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161.
Sand dune movement in the Victoria Valley, Antarctica 总被引:3,自引:0,他引:3
We use vertical aerial photographs and LiDAR topographic survey data to estimate dune migration rates in the Victoria Valley dunefield, Antarctica, between 1961 and 2001. Results confirm that the dunes migrated an average of 1.5 m/year. These values are consistent with other estimates of dune migration from cold climate deserts and are significantly lower than estimates from warm deserts. Dune migration rates are retarded by the presence of entrained ice, soil moisture and a reversing wind regime. Dune absorption, merging and limb extension are apparent from the time-series images and account for significant changes in dune form and the field-scale dune pattern. Dune-field pattern analysis shows an overall increase in dune-field organization with an increase in mean dune spacing and a reduction in total crest length and defect density. These data suggest that dunes in other cold desert environments on Earth, Mars or Titan, that may also have inter-bedded frozen laminae, still have the potential to migrate and organize, albeit at lower rates than dunes in warm deserts. 相似文献
162.
In this paper, we examine heuristically the reasons for locking in poroelasticity. As a first step, we first reexamine the
problem of locking in linear elasticity. From this, we discover how the problem arises in the poroelasticity setting and how
the problem might be overcome. 相似文献
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David E. Pitts Michael R. Helfert Kamlesh P. Lulla Mary Fae McKay Victor S. Whitehead David L. Amsbury 《国际地球制图》2013,28(4):69-80
Abstract The impact of animals upon the landscape, through such actions as trampling, feeding, burrowing, mounding, and dam building, is a topic of interest in university geography classrooms. However, the relatively fine‐scale nature of most such impacts precludes its examination via remote sensing. Nevertheless, remote sensing of many types of animal impact is possible, and in this paper I illustrate several such examples, primarily drawn from free‐access sites on the World Wide Web, using a variety of remote sensing platforms. Instructors of physical geography or resource/land use management courses can thus introduce a variety of remote sensing concepts and imagery types in their classrooms while at the same time examining the role of animals on the landscape. 相似文献
166.
Marine debris from the Oregon Dungeness crab fishery recovered in the Northwestern Hawaiian Islands: identification and oceanic drift paths 总被引:1,自引:0,他引:1
Two Dungeness crab trap tags and floats lost off the State of Oregon, USA during the 2006-2007 fishing season were recovered 4years later in the Northwestern Hawaiian Islands (NWHI): on Lisianski Island on July 15, 2010; and on Kure Atoll on December 10, 2010. This is the first documented recovery of marine debris from Oregon fisheries in the NWHI. We simulate the oceanic drift tracks of the derelict fishing gear with the Ocean Surface Current Simulator (OSCURS) model using estimated loss dates in Oregon based on interviews with the crab trap owners and known recovery sites and dates in the NWHI. These data confirm the US Pacific Northwest as a source of marine debris deposited in the NWHI and provide enhanced understanding of the oceanic drift pathways of marine debris in the North Pacific Ocean. 相似文献
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Mary R. Reid Jorge A. Vazquez Axel K. Schmitt 《Contributions to Mineralogy and Petrology》2011,161(2):293-311
Zircon has the outstanding capacity to record chronological, thermal, and chemical information, including the storage history
of zoned silicic magma reservoirs like the one responsible for the Bishop Tuff of eastern California, USA. Our novel ion microprobe
approach reveals that Bishop zircon rims with diverse chemical characteristics surround intermediate domains with broadly
similar compositions. The highest Y, REE, U, and Th concentrations tend to accompany the largest excesses in Y + REE3+:P beyond what can be explained by xenotime substitution in zircon. Apparent Ti-in-zircon temperatures of <720°C for zircon
rims are distinctly lower than most of the range in eruption temperatures, as estimated from FeTi-oxide equilibria and zircon
solubility at quench. While permissive of crystallization of zircon at near-solidus conditions, the low Ti-in-zircon temperatures
are probably better explained by sources of inaccuracy in the temperature estimates. After apparently nucleating from different
melts, zircons from across the Bishop Tuff compositional spectrum may have evolved to broadly similar chemical and thermal
conditions and therefore it is possible that there was no significant thermal gradient in the magma reservoir at some stage
in its evolution. There is also no compelling evidence for punctuated heat ± chemical influxes during the intermediate stages
of zircon growth. Judging by the zircon record, the main volume of the erupted magma evolved normally by secular cooling but
the latest erupted portion is characterized by a reversal in chemistry that appears to indicate perfusion of the magma reservoir
by—or zircon entrainment in—a less evolved melt from the one in which the zircons had previously resided. 相似文献
170.
Metal ion complex formation constants of some sedimentary humic acids with Zn(II), Cu(II) and Cd(II)
Metal ion complex formation constants were determined for several sedimentary humic acids (SHA) derived from a fresh water lake and several coastal marine environments, using a method based on size exclusion chromatography. Only one type of binding site was observed in all cases, and conditional log Kf values of between 5 and 7 (at pH 8, I = 0.01 M) were found. Elemental composition of the SHA was similar to soil HA, except that nitrogen content was significantly higher in the SHA. Other chemical properties of the SHA were consistent with those reported by other workers. While spectroscopic measurements indicated that the SHA may have contained significant amounts of polysaccharide compounds which were not removed by conventional separation and purification procedures, analysis indicated only very low levels of polysaccharides were present in the SHA. 相似文献