-liquid extraction. The extracts were derivatized with N-Methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA) and analyzed by GC-MS using a capillary column. The standard curve was linear (r = 0.99) over the concentration range of 50-750 ng/mL. Intra- and inter-day precision, expressed as the relative standard deviation were less than 5.0%, and accuracy (relative error) was better than 7.0%. The analytical recovery of atenolol from human urine has averaged 91%. The limit of quantification was 50 ng/mL. Also, the method was successfully applied to a patient with hypertension who had been given an oral tablet of 50 mg atenolol. 相似文献
95.
Serpil Demir?smail Özdemir Bekir ÇetinkayaHakan Arslan Don VanDerveer 《Polyhedron》2011,30(1):195-200
The new well-defined and air-stable ortho-xylyl-linked N-heterocyclic carbene (NHC) Pd complexes (2a-d) have been synthesized and characterized by elemental analysis, 1H NMR, 13C NMR, IR spectroscopy, and single crystal X-ray diffraction studies. The palladium atom in the complex 2a lies on a crystallographic mirror plane and can be described as having a square-planar coordination environment with the carbene atoms of the benzimidazole rings of the ligand occupying two coordination sites in cis positions. Two further coordination sites are occupied by chloride ligands. The benzimidazole rings are connected to each other by an ortho-xylyl bridge. The catalytic activity of these palladium complexes has been tested in the coupling reactions of various N-containing substrates with bromobenzene. A preliminary catalytic study shows that the bis(NHC)-Pd complexes are highly active in the Buchwald-Hartwig amination reaction. 相似文献
96.
Yasin Arslan Emrah YildirimMehrdad Gholami Sezgin Bakirdere 《Trends in analytical chemistry : TRAC》2011,30(4):569-585
Speciation studies are much more important than total element determination because toxicity of many elements depends on their chemical forms. Nobody can claim that a foodstuff is very dangerous to eat by determining total arsenic due to the possibility that the arsenic could be present in non-toxic forms. Hence, speciation studies are crucial in any matrix relevant to human beings.Trace-element speciation requires sufficiently sensitive procedures to monitor each species at trace levels. One way to increase the sensitivity for elements forming volatile species is coupling high-performance liquid chromatography (HPLC) with chemical-vapor generation (CVG). This review aims to highlight not only development of HPLC-CVG techniques for ultratrace-elemental speciation in a variety of matrices but also their application. In addition, we discuss the advantages and the disadvantages of these techniques. 相似文献
97.
Musharraf SG Ali A Ali RA Yousuf S Rahman AU Choudhary MI 《Rapid communications in mass spectrometry : RCM》2011,25(1):104-114
Structural elucidation and gas‐phase fragmentation of ten withanolides (steroidal lactones) were studied using a positive ion electrospray ionization quadropole time‐of‐flight mass spectrometry (ESI‐QqTOF‐MS/MS) hybrid instrument. Withanolides form an important class of plant secondary metabolites, known to possess a variety of biological activities. Withanolides which possess hydroxyl groups at C‐4, C‐5, C‐17, C‐20, and C‐27, and an epoxy group at C‐5/C‐6, were evaluated to determine the characteristic fragments and their possible pathways. ESI‐QqTOF‐MS (positive ion mode) showed the presence of the protonated molecules [M + H]+. Low‐energy collision‐induced dissociation tandem mass spectrometric (CID‐MS/MS) analysis of the protonated molecule [M + H]+ indicated multiple losses of water and the removal of the C‐17‐substituted lactone moiety affording the [M + H–Lac]+ product ion as the predominant pathways. However, withanolides containing a hydroxyl group at C‐24 of the lactone moiety showed a different fragmentation pathway, which include the loss of steroidal part as a neutral molecule, with highly diagnostic ions at m/z 95 and 67 being generated from the cleavage of lactone moiety. Our results also determined the influence of the presence and positions of hydroxyl and epoxy groups on product ion formation and stability. Moreover, the knowledge of the fragmentation pattern was utilized in rapid identification of withanolides by the LC/MS/MS analysis of a Withania somnifera extract. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
98.
Sezgin Bakırdere Selin Bora E. Gülhan Bakırdere Fırat Aydın Yasin Arslan O. Tarık Komesli Işıl Aydın Emrah Yıldırım 《Central European Journal of Chemistry》2012,10(3):675-685
Carcinogenic and mutagenic properties of aflatoxin species are known in literature. Their intake over a long time period might
be health-dangerous for human even at trace levels. It is well known that different foodstuffs can be contaminated by aflatoxin
species through growing and storage. Due to the serious health effects, sensitive determination of aflatoxin species in any
matrices related with the human being is very crucial at trace levels. In literature, there are sensitive techniques to analyze
the different samples for the contents of their aflatoxin species. Each technique has some advantages and disadvantages over
the other techniques. This review aims to summarize the different health effects of aflatoxin species, development of analytical
techniques and applications of developed techniques in a variety of matrices.
相似文献
99.
The possible stable forms of 3-phenylpropylamine (3-PPA) molecule were experimentally and theoretically studied by infrared and Raman spectroscopy. FT-IR and Raman spectra of 3-PPA were recorded in the regions of 4000–400 cm−1 and 3700–60 cm−1, respectively. The potential energy surface corresponding to the internal rotations of the molecule was investigated by semi-empirical quantum mechanical methods, and appropriate conformers defined with B3LYP hybrid density functional theory method along with the basis sets of different size and type. Results from experimental and theoretical data showed the trans–trans–gauche (TTG) to be the most stable form of a 3-PPA molecule. 相似文献
100.
In this study, multiwalled boron nitride microtubes (BNMTs) were synthesised from amorphous boron powder in pure nitrogen atmosphere controlled graphite furnace at 1300°C for 6?h with amorphous boron/manganese (IV) oxide (MnO2) catalyst mass ratio of 1/1. It was found that the synthesised BNMTs outer diameters and the lengths vary between 0.68 and 1.57?µm and between 6.79 and 31.23?µm, respectively, by the scanning electron microscope analysis. The surface layer of AISI 1040 steel material was coated with multiwalled BNMTs at 950°C for 4?h in a foundry furnace. Transport phenomena of BNMT molecules on surfaces of the steel were considered by diffusion. Neutrons from obtained 241Am-Be source were irradiated on the 58Fe nuclei. The irradiation properties of the without and with BNMT coated steel materials were studied in the field of gamma emitted by 60Co. The radiation exposure rate of gamma radiation sources used at 1099 and 1291?keV, respectively. The higher peak area was obtained in steel coated with BNMT according to non-coated steel from irradiation results of samples. These results show that BNMT coated steel was more capable for radiation shielding. 相似文献