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61.
A series of experiments in a novel quench flow reactor was used to study the influence of the means of adding TEA to the catalyst, the reaction temperature and the hydrogen concentration on the kinetics and morphology of the nascent phase of the polymerisation of ethylene in heptane slurry. It was shown that regardless of the way in which the alkyl was added, an extremely rapid reaction rate was observed for the first few fractions of a second, but that precontacting the catalyst and the TEA cocatalyst led to a slightly higher initial rate. On the other hand, the nascent morphology of the particle/support complex was strongly influenced by the means of adding the alkyl, with precontacting of the two components leading to a better defined product. The influence of the temperature was found to be less significant; however, this was attributed to the particular catalyst.
62.
Martin AN Farquar GR Jones AD Frank M 《Rapid communications in mass spectrometry : RCM》2007,21(22):3561-3568
Single over-the-counter medication tablets were analyzed in real time using Single Particle Aerosol Mass Spectrometry (SPAMS). Dual-polarity time-of-flight mass spectra were obtained for micrometer-sized single particles dislodged from a single tablet without destroying the shape or markings of each tablet. The solid tablet was placed in a modified-top glass vial and shaken to dislodge and introduce micrometer-sized particles into the SPAMS system. Unique spectra from these particles were obtained in less than 1 s for single tablets of aspirin, ibuprofen, pseudoephedrine, phenylephrine, loratadine, or diphenhydramine. The signals obtained allowed the non-destructive identification of an individual tablet in seconds. SPAMS presents an ideal system for high-throughput analysis of solid drugs. 相似文献
63.
Artzner F Geiger S Olivier A Allais C Finet S Agnely F 《Langmuir : the ACS journal of surfaces and colloids》2007,23(9):5085-5092
Poloxamers F88 (EO97PO39EO97) and P85 (EO27PO39EO27) are triblock copolymers of ethylene oxide (EO) and propylene oxide (PO), which have the same hydrophobic PO block. We studied aqueous solutions of these two copolymers by the conjoint use of differential scanning calorimetry (DSC), rheology, and small-angle X-ray scattering (SAXS). The results showed that the temperature-induced micellization of aqueous solutions of F88 and P85 was a progressive process followed by gelation for sufficiently concentrated samples. Gelation was due to the ordered packing of micelles under a hexagonal compact (HC) structure for P85 and a body-centered cubic (BCC) phase for F88. Importantly, the phase diagram of F88/P85 mixtures in water was elucidated and showed the destabilization of the HC phase upon addition of small amounts of F88. 相似文献
64.
Oxidative Addition of Haloheteroarenes to Palladium(0): Concerted versus SNAr‐Type Mechanism 下载免费PDF全文
Prof. Bert U. W. Maes Dr. Stefan Verbeeck Dr. Tom Verhelst Audrey Ekomié Niklas von Wolff Dr. Guillaume Lefèvre Dr. Emily A. Mitchell Prof. Anny Jutand 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(21):7858-7865
The kinetics of the oxidative additions of haloheteroarenes HetX (X=I, Br, Cl) to [Pd0(PPh3)2] (generated from [Pd0(PPh3)4]) have been investigated in THF and DMF and the rate constants have been determined. In contrast to the generally accepted concerted mechanism, Hammett plots obtained for substituted 2‐halopyridines and solvent effects reveal a reaction mechanism dependent on the halide X of HetX: an unprecedented SNAr‐type mechanism for X=Br or Cl and a classical concerted mechanism for X=I. These results are supported by DFT studies. 相似文献
65.
Audrey Devatine Jean Paul Canselier Nadine Gabas Joël Jaud 《Journal of chemical crystallography》2003,33(2):85-90
The new crystal and molecular structures of a less common hydrated calcium L(–)-malate (calcium (2S) 2-hydroxybutanedioate trihydrate) Ca(C4H4O5)3H2O, are reported. X-ray crystallographic data are as follows: a = 6.6460(3) Å, b = 8.3795(3) Å, c = 8.2707(4) Å, = 112.640(2)°, V = 425.1(4) Å3, space group P21 (No. 4), Z = 2, D
calc = 1.767 g cm–3. The calcium ion coordination number is seven. One of the three water molecules present in the unit cell is less strongly bound, only interacting with a calcium ion. In aqueous or hydroalcoholic solution, both di- and trihydrated species crystallize simultaneously. 相似文献
66.
67.
Dr. Audrey Llevot Patrick‐Kurt Dannecker Marc von Czapiewski Lena C. Over Zafer Söyler Prof. Dr. Michael A. R. Meier 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(33):11510-11521
Taking advantage of the structural diversity of different biomass resources, recent efforts were directed towards the synthesis of renewable monomers and polymers, either for the substitution of petroleum‐based resources or for the design of novel polymers. Not only the use of biomass, but also the development of sustainable chemical approaches is a crucial aspect for the production of sustainable materials. This review discusses the recent examples of chemical modifications and polymerizations of abundant biomass resources with a clear focus on the sustainability of the described processes. Topics such as synthetic methodology, catalysis, and development of new solvent systems or greener alternative reagents are addressed. The chemistry of vegetable oil derivatives, terpenes, lignin, carbohydrates, and sugar‐based platform chemicals was selected to highlight the trends in the active field of a sustainable use of renewable resources. 相似文献
68.
69.
Richard K. Johnson Audrey Zink-Sharp Scott H. Renneckar Wolfgang G. Glasser 《Cellulose (London, England)》2009,16(2):227-238
Utilization of TEMPO-oxidized celluloses in bio-based nanocomposites is reported for the first time. TEMPO-oxidized wood pulps
(net carboxylate content 1.1 mmol/g cellulose) were fibrillated to varying degrees using a high intensity ultrasonic processor.
The degree of fibrillation was controlled by varying sonication time from 1 to 20 min. The sonication products were then characterized
independently and as fillers (5 wt% loading) in hydroxypropyl cellulose nanocomposite films. Nanofibril yields ranging from
11 to 98 wt% (on fiber weight basis) were obtained over the range of sonication times used. Suspension viscosities increased
initially with sonication time, peaked with gel-like behavior at 10 min of sonication and then decreased with further sonication.
The thermal degradation temperature of unfibrillated oxidized pulps was only minimally affected (6 °C decrease) by the fibrillation
process. Dynamic mechanical analysis of the nanocomposites revealed strong fibril-matrix interactions as evidenced by remarkable
storage modulus retention at high temperatures and a suppression of matrix glass transition at “high” (~5 wt%) nanofibril
loadings. Creep properties likewise exhibited significant (order of magnitude) suppression of matrix flow at high temperatures.
It was also believed, based on morphologies of freeze-fracture surfaces that the nanocomposites may be characterized by high
fracture toughness. Direct fracture testing will however be necessary to verify this suspicion. 相似文献
70.
Audrey Sassolas Loïc J. Blum Béatrice D. Leca-Bouvier 《Analytical and bioanalytical chemistry》2009,394(4):971-980
Performant reagentless electrochemiluminescent (ECL) (bio)sensors have been developed using polymeric luminol as the luminophore.
The polyluminol film is obtained by cyclic voltammetry (CV) on a screen-printed electrode either in a commonly used H2SO4 medium or under more original near-neutral buffered conditions. ECL responses obtained after performing polymerization either
at acidic pH or at pH 6 have been compared. It appears that polyluminol formed in near-neutral medium gives the best responses
for hydrogen peroxide detection. Polymerization at pH 6 by cyclic voltammetry gives a linear range extending from 8 × 10−8 to 1.3 × 10−4 M H2O2 concentrations. Based on this performant sensor for hydrogen peroxide detection, an enzymatic biosensor has been developed
by associating the polyluminol film with an H2O2-producing oxidase. Here, choline oxidase (ChOD) has been chosen as a model enzyme. To develop the biosensor, luminol has
been polymerized at pH 6 by CV, and then an enzyme-entrapping matrix has been formed on the above modified working electrode.
Different biological (chitosan, agarose, and alginate) and chemical (silica gels, photopolymers, or reticulated matrices)
gels have been tested. Best performances have been obtained by associating a ChOD-immobilizing photopolymer with the polyluminol
film. In this case, choline can be detected with a linear range extending from 8 × 10−8 to 1.3 × 10−4 M.
This paper is based on the results presented in a poster that received a Poster Award on the occasion of XIII International
Symposium on Luminescence Spectrometry in Bologna, Italy, on September, 7th-11th, 2008. 相似文献