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81.
Multiple units of Standard Reference Materials (SRMs) 1566 Oyster Tissue, 1567 Wheat Flour, 1568 Rice Flour, and 1570 Trace Elements in Spinach, produced by the National Institute of Standards and Technology (NIST, then the National Bureau of Standards), were analyzed 17-20 years after the original certification dates and 12-15 years after the certificates became invalid. Instrumental neutron activation analysis and thermal neutron prompt gamma-ray activation analysis were used to measure mass fractions for 27 elements in these SRMs to revalidate them for use in quality assurance (QA) programs required for food analysis programs within the U.S. Food and Drug Administration. With the exception of Se in SRM 1567, all element mass fractions were in agreement with certified values and literature data. Some evidence of B loss from SRM 1568 was observed. These materials were judged to be suitable for continued use in QA programs. Findings showed that these matrixes exhibited stability of moisture, mass fraction, and weight basis for far longer (> or =15 years) than was indicated by the 5-year validity statement on the NIST Certificates of Analysis. 相似文献
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84.
Hopf H Mlynek C McMahon RJ Menke JL Lesarri A Rosemeyer M Grabow JU 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(47):14115-14123
In support of a deeper understanding of the chemistry of cyanoacetylene--a known constituent of planetary atmospheres and interstellar space--theoretical and experimental studies address the chemical mechanism of dimerization and trimerization, and provide high-resolution rotational spectra of two of the trimeric products, 1,2,3- and 1,2,4-tricyanobenzene. Analysis of the rotational spectra is particularly challenging because of quadrupolar coupling from three (14)N nuclei. The laboratory rotational spectra provide the basis for future searches for these polar aromatic compounds in interstellar space by radio astronomy. 相似文献
85.
A systematic investigation of the solvent's dynamic influence on activated barrier crossings on an electronic ground state is performed using ultrafast two-dimensional infrared chemical exchange spectroscopy. These measurements facilitate a direct comparison with the widely adopted Kramers theory of condensed phase reaction kinetics, and for the first time avoid the significant complication of electronic excitation to probe directly in the time domain a ground electronic state reaction with a well-defined transition state. The picosecond timescale interconversion between two stable isomers of the metal carbonyl complex Co(2)(CO)(8) in a series of linear alkane solvents shows negligible energetic variation with solvent carbon chain length, providing an exclusive probe of the effects of solvent friction. Relative to the linear alkane series, cyclohexane does alter the potential energy surface by preferentially stabilizing one of the isomers. Despite this pronounced modification of the reaction barrier energetics, combination of experiment and computation enables the removal of the nondynamical barrier contribution to the rate constant, isolating the dynamical influence of solvent friction. The experimental data, supported with quantum and classical computations, show agreement with a simple Markovian Kramers theory for the isomerization rate constant's dependence on solvent viscosity. 相似文献
86.
Allegrand J Touboul D Schmitz-Afonso I Guérineau V Giuliani A Le Ven J Champy P Laprévote O 《Rapid communications in mass spectrometry : RCM》2010,24(24):3602-3608
Collision‐induced dissociation experiments of seven annonaceous acetogenins were carried out under high and low collision energy conditions. Each compound was studied as protonated or deprotonated and lithium‐ or sodium‐ cationized molecules, using ElectroSpray Ionisation (ESI) with a hybrid linear trap/orbitrap mass spectrometer (LTQ‐Orbitrap®). The same ion species were studied with a Matrix‐Assisted Laser Desorption Ionisation (MALDI) tandem mass spectrometer in a high collision energy regime (1 or 2 keV). Although each of the techniques showed some limitations in the detection of functional groups, unambiguous structural identification of the acetogenins was obtained. MALDI ToF‐ToF has the advantage over ESI‐based methods to provide mass spectra rich in informative fragments which allows the confirmation of some functional groups position. By contrast, ESI‐LTQ‐Orbitrap® analysis has the advantage over MALDI that the mass spectra are relatively simple with only fragments close to the functional groups. However, this technique needs to carry out experiments both in negative and positive ionization modes. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
87.
Fairchild JN Horvath K Gooding JR Campagna SR Guiochon G 《Journal of chromatography. A》2010,1217(52):8161-8166
Off-line two-dimensional liquid chromatography with tandem mass spectrometry detection (2D-LC/MS-MS) was used to separate a set of metabolomic species. Water-soluble metabolites were extracted from Escherichia coli and Saccharomyces cerevisae cultures and were immediately analyzed using strong cation exchange (SCX)-hydrophilic interaction chromatography (HILIC). Metabolite mixtures are well-suited for multidimensional chromatography as the range of components varies widely with respect to polarity and chemical makeup. Some currently used methods employ two different separations for the detection of positively and negatively ionized metabolites by mass spectrometry. Here we developed a single set of chromatographic conditions for both ionization modes and were able to detect a total of 141 extracted metabolite species, with an overall peak capacity of ca. 2500. We show that a single two-dimensional separation method is sufficient and practical when a pair or more of unidimensional separations are used in metabolomics. 相似文献
88.
Jessica Baur Michael Holzinger Chantal Gondran Serge Cosnier 《Electrochemistry communications》2010,12(10):1287-1290
A novel and simple immobilization strategy for biotinylated biological macromolecules onto electropolymerized poly(pyrrole-nitrilotriacetic acid)(NTA)–Cu2+ films without avidin as connecting bridge is reported. After complexation of Cu2+ by the polymerized NTA chelator, biotinylated biomolecules were immobilized by coordination of the biotin groups on the NTA–Cu2+ complex. The anchoring of biotinylated glucose oxidase was demonstrated by fluorescent characterization via FITC-labeled avidin and amperometric measurement of glucose. The resulting calibration curve led to a sensitivity and maximum current density values of 0.6 mA mol?1 L cm? 2 and 13.2 μA cm? 2, respectively. Thus, biotinylated polyphenol oxidase was fixed leading to a catechol sensor with a sensitivity of 656 mA mol?1 L cm? 2 and maximum current density of 25.4 μA cm? 2. This system was also applied to the efficient immobilization of biotinylated DNA, illustrated by impedimetric detection of the formation of the DNA duplex. 相似文献
89.
Jessica A. Zimberlin Alfred J. Crosby 《Journal of polymer science. Part A, Polymer chemistry》2010,48(13):1423-1427
Using the cavitation rheology (CR) technique developed in our labs, we show that fluids with negligible interfacial tensions with a surrounding material can be used to induce an elastic, cavitation instability in that material. We do this by changing the cavitation media from air, which was demonstrated to induce cavitation at the tip of a syringe needle in previous studies, to water, which has a negligible surface tension with the surrounding poly(vinyl alcohol) hydrogel material. In this case, the critical pressure in which this instability occurs can be directly related to the elastic modulus of the surrounding network and is shown to be nearly independent of length scale. This independence of size scale has important implications in the use of CR for the characterization of mechanical properties from molecular to macroscopic length scales. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1423–1427, 2010 相似文献
90.
Berwyck L. J. Poad Huong T. Pham Michael C. Thomas Jessica R. Nealon J. Larry Campbell Todd W. Mitchell Stephen J. Blanksby 《Journal of the American Society for Mass Spectrometry》2010,21(12):1989-1999
Ozone-induced dissociation (OzID) exploits the gas-phase reaction between mass-selected lipid ions and ozone vapor to determine
the position(s) of unsaturation. In this contribution, we describe the modification of a tandem linear ion-trap mass spectrometer
specifically for OzID analyses wherein ozone vapor is supplied to the collision cell. This instrumental configuration provides
spatial separation between mass-selection, the ozonolysis reaction, and mass-analysis steps in the OzID process and thus delivers
significant enhancements in speed and sensitivity (ca. 30-fold). These improvements allow spectra revealing the double-bond
position(s) within unsaturated lipids to be acquired within 1 s: significantly enhancing the utility of OzID in high-throughput
lipidomic protocols. The stable ozone concentration afforded by this modified instrument also allows direct comparison of
relative reactivity of isomeric lipids and reveals reactivity trends related to (1) double-bond position, (2) substitution
position on the glycerol backbone, and (3) stereochemistry. For cis- and trans-isomers, differences were also observed in the branching ratio of product ions arising from the gas-phase ozonolysis reaction,
suggesting that relative ion abundances could be exploited as markers for double-bond geometry. Additional activation energy
applied to mass-selected lipid ions during injection into the collision cell (with ozone present) was found to yield spectra
containing both OzID and classical-CID fragment ions. This combination CID-OzID acquisition on an ostensibly simple monounsaturated
phosphatidylcholine within a cow brain lipid extract provided evidence for up to four structurally distinct phospholipids
differing in both double-bond position and sn-substitution. 相似文献