全文获取类型
收费全文 | 504篇 |
免费 | 21篇 |
国内免费 | 1篇 |
专业分类
化学 | 444篇 |
晶体学 | 5篇 |
力学 | 7篇 |
数学 | 22篇 |
物理学 | 48篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 59篇 |
2021年 | 30篇 |
2020年 | 16篇 |
2019年 | 18篇 |
2018年 | 22篇 |
2017年 | 15篇 |
2016年 | 21篇 |
2015年 | 16篇 |
2014年 | 20篇 |
2013年 | 29篇 |
2012年 | 22篇 |
2011年 | 50篇 |
2010年 | 21篇 |
2009年 | 17篇 |
2008年 | 25篇 |
2007年 | 26篇 |
2006年 | 13篇 |
2005年 | 16篇 |
2004年 | 16篇 |
2003年 | 10篇 |
2002年 | 11篇 |
2000年 | 10篇 |
1999年 | 3篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1982年 | 1篇 |
1975年 | 1篇 |
1964年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有526条查询结果,搜索用时 78 毫秒
491.
Khan AN Fatima I Khaliq UA Malik A Miana GA Qureshi ZU Rasheed H 《Molecules (Basel, Switzerland)》2011,16(3):2053-2064
New naturally occurring nitrogenous compounds 1 and 2, along with a new dimeric lignan glucoside 3, have been isolated from the ethyl acetate soluble fraction of Centaurea iberica. Their structures have been elucidated through spectroscopic techniques. All the isolated compounds showed significant platelet aggregation inhibition. 相似文献
492.
Fatima Tahiri Yunsen Li David Hawke Luciane Ganiko Igor Almeida Steven Levery 《Journal of carbohydrate chemistry》2013,32(1):44-67
α-1,3-Terminated galactose residues on glycoproteins and glycosphingolipids are recognized by natural anti-α-1,3-galactose antibodies in human serum and cause hyperacute rejection in pig-to-human xenotransplantation. Genetic depletion of α-1,3-galactosyl- transferase-1 in pigs abolishes the hyperacute rejection reaction. However, the isoglo- botriosylceramide (iGb3) synthase in pigs may produce additional α-1,3-terminated galactose residues on glycosphingolipids. In both α-1,3-galactosyltranserase-1 knockout mice and pigs, cytotoxic anti-α-1,3-galactose antibodies could be induced; thus, a paradox exists that anti-α-1,3-galactose antibodies are present in animals with functional iGb3 synthases. Furthermore, iGb3 has been found to be an endogenous antigen for natural killer T (NKT) cells, an innate type of lymphocyte that may initiate the adaptive immune responses. It has been reasoned that iGb3 may trigger the activation of NKT cells and cause the rejection of α-1,3-galactosyltransferase-1-deficient organs through the potent stimulatory effects of NKT cells on adaptive immune cells (see ref.[20]). In this study, we examined the expression of iGb3 and the isoglobo-series glycosphingolipids in pig organs, including the heart, liver, pancreas, and kidney, by ion-trap mass spectrometry, which has a sensitivity of measuring 1% iGb3 among Gb3 isomers, when 5 μg/mL of the total iGb3/Gb3 mixture is present (see ref.[35]). We did not detect iGb3 or other isoglobo-series glycosphingolipids in any of these organs, although they were readily detected in mouse and human thymus and dendritic cells. The lack of iGb3 and isoglobo-series glycosphingolipids in pig organs indicates that iGb3 is unlikely to be a relevant immune epitope in xenotransplantation. 相似文献
493.
Fatima Tuz Johra Mi-Jung Lee Woo-Gwang Jung 《Journal of Sol-Gel Science and Technology》2013,66(3):481-487
Graphene-based composites represent a new class of materials with potential for many applications. Graphene can be attached to a metal, a semiconductor, or any polymer. In this work, our approach was to attach graphene to a well-known semiconductor, ZnO. We synthesized graphene–ZnO composites by a simple, low-cost, environmentally friendly solvothermal method, carrying out the reaction in different conditions in order to discover the optimum condition, and also to obtain a high-quality product. Our research demonstrated that the optimum temperature to obtain a high-quality product is 180 °C for 20 h. All obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy, electron dispersion spectrometry, X-ray photoelectron spectrometry, Raman spectroscopy, Fourier transform infrared spectrometry, UV–visible spectrophotometry, and thermogravimetric analysis. The XRD confirmed that the crystal structure of the ZnO in the nanocomposite was wurtzite type. The prepared composite was stable to 800 °C with its 80 % weight. 相似文献
494.
Pilar Rodríguez-Rodríguez Silvia M. Arribas Angel Luis López de Pablo M. Carmen González Fatima Abderrahim Luis Condezo-Hoyos 《Analytical and bioanalytical chemistry》2013,405(21):6863-6871
The assessment of collagen content in tissues is important in biomedical research, since this protein is altered in numerous diseases. Hydroxyproline and Sirius red based assays are the most common methods for collagen quantification. However, these procedures have some pitfalls, such as the requirement of oxygen-free medium or expensive equipment and large sample size or being unsuitable for hydrolyzed collagen, respectively. Our objective was to develop a specific, versatile, and user-friendly quantitative method applicable to small tissue samples and extracts obtained from elastin purification, therefore, suitable for simultaneous quantification of elastin. This method is based on the binding of Sirius red to collagen present in a sample immobilized on a PVDF membrane, as in the dot-blot technique, and quantified by a scanner and image analysis software. Sample loading, Sirius red concentration, temperature and incubation time, type of standard substance, albumin interference, and quantification time are optimized. The method enabled the quantification of (1) intact collagen in several rat tissue homogenates, including small resistance-sized arteries, (2) partially hydrolyzed collagen obtained from NaOH extracts, compatible with elastin purification, and (3) for the detection of differences in collagen content between hypertensive and normotensive rats. We conclude that the developed technique can be widely used since it is versatile (quantifies intact and hydrolyzed collagen), requires small sample volumes, is user-friendly (low-cost, easy to use, minimum toxic materials, and reduced time of test), and is specific (minimal interference with serum albumin). Figure
Dot-blot–Sirius red-based assay for collagen quantification 相似文献
495.
Yunshan Zhou Sadaf ul Hassan Lijuan Zhang Xianqi Li Waqar Ahmad 《Journal of Cluster Science》2013,24(1):243-257
A new ferrous molybdenum(V) phosphate, [H2deta]4[H3O]{Na[FeIIMo 12 V O24(OH)6(HPO4)6(PO4)2]}·6H2O 1 (deta = diethylenetriamine) has been prepared under hydrothermal condition and thoroughly characterized by IR, UV–Vis spectroscopy, elemental analyses, single–crystal X-ray diffraction, powder XRD and TG–DTA. The structural analysis reveals that isolated V-shaped water trimers and protonated diethylenetriamine molecules coexist in the crystal lattice of 1 and form an unprecedented 1-D strip-like arrangement via hydrogen bonding interactions. The strip-like arrangement further interacts through intermolecular non-covalent interactions with its surroundings, viz., the new 1-D inorganic anionic chain constructed by the versatile Fe[Mo6P4O31] building blocks which is covalently connected with NaO6 octahedra, and finally results in a supramolecular entity that is favourable in terms of packing efficiency and system energy minimization. The electrochemical properties of the compound 1 is also investigated by voltammetric method. 相似文献
496.
Riyazuddeen Dheeraj Kumar Sadaf Afrin 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2014,88(1):52-56
Densities of L-serine, L-isoleucine, L-glutamine in 1.5 mol kg?1 aqueous NaCl, and NaNO3 solutions have been measured for several molal concentrations of amino acids at temperatures from 298.15 to 323.15 K. The partial molar volumes (? v 0 ) of L-serine, L-isoleucine, and L-glutamine in 1.5 mol kg?1 aqueous NaCl/NaNO3 solutions have been computed using density data. The transfer partial molar volumes (Δtr? v 0 ) of L-serine, L-isoleucine, and L-glutamine from water to 1.5 mol kg?1 aqueous NaCl/1.5 mol kg?1 aqueous NaNO3 solutions have been determined at 298.15 K. The trends of variation of ? v 0 and Δtr? v 0 with change in temperature have been discussed in terms of ion-ion, ion-hydrophilic, and ion-hydrophobic interactions operative in solutions. 相似文献
497.
Fatima Aouinti Bouchra Imelouane Mustapha Tahri Jean Paul Wathelet Hassan Amhamdi Ali Elbachiri 《Research on Chemical Intermediates》2014,40(8):2873-2886
The present study describes the chemical composition of essential oils of Pistacia lentiscus L., collected from different regions of Eastern Morocco. The essential oils were obtained by hydro-distillation of the areal parts and analyzed by gas chromatography and gas chromatography coupled to a mass spectrometry. The study was conducted to determine the phytochemistry and antibacterial activities of oil from P. lentiscus leaves against both bacteria using the disc diffusion method. For Gram-negative, Salmonella sp., Klebsiella, Escherichia coli, and Pseudomonas, and for Gram-positive, Staphylococcus aureus, and Streptococcus were used as test bacterial strains. In the end, we completed the previous study by determining the minor and major mineral contents of leaves of P. lentiscus. The yield of P. lentiscus oil ranged between 0.13 and 0.23 %, with the chemical composition changing from one region to another. The variations are important between plant populations. The major oil components of PLL oil from Taforalt and Saidia (humid climate) were limonene and α-pinene, while myrcene, β-caryophyllene were found to be the major components of Laayoune and Jerada oil (semi-arid climate). For the mineral composition of PLL, the results show that trace element profiles of leaves from different regions differed significantly; the highest levels of K, Mg, Fe, and Ca were found in leaves of all locations, while the leaves collected from the Jerada region had the highest content of mineral substrates. This work also attempts to contribute to the knowledge of the nutritional properties of this plant; the results will be investigated for the evaluation of dietary information. 相似文献
498.
Label‐Free Photoelectrochemical Detection of Double‐Stranded HIV DNA by Means of a Metallointercalator‐Functionalized Electrogenerated Polymer
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Fatima Haddache Dr. Alan Le Goff Bertrand Reuillard Dr. Karine Gorgy Dr. Chantal Gondran Dr. Nicolas Spinelli Prof. Eric Defrancq Dr. Serge Cosnier 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(47):15555-15560
The design of photoactive functionalized electrodes for the sensitive transduction of double‐stranded DNA hybridization is reported. Multifunctional complex [Ru(bpy‐pyrrole)2(dppn)]2+ (bpy‐pyrrole=4‐methyl‐4′‐butylpyrrole‐2,2′‐bipyridine, dppn=benzo[i]dipyrido[3,2‐a:2′,3′‐c]phenazine) exhibiting photosensitive, DNA‐intercalating, and electropolymerizable properties was synthesized and characterized. The pyrrole groups undergo oxidative electropolymerization on planar electrodes forming a metallopolymer layer on the electrode. Thanks to the photoelectrochemical and intercalating properties of the immobilized RuII complex, the binding of a double‐stranded HIV DNA target was photoelectrochemically detected on planar electrodes. Photocurrent generation through visible irradiation was correlated to the interaction between double‐stranded DNA and the metallointercalator polymer. These interactions were well fitted by using a Langmuir isotherm, which allowed a dissociation constant of 2×106 L mol?1 to be estimated. The low detection limit of 1 fmol L?1 and sensitivity of 0.01 units per decade demonstrate excellent suitability of these modified electrodes for detection of duplex DNA. 相似文献
499.
Kirillov AM Karabach YY Haukka M Guedes da Silva MF Sanchiz J Kopylovich MN Pombeiro AJ 《Inorganic chemistry》2008,47(1):162-175
The new copper(II) or copper(II)/sodium(I) 1D coordination polymers [Cu2(Hmdea)2(mu-H2O)(mu2-tpa)]n.2nH2O (1), [Cu2(H2tipa)2(mu2-ipa)]n.4nH2O (2), [Cu2(H2tea)2Na(H2O)2(mu2-tma)]n.6nH2O (3), [Cu2(H2tea)2(mu2-ipa)]n.nH2O (4a), and [Cu2(H2tea)2{mu3-Na(H2O)3}(mu3-ipa)]n(NO3)n.0.5nH2O (4b) have been prepared in aqueous medium by self-assembly from copper(II) nitrate, aminopolyalcohols [methyldiethanolamine (H2mdea), triisopropanolamine (H3tipa), and triethanolamine (H3tea)] as main chelating ligands and benzenepolycarboxylic acids [terephthalic (H2tpa), isophthalic (H2ipa), and trimesic (H3tma) acid] as spacers. They have been characterized by IR spectroscopy, elemental and single-crystal X-ray diffraction analyses, the latter indicating the formation of unusual multinuclear metal cores interconnected by various benzenepolycarboxylate spacers, leading to distinct wavelike, zigzag, or linear 1D polymeric metal-organic chains. These are further extended to 2D or 3D hydrogen-bonded supramolecular networks via extensive interactions with the intercalated crystallization water molecules. The latter are associated, also with aqua ligands, by hydrogen bonds resulting in acyclic (H2O)3 clusters in 1, (H2O)8 clusters in 2, infinite 1D water chains in 3, and disordered water-nitrate associates in 4b, all playing a key role in the structure stabilization and its extension to further dimensions. Variable-temperature magnetic susceptibility measurements have shown that 1-4 exhibit a moderately strong ferromagnetic coupling through the alkoxo bridge. The small Cu-O-Cu bridging angle and the large out-of-plane displacement of the carbon atom of the alkoxo group accounts for this behavior. The magnetic data have been analyzed by means of a dinuclear and a 1D chain model, and the magnetic parameters have been determined. The magnetic exchange coupling in 3, to our knowledge, is the highest found in alkoxo-bridged copper(II) complexes. 相似文献
500.
Ruiz M Ruanova TM Blanco O Núñez F Pato C Ojea V 《The Journal of organic chemistry》2008,73(6):2240-2255
A general strategy for the synthesis of 1-deoxy-azasugars from a chiral glycine equivalent and 4-carbon building blocks is described. Diastereoselective aldol additions of metalated bislactim ethers to matched and mismatched erythrose or threose acetonides and intramolecular N-alkylation (by reductive amination or nucleophilic substitution) were used as key steps. The dependence of the yield and the asymmetric induction of the aldol addition with the nature of the metallic counterion of the azaenolate and the gamma-alkoxy protecting group for the erythrose or threose acetonides has been studied. The stereochemical outcome of the aldol additions with tin(II) azaenolates has been rationalized with the aid of density functional theory (DFT) calculations. In accordance with DFT calculations with model glyceraldehyde acetonides, high trans,syn,anti-selectivitity for the matched pairs and moderate to low trans,anti,anti-selectivity for the mismatched ones may originate from (1) the intervention of solvated aggregates of tin(II) azaenolate and lithium chloride as the reactive species and (2) favored chair-like transition structures with a Cornforth-like conformation for the aldehyde moiety. DFT calculations indicate that aldol additions to erythrose acetonides proceed by an initial deprotonation, followed by coordination of the alkoxy-derivative to the tin(II) azaenolate and final reorganization of the intermediate complex through pericyclic transition structures in which the erythrose moiety is involved in a seven-membered chelate ring. The preparative utility of the aldol-based approach was demonstrated by application in concise routes for the synthesis of the glycosidase inhibitors 1-deoxy-d-allonojirimycin, 1-deoxy-L-altronojirimycin, 1-deoxy-D-gulonojirimycin, 1-deoxy-D-galactonojirimycin, 1-deoxy-L-idonojirimycin and 1-deoxy-D-talonojirimycin. 相似文献