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91.
Abstract A nearly complete skeleton of a fossil sperm whale from the Middle Miocene age Bessho Formation at Shiga-mura, Nagano Prefecture, the most complete fossil physeterid skeleton found in Japan, is here named Scaldicetus shigensis, new species. Its abruptly tapered rostrum, deep supracranial basin, and high occipital crest are typical of physeterids. Large teeth with crenulate enamel on conical crowns, present in both the palate and mandible, are consistent with the genus Scaldicetus du Bus, 1867, a genus originally based on fossils discovered in the Antwerp Basin, Belgium. Scaldicetus shigensis is relatively primitive, having a relatively long, slender rostrum, large zygomatic arches, large tympanic bullae, prominent occipital condyles, low tooth count and a sloping occipital shield that is deeply emarginated laterally by large temporal fossae. The probable mandibular tooth count is 12, only one more than the primitive eutherian mammalian dentition. Despite its abundant primitive characters, Scaldicetus shigensis has very asymmetrical external nares, comparable to the living sperm whale, Physeter catodon, and is in this way more derived than most of the contemporaneous fossil physeterids. At a time when other sperm whales were more highly evolved, Scaldicetus shigensis retained a primitive occipital shield, large tympanic bullae, and low tooth count, as in primitive Oligocene odontocetes such as Agorophiidae. It was a relict form in Middle Miocene time, and provides an indication of a primitive stage of sperm whale evolution heretofore undocumented. Fossils from elsewhere previously referred to as Scaldicetus, largely on the basis of tooth characters, range in age from Early Miocene to Plio-Pleistocene time. Cranial material that would clarify relationships is lacking for most of these, and this time range seems too long for a cetacean genus. Because of this simplistic approach to identifications, Scaldicetus is probably a grade taxon, not a natural biological grouping. However, the tooth morphology of Scaldicetus shigensis is correct for the genus Scaldicetus, so we provisionally assign it to this genus. Redefinition of the genus Scaldicetus and revision of the Physeteridae are beyond the scope of the present study. 相似文献
92.
Quantitative determinations of helium and other noble gas concentrations in pore waters of marine sediments permit the calculation of helium fluxes out of the sedimentary column. Values of 1.1 and 6.4 × 104 atoms/cm2 sec were found for two locations in the northeast Pacific. These fluxes are one to two orders of magnitude less than those based on theoretical degassing models of the earth or on measurements of excess helium in the deep ocean water. 相似文献
93.
94.
95.
During equilibration of K-feldspar, quartz and muscovite with dilute KCl-solutions, the change in pH of the solution was measured as a function of time. The resulting equilibrium constant, K
T = aK + /aH +, is 104.21±0.06, 105.86±0.03 and 106.01±0.03 at 300, 60 and 30° C respectively (standard states at 1 bar) and are consistent with the best higher temperature data. At 30° C this constant is consistent with the aK + /aH + ratio of seawater. From K
T and the activity of K
+ in seawater, a pH of 8.2 is calculated, essentially identical with the pH which results from dissolution of CaCO3 under atmospheric CO2-pressure. Consequently, detrital K-feldspar, quartz, muscovite, and calcite are stable in seawater. Apparently, the seawater pH is controlled by CaCO3 as well as K-feldspar, quartz and muscovite. Independently both equilibria show virtually the same pH, within the variability due to disordering, solid solution and surface energy effects.Assuming that the K-concentrations of pore solutions vary between about 4000 and 40 ppm, these solutions have alkalic pH-values in the temperature range between 30 and 300° C if K-feldspar, quartz and muscovite are present. In limestones the pH is fixed by the dissociation of CaCO3; the occasionally observed formation of K-feldspar in these rocks requires a minimum K-concentration of approximately 4 ppm.
Die Untersuchungen wurden am Department of Mineralogy and Geochemistry der Pennsylvania State University durchgeführt. Der erste Autor (H. E. Usdowski) bedankt sich für die freundliche Aufnahme und die ausgezeichneten Arbeitsmöglichkeiten. Besonderer Dank gilt Dr. George Helz für viele Diskussionen und manche Hilfe im Labor. Die Deutsche Forschungsgemeinschaft hat die Untersuchungen durch einen Forschungsauftrag unterstützt. 相似文献
Die Untersuchungen wurden am Department of Mineralogy and Geochemistry der Pennsylvania State University durchgeführt. Der erste Autor (H. E. Usdowski) bedankt sich für die freundliche Aufnahme und die ausgezeichneten Arbeitsmöglichkeiten. Besonderer Dank gilt Dr. George Helz für viele Diskussionen und manche Hilfe im Labor. Die Deutsche Forschungsgemeinschaft hat die Untersuchungen durch einen Forschungsauftrag unterstützt. 相似文献
96.
This paper presents the overall sinkhole distributions and conducts hypothesis tests of sinkhole distributions and sinkhole formation using data stored in the Karst Feature Database (KFD) of Minnesota. Nearest neighbor analysis (NNA) was extended to include different orders of NNA, different scales of concentrated zones of sinkholes, and directions to the nearest sinkholes. The statistical results, along with the sinkhole density distribution, indicate that sinkholes tend to form in highly concentrated zones instead of scattered individuals. The pattern changes from clustered to random to regular as the scale of the analysis decreases from 10–100 km2 to 5–30 km2 to 2–10 km2. Hypotheses that may explain this phenomenon are: (1) areas in the highly concentrated zones of sinkholes have similar geologic and topographical settings that favor sinkhole formation; (2) existing sinkholes change the hydraulic gradient in the surrounding area and increase the solution and erosional processes that eventually form more new sinkholes. 相似文献
97.
The intrusive complex at Hortavær represents a magma transfer zone in which multiple pulses of gabbroic and dioritic magmas evolved along Fe- and alkali-enrichment trends. Extreme alkali enrichment resulted in nepheline-normative and sparse nepheline-bearing monzodioritic and monzonitic rocks. More evolved monzonitic and syenitic rocks are silica saturated and, in some cases, quartz bearing. Previous and current research recognized an abundance of clinopyroxene and other Ca-rich phases, such as scapolite, grossular-rich garnet, and igneous-textured calcite among the mafic and intermediate rocks. Even the most pyroxene-rich samples contain low Sc concentrations, which suggests early, intense fractionation of clinopyroxene. These features and the alkali enrichment are consistent with assimilation of carbonate-rich host rocks. Carbon isotope ratios of the igneous-textured calcite indicate an origin of the carbon from host rocks rich in calcite, consistent with assimilation. However, low Nd values (−3.4 to −10.2) and moderate initial 87Sr/86Sr values (0.7052 to 0.7099) indicate the need for assimilation of quartzofeldspathic rocks as well. Models of combined assimilation and fractional crystallization indicate that assimilation of simple end members, either carbonate or silicate, cannot explain the entire data set. Instead, variable proportions of carbonate and silicate materials were assimilated, with the most pronounced assimilation effects in the mafic rocks. The reasons for variable degrees of assimilation are, as yet, uncertain. It is possible that assimilation of calc-silicate rocks with variable carbonate/silicate proportions resulted in the range of observed compositions. However, the importance of carbonate assimilation in mafic rocks compared to felsic ones suggests that assimilation of carbonates was predominant at high temperature and/or mafic magma compositions and assimilation of silicates was predominant at lower temperature and/or felsic magma compositions. We suggest that the ability of the mafic magma to dissolve higher proportions of carbonate contaminants is the result of the magma's ability to form clinopyroxene as a product of assimilation. In any case, extensive carbonate assimilation was possible because CO2 escaped from the system. 相似文献
98.
Birchenough AC Barnes N Evans SM Hinz H Krönke I Moss C 《Marine pollution bulletin》2002,44(6):534-543
It is evident from measures of butyltin tissue burdens and imposex or intersex in neogastropods that tributyltin (TBT) contamination of coastal waters and open parts of the North Sea is now low. It has been declining for at least the past decade. This is probably due to two measures. First, regulations prohibiting the use of TBT-based paints on small boats and fish farms have reduced inputs of TBT from these sources so that they are now negligible (except possibly where the regulations are flaunted). Second, there is evidence from sites, where commercial vessels are the sole source of TBT, that the adoption of TBT SPC paints has been effective in reducing environmental levels of these contaminants. However, poor dockyard practices, allowing TBT-contaminated wastes, including paint flakes, to accumulate in sediments have left a legacy of hot-spots of contamination in some ports. The impact is localised so that TBT contamination is low in coastal areas immediately adjacent to ports. 相似文献
99.
100.
The products of the 254 nm photolysis of ppm levels of DMDS have been studied as a function of the O2 partial pressure at 760 Torr (N2 + O2) and 298±2 K. The major sulfur containing compounds detected were SO2 and CH3SO3H (methane sulfonic acid, MSA) and the major carbon containing compounds were CO, HCHO, CH3OH and CH3OOH (methyl hydroperoxide). Within the experimental error limits the observed sulfur and carbon balances were approximately 100%. CH3OOH has been observed for the first time in such a photooxidation system. Its observation provides evidence for the formation of CH3 radicals by the further oxidation of the CH3S radicals formed in the primary photolysis step.From the behavior of the DMDS photolysis products as a function of the O2 partial pressure, O3 concentration and added OH radical source it is postulated that the further reactions of CH3SOH (methyl sulfenic acid), formed in the reaction OH + CH3SCCH3 CH3SOH + CH3S, are the main source of MSA in the 254 nm photolysis of DMDS.Some of the possible implications of the results of this study for the degradation mechanisms of other atmospherically important organic sulfur compounds, in particular DMS, are briefly considered. 相似文献