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61.
Anthony P. Gies Anton Schotman David M. Hercules 《Analytical and bioanalytical chemistry》2010,396(4):1481-1490
In the present study, we address the possibility of matrix-assisted laser desorption/ionization (MALDI)–time-of-flight MS
analysis-induced chain fragmentation in poly(p-phenylene terephthalamide) (PPD-T) by considering two possible sources: (1) grinding-induced fragmentation resulting from
the evaporation–grinding MALDI sample preparation method (E-G method) and (2) in-source/metastable fragmentation induced by
the MALDI laser. An analysis of variance (ANOVA) statistical study found, with a high probability, that obtaining MALDI spectra
with the effective laser area as large as possible (the “fanned-out” setting) did not cause any chain fragmentation due to
the E-G MALDI sample preparation method, even when three additional grinding steps were used. However, the effect of laser
fluence was less clear. A significant effect of laser fluence was observed for lower mass oligomers (<1,400 Da), but there
was essentially no effect for higher mass species up to our limit of ANOVA measurement (∼2,300 Da). Plausible explanations
are presented to explain these observations. The most likely scenario is that “unexpected” end-group modifications occur during
PPD-T synthesis, producing small quantities of low mass species, which are amplified by the MALDI-EG extraction procedure. 相似文献
62.
Holger Gies Michael M. Scherer 《The European Physical Journal C - Particles and Fields》2010,66(3-4):387-402
We study the triviality and hierarchy problem of a Z 2-invariant Yukawa system with massless fermions and a real scalar field, serving as a toy model for the standard-model Higgs sector. Using the functional RG, we look for UV stable fixed points which could render the system asymptotically safe. Whether a balancing of fermionic and bosonic contributions in the RG flow induces such a fixed point depends on the algebraic structure and the degrees of freedom of the system. Within the region of parameter space which can be controlled by a nonperturbative next-to-leading order derivative expansion of the effective action, we find no non-Gaußian fixed point in the case of one or more fermion flavors. The fermion-boson balancing can still be demonstrated within a model system with a small fractional flavor number in the symmetry-broken regime. The UV behavior of this small-N f system is controlled by a conformal Higgs expectation value. The system has only two physical parameters, implying that the Higgs mass can be predicted. It also naturally explains the heavy mass of the top quark, since there are no RG trajectories connecting the UV fixed point with light top masses. 相似文献
63.
H. Gies 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,55(2):311-317
Upcoming high-intensity laser systems will be able to probe the
quantum-induced nonlinear regime of electrodynamics. So far unobserved QED
phenomena such as the discovery of a nonlinear response of the quantum
vacuum to macroscopic electromagnetic fields can become accessible. In
addition, such laser systems provide for a flexible tool for
investigating fundamental physics. Primary goals consist in verifying so far
unobserved QED phenomena. Moreover, strong-field experiments can search for
new light but weakly interacting degrees of freedom and are thus
complementary to accelerator-driven experiments. I review recent
developments in this field, focusing on photon experiments in strong
electromagnetic fields. The interaction of particle-physics candidates with
photons and external fields can be parameterized by low-energy effective
actions and typically predict characteristic optical signatures. I perform
first estimates of the accessible new-physics parameter space of
high-intensity laser facilities such as POLARIS and ELI. 相似文献
64.
The importance of protection against solar ultraviolet radiation (UVR) in childhood has lead to SunSmart policies at Australian schools, in particular primary schools, where children are encouraged and in many cases required to wear hats at school. Hat styles change regularly and the UVR protection provided by some of the hat types currently used and recommended for sun protection by the various Australian state cancer councils had not been previously evaluated. The UVR protection of the hats was measured using UVR sensitive polysulphone film badges attached to different facial sites on rotating headforms. The sun protection type hats included in this study were broad-brimmed hats, "bucket hats" and legionnaires hats. Baseball caps, which are very popular, were also included. The broad-brimmed hats and bucket hats provided the most UVR protection for the six different sites about the face and head. Legionnaires hats also provided satisfactory UVR protection, but the caps did not provide UVR protection to many of the facial sites. The highest measured UVR protection factors for facial sites other than the forehead were 8 to 10, indicating that, while some hats can be effective, they need to be used in combination with other forms of UVR protection. 相似文献
65.
Jessica Cargill Robyn M. Lucas Peter Gies Kerryn King Ashwin Swaminathan Martin W. Allen Emily Banks 《Photochemistry and photobiology》2013,89(1):219-226
Self‐reported sun exposure is commonly used in research, but how well this represents actual sun exposure is poorly understood. From February to July 2011, a volunteer sample (n = 47) of older adults (≥45 years) in Canberra, Australia, answered brief questions on time outdoors (weekdays and weekends) and natural skin color. They subsequently maintained a sun diary and wore an ultraviolet radiation (UVR) digital dosimeter for 7 days. Melanin density was estimated using reflectance spectrophotometry; lifetime sun damage was assessed using silicone casts of the back of the hand; and serum 25‐hydroxyvitamin D (25(OH)D) concentration was assayed. Questionnaire‐reported time outdoors correlated significantly with diary‐recorded time outdoors (Spearman correlation rs = 0.66; 95% CI 0.46, 0.80; P < 0.001) and UVR dosimeter dose (rs = 0.46; 95% CI 0.18, 0.68; P = 0.003), but not 25(OH)D concentration (rs = 0.24; 95% CI ?0.05, 0.50; P = 0.10). Questionnaire‐reported untanned skin color correlated significantly with measured melanin density at the inner upper arm (rs = 0.49; 95% CI 0.24, 0.68; P < 0.001). In a multiple linear regression model, statistically significant predictors of 25(OH)D concentration were self‐reported frequency of physical activity, skin color and recent osteoporosis treatment (R2 = 0.54). In this study, brief questionnaire items provided valid rankings of sun exposure and skin color, and enabled the development of a predictive model for 25(OH)D concentration. 相似文献
66.
Framework Stability and Brønsted Acidity of Isomorphously Substituted Interlayer‐Expanded Zeolite COE‐4: A Density Functional Theory Study
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Haichao Li Prof. Dr. Danhong Zhou Dr. Dongxu Tian Prof. Dr. Chuan Shi Dr. Ulrich Müller Dr. Mathias Feyen Dr. Bilge Yilmaz Prof. Dr. Hermann Gies Prof. Dr. Feng‐Shou Xiao Prof. Dr. Dirk De Vos Prof. Dr. Toshiyuki Yokoi Prof. Dr. Takashi Tatsumi Prof. Dr. Xinhe Bao Prof. Dr. Weiping Zhang 《Chemphyschem》2014,15(8):1700-1707
COE‐4 zeolites possess a unique two‐dimensional ten‐ring pore structure with the Si(OH)2 hydroxyl groups attached to the linker position between the ferrierite‐type layers, which has been demonstrated through the interlayer‐expansion approach in our previous work (H. Gies et al. Chem. Mater. 2012 , 24, 1536). Herein, density functional theory is used to study the framework stability and Brønsted acidity of the zeolite T‐COE‐4, in which the tetravalent Si is isomorphously substituted by a trivalent Fe, B, Ga, or Al heteroatom at the linker position. The influences of substitution energy and equilibrium geometry parameters on the stability of T‐COE‐4 are investigated in detail. The relative acid strength of the linker position is revealed by the proton affinity, charge analysis, and NH3 adsorption. It is found that the range of the 〈T‐O‐Si〉 angles is widened to maintain the stability of isomorphously substituted T‐COE‐4 zeolites. The smaller the 〈O1‐T‐O2〉 bond angle is, the more difficult is to form the regular tetrahedral unit. Thus, the substitution energies at the linker positions increase in the following sequence: Al‐COE‐4 < Ga‐COE‐4 < Fe‐COE‐4 < B‐COE‐4. The adsorption of NH3 as a probe molecule indicates that the acidity can affect the hydrogen‐bonding interaction between (N?H???O2) and (N???H?O2). The relative Brønsted‐acid strength of the interlayer‐expanded T‐COE‐4 zeolite decreases in the order of Al‐COE‐4 > Ga‐COE‐4 > Fe‐COE‐4 > B‐COE‐4. These findings may be helpful for the structural design and functional modification of interlayer‐expanded zeolites. 相似文献
67.
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69.
The transverse and longitudinal magneto-conductivity of an electron-impurity system is calculated using a kinetic approximation based on the Mori formalism. The numerical results agree qualitatively with measurements on narrow gap semiconductors.Dedicated to B. Mühlschlegel on the occasion of his 60th birthday 相似文献
70.
K. H. Althoff M. Gies O. Kaul K. Königsmann D. Menze W. Meyer T. Miczaika W. Pfeil E. Roderburg W. J. Schwille 《Zeitschrift fur Physik C Particles and Fields》1979,1(4):327-336
At the Bonn 2.5 GeV electron synchrotron we have measured the differential cross section of the reaction γp→π0 p at a pion CM angle of 170° and at photon energiesK γ between 0.6 and 1.8 GeV. In comparison to previous measurements the accuracy of the data was improved substantially. For the first time in neutral pion photoproduction a cusp structure at the η-threshold has been confirmed [1]. 相似文献