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101.
Petr Řepa Ladislav Peksa Tomáš Gronych Radek Ulman Jan Wild Oldřich Schneeweiss 《Czechoslovak Journal of Physics》2006,56(12):1389-1399
This article describes a measuring system that was proposed so as to enable measurement of the content of dissolved gas in
samples, whose shape is determined by the specific requirements of the simultaneous measurements and cannot be modified to
satisfy the requirements on solubility measurements. The apparatus — a dynamic UHV vacuum system — consists of a measuring
chamber fitted with a heater based on electron bombardment, which permits a change in the sample temperature according to
the selected schedule. The design of the heater permits reduction of additional heating in the actual measuring chamber, so
that the increase in pressure caused by the action of the heater can be neglected. The measuring part of the system permits
recording of changes in the overall pressure and partial pressures of selected gases in the measuring chamber. The lowest
detectable amount of dissolved gas is less than 10−5 Pa m3.
The results of measurement of the solubility of hydrogen in Ti and Fe aluminides in samples that are simultaneously used to
measure the electrical conductivity are given as an example of the suitability of the apparatus for such measurements.
This work is a part of research plan MSM 0021620834 financed by the Ministry of Education, Youth and Sports of the Czech Republic. 相似文献
102.
103.
2‐Substituted dATP Derivatives as Building Blocks for Polymerase‐Catalyzed Synthesis of DNA Modified in the Minor Groove
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Ján Matyašovský Dr. Pavla Perlíková Dr. Vincent Malnuit Dr. Radek Pohl Prof. Dr. Michal Hocek 《Angewandte Chemie (International ed. in English)》2016,55(51):15856-15859
2′‐Deoxyadenosine triphosphate (dATP) derivatives bearing diverse substituents (Cl, NH2, CH3, vinyl, ethynyl, and phenyl) at position 2 were prepared and tested as substrates for DNA polymerases. The 2‐phenyl‐dATP was not a substrate for DNA polymerases, but the dATPs bearing smaller substituents were good substrates in primer‐extension experiments, producing DNA substituted in the minor groove. The vinyl‐modified DNA was applied in thiol–ene addition and the ethynyl‐modified DNA was applied in a CuAAC click reaction to form DNA labelled with fluorescent dyes in the minor groove 相似文献
104.
Petr Chocholouš Dalibor Šatínský Radek Sladkovský Marie Pospíšilová Petr Solich 《Talanta》2008,77(2):566-570
Sequential injection chromatography system equipped with miniaturized 10 mm monolithic column was used for fast simultaneous determination of two pesticides—fenoxycarb (FC) and permethrin (PM). The system was composed of a commercial sequential injection analysis (SIA) system (FIAlab® 3000, 6-port selection valve and 5.0 mL syringe pump), commercially available column Chromolith™ RP-18e (10 mm × 4.6 mm i.d.) (Merck®, Germany) and CCD UV-vis detector (USB 2000, Ocean-optics) with 1.0 cm Z-flow cell, absorbance was monitored at 225 nm. The mobile phase used for analysis was acetonitrile/water (60:40, v/v), flow rates were 0.6 mL min−1 for elution of fenoxycarb and 1.2 mL min−1 for elution of permethrin. For each analysis 4.8 mL of mobile phase was used. The chromatographic resolution between both compounds was >8 and analysis time was <6.5 min under the optimal conditions. Limits of detection were determined at 2.0 μg mL−1 for fenoxycarb and 1.0 μg mL−1 for permethrin. Samples were prepared by diluting with mobile phase and injected volume was 10 μL for each analysis. Developed method was applied to analysis of both pesticides in veterinary pharmaceutical foams and sprays ARPALIT® Neo (Aveflor, Czech Republic). SIC method was compared with validated method (HPLC, reverse phase 100 mm monolithic column, gradient elution). 相似文献
105.
Grycová L Hulová D Maier L Standara S Necas M Lemière F Kares R Dostál J Marek R 《Magnetic resonance in chemistry : MRC》2008,46(12):1127-1134
Adducts of the quaternary protoberberine alkaloids (QPA) berberine, palmatine, and coptisine were prepared with nucleophiles derived from pyrrole, pyrazole, imidazole, and 1,2,4-triazole. The products, 8-substituted 7,8-dihydroprotoberberines, were identified by mass spectrometry and 1D and 2D NMR spectroscopy, including (1)H--(15)N shift correlations at natural abundance. In addition, two adducts of QPA with chloroform and methanethiolate were characterized by using NMR data. Single-crystal X-ray structures of 8-pyrrolyl-7,8-dihydroberberine, 8-pyrazolyl-7,8-dihydroberberine, and 8-imidazolyl-7,8-dihydroberberine are also presented. 相似文献
106.
Trouillas P Marsal P Svobodová A Vostálová J Gazák R Hrbác J Sedmera P Kren V Lazzaroni R Duroux JL Walterová D 《The journal of physical chemistry. A》2008,112(5):1054-1063
Flavonolignans from silymarin, the standardized plant extract obtained from thistle, exhibit various antioxidant activities, which correlate with the other biological and therapeutic properties of that extract. To highlight the mode of action of flavonolignans as free radical scavengers and antioxidants, 10 flavonolignans, selectively methylated at different positions, were tested in vitro for their capacity to scavenge radicals (DPPH and superoxide) and to inhibit the lipid peroxidation induced on microsome membranes. The results are rationalized on the basis of (i) the oxidation potentials experimentally obtained by cyclic voltammetry and (ii) the theoretical redox properties obtained by quantum-chemical calculations (using a polarizable continuum model (PCM)-density functional theory (DFT) approach) of the ionization potentials and the O-H bond dissociation enthalpies (BDEs) of each OH group of the 10 compounds. We clearly establish the importance of the 3-OH and 20-OH groups as H donors, in the presence of the 2,3 double bond and the catechol moiety in the E-ring, respectively. For silybin derivatives (i.e., in the absence of the 2,3 double bond), secondary mechanisms (i.e., electron transfer (ET) mechanism and adduct formation with radicals) could become more important (or predominant) as the active sites for H atom transfer (HAT) mechanism are much less effective (high BDEs). 相似文献
107.
Dr. Mariana Amaro Dr. Radek Šachl Gokcan Aydogan Dr. Ilya I. Mikhalyov Dr. Robert Vácha Prof. Martin Hof 《Angewandte Chemie (International ed. in English)》2016,55(32):9411-9415
β‐Amyloid (Aβ) oligomers are neurotoxic and implicated in Alzheimer's disease. Neuronal plasma membranes may mediate formation of Aβ oligomers in vivo. Membrane components sphingomyelin and GM1 have been shown to promote aggregation of Aβ; however, these studies were performed under extreme, non‐physiological conditions. We demonstrate that physiological levels of GM1, organized in nanodomains do not seed oligomerization of Aβ40 monomers. We show that sphingomyelin triggers oligomerization of Aβ40 and that GM1 is counteractive thus preventing oligomerization. We propose a molecular explanation that is supported by all‐atom molecular dynamics simulations. The preventive role of GM1 in the oligomerization of Aβ40 suggests that decreasing levels of GM1 in the brain, for example, due to aging, could reduce protection against Aβ oligomerization and contribute to the onset of Alzheimer's disease. 相似文献
108.
Resolving Electronic Transitions in Synthetic Fluorescent Protein Chromophores by Magnetic Circular Dichroism
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Petr Štěpánek Thomas Y. Cowie Dr. Martin Šafařík Dr. Jaroslav Šebestík Dr. Radek Pohl Prof. Petr Bouř 《Chemphyschem》2016,17(15):2348-2354
The detailed electronic structures of fluorescent chromophores are important for their use in imaging of living cells. A series of green fluorescent protein chromophore derivatives is examined by magnetic circular dichroism (MCD) spectroscopy, which allows the resolution of more bands than plain absorption and fluorescence. Observed spectral patterns are rationalized with the aid of time‐dependent density functional theory (TDDFT) computations and the sum‐over‐state (SOS) formalism, which also reveals a significant dependence of MCD intensities on chromophore conformation. The combination of organic and theoretical chemistry with spectroscopic techniques also appears useful in the rational design of fluorescence labels and understanding of the chromophore's properties. For example, the absorption threshold can be heavily affected by substitution on the phenyl ring but not much on the five‐member ring, and methoxy groups can be used to further tune the electronic levels. 相似文献
109.
A novel modular and practical methodology for preparation of 6-substituted pyridin-3-yl C-nucleosides was developed. The Heck reaction of 2-chloro-5-iodopyridine with a 3'-TBDMS-protected glycal gave a 6-chloropyridin-3-yl nucleoside analogue, which was then desilylated, selectively reduced, and reprotected to give the TBDMS-protected 6-chloropyridin-3-yl C-2'-deoxyribonucleoside as a pure beta-anomer in a total yield of 39% over four steps. This key intermediate was then subjected to a series of palladium-catalyzed cross-coupling reactions, aminations, and alkoxylations to give a series of protected 1beta-(6-alkyl-, 6-aryl-, 6-hetaryl, 6-amino-, and 6-tert-butoxypyridin-3-yl)-2'-deoxyribonucleosides. 6-Unsubstituted pyridin-3-yl C-nucleoside was prepared by catalytic hydrogenation of the chloro derivative and 6-oxopyridine C-nucleoside by treatment of the 6-tert-butoxy derivative with TFA. Deprotection of all the silylated nucleosides by Et3N.3HF gave a series of free C-nucleosides (10 examples). 相似文献
110.
Martin Robinson Chong Luo Patrick E. Farrell Radek Erban Apala Majumdar 《Liquid crystals》2017,44(14-15):2267-2284
We study nematic equilibria on a square with tangent Dirichlet conditions on the edges, in three different modelling frameworks: (i) the off-lattice Hard Gaussian Overlap and Gay–Berne models; (ii) the lattice-based Lebwohl–Lasher model; and the (iii) two-dimensional Landau-de Gennes model. We compare the modelling predictions, identify regimes of agreement and in the Landau-de Gennes case, find up to 21 different equilibria. Of these, two are physically stable. 相似文献