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Marcela Dvorakova Marie Pribylova Radek Pohl Marie E. Migaud Tomas Vanek 《Tetrahedron》2012,68(33):6701-6711
A migration of methyloxycarbonyl group from secondary to primary hydroxyl was observed in furanosides (ribosides and xylosides) under usual desilylation conditions using tetrabutylammonium fluoride. The migration was studied further on several alkyloxycarbonyl furanosides under either basic or acidic conditions. As follows from 13C labelling experiments and product distribution, the migration in xylosides, proceeds intramolecularly via six-membered cyclic carbonate, whereas in ribosides, the migration is intermolecular. Acidic conditions prevented the migration in ribosides whereas the migration in xylosides was circumvented under neutral conditions. 相似文献
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-5-Aryl-1-[2-(phosphonomethoxy)ethyl]uracils were prepared via Pd-catalyzed Suzuki-Miyaura coupling reaction of the appropriate 5-bromouracil derivative with a series of arylboronic acids followed by deprotection. These compounds were designed as potential multisubstrate inhibitors of thymidine phosphorylase based on an assumption that the potential hydrophobic effect of the aryl groups might modify the inhibitory effect towards this enzyme and they may also demonstrate cytostatic activity. 相似文献
26.
The mechanism of the decomposition of acryloylcarbamates 7a–b yielding highly reactive isocyanates 3a–b was proposed based on NMR measurements and quantum chemical calculations. A good agreement between the experimental kinetic data and DFT calculations allowed us to demonstrate that the stability of 7a–d depends on the presence of methyl in the acryloyl moiety and the position of the nitro group in the nitrophenolic part of the molecule. Furthermore, the reactivity of 7a–d with weakly nucleophilic and sterically hindered 2,4,6‐tri‐tert‐butylaniline was explored by 1H NMR demonstrating the usefulness of reagents 7a–d offering access to a variety of 1‐N‐substituted uracils and thymines with potentially interesting biological properties. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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Dr. Pavlína Košinová Dr. Radek Gažák Prof. Jean‐Luc Duroux Prof. Roberto Lazzaroni Prof. Vladimír Křen Prof. Xavier Assfeld Dr. Patrick Trouillas 《Chemphyschem》2011,12(6):1135-1142
Natural polyphenols are known to be oxidized by free radicals, which partially explains the antioxidant properties of a number of these compounds. This oxidation may also be used to synthesise new compounds of biological interest, for example, dimers. The present theoretical study describes the existing experimental evidence showing that silybin and dehydrosilybin [natural polyphenols isolated from milk thistle (Silybum marianum)] form dimers regioselectively. Based on DFT calculations, thermodynamic and kinetic values were computed in order to better understand the physicochemical behaviour of these dimerisation processes. Calculations showed that after H‐atom transfer (from polyphenol to radical), dimerisation could proceed in two steps: 1) bond formation and, when possible, 2) tautomerisation reorganisation. The former step is the limiting step, while the latter is crucial for the process to be thermodynamically favourable (ΔG<0). If this rearrangement is impossible then dimerisation is not feasible, or at least becomes a minor process (e.g., dehydrosilybin dimerisation after H‐atom abstraction from the 3‐OH group). This explains the regioselectivity of polyphenol dimerisation. 相似文献
28.
Substituting CF2 for O4′ in Components of Nucleic Acids: Towards Systems with Reduced Propensity to Form Abasic Lesions
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Dr. Yevgen P. Yurenko Dr. Jan Novotný Prof. Dr. Vladimir Sklenář Prof. Dr. Radek Marek 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(49):17933-17943
Intrinsic structural features and energetics of nucleotides containing variously fluorinated sugars as potential building blocks of DNA duplexes and quadruplexes are explored systematically using the modern methods of density functional theory (DFT) and quantum chemical topology (QCT). Our results suggest that fluorination at the 2′‐β or 2′‐α,β positions somewhat stabilizes in vacuo the AI relative to the BI conformations. In contrast, substitution of the CF2 group for the O4′ atom (O4′‐CF2 modification) leads to a preference of the BI relative to AI DNA‐like conformers. All the studied modifications result in a noticeable increase in the stability of the glycosidic bond [estimated by the relaxed force constants (RFC) approach], with particularly encouraging results for the O4′‐CF2 derivative. Consequently, the O4′‐CF2 modified systems are suggested and explored as promising scaffolds for the development of duplex and quadruplex structures with reduced propensity to form abasic lesions and to undergo DNA damage. 相似文献
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A single piston capillary rheometer was modified by the addition of a second chamber with a restricting valve (developed at
the Polymer Centre, Zlín, Czech Republic), which provides backpressure and increasing the pressure in the melted material
during the flow through the die. The Carreau–Yasuda model was employed to fit the measured viscosity data and determine the
temperature and pressure coefficients for polyolefin based binder and its compounds with carbide powder. Both temperature
and pressure sensitivity coefficients are largely dependent on the structure of a polymer, which should be taken into account
for binder-formation’s development. Increasing the loading level of the powder in the compound diminishes the pressure sensitivity
of their flow properties. 相似文献
30.
Virender K. Sharma Karolina M. Siskova Radek Zboril Jorge L. Gardea-Torresdey 《Advances in colloid and interface science》2014
This review paper presents the overview of processes involved in transformation of organic-coated silver nanoparticles (AgNPs) in biological systems and in the aquatic environment. The coating on AgNPs greatly influences the fate, stability, and toxicity of AgNPs in aqueous solutions, biological systems, and the environment. Several organic-coated AgNP systems are discussed to understand their stability and toxicity in biological media and natural water. Examples are presented to demonstrate how a transformation of organic-coated AgNPs in an aqueous solution is affected by the type of coating, pH, kind of electrolyte (mono- or divalent), ionic strength, organic ligands (inorganic and organic), organic matter (fulvic and humic acids), redox conditions (oxic and anoxic), and light. Results of cytotoxicity, genotoxicity, and ecotoxicity of coated AgNPs to food chain members (plants, bacteria, and aquatic and terrestrial organisms) are reviewed. Key factors contributing to toxicity are the size, shape, surface coating, surface charge, and conditions of silver ion release. AgNPs may directly damage the cell membranes, disrupt ATP production and DNA replication, alternate gene expressions, release toxic Ag+ ion, and produce reactive oxygen species to oxidize biological components of the cell. A progress made on understanding the mechanism of organic-coated AgNP toxicity using different analytical techniques is presented. 相似文献