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排序方式: 共有204条查询结果,搜索用时 15 毫秒
81.
G. Carson A.J. Mulholland A. Nordon M. Tramontana A. Gachagan G. Hayward 《Journal of sound and vibration》2008,317(1-2):142-157
In continuously stirred reactor vessels the non-invasive recovery of the particle size could be used to monitor the reaction process. Experimental and numerical investigations have shown empirically that the frequency of the peak vibration response arising from the particle–wall impact is inversely proportional to the particle size. The passive monitoring of these impact vibrations using an ultrasonic transducer has the potential therefore of non-invasively recovering the particle size. However, the vessel geometry, fluid loading, variable impact position and velocity, stirrer and transducer effects, and noise levels make this problem very complex. There are a large number of system parameters and this makes empirical derivations of cause and effects extremely difficult. The first objective of this paper is to derive an analytical expression for the vibrations arising from a spherical particle impacting a circular plate. Using a series expansion in terms of the plate loss parameter, an expression for the frequency of the peak pressure in terms of the system parameters is derived. In particular, its explicit dependency on the impacting particle size and the impact velocity is found. The inverse problem of recovering the particle size from the experimental data is then investigated. A set of experiments are described where the impact vibrations are recorded using an ultrasonic transducer attached to the rear of a thin plate. The results show that it is possible to recover the particle size using this approach. Data from a second set of experiments, involving multi-particle impacts with a vessel wall in a continuously stirred reactor, are then used. The inverse problem of recovering the particle size from the vibration spectrum was then investigated with encouraging results. 相似文献
82.
Adams CJ Bartlett IM Boonyuen S Connelly NG Harding DJ Hayward OD McInnes EJ Orpen AG Quayle MJ Rieger PH 《Dalton transactions (Cambridge, England : 2003)》2006,(28):3466-3477
Reduction of [M(CO)2(eta-RC[triple bond]CR')Tp']X {Tp' = hydrotris(3,5-dimethylpyrazolyl)borate, M = Mo, X = [PF6]-, R = R' = Ph, C6H4OMe-4 or Me; R = Ph, R' = H; M = W, X = [BF4]-, R = R' = Ph or Me; R = Ph, R' = H} with [Co(eta-C5H5)2] gave paramagnetic [M(CO)2(eta-RC[triple bond]CR')Tp'], characterised by IR and ESR spectroscopy. X-Ray structural studies on the redox pair [Mo(CO)2(eta-PhC[triple bond]CPh)Tp'] and [Mo(CO)2(eta-PhC[triple bond]CPh)Tp'][PF6] showed that oxidation is accompanied by a lengthening of the C[triple bond]C bond and shortening of the Mo-C(alkyne) bonds, consistent with removal of an electron from an orbital antibonding with respect to the Mo-alkyne bond, and with conversion of the alkyne from a three- to a four-electron donor. Reduction of [Mo(CO)(NCMe)(eta-MeC[triple bond]CMe)Tp'][PF6] with [Co(eta-C5H5)2] in CH2Cl2 gives [MoCl(CO)(eta-MeC[triple bond]CMe)Tp'], via nitrile substitution in [Mo(CO)(NCMe)(eta-MeC[triple bond]CMe)Tp'], whereas a similar reaction with [M(CO){P(OCH2)3CEt}(eta-MeC[triple bond]CMe)Tp']+ (M = Mo or W) gives the phosphite-containing radicals [M(CO){P(OCH2)3CEt}(eta-MeC[triple bond]CMe)Tp']. ESR spectroscopic studies and DFT calculations on [M(CO)L(eta-MeC[triple bond]CMe)Tp'] {M = Mo or W, L = CO or P(OCH2)3CEt} show the SOMO of the neutral d5 species (the LUMO of the d4 cations) to be largely d(yz) in character although much more delocalised in the W complexes. Non-coincidence effects between the g and metal hyperfine matrices in the Mo spectra indicate hybridisation of the metal d-orbitals in the SOMO, consistent with a rotation of the coordinated alkyne about the M-C2 axis. 相似文献
83.
Dr. Fabio Denis Romero Alice Leach Dr. Johannes S. Möller Francesca Foronda Prof. Stephen J. Blundell Prof. Michael A. Hayward 《Angewandte Chemie (International ed. in English)》2014,53(29):7556-7559
A series of strontium vanadium oxide–hydride phases prepared by utilizing a low‐temperature synthesis strategy in which oxide ions in Srn+1VnO3n+1 (n=∞, 1, 2) phases are topochemically replaced by hydride ions to form SrVO2H, Sr2VO3H, and Sr3V2O5H2, respectively. These new phases contain sheets or chains of apex‐linked V3+O4 squares stacked with SrH layers/chains, such that the n=∞ member, SrVO2H, can be considered to be analogous to “infinite‐layer” phases, such as Sr1?xCaxCuO2 (the parent phase of the high‐Tc cuprate superconductors), but with a d2 electron count. All three oxide–hydride phases exhibit strong antiferromagnetic coupling, with SrVO2H exhibiting an antiferromagnetic ordering temperature, TN>300 K. The strong antiferromagnetic couplings are surprising given they appear to arise from π‐type magnetic exchange. 相似文献
84.
Hayward Tammy Kay Hamilton Jenny Tholudur Arun McMillan James D. 《Applied biochemistry and biotechnology》2000,84(1-9):859-874
Researchers studying cellulase enzymes for the economical production of fuel ethanol envision cellulose as the carbon source.
However, submerged Trichoderma reesei cultures grown on cellulose exhibit high run-to-run variability. Thus, an investigation of 30 batch cellulase production
experiments was instrumental in determining fermentation conditions that improved enzyme titers, yields, and productivities.
Eighteen of the 30 batch experiments experienced minimal process upsets and were classified into eight groups based on agitation
rate, gas sparge rate, and the use of oxygen supplementation. Comparing corn steep liquor with yeast extract/peptone also
tested the effect of different sources of nitrogen in the media. Average 7-d enzyme titers were doubled from 4 to 8 FPU/mL
primarily by increasing aeration. 相似文献
85.
The synthesis of the Mn(II) phase 4H-Ba(0.5)Sr(0.5)MnO(2+delta) via the topotactic reduction of 4H-Ba(0.5)Sr(0.5)MnO(3-x) with the novel reducing agent LiH, is described. Neutron powder diffraction data show that oxide ions are deintercalated from the host structure in a disordered manner to yield "tetrahedral" MnO(4) coordination sites. Magnetic susceptibility and neutron powder diffraction data show that the title phase adopts a canted antiferromagnetically ordered state below T(N) = 355K, consistent with the strong magnetic coupling expected between d(5) centers. 相似文献
86.
Lee E Hammer B Kim JK Page Z Emrick T Hayward RC 《Journal of the American Chemical Society》2011,133(27):10390-10393
We report on the solution-state assembly of all-conjugated polythiophene diblock copolymers containing nonpolar (hexyl) and polar (triethylene glycol) side chains. The polar substituents provide a large contrast in solubility, enabling formation of stably suspended crystalline fibrils even under very poor solvent conditions for the poly(3-hexylthiophene) block. For appropriate block ratios, complexation of the triethylene glycol side chains with added potassium ions drives the formation of helical nanowires that further bundle into superhelical structures. 相似文献
87.
David W. Templeton Amie D. Sluiter Tammy K. Hayward Bonnie R. Hames Steven R. Thomas 《Cellulose (London, England)》2009,16(4):621-639
Corn stover, the above-ground, non-grain portion of the crop, is a large, currently available source of biomass that potentially
could be collected as a biofuels feedstock. Biomass conversion process economics are directly affected by the overall biochemical
conversion yield, which is assumed to be proportional to the carbohydrate content of the feedstock materials used in the process.
Variability in the feedstock carbohydrate levels affects the maximum theoretical biofuels yield and may influence the optimum
pretreatment or saccharification conditions. The aim of this study is to assess the extent to which commercial hybrid corn
stover composition varies and begin to partition the variation among genetic, environmental, or annual influences. A rapid
compositional analysis method using near-infrared spectroscopy/partial least squares multivariate modeling (NIR/PLS) was used
to evaluate compositional variation among 508 commercial hybrid corn stover samples collected from 47 sites in eight Corn
Belt states after the 2001, 2002, and 2003 harvests. The major components of the corn stover, reported as average (standard
deviation) % dry weight, whole biomass basis, were glucan 31.9 (2.0), xylan 18.9 (1.3), solubles composite 17.9 (4.1), and
lignin (corrected for protein) 13.3 (1.1). We observed wide variability in the major corn stover components. Much of the variation
observed in the structural components (on a whole biomass basis) is due to the large variation found in the soluble components.
Analysis of variance (ANOVA) showed that the harvest year had the strongest effect on corn stover compositional variation,
followed by location and then variety. The NIR/PLS rapid analysis method used here is well suited to testing large numbers
of samples, as tested in this study, and will support feedstock improvement and biofuels process research. 相似文献
88.
Kevin R. Chalek Xinning Dong Fei Tong Ryan A. Kudla Lingyan Zhu Adam D. Gill Wenwen Xu Chen Yang Joshua D. Hartman Alviclr Magalhes Rabih O. Al-Kaysi Ryan C. Hayward Richard J. Hooley Gregory J. O. Beran Christopher J. Bardeen Leonard J. Mueller 《Chemical science》2021,12(1):453
Crystals composed of photoreactive molecules represent a new class of photomechanical materials with the potential to generate large forces on fast timescales. An example is the photodimerization of 9-tert-butyl-anthracene ester (9TBAE) in molecular crystal nanorods that leads to an average elongation of 8%. Previous work showed that this expansion results from the formation of a metastable crystalline product. In this article, it is shown how a novel combination of ensemble oriented-crystal solid-state NMR, X-ray diffraction, and first principles computational modeling can be used to establish the absolute unit cell orientations relative to the shape change, revealing the atomic-resolution mechanism for the photomechanical response and enabling the construction of a model that predicts an elongation of 7.4%, in good agreement with the experimental value. According to this model, the nanorod expansion does not result from an overall change in the volume of the unit cell, but rather from an anisotropic rearrangement of the molecular contents. The ability to understand quantitatively how molecular-level photochemistry generates mechanical displacements allows us to predict that the expansion could be tuned from +9% to −9.5% by controlling the initial orientation of the unit cell with respect to the nanorod axis. This application of NMR-assisted crystallography provides a new tool capable of tying the atomic-level structural rearrangement of the reacting molecular species to the mechanical response of a nanostructured sample.NMR crystallography establishes absolute unit-cell orientations relative to the shape change, revealing the atomic-resolution mechanism for the nanorod''s photomechanical response. 相似文献
89.
90.
Mn(I) in an extended oxide: the synthesis and characterization of La(1-x)Ca(x)MnO(2+δ) (0.6 ≤ x ≤ 1)
Dixon E Hadermann J Ramos S Goodwin AL Hayward MA 《Journal of the American Chemical Society》2011,133(45):18397-18405
Reduction of La(1-x)Ca(x)MnO(3) (0.6 ≤ x ≤ 1) perovskite phases with sodium hydride yields materials of composition La(1-x)Ca(x)MnO(2+δ). The calcium-rich phases (x = 0.9, 1) adopt (La(0.9)Ca(0.1))(0.5)Mn(0.5)O disordered rocksalt structures. However local structure analysis using reverse Monte Carlo refinement of models against pair distribution functions obtained from neutron total scattering data reveals lanthanum-rich La(1-x)Ca(x)MnO(2+δ) (x = 0.6, 0.67, 0.7) phases adopt disordered structures consisting of an intergrowth of sheets of MnO(6) octahedra and sheets of MnO(4) tetrahedra. X-ray absorption data confirm the presence of Mn(I) centers in La(1-x)Ca(x)MnO(2+δ) phases with x < 1. Low-temperature neutron diffraction data reveal La(1-x)Ca(x)MnO(2+δ) (x = 0.6, 0.67, 0.7) phases become antiferromagnetically ordered at low temperature. 相似文献