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101.
A new regioselective synthesis of 5- and 6-aryluracil bases based on direct C-H arylations of diverse 1,3-protected uracils has been developed. Benzyl-protected uracils were selected as the most practical in terms of stability during the arylation and facile cleavage of the benzyl groups. Pd-catalyzed C-H arylations in the absence of CuI gave preferentially 5-aryl-, whereas the reactions in the presence of CuI gave 6-aryl-1,3-dibenzyluracils. Final deprotection either by transfer hydrogenolysis over Pd/C or by treatment with BBr(3) gave the desired free arylated uracil bases in good yields. 相似文献
102.
Filip J Yngard RA Siskova K Marusak Z Ettler V Sajdl P Sharma VK Zboril R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(36):10097-10105
The reaction of potassium ferrate(VI), K2FeO4, with weak‐acid dissociable cyanides—namely, K2[Zn(CN)4], K2[Cd(CN)4], K2[Ni(CN)4], and K3[Cu(CN)4]—results in the formation of iron(III) oxyhydroxide nanoparticles that differ in size, crystal structure, and surface area. During cyanide oxidation and the simultaneous reduction of iron(VI), zinc(II), copper(II), and cadmium(II), metallic ions are almost completely removed from solution due to their coprecipitation with the iron(III) oxyhydroxides including 2‐line ferrihydrite, 7‐line ferrihydrite, and/or goethite. Based on the results of XRD, Mössbauer and IR spectroscopies, as well as TEM, X‐ray photoelectron emission spectroscopy, and Brunauer–Emmett–Teller measurements, we suggest three scavenging mechanisms for the removal of metals including their incorporation into the ferrihydrite crystal structure, the formation of a separate phase, and their adsorption onto the precipitate surface. Zn and Cu are preferentially and almost completely incorporated into the crystal structure of the iron(III) oxyhydroxides; the formation of the Cd‐bearing, X‐ray amorphous phase, together with Cd carbonate is the principal mechanism of Cd removal. Interestingly, Ni remains predominantly in solution due to the key role of nickel(II) carbonate, which exhibits a solubility product constant several orders of magnitude higher than the carbonates of the other metals. Traces of Ni, identified in the iron(III) precipitate, are exclusively adsorbed onto the large surface area of nanoparticles. We discuss the relationship between the crystal structure of iron(III) oxyhydroxides and the mechanism of metal removal, as well as the linear relationship observed between the rate constant and the surface area of precipitates. 相似文献
103.
The on time diagnostics of bacterial diseases is one of the essential steps in the foregoing treatment of such pathogens. Here we sought to present an easy to use and robust method for the discrimination between Gram-positive (Enterococcus faecalis and Streptococcus pyogenes) and Gram-negative (Acinetobacter baumannii and Klebsiella pneumoniae) bacterial genera based on surface enhanced Raman scattering (SERS) spectroscopy. The robustness of our approach lies in the novel method for the production of the SER substrate based on silver nanoparticles and their subsequent re-crystallization in solutions containing high concentrations of chloride ions. The method presented here could be an interesting alternative both to commonly used histochemical approaches and commercial SERS substrates. 相似文献
104.
Ondřej Číp Radek Šmíd Martin Čížek Zdeněk Buchta Josef Lazar 《Central European Journal of Physics》2012,10(2):447-453
The work presents measurements of the length stability of Zerodur glass ceramic with temperature change. Measurement of this
thermal characteristic is necessary for determination of the optimal temperature at which the Zerodur glass ceramic has a
coefficient of thermal expansion close to zero. The principle of the measurement is to monitor the length changes using an
optical resonator with a cavity mirror spacer made from the Zerodur material to be studied. The resonator is placed inside
a vacuum chamber with a temperature control. A tunable laser diode is locked to a certain optical mode of the resonator to
monitor the optical frequency of this mode. A beat-note signal from optical mixing between the laser and a stabilized femtosecond
frequency comb is detected and processed. The temperature dependence of the glass ceramics was determined and analyzed. The
resolution of the length measurement of the experimental set-up is on the order of 0.1 nm. 相似文献
105.
A table-top micro X-ray fluorescence apparatus composed of a conventional X-ray tube with a polycapillary lens and a silicon drift X-ray detector was parametrized according to an independent parameter approach. The tube bremsstrahlung spectrum was calculated from the Bethe-Heitler equation, convoluted by the energy distribution of radiating electrons in the target. In this paper, we propose a simple analytical approximation for this energy distribution. An analytical approximation is also proposed for transmission of the lens composed of curved capillaries. 相似文献
106.
Radek Procházka Vojtěch Ettler Viktor Goliáš Mariana Klementová Martin Mihaljevič Ondřej Šebek Ladislav Strnad 《Journal of Non》2009,355(43-44):2134-2142
The alteration features of historical U-colored glasses exposed to natural weathering for over 150 years were compared with the experimental alteration of similar glass with ~0.3 wt% of uranium using a long-term (up to 426 days) kinetic laboratory batch leaching test in deionized water. Two types of natural corrosion crusts were identified by a combination of SEM/EDS, HRTEM/SAED, EPMA and XRD: (i) formation of a leached layer (up to ~600 μm thick) depleted in alkalis and enriched in Si with stable concentration of U and Al and (ii) formation of lamellae depleted in alkalis, Si and U and enriched in Al. The presence of newly formed gibbsite (Al(OH)3) and kaolinite (Al2Si2O5(OH)4) were confirmed in the second type of corrosion crust by HRTEM. Dissolution of the glass components including uranium was determined during the laboratory leaching test. Several μm thick alkali-depleted alteration zones with stable U content relatively enriched in Si and Al were formed on the glass surface. The PHREEQC-2 modeling also predicted the precipitation of secondary gibbsite and kaolinite in the late stages of the leaching. These phases may form especially when sufficient amounts of Al are available from the environment (e.g., soil). Furthermore, they provide surfaces for sorption and may, in some cases, affect the mobility of U ions released from the glass in dependence on pH and U speciation. 相似文献
107.
Jan Vícha Michal Maloň Petra Veselá Otakar Humpa Miroslav Strnad Radek Marek 《Magnetic resonance in chemistry : MRC》2010,48(4):318-322
The 1H and 13C NMR resonances of 16 purine glucosides were assigned by a combination of one‐ and two‐dimensional NMR experiments, including gs‐COSY, gs‐HSQC, and gs‐HMBC, in order to characterize the effect of substituent and the position of glucose unit on the NMR chemical shifts. In addition, 15N NMR chemical shifts for selected derivatives were investigated by using 1H? 15N chemical shift correlation techniques. To map the influence of sugar moiety on the directly bonded nitrogen atom, selected N9‐glucosides and their ribose analogs were compared. Characteristic long‐range 1H? 15N coupling constants, measured by using 1H? 15N gradient‐selected single‐quantum multiple bond correlation (GSQMBC), are also reported and discussed. All compounds investigated here belong to cytokinins, an important group of plant hormones. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
108.
Montes VA Pohl R Shinar J Anzenbacher P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(17):4523-4535
The unique electron-transport and emissive properties of tris(8-quinolinolate) aluminum(III) (Alq(3)) have resulted in extensive use of this material for small molecular organic light-emitting diode (OLED) fabrication. So far, efforts to prepare stable and easy-to-process red/green/blue (RGB)-emitting Alq(3) derivatives have met with only a limited success. In this paper, we describe how the electronic nature of various substituents, projected via an arylethynyl or aryl spacer to the position of the highest HOMO density (C5), may be used for effective emission tuning to obtain blue-, green-, and red-emitting materials. The synthetic strategy consists of four different pathways for the attachment of electron-donating and electron-withdrawing aryl or arylethynyl substituents to the 5-position of the quinolinolate ring. Successful tuning of the emission color covering the whole visible spectrum (lambda=450-800 nm) was achieved. In addition, the photophysical properties of the luminophores were found to correlate with the Hammett constant of the respective substituents, providing a powerful strategy with which to predict the optical properties of new materials. We also demonstrate that the electronic nature of the substituent affects the emission properties of the resulting complex through effective modification of the HOMO levels of the quinolinolate ligand. 相似文献
109.
Azidopropylvinylsulfonamide as a New Bifunctional Click Reagent for Bioorthogonal Conjugations: Application for DNA–Protein Cross‐Linking 下载免费PDF全文
Jitka Dadová Dr. Milan Vrábel Matej Adámik Dr. Marie Brázdová Dr. Radek Pohl Prof. Dr. Miroslav Fojta Prof. Dr. Michal Hocek 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(45):16091-16102
N‐(3‐Azidopropyl)vinylsulfonamide was developed as a new bifunctional bioconjugation reagent suitable for the cross‐linking of biomolecules through copper(I)‐catalyzed azide–alkyne cycloaddition and thiol Michael addition reactions under biorthogonal conditions. The reagent is easily clicked to an acetylene‐containing DNA or protein and then reacts with cysteine‐containing peptides or proteins to form covalent cross‐links. Several examples of bioconjugations of ethynyl‐ or octadiynyl‐modified DNA with peptides, p53 protein, or alkyne‐modified human carbonic anhydrase with peptides are given. 相似文献
110.
Toward a Consistent Interpretation of the QTAIM: Tortuous Link between Chemical Bonds,Interactions, and Bond/Line Paths 下载免费PDF全文
Dr. Cina Foroutan‐Nejad Prof. Dr. Shant Shahbazian Prof. Dr. Radek Marek 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(32):10140-10152
Currently, bonding analysis of molecules based on the Quantum Theory of Atoms in Molecules (QTAIM) is popular; however, “misinterpretations” of the QTAIM analysis are also very frequent. In this contribution the chemical relevance of the bond path as one of the key topological entities emerging from the QTAIM’s topological analysis of the one‐electron density is reconsidered. The role of nuclear vibrations on the topological analysis is investigated demonstrating that the bond paths are not indicators of chemical bonds. Also, it is argued that the detection of the bond paths is not necessary for the “interaction” to be present between two atoms in a molecule. The conceptual disentanglement of chemical bonds/interactions from the bonds paths, which are alternatively termed “line paths” in this contribution, dismisses many superficial inconsistencies. Such inconsistencies emerge from the presence/absence of the line paths in places of a molecule in which chemical intuition or alternative bonding analysis does not support the presence/absence of a chemical bond. Moreover, computational QTAIM studies have been performed on some “problematic” molecules, which were considered previously by other authors, and the role of nuclear vibrations on presence/absence of the line paths is studied demonstrating that a bonding pattern consistent with other theoretical schemes appears after a careful QTAIM analysis and a new “interpretation” of data is performed. 相似文献