全文获取类型
收费全文 | 5330篇 |
免费 | 550篇 |
国内免费 | 160篇 |
专业分类
测绘学 | 236篇 |
大气科学 | 596篇 |
地球物理 | 1973篇 |
地质学 | 2135篇 |
海洋学 | 315篇 |
天文学 | 347篇 |
综合类 | 193篇 |
自然地理 | 245篇 |
出版年
2022年 | 6篇 |
2021年 | 21篇 |
2020年 | 7篇 |
2019年 | 11篇 |
2018年 | 437篇 |
2017年 | 375篇 |
2016年 | 252篇 |
2015年 | 149篇 |
2014年 | 117篇 |
2013年 | 123篇 |
2012年 | 649篇 |
2011年 | 427篇 |
2010年 | 116篇 |
2009年 | 141篇 |
2008年 | 125篇 |
2007年 | 115篇 |
2006年 | 132篇 |
2005年 | 833篇 |
2004年 | 885篇 |
2003年 | 654篇 |
2002年 | 182篇 |
2001年 | 75篇 |
2000年 | 49篇 |
1999年 | 19篇 |
1998年 | 8篇 |
1997年 | 21篇 |
1996年 | 11篇 |
1995年 | 3篇 |
1991年 | 14篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1987年 | 4篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 7篇 |
1973年 | 2篇 |
1969年 | 2篇 |
1968年 | 2篇 |
1965年 | 3篇 |
1963年 | 2篇 |
1961年 | 2篇 |
1959年 | 2篇 |
1955年 | 2篇 |
1954年 | 2篇 |
1951年 | 2篇 |
1948年 | 2篇 |
排序方式: 共有6040条查询结果,搜索用时 26 毫秒
101.
Tim?M.?O’BrienEmail author Elizabeth?L.?Miller 《Contributions to Mineralogy and Petrology》2014,168(4):1071
Microtextural, U–Pb, trace element and Lu–Hf analyses of zircons from gneisses dredged from the Chukchi Borderland indicate a long-lived, Cambrian–Ordovician, granulite facies metamorphism. These results reveal a complete prograde, peak and cooling history of zircon growth during anatexis. Early increasing temperatures caused modification and Pb-loss of Precambrian zircons by recrystallization and dissolution/re-precipitation of existing grains. Small variations in initial 176Hf/177Hf results (0.282325–0.282042) and flat HREE patterns of these zircons indicate that they grew by dissolution/re-precipitation in the presence of garnet. Zircons subsequently crystallized from a partial melt during peak to post-peak metamorphism from 530 to 485 Ma. A broad range of initial 176Hf/177Hf ratios (0.282693–0.282050) and mineral inclusions within zircons suggest that this phase of growth incorporated Zr and Hf obtained from the breakdown of Zr-enriched phases. Microtextural evidence along with trace element and isotopic data suggests that final growth of metamorphic rims on zircon occurred during slow cooling and crystallization of residual partial melts during the early Ordovician (485–470 Ma). Younger, late Ordovician–Silurian (420–450 Ma) euhedral, oscillatory-zoned, trace element-enriched zircons crystallized within leucocratic veins that intrude the gneisses. Their age corresponds to granitoids dated from this same dredge. The intrusives and veins provide evidence that the Chukchi Borderland rifted from a position near Pearya and northwest Svalbard, which represent the northern continuation of the Caledonian orogen. Evidence for earlier Cambrian metamorphism has not been reported from this region. The age of granulite facies metamorphism reported here represents the earliest phase of deformation in the Arctic Caledonides. 相似文献
102.
Dehydration melting of solid amphibolite at 2.0 GPa: Effects of time and temperature 总被引:3,自引:0,他引:3
ZHOU Wenge XIE Hongsen LIU Yonggang ZHENG Xiaogang ZHAO Zhidan & ZHOU Hui . Laboratory of Material in the Earth’s Interior Institute of Geochemistry Chinese Academy of Sciences Guiyang China . Department of Geology China University of Geosciences Beijing China . Department of Geology Peking University Beijing China 《中国科学D辑(英文版)》2005,48(8):1120-1133
The dehydration melting of the natural rock at high pressure is important to investigating the magma formation in the earth’s interior. Since the 1970s, a lot of geological scientists have paid more atten- tion to the dehydration melting of the natural rock[1―5]. Previous experiments of dehydration melting and observations of fieldwork argued that the dehy- dration melting of the rock was probably the most important fashion for the melting of the lower crust rock[6―12]. The genesis of most … 相似文献
103.
Ping?Li Xinzhuan?GuoEmail author Sibo?Chen Chao?Wang Junlong?Yang Xingfan?Zhou 《Contributions to Mineralogy and Petrology》2018,173(2):16
In order to investigate the origin of the high conductivity anomalies geophysically observed in the mid-lower crust of Tibet Plateau, the electrical conductivity of plagioclase–NaCl–water system was measured at 1.2 GPa and 400–900 K. The relationship between electrical conductivity and temperature follows the Arrhenius law. The bulk conductivity increases with the fluid fraction and salinity, but is almost independent of temperature (activation enthalpy less than 0.1 eV). The conductivity of plagioclase–NaCl–water system is much lower than that of albite–NaCl–water system with similar fluid fraction and salinity, indicating a strong effect of the major mineral phase on the bulk conductivity of the brine-bearing system. The high conductivity anomalies of 10?1 and 100 S/m observed in the mid-lower crust of Tibet Plateau can be explained by the aqueous fluid with a volume fraction of 1 and 9%, respectively, if the fluid salinity is 25%. The anomaly value of 10?1 S/m can be explained by the aqueous fluid with a volume fraction of 6% if the salinity is 10%. In case of Southern Tibet where the heat flow is high, the model of a thin layer of brine-bearing aqueous fluid with a high salinity overlying a thick layer of partial melt is most likely to prevail. 相似文献
104.
Ulrike?WackerEmail author K.?V.?Jayaraman?Potty Christof?Lüpkes J?rg?Hartmann Matthias?Raschendorfer 《Boundary-Layer Meteorology》2005,117(2):301-336
The mesoscale weather prediction model ’Lokal-Modell’ (LM) of the Deutscher Wetterdienst is applied to the situation of an
Arctic cold air outbreak in the Fram Strait region in April 1998. Observations are available from a flight along 50E carried out during the ARTIST campaign. Initial and time-dependent boundary data for the simulation are taken from a larger
scale operational model system.
Using the standard configuration of LM, the simulation reproduced the propagation of cold air and the characteristic structure
of the atmospheric boundary layer (ABL) in fair agreement with the observations. However, a detailed comparison revealed three
basic problems. Firstly, there is evidence that the available data on sea-ice conditions were insufficient approximations
to the true state for several reasons. A modification of the sea-ice data towards observations revealed that parts of the
discrepancies were due to the original sea-ice data. Secondly, a control run with the model in its standard configuration
shows an insufficient warming of the ABL downstream of the ice edge due to underestimation of surface heat fluxes. A simple
modification of the approach for the scalar roughness length resulted in the strongest benefit, while comparative studies
showed only a slight sensitivity to different types of parametrisation of turbulent mixing or the inclusion of an additional
moist convection parametrisation. Thirdly, in all the simulations the deepening of the convective ABL downstream of the ice
edge is weaker than observed. This may be partly due to the thermal stratification above the ABL in the analysis data, which
is more stable than observed; but it may also be a hint to the fact that processes near the inversion are insufficiently parametrised
in mesoscale models with resolutions as used in LM. The simulated cloud layer in the convective ABL is similar to that observed
with respect to condensate content, a sharply defined cloud top, a diffuse lower bound, and continuous light precipitation. 相似文献
105.
Metamorphic condition of a regional metamorphic complex in the Omuta district in northern Kyushu,southwest Japan 下载免费PDF全文
A high‐temperature (T) metamorphic complex occurs in the Omuta district, northern Kyushu, Japan. Three metamorphic zones are defined based on pelitic mineral assemblage, i.e. chlorite–biotite zone, muscovite–andalusite zone and sillimanite–K‐feldspar zone with ascending metamorphic grade from north to south. Two isograds trend approximately east–west, which is oblique to the boundary between the metamorphic complex and the Tamana Granodiorite located on the southeast. The metamorphic condition of two pelitic rocks that occur in the muscovite–andalusite zone and sillimanite–K‐feldspar zone are estimated as 510 ±30 °C, 300 ±60 MPa and 720 ±30 °C, 620 ±60 MPa, respectively. Thermodynamic consideration reveals that use of the same geothermobarometer enables precise determination of the difference in pressure between the samples as 320 ±10 MPa. This indicates that the pelitic samples were metamorphosed at different depth by 11–12 km that is significantly larger than the geographic distance of 6.8 km between the sample localities. This also suggests that crustal thinning took place after the high‐T metamorphism. The high‐T metamorphic complex is, therefore, not of static contact metamorphism but of dynamic regional metamorphism. The present result combined with petrological and chronological similarities implies that this complex suffered the regional Ryoke metamorphism. 相似文献
106.
Katharina?MarquardtEmail author Gregory?S.?Rohrer Luiz?Morales Erik?Rybacki Hauke?Marquardt Brian?Lin 《Contributions to Mineralogy and Petrology》2015,170(4):40
Rocks consist of crystal grains separated by grain boundaries that impact the bulk rock properties. Recent studies on metals and ceramics showed that the grain boundary plane orientation is more significant for grain boundary properties than other characteristics such as the sigma value or disorientation (in the Earth’s science community more frequently termed misorientation). We determined the grain boundary character distribution (GBCD) of synthetic and natural polycrystalline olivine, the most abundant mineral of Earth’s upper mantle. We show that grain boundaries of olivine preferentially contain low index planes, in agreement with recent findings on other oxides (e.g. MgO, TiO2, Al2O3 etc.). Furthermore, we find evidence for a preferred orientation relationship of 90° disorientations about the [001] direction forming tilt and twist grain boundaries, as well as a preference for the 60° disorientation about the [100] axis. Our data indicate that the GBCD, which is an intrinsic property of any mineral aggregate, is fundamental for understanding and predicting grain boundary related processes. 相似文献
107.
Terrain Pattern Recognition and Spatial Decision Making for Regional Slope Stability Studies 总被引:1,自引:0,他引:1
George?MiliaresisEmail author Nikos?Sabatakakis George?Koukis 《Natural Resources Research》2005,14(2):91-100
A terrain partition scheme is presented that allows the identification of regions with high landslide risk in natural terrain zones on the basis of geomorphometric criteria from moderate resolution DEMs. The key factor being the terrain segmentation to aspect regions (regions formed by points preserving the same aspect direction) instead of using an artificial regular-grid terrain partition scheme. The study area is in western Greece (NW Peloponnesus) whereas a moderate resolution digital elevation model with spacing 75 m is used. Landslide inventory analysis and knowledge conceptualization identified that the landslide susceptibility of a particular aspect region is high, if the mean elevation is low and the mean gradient is high. Each aspect region was parametrically represented on the basis of its mean gradient and elevation. The domain of each parameter was divided to seven slices (classes) on the basis of the observed density. Subsequent knowledge based mapping identified aspect regions with high landslide susceptibility for the following spatial rule: (a) “mean slope in class 6 or 7” and (b) “mean elevation in class 1 to 5”. Alternatively the rule is expressed as mean slope to be equal or greater than 15∘ whereas mean elevation to be in the range 0 to 750 m. These identified zones correspond to regions where historical landslides occurred (populated coastal areas in the North) as well as to south regions (natural terrain zone) where no landslide record is available, because of the limitations posed by the natural terrain landslide mapping program in Greece. The presented terrain segmentation technique combined to the spatial decision-making process, provided both an object framework for integrating geomorphometric parameters and a method for landslide risk analysis in natural terrain zones. 相似文献
108.
Vinu Valsala Hayyan M. Alsibai Motoyoshi Ikeda Shamil Maksyutov 《Climate Dynamics》2011,36(7-8):1435-1452
The global ocean Chlorofluorocarbon (CFC-11) was simulated in an offline model driven by re-analysis ocean currents in order to identify the mechanisms of interannual to interdecadal variability of air?Csea CFC fluxes. The model was forced with the observed anthropogenic perturbations of atmospheric CFC-11 from the post industrial period (1938) following the OCMIP-II flux protocols along with the observed winds from 1960 to 1999 in the formulation of surface gas exchanges. The model ocean CFC-11 inventories, at the end of 1990s, accounted approximately 1% of the total atmospheric CFC-11, which is consistent with the corresponding observations. The mid-to-high latitude oceans were venue for strong (weak) oceanic sinks (sources) of CFC-11 during the winter (summer) months. The Southern Ocean (south of 40°S) and the North Atlantic (north of 35°N) provided two largest sinks of CFC-11, through which 31.4 and 14.6% of the global ocean CFC-11 entered, respectively. The eastern tropical Pacific Ocean exhibited large interannual variability of CFC-11 flux with a strong (weak) sink during La Ni?a (El Ni?o) years and represented 36% of the global CFC-11 flux variability. The North Atlantic and Southern Ocean were found as regions of large sink efficiency: a capacity to sink more CFC than outsource, although it reduced by 80 and 70%, respectively, in the last 40?years compared to 1960. The sink to source ratio of global ocean CFC-11 fluxes were reduced from 90 to 50% in the last 40?years. This indicates a saturation of CFC in the above-thermocline subsurface that makes the upper ocean less efficient in absorbing CFC in recent decades. A positive trend in CFC sink is now limited to the Southern Ocean, central tropical Pacific and western boundary current regions which possess active upwelling of old water with long time since last atmospheric contact. However, a globally averaged trend was a reduced CFC-11 sink, by emitting 30% of the total ocean CFC-11 that was absorbed during last 40?years. 相似文献
109.
Andrew?SwalesEmail author Iain?T.?MacDonald Malcolm?O.?Green 《Estuaries and Coasts》2004,27(2):225-243
Isolated patches ofSpartina anglica (cordgrass) at two sites on a wave-exposed mid-intertidal flat of the 340 km2 Manukau Harbor (Auckland, New Zealand) have developed very differently since being planted in the mid-1970s. Although the
two sites are only 0.5 km apart and at the same intertidal elevation,Spartina patches at the easternmost site (site 1) have as much as an order of magnitude higher biomass and accumulated sediment volume
thanSpartina patches at site 2. A field experiment was conducted to characterize waves and associated sediment dynamics at each site,
which might explain whySpartina patches at the two sites have developed so differently over the past 25 yr or so. Suspended sediments were measured and wave
characteristics were inferred from subsurface pressure data measured for 5 wk at bothSpartina sites and at an intermediate location. Bed-orbital speeds and frictional wave-energy dissipation were consistently lower
at the easternmost site with the largerSpartina patches. The west-to-east reduction in wave energy is due to the spatial arrangement of theSpartina sites relative to the predominant wind fetches. The wave-energy gradient is maintained by tidal-cycle variations in fetch
and bed friction and results in a west-to-east reduction in sand suspension. Silt, which is largely resuspended under southwest
winds, is redeposited in the low wave-energy conditions in and around the larger site 1Spartina patches. Shell accumulation bySpartina patches at site 1 occurs infrequently, during southwest winds >10 m s−1 and water depths >0.7 m, when waves are least attenuated by bed friction. Large between-site differences in the growth of
and sediment accumulation by theSpartina patch are consistent with the observed wave-energy gradient. The resulting spatial patterns of silt, sand, and shell resuspension
and deposition directly influence the rate of sediment accumulation bySpartina patches and the composition of accumulated sediment on this wave-exposed intertidal flat. 相似文献
110.
Xiyuan?Chi Pengzhen?He Zhuang?Jiang Xiawei?Yu Fange?Yue Longquan?Wang Bokun?Li Hui?Kang Cheng?Liu Zhouqing?XieEmail author 《Acta Meteorologica Sinica》2018,32(1):14-25
We investigated the acidity and concentrations of water-soluble ions in PM2.5 aerosol samples collected from an urban site in Beijing and a rural site in Gucheng, Hebei Province from November 2016 to January 2017 to gain an insight into the formation of secondary inorganic species. The average SO42–, NO3–, and NH4+ concentrations were 8.3, 12.5, and 14.1 μg m–3, respectively, at the urban site and 14.0, 14.2, and 24.2 μg m–3, respectively, at the rural site. The nitrogen and sulfur oxidation ratios in urban Beijing were correlated with relative humidity (with correlation coefficient r = 0.79 and 0.67, respectively) and the aerosol loadings. Based on a parameterization model, we found that the rate constant of the heterogeneous reactions for SO2 on polluted days was about 10 times higher than that on clear days, suggesting that the heterogeneous reactions in the aerosol water played an essential role in haze events. The ISORROPIA II model was used to predict the aerosol pH, which had a mean (range) of 5.0 (4.9–5.2) and 5.3 (4.6–6.3) at the urban and rural site, respectively. Under the conditions with this predicted pH value, oxidation by dissolved NO2 and the hydrolysis of N2O5 may be the major heterogeneous reactions forming SO42– and NO3– in haze. We also analyzed the sensitivity of the aerosol pH to changes in the concentrations of SO42–, NO3–, and NH4+ under haze conditions. The aerosol pH was more sensitive to the SO42– and NH4+ concentrations with opposing trends, than to the NO3– concentrations. The sensitivity of the pH was relatively weak overall, which was attributed to the buffering effect of NH3 partitioning. 相似文献