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排序方式: 共有402条查询结果,搜索用时 31 毫秒
361.
Caban M Stepnowski P Kwiatkowski M Migowska N Kumirska J 《Journal of chromatography. A》2011,1218(44):8110-8122
There is a growing demand for the rapid screening of multiple β-blockers and β-agonists in a single analytical run in clinical toxicology, antidoping control, forensic and environmental science. Although GC-MS is very often used to determine pharmaceuticals from these groups of drugs, the literature data on the derivatization and MS analysis of mixtures of these compounds is limited. This paper compares and evaluates derivatization procedures for the determination of six β-blockers (acebutolol, atenolol, metoprolol, nadolol, propranolol, pindolol) and two β-agonists (salbutamol, terbutaline) using GC techniques. Nineteen different derivatizing reagents (nine of them used for the first time with almost all the drugs) were employed in order to obtain a single derivative for each target compound with the greatest effectiveness of this reaction. Trimethylsilylation, tert-butyldimethylsilylation, acylation (e.g. trifluoroacetylation), combined trimethylsilylation and acylation, and the formation of cyclized silyl derivatives were carried out and the mass spectra (EI, 70 eV) recorded. The influence of the reaction time and temperature on these procedures was investigated. Additionally, the effects of the type of solvent and the amount of added trimethylchlorosilane (TMCS) on the silylation of the target compounds using N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) were tested. Among of the five mentioned above derivatization procedures applied - trimethylsilylation was found to be the most effective for derivatizing the analytes. The best results were obtained with a 1:1 (v/v) mixture of 99% BSTFA+1% TMCS and ethyl acetate at 60 °C for 30 min. The MS data for different types of β-blocker and β-agonist derivatives is presented. The information in this paper is valuable for scientists working on the determination of β-blockers and β-agonists in biological and environmental matrices. 相似文献
362.
Katarzyna Wykpis Jolanta Niedba?a Magdalena Popczyk Antoni Budniok Eugeniusz ?agiewka 《Russian Journal of Electrochemistry》2012,48(11):1123-1129
The Zn-Ni+Ni coatings were deposited under galvanostatic conditions at the current density range from 20 to 60 mA cm?2. The influence of deposition current density on surface morphology, chemical and phase composition and corrosion resistance of obtained coatings, was investigated. Structural investigations were conducted by X-ray diffraction method. Surface morphology and surface chemical composition of the obtained coatings were determined by a scanning electron microscope. Studies of electrochemical corrosion resistance were carried out in the 5% NaCl solution, using potentiodynamic and Scanning Kelvin Probe (SKP) methods. A possibility of incorporation of nickel powder from a suspension bath to the Zn-Ni matrix, during galvanostatic deposition was demonstrated. The results of chemical composition analysis show that the Zn-Ni + Ni coatings contain approximately 15?C18% at Ni. It was found that surface morphology, surface chemical and phase composition of Zn-Ni + Ni coatings depend in small degree on deposition current density. However, the current density influences distribution of nickel powder on the surface of these coatings. The optimal values of current density on account of corrosion resistance, are found to be j = 40?C50 mA cm?2. 相似文献
363.
The fundamental nature of reactivity in cytochrome P450 enzymes is currently controversial. Modelling of bacterial P450cam has suggested an important role for the haem propionates in the catalysis, though this finding has been questioned. Understanding the mechanisms of this enzyme family is important both in terms of basic biochemistry and potentially in the prediction of drug metabolism. We have modelled the hydroxylation of camphor by P450cam, using combined quantum mechanics/molecular mechanics (QM/MM) methods. A set of reaction pathways in the enzyme was determined. We were able to pinpoint the source of the discrepancies in the previous results. We show that when a correct ionization state is assigned to Asp297, no spin density appears on the haem propionates and the protein structure in this region remains preserved. These results indicate that the haem propionates are not involved in catalysis. 相似文献
364.
Jolanta Sarowska Dorota Wojnicz Agnieszka Jama-Kmiecik Magdalena Frej-Mdrzak Irena Choroszy-Krl 《Molecules (Basel, Switzerland)》2021,26(15)
Human noroviruses, which belong to the enterovirus family, are one of the most common etiological agents of food-borne diseases. In recent years, intensive research has been carried out regarding the antiviral activity of plant metabolites that could be used for the preservation of fresh food, because they are safer for consumption when compared to synthetic chemicals. Plant preparations with proven antimicrobial activity differ in their chemical compositions, which significantly affects their biological activity. Our review aimed to present the results of research related to the characteristics, applicability, and mechanisms of the action of various plant-based preparations and metabolites against norovirus. New strategies to combat intestinal viruses are necessary, not only to ensure food safety and reduce infections in humans but also to lower the direct health costs associated with them. 相似文献
365.
In this paper we examine various types filters that appear in the context of continuous relations, pseudo-uniform spaces and pseudotopological spaces. There arise compactoid, precompact, totally bounded, bounded and other filters. We study their properties and relationships among them. 相似文献
366.
Zurek Jolanta Bowman Anna L. Sokalski W. Andrzej Mulholland Adrian J. 《Structural chemistry》2004,15(5):405-414
Aminoacyl-tRNA synthetases are centrally important enzymes in protein synthesis. We have investigated threonyl-tRNA synthetase from E. coli, complexed with reactants, using molecular mechanics and combined quantum mechanical/molecular mechanical (QM/MM) techniques. These modeling methods have the potential to provide molecular level understanding of enzyme catalytic processes. Modeling of this enzyme presents a number of challenges. The procedure of system preparation and testing is described in detail. For example, the number of metal ions at the active site, and their positions, were investigated. Molecular dynamics simulations suggest that the system is most stable when it contains only one magnesium ion, and the zinc ion is removed. Two different QM/MM methods were tested in models based on the findings of MM molecular dynamics simulations. AM1/CHARMM calculations resulted in unrealistic structures for the phosphates in this system. This is apparently due to an error of AM1. PM3/CHARMM calculations proved to be more suitable for this enzyme system. These results will provide a useful basis for future modeling investigations of the enzyme mechanism and dynamics. 相似文献
367.
Karol Bula Teofil Jesionowski Andrzej Krysztafkiewicz Jolanta Janik 《Colloid and polymer science》2007,285(11):1267-1273
Dispersion and distribution of nanosized precipitated amorphous silica particles in poly(ethylene terephthalate) PET and poly(butylene
terephthalate) PBT matrices have been studied. The effect of silane coupling agent as well as processing conditions has been
analysed on the basis of microscopic analysis of sample morphology. N-2-(aminoethyl)-3-aminopropyltrimethoxysilane (A-1120) has been used as a silica surface modifier. The effect of the extrusion
process performance with a single and a twin screw extruder has been tested. It has been found that the processing conditions
are more important factors determining fine dispersion and homogenous distributions of filler particles in the matrix than
the filler surface modification. The results obtained have revealed that single screw extrusion is preferred only for processing
the composites comprising the silica modified with aminosilane, while the application of twin screw extrusion leads to homogenous
dispersion and fully deagglomeration of filler particles without silane treatment. It has been established that when the concentration
of silica filler increased from 3 up to 7% by weight, the secondary process of particle aggregation occurs. 相似文献
368.
Cezary A. Kozlowski Tomasz Girek WladysŁaw Walkowiak Jolanta Kozlowska 《Journal of inclusion phenomena and macrocyclic chemistry》2006,55(1-2):71-77
β-Cyclodextrin (β-CD) polymers were prepared by cross-linking of β-CD with phtalic and 3-nitrophtalic anhydride in anhydrous N,N-dimethylformamide (DMF) in the presence of NaH. The weight-average molecular weight (M
W) and the chemical structure of the polymers were determined using high performance size exclusion chromatography (HPSEC) with refractive index (RI) detector, and 1H NMR spectroscopy. The molecular weight of the polymer increased with molar ratio of substrates and reaction temperature. 1H NMR spectra revealed that the β-CD polymers contained both mono- and diesters of phtalic and 3-nitrophtalic acids. In the case of phtalic moieties about four or five diester moieties groups and for 3-nitrophtalic moieties about to or three diester moieties are linkages for β-CD molecule, respectively. Results of copper(II) flotation obtained with the use of nonylphenol polyoxyethyl glycol ether as an non-anionic surfactant and β-CD polymers as complexation collector agent, show␣that the removal of Cu2+ decreases with increase of molecular mass of β-CD polymers linked by phtalic or␣3-nitrophtalic anhydrides. For both derivatives with pH increase the copper(II) removal increase. The highest flotation removal, i.e. 93%, was found for β-CD polymers synthesized at 100 °C with molar ratio CD:NaH:3-nitrophtalic anhydride equal to 1:7:7. 相似文献
369.
Vytautas Getautis Albina Stanisauskaite Tadas Malinauskas Jolanta Stumbraite Valentas Gaidelis Vygintas Jankauskas 《Monatshefte für Chemie / Chemical Monthly》2006,137(11):1401-1409
Summary. Hydrazones containing 1-phenyl-1,2,3,4-tetrahydroquinoline units were synthesized starting from diphenylamine. These compounds
were found to constitute novel hole transporting materials and were characterized by the time of flight method. The hole drift
mobility in these compounds exceeds 10−6 cm2 V−1 s−1 at an electric field of 106 V cm−1. 相似文献
370.
JPC – Journal of Planar Chromatography – Modern TLC - The lipophilicity of thirty-seven N-[(4-arylpiperazin-1-yl)alkyl]-2- azaspiro[4.4]nonane- and [4.5]decane-1,3-dione derivatives has... 相似文献