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921.
John B. Vincent 《The Chemical Educator》1999,4(3):102-104
The Shroud of Turin, a piece of linen cloth bearing an anatomically correct image of a crucified human being, which resembles Jesus of Nazareth, has been an enigma to scientists. While recent studies including radiocarbon dating suggest the cloth is a medieval relic, few if any proposals have been put forward that satisfactorily explain how the image was generated. In combination with a lecture on the scientific method and the problem of bias, a laboratory experiment has been developed that allows science students to attempt to simulate the image on the Shroud. The experiment involves an active-learning experience in which students discover which techniques do not work to generate the image and which begin to suggest how such an image could have been generated. 相似文献
922.
Nyambeni Luruli Thijs Pijpers Robert Brüll Valérie Grumel Harald Pasch Vincent Mathot 《Journal of Polymer Science.Polymer Physics》2007,45(21):2956-2965
The short chain branching distribution (SCBD) and thermal properties of ethylene/1‐pentene copolymers were studied using SEC‐FTIR and SEC‐HPer DSC. The copolymers, synthesized with Cp2ZrCl2/MAO, were fractionated using size exclusion chromatography (SEC). The infrared analysis of the fractions showed that the copolymers had—on average—higher 1‐pentene concentration in the low molecular weight range. Furthermore, the thermal properties of the SEC deposits of these copolymers on a Germanium disc were studied using high performance differential scanning calorimetry (HPer DSC). Single SEC separations were used to accumulate fractions in the microgram range that were directly analyzed with regard to their thermal properties, thus allowing us to study SCBD as well as thermal behavior simultaneously. When these fractions (with masses ranging from 10–80 μg) were analyzed using HPer DSC, good melting and crystallization temperature distributions were obtained, proving that HPer DSC can be used as a complementary method to SEC‐FTIR. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2956–2965, 2007 相似文献
923.
Perrine Pivette Vincent Faivre Georges Daste Michel Ollivon Sylviane Lesieur 《Journal of Thermal Analysis and Calorimetry》2009,98(1):47-55
Two lipid binders, glyceryl behenate and paraffin wax, were examined regarding their ability to be used in a prilling process.
Prilling has the advantage to produce microgranules very reproducible in size and shape but involves ultrafast cooling of
liquid droplets. The different steps to produce solid micropheres from the molten state were successfully modelled to predict
crystallisation time as a function of the binder used. Bulk versus microgranules characterization by differential scanning
calorimetry, X-ray diffraction and microscopies showed the peculiar suitability of the 50/50 mixture of the two lipid binders
for prilling, in agreement with the theoretical approach. 相似文献
924.
Reine Nehmé Catherine Perrin Vincent Guerlavais Jean‐Alain Fehrentz Hervé Cottet Jean Martinez Huguette Fabre 《Electrophoresis》2009,30(21):3772-3779
The diastereoisomeric separation of peptidomimetics of hexarelin, a strong growth hormone secretagogue, in CE has been studied. Highly sulfated‐γ‐CD was found to be an appropriate selector for the separation of the stereoisomers. However, non‐repeatable analyses were obtained on bare fused silica capillary due to the progressive adsorption of the analytes on the capillary wall. Two types of polyelectrolyte coating agents were tested to prevent this phenomenon. Coating with neutral polyethylene oxide was found to be efficient but resulted in a very long analysis time (about 40 min). Coating with cationic poly(diallyldimethylammonium) chloride was found both to prevent analyte adsorption, reduce analysis time and alter separation selectivity. EOF measurement revealed that the highly sulfated‐γ‐CDs were strongly adsorbed on the poly(diallyldimethylammonium) chloride coating surface yielding a stable strong cathodic EOF, which considerably reduced analysis time (about 12 min). Very good repeatability of analysis was obtained (RSDmigration time<1%). 相似文献
925.
Free charge carrier repartition over the surface of photosensitive materials: Why and how to manage?
A. A. Evstratov C. Chis A. A. Malygin J. -M. Taulemesse P. Gaudon T. Vincent 《Russian Journal of General Chemistry》2008,78(5):1070-1080
The free charge carrier repartition over the surface of the photosensitive solids can be efficiently managed by selective elimination of the “parasite” free charge carriers (FCCs) from the exited body. This makes it possible to “correct” the natural FCC repartition law represented by the well-known fifty-fifty ratio (1 generated electron in conduction band versus 1 hole formed in valence band) and to better protect the FCCs against recombination. The chemical design principles of the FCC selective photo-generators (FCCP-Ss) were formulated. The functioning mechanism of the hole selective nanocomposite photo-generators (Sh+-FCCPs) was examined. This type of active materials generating mainly the most powerful oxidation agents (OH0 radicals) is suitable for application in oxidation photocatalysis, microbiological object sterilization, and self-cleaning surface development. 相似文献
926.
P. Bonville V. Dupuis E. Vincent P. E. Lippens A. S. Wills 《Hyperfine Interactions》2006,168(1-3):1085-1089
57Fe Mössbauer spectra are presented from (H3O)Fe3(SO4)2(OH)6 (or H3O-jarosite), which is a model kagomé antiferromagnet which features geometrical frustration and spin-glass-like behaviour. Dynamic scaling of the freezing temperature as a function of frequency is observed over a large frequency range, which indicates the presence of a spin-glass transition. A fast relaxation model between “up” and “down” states, separated by an energy gap, is presented to account for the shape of the Mössbauer spectra below the freezing temperature. From a calculation of the Electric Field Gradient tensor, it is suggested that H3O-jarosite is an XY-Heisenberg antiferromagnet, where the Fe3+ moments lie in the kagomé planes. 相似文献
927.
Manuel Salmern Snchez Vincent Mathot Geert Vanden Poel Gabriel Groeninckx Willie Bruls 《Journal of Polymer Science.Polymer Physics》2006,44(5):815-825
The crystallization of submicrometer PA6 droplets dispersed in an ethylene‐1‐octene copolymer matrix, using PE‐g‐MA as a compatibilizer agent, is investigated. This system shows a nonconventional mechanical behavior at high temperatures. Up to ~100 °C above the final melting temperature of the ethylene‐1‐octene copolymer matrix, the system shows good thermal and mechanical properties including dimensional stability. Because of the dispersed phase morphology of the system, so‐called fractionated/homogeneous crystallization takes place leading to an extra supercooling of PA6: ~50 °C compared to the bulk PA6 crystallization temperature. Thus—though this is most probably just of interest for small‐scale research—the system can be processed at lowered temperatures while still providing exceptional high‐temperature properties. While the matrix is in the melt state when crystallization of the dispersed PA6 phase occurs, the possibility of matrix induced crystallization is absent, contrary to almost all of the ‘dispersed droplets in a matrix’ systems reported so far. The kinetics of this phenomenon is investigated in detail by DSC: the existence of fractionated/homogeneous crystallization is shown to be related to the lack of active nuclei in the dispersed droplets by means of self‐seeding experiments. The occurrence of extensive cold crystallization of PA6 in the confined environment is studied as is the crystallization kinetics, including the characterization of its time dependences showing its sporadic nature. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 815–825, 2006 相似文献
928.
Y Q Xia C E Hop D Q Liu S H Vincent S H Chiu 《Rapid communications in mass spectrometry : RCM》2001,15(22):2135-2144
A method with parallel extraction columns and parallel analytical columns (PEC-PAC) for on-line high-flow liquid chromatography/tandem mass spectrometry (LC/MS/MS) was developed and validated for simultaneous quantification of a drug candidate and its six metabolites in dog plasma. Two on-line extraction columns were used in parallel for sample extraction and two analytical columns were used in parallel for separation and analysis. The plasma samples, after addition of an internal standard solution, were directly injected onto the PEC-PAC system for purification and analysis. This method allowed the use of one of the extraction columns for analyte purification while the other was being equilibrated. Similarly, one of the analytical columns was employed to separate the analytes while the other was undergoing equilibration. Therefore, the time needed for re-conditioning both extraction and analytical columns was not added to the total analysis time, which resulted in a shorter run time and higher throughput. Moreover, the on-line column extraction LC/MS/MS method made it possible to extract and analyze all seven analytes simultaneously with good precision and accuracy despite their chemical class diversity that included primary, secondary and tertiary amines, an alcohol, an aldehyde and a carboxylic acid. The method was validated with the standard curve ranging from 5.00 to 5000 ng/mL. The intra- and inter-day precision was no more than 8% CV and the assay accuracy was between 95 and 107%. 相似文献
929.
930.
Aurlie Botella Jrme Dupuy Alain‐Andr Roche Henry Sautereau Vincent Verney 《Macromolecular rapid communications》2004,25(12):1155-1158
Summary: A suitable rheometer for simultaneous dynamic mechanical analysis (DMA) and NIR (Near Infra‐Red) in situ analysis during UV curing was developed. The conversion and viscoelastic properties of a dimethacrylate/styrene‐based system were investigated. The results were plotted against both irradiation time and total average conversion. For the same conversion, a lower intensity delays the reaction but does not affect the viscoelastic properties.