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Observations of shear-wave splitting have previously been made for paths that traverse D" under the Caribbean and under Alaska. SH leads SV , the reverse of the Hockley observations, but in these areas the fact that SV leads SH in the HKT data shown here suggests a different sort of anisotropy under the central Pacific from that under Alaska and the Caribbean. The case of SH travelling faster than SV is consistent with transverse isotropy with a vertical axis of symmetry (VTI) and does not require variations with azimuth. The case of SV leading SH is consistent with transverse isotropy with a horizontal axis of symmetry (HTI), an azimuthally anisotropic medium, and with a VTI medium formed by a hexagonal crystal. Given that (Mg,Fe)SiO
Examples of reflection seismograms for 2-D structures computed by elastic KH theory are shown. Those for a vertical fault scarp structure are compared with the seismograms obtained by physical modelling. Then OBS data obtained from the mid-America trench offshore Guatemala area are analysed by computing KH synthetics for a velocity model that has been proposed for that area. Our analysis indicates the existence of a small low-velocity zone off the trench axis.
No head wave arrivals are obtained in our KH synthetics since we do not consider multiple interactions of a ray with an interface. The nearly discontinuous behaviour of elastic R/T coefficients near the critical angle causes small spurious phases which arrive later than the correct arrivals. 相似文献
Triclosan (TCS) is an antimicrobial compound found in many household products used across the world. TCS is not completely removed in wastewater systems, resulting in trace-level concentrations present ubiquitously in surface waters. The direct photodegradation of TCS has been widely studied, with results indicating that TCS breaks down to chlorophenols and dioxins. To date, no studies have specifically investigated the effects of alkalinity on the photolysis of the acidic form of TCS. This study assessed the effect of carbonate/bicarbonate alkalinity, which is ubiquitous in natural waters, on the photolysis rate of TCS. Results indicate that bicarbonate enhances the photodegradation of TCS at pH values well below the pKa of TCS (7.9), with direct photolysis reaction kinetics that are very slow in the absence of buffers, but significant in the presence of bicarbonate (0.711 h?1 at pH 6.55). At pH values well above its pKa, both unbuffered- and buffered-mediated photolysis increased dramatically (1.92 h?1 for direct photolysis and 2.86 h?1 in buffered water) and is attributable to the increased photoreactivity of TCS by its conjugate base. Photolysis of methyl triclosan (MeTCS), a non-acidic analog of TCS, demonstrated the importance of TCS’s acidic functionality as MeTCS did not degrade at any pH. The observed influence of alkalinity on the acidic form of TCS photolysis was attributed to both a decrease in its excited state pKa, coupled with TCS deprotonation through an excited state proton transfer to a base (bicarbonate and to a lesser degree hydrogen phosphate) resulting in the more photo-labile conjugate base form of TCS.
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