全文获取类型
收费全文 | 475篇 |
免费 | 7篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 32篇 |
大气科学 | 25篇 |
地球物理 | 97篇 |
地质学 | 208篇 |
海洋学 | 58篇 |
天文学 | 29篇 |
综合类 | 2篇 |
自然地理 | 33篇 |
出版年
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 11篇 |
2017年 | 12篇 |
2016年 | 3篇 |
2015年 | 15篇 |
2014年 | 17篇 |
2013年 | 23篇 |
2012年 | 18篇 |
2011年 | 25篇 |
2010年 | 21篇 |
2009年 | 22篇 |
2008年 | 20篇 |
2007年 | 30篇 |
2006年 | 19篇 |
2005年 | 17篇 |
2004年 | 11篇 |
2003年 | 15篇 |
2002年 | 18篇 |
2001年 | 11篇 |
2000年 | 14篇 |
1999年 | 16篇 |
1998年 | 15篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1978年 | 2篇 |
1976年 | 5篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1969年 | 3篇 |
1967年 | 2篇 |
1966年 | 4篇 |
1960年 | 2篇 |
1959年 | 2篇 |
1955年 | 2篇 |
1953年 | 3篇 |
排序方式: 共有484条查询结果,搜索用时 58 毫秒
121.
Rolf L. Romer Leander Franz Richard Wirth 《Contributions to Mineralogy and Petrology》2006,151(2):174-186
Fluid inclusions may provide compositional and isotopic information about fluids from which the host mineral precipitated
as long as the host mineral does not react with the fluid. Our transmission electron microscope (TEM) investigation of grain
boundaries and of fluid inclusions in zoisite and quartz of high-pressure metamorphic rocks from Dabie Shan (eastern China)
demonstrates daughter minerals, such as margarite, muscovite, calcite, and anhydrite. Their precipitation changes (1) the
composition of the fluid by selective and mineral-specific removal of CO2 (carbonates), H2O (sheet silicates, hydration of the walls), or S (gypsum, anhydrite, sulfides), (2) the concentrations and proportions of
ions dissolved in the fluid, and (3) the isotopic composition of the fluid because of isotopic fractionation between mineral
precipitate and fluid and between unmixed fluids. Fluid leakage from overpressurized fluid inclusions with daughter minerals
changes the overall chemical and isotopic composition of the inclusion irreversibly, even when the daughter crystals later
redissolve. Such fluid loss yields a wide range of compositionally and isotopically different fluids from a single starting
fluid. Depending on the relation between mineral reactions in and fluid loss from the inclusion, the fluid remaining in the
inclusion and the fluid lost from the inclusion may appear entirely unrelated. 相似文献
122.
Janet Riedl Stefanie Rotter Sonja Faetsch Mechthild Schmitt-Jansen Rolf Altenburger 《Environmental Earth Sciences》2013,70(8):3907-3920
Hydraulic fracturing is increasingly being used to produce gas from unconventional resource sites for energy supply. Therefore, concerns about risks of this technology related to human health and the environment have to be addressed. Among the major issues is the potential contamination of surrounding water systems by chemical additives used in fracturing fluids. In this study, the ecotoxicological hazards of fracturing fluids, both, their individual components (chemicals) as well as their mixtures (product) were assessed using a component-based mixture approach. For five exemplary fracturing fluids, 40–90 wt% of the contained substances could unambiguously be defined in their chemical identity. The concentrations used in the applied fluid mixture were considered as (maximum) exposure concentrations. For components with mass fractions between 10 and 74 wt%, the effect concentrations for acute and chronic toxicity of fish, daphnia and algae were retrieved from experimental databases and through predictive modeling. The hazard indices calculated from the ratio of exposure to effect concentration were >1 for all fracturing fluids, using different scenarios. This indicated a hazard from the undiluted fracturing fluids. The assessment framework presented in this study allows for dealing with data gaps and uncertainties in a tiered fashion and in particular accommodates for combined effects resulting from chemical mixtures. It might be employed for ecotoxicological risk assessment of products containing chemical mixtures and optimization of their environmental performance. 相似文献
123.
Grant D. Zazula Duane G. Froese Scott A. Elias Svetlana Kuzmina Rolf W. Mathewes 《Quaternary Science Reviews》2011,30(17-18):2220-2237
Fossil arctic ground squirrel (Spermophilus parryii) middens were recovered from ice-rich loess sediments in association with Sheep Creek-Klondike and Dominion Creek tephras (ca 80 ka) exposed in west-central Yukon. These middens provide plant and insect macrofossil evidence for a steppe-tundra ecosystem during the Early Wisconsinan (MIS 4) glacial interval. Midden plant and insect macrofossil data are compared with those previously published for Late Wisconsinan middens dating to ~25–2914C ka BP (MIS 3/2) from the region. Although multivariate statistical comparisons suggest differences between the relative abundances of plant macrofossils, the co-occurrence of steppe-tundra plants and insects (e.g., Elymus trachycaulus, Kobresia myosuroides, Artemisia frigida, Phlox hoodii, Connatichela artemisiae) provides evidence for successive reestablishment of the zonal steppe-tundra habitats during cold stages of the Late Pleistocene. Arctic ground squirrels were well adapted to the cold, arid climates, steppe-tundra vegetation and well-drained loessal soils that characterize cold stages of Late Pleistocene Beringia. These glacial conditions enabled arctic ground squirrel populations to expand their range to the interior regions of Alaska and Yukon, including the Klondike, where they are absent today. Arctic ground squirrels have endured numerous Quaternary climate oscillations by retracting populations to disjunct “interglacial refugia” during warm interglacial periods (e.g., south-facing steppe slopes, well-drained arctic and alpine tundra areas) and expanding their distribution across the mammoth-steppe biome during cold, arid glacial intervals. 相似文献
124.
Francisco Javier López-Moro Miguel López-Plaza Rolf L. Romer 《International Journal of Earth Sciences》2012,101(5):1273-1298
The Tormes dome consists of S-type granites that intruded into Ordovician augen gneisses and Neoproterozoic–Lower Cambrian metapelites/metagreywackes at different extents of migmatization. S-type granites are mainly equigranular two-mica granites, occurring as: (1) enclave-laden subvertical feeder dykes, (2) small external sill-like bodies with size and shape relations indicative for self-similar pluton growth, and (3) as large pluton bodies, emplaced at higher levels than the external ones. These magmas were highly mobile as it is inferred from the high contents of fluxing components, the disintegration and alignment of pelitic xenoliths in feeder dykes and at the bottom of some sill-like bodies. Field relations relate this 311?Ma magmatism (U–Pb monazite) to the regional shearing of the D3 Variscan event. Partial melting modeling and the relatively high estimated liquidus temperatures indicate biotite-dehydration partial melting (800–840°C and 400–650?MPa) rather than water-fluxed melting, implying that there was no partial melting triggered by externally derived fluids in the shear zones. Instead, the subvertical shear zones favored extraction of melts that formed during the regional migmatization event around 320?Ma. Nd isotope variation among the granites might reflect disequilibrium partial melting or different protoliths. Mass-balance and trace element partial melting modeling strongly suggest two kinds of fertile crustal protoliths: augen gneisses and metapelites. Slight compositional variation among the leucogranites does not reflect different extent of protolith melting but is related to a small amount of fractional crystallization (<13% for the equigranular granites), which is generally more pronounced in shallower batholitic leucogranites than in the small and homogeneous sill-like bodies. The lower extent of fractional crystallization and the higher-pressure emplacement conditions of the sill-like bodies support a more restricted movement through the crust than for batholitic leucogranites. 相似文献
125.
During the evolution of continents, compressive tectonic phases can leave certain tectonic patterns in the lithosphere to be observed by reflection seismology. Also, in the area of the trans-European suture zone (TESZ) in the Baltic Sea, several relatively short, but occasionally strong, compressive phases have left their marks in the lithosphere in form of characteristic fault and thrust zones in the rigid parts of crust and mantle, especially clear and well investigated in some sediment troughs. At depth, interwedging processes seem to be generated by colliding tectonic units with different rheology, creating bi-vergent fault structures, possibly—but not necessarily—initiated by a previous subduction of intervening oceanic lithosphere. Near the surface, reactivation and inversion of previous faults are very selective. Transpressional processes and the reduced friction inside the faults are suggested to play a major role. It is assumed that the transfer of plate boundary stressed over long distances is performed mainly through the thick and rigid mantle lid, not through the thin, rigid, and heterogeneous upper crust. This assumption involves mechanisms of a vertical transfer of stresses from the mantle into the inversion area, and some signs of such a process are seen around the Tornquist Zone (TZ). Several examples of compressive transfer of stresses are shown. 相似文献
126.
Rolf D. Weidelt 《Astrophysics and Space Science》1970,6(2):205-216
We consider a spherically symmetric, isothermal and stationary stellar atmosphere whose gravitational potential cannot be neglected. If , the ratio of the density on the base of the corona to the mean density of the star is not zero, the density vanishes at infinity for any solution of the hydrodynamic equations. We deduce the maximum mass loss depending on two dimensionless parameters, the ratio of the gravitational to the thermal energy and . This mass loss has itself a maximum for =1/3. 相似文献
127.
We present a survey of different kinds of instabilities in the context of radiative colliding flows which greatly contribute
to structure formation. In particular, this includes analytical results for different kinds of thin shell instabilities (DI,
NDI, NTSI). New numerical results for the non-linear evolution of such instabilities in two dimensions, and their coupling
with the thermal cooling instability are presented. The astrophysical implications are briefly outlined, in particular the
formation of knots and filaments.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
128.
Rolf Brahde 《Solar physics》1972,26(2):318-334
A numerical method for correction of stray light in solar observations has been developed. In particular a regular sunspot, where the circular contours of penumbra and umbra are projected as ellipses, has been studied. When a specified set of values for the stray light parameters is given, and also tentative values for the relative intensities of penumbra and umbra, the integration of stray light can be performed in any point. The result will be the observable intensity if the conditions were as given by these initial values.By means of limb observations the stray light parameters may be improved, and finally a variation of the penumbra- and umbra intensities in the computation, enables a determination of these quantities by comparison with observations.The method is tested on observations of the transit of Mercury, May 9, 1970. Calculation of isophotes with Mercury close to the limb shows the black drop phenomenon; which thus may be explained as an effect of stray light only.It is also shown that the Wilson effect on a sunspot cannot be produced by stray light alone. 相似文献
129.
130.
Mahatma Lanuru Rolf Riethmüller Carlo van Bernem Kerstin Heymann 《Estuarine, Coastal and Shelf Science》2007,72(4):603-614
The erosion potential over bedforms in a tidal flat of the East Frisian Wadden Sea was studied by conducting erosion and physical and biological sediment property measurements on the crests and troughs of bedforms. Five stations along a cross-shore transect of 1.5 km length from immediately below the salt marsh to the mid tide-level of the tidal flat were visited during two field campaigns in June and September 2002. Measurements of sediment erodibility were made on both crests and troughs using an EROMES erosion device and quantified in terms of critical erosion shear stress and erosion rate. Surface sediment scrape samples (upper 1 mm layer) were taken from crests and troughs to determine various physical and biological properties of the sediment. The results show that crests are generally more stable (i.e. higher critical erosion shear stresses and lower erosion rates) than troughs. In general, crests contained more chlorophyll a, colloidal carbohydrate, and EPS (extracellular polymeric substance) than troughs. Median grain-size, water content and wet bulk density of the crests showed no statistically significant difference from those of the troughs with the exception at the most landward station immediately below the salt marsh margin, where crests had significantly lower water content and higher wet bulk density than troughs.Two different processes were identified for the difference in erodibility between crests and troughs: (1) At stations with emersion times less than 6 h, the higher benthic diatom biomass (measured as chlorophyll a concentration) on the crests increases the amount of EPS, which is likely to stabilize the sediment surface of these features; (2) in a saltmarsh transition area (most landward station), physical processes such as surface drying and compaction seem to enhance in a synergistic way the sediment stability on the crests. 相似文献