全文获取类型
收费全文 | 553篇 |
免费 | 18篇 |
国内免费 | 9篇 |
专业分类
测绘学 | 21篇 |
大气科学 | 26篇 |
地球物理 | 144篇 |
地质学 | 222篇 |
海洋学 | 30篇 |
天文学 | 87篇 |
综合类 | 7篇 |
自然地理 | 43篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 7篇 |
2020年 | 11篇 |
2019年 | 11篇 |
2018年 | 18篇 |
2017年 | 11篇 |
2016年 | 17篇 |
2015年 | 22篇 |
2014年 | 32篇 |
2013年 | 23篇 |
2012年 | 24篇 |
2011年 | 28篇 |
2010年 | 24篇 |
2009年 | 23篇 |
2008年 | 22篇 |
2007年 | 17篇 |
2006年 | 22篇 |
2005年 | 18篇 |
2004年 | 16篇 |
2003年 | 15篇 |
2002年 | 28篇 |
2001年 | 9篇 |
2000年 | 3篇 |
1999年 | 6篇 |
1998年 | 11篇 |
1997年 | 3篇 |
1996年 | 15篇 |
1995年 | 9篇 |
1994年 | 6篇 |
1993年 | 7篇 |
1992年 | 8篇 |
1991年 | 10篇 |
1990年 | 3篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 7篇 |
1975年 | 6篇 |
1973年 | 2篇 |
1972年 | 4篇 |
1968年 | 3篇 |
排序方式: 共有580条查询结果,搜索用时 15 毫秒
491.
Steven Y. Litvin Michael P. Weinstein Marcus Sheaves Ivan Nagelkerken 《Estuaries and Coasts》2018,41(6):1539-1550
Estuaries and other coastal habitats are considered essential for the survival of early life stages of commercial, recreational, and other ecologically important species. While early designations simply referred to habitats with higher densities of juveniles as nurseries, the definition was improved by arguing that contribution per unit area to the production of individuals that recruit to adult populations is greater, on average, in nursery habitats. However, this and related approaches typically consider critical habitats as individual, homogeneous entities that are static in nature and do not specifically incorporate important dynamics that determine nursery function. The latter include environmental variability, estuarine hydrodynamics, trophic coupling, ontogenetic habitat shifts, and spatially explicit usage of habitat patches and corridors within larger seascapes. Subsequent studies have identified important factors that regulate nursery value, and researchers working independently across the globe have not only supported the advances made in defining the processes underlying nursery function but, as set forth in this narrative, have advanced it while suggesting that much work still needs to be done to improve our understanding of the links between juvenile nekton survival and the estuarine-coastal seascape. We discuss the current nursery role hypothesis and the data supporting (or refuting) it along with the implications for management of estuarine habitats for the conservation or restoration of nursery function. 相似文献
492.
Ivan Gláucio Paulino-Lima Sérgio Pilling Eduardo Janot-Pacheco João Alexandre Ribeiro Gonçalves Barbosa Alvaro Costa Leitão 《Planetary and Space Science》2010,58(10):1180-1040
The radiation-resistant bacterium Deinococcus radiodurans was exposed to a simulated interplanetary UV radiation at the Brazilian Synchrotron Light Laboratory (LNLS). Bacterial samples were irradiated on different substrates to investigate the influence of surface relief on cell survival. The effects of cell multi-layers were also investigated. The ratio of viable microorganisms remained virtually the same (average 2%) for integrated doses from 1.2 to 12 kJ m−2, corresponding to 16 h of irradiation at most. The asymptotic profiles of the curves, clearly connected to a shielding effect provided by multi-layering cells on a cavitary substrate (carbon tape), means that the inactivation rate may not change significantly along extended periods of exposure to radiation. Such high survival rates reinforce the possibility of an interplanetary transfer of viable microbes. 相似文献
493.
The Santa Lucia Shear Zone (SLSZ, Corsica) is a granulite-facies Permian shear zone that developed after the emplacement of
a deep-seated gabbroic intrusion. New structural data shows that the SLSZ results from the juxtaposition of three spatially
distinct mylonite belts, which are the product of the interaction between magmatism, metamorphism and shearing over a temperature
range from ~800 to ~400°C. During the earlier high-grade deformation stage, which was accompanied by decompression from ~7
to ~5 kb at ~800°C, the SLSZ has accommodated high finite strain on a shear zone ≥1 km wide. Strain became increasingly localized
as temperature decreased, but rather than reactivating pre-existing shear zones as commonly expected, younger mylonites expanded
into previously unsheared rock, extending the total width of the shear zone. The zonation of different fabrics across the
SLSZ suggests that pre-existing compositional and grain size heterogeneities in the starting material played a key role in
governing superposed generations of shear zones. 相似文献
494.
Joanna K. York Gabrielle Tomasky Ivan Valiela Anne E. Giblin 《Estuaries and Coasts》2010,33(5):1069-1079
We measured fluxes of NH4+ and NO3− and δ15N of NH4+, sediment, and porewater NH4+ from incubated sediment cores along a nitrate gradient and in different seasons from Childs River, MA. NH4+ flux was low at the downstream site with the lowest concentration of organic matter (high salinity) but otherwise did not
differ along the estuary. The δ15N of regenerated NH4+ ranged from +6.1‰ to +15.3‰ but did not vary significantly with season or salinity; the mean for the entire estuary was +10.4 ± 0.5‰.
Based on differences between the δ15N of regenerated NH4+ and sediment, and expected isotopic fractionation due to remineralization, we concluded that nitrification occurred after
remineralization of NH4+. Differences between the δ15N of regenerated NH4+ and the δ15N of porewater NH4+ provided further evidence of nitrification. We estimated that 11% to 48% of remineralized NH4+ underwent coupled nitrification–denitrification before release into the water column. In spite of losses to denitrification,
NH4+ flux released 1.4 mol N m−2 year−1 to the water column and could provide 42% of phytoplankton nitrogen requirements. 相似文献
495.
Christophe Lécuyer Vincent Balter François Fourel Romain Amiot Olga Otero Gérard Panczer Rossana Martini 《Geochimica et cosmochimica acta》2010,74(7):2072-584
The oxygen isotope fractionation between the structural carbonate of inorganically precipitated hydroxyapatite (HAP) and water was determined in the range 10-37 °C. Values of 1000 ln α() are linearly correlated with inverse temperature (K) according to the following equation: 1000 ln α() = 25.19 (±0.53)·T−1 − 56.47 (±1.81) (R2 = 0.998). This fractionation equation has a slightly steeper slope than those already established between calcite and water (
[O’Neil et al., 1969] and [Kim and O’Neil, 1997]) even though measured fractionations are of comparable amplitude in the temperature range of these experimental studies. It is consequently observed that the oxygen isotope fractionation between apatite carbonate and phosphate increases from about 7.5‰ up to 9.1‰ with decreasing temperature from 37 °C to 10 °C. A compilation of δ18O values of both phosphate and carbonate from modern mammal teeth and bones confirms that both variables are linearly correlated, despite a significant scattering up to 3.5‰, with a slope close to 1 and an intercept corresponding to a 1000 ln α() value of 8.1‰. This apparent fractionation factor is slightly higher or close to the fractionation factor expected to be in the range 7-8‰ at the body temperature of mammals. 相似文献
496.
Towards Reconciling the Large-Scale Structure of Turbulent Boundary Layers in the Atmosphere and Laboratory 总被引:1,自引:1,他引:0
Nicholas Hutchins Kapil Chauhan Ivan Marusic Jason Monty Joseph Klewicki 《Boundary-Layer Meteorology》2012,145(2):273-306
A collaborative experimental effort employing the minimally perturbed atmospheric surface-layer flow over the salt playa of western Utah has enabled us to map coherence in turbulent boundary layers at very high Reynolds numbers, \({Re_{\tau}\sim\mathcal{O}(10^6)}\) . It is found that the large-scale coherence noted in the logarithmic region of laboratory-scale boundary layers are also present in the very high Reynolds number atmospheric surface layer (ASL). In the ASL these features tend to scale on outer variables (approaching the kilometre scale in the streamwise direction for the present study). The mean statistics and two-point correlation map show that the surface layer under neutrally buoyant conditions behaves similarly to the canonical boundary layer. Linear stochastic estimation of the three-dimensional correlation map indicates that the low momentum fluid in the streamwise direction is accompanied by counter-rotating roll modes across the span of the flow. Instantaneous flow fields confirm the inferences made from the linear stochastic estimations. It is further shown that vortical structures aligned in the streamwise direction are present in the surface layer, and bear attributes that resemble the hairpin vortex features found in laboratory flows. Ramp-like high shear zones that contribute significantly to the Reynolds shear-stress are also present in the ASL in a form nearly identical to that found in laboratory flows. Overall, the present findings serve to draw useful connections between the vast number of observations made in the laboratory and in the atmosphere. 相似文献
497.
498.
Pete Smith Gert-Jan Nabuurs Ivan A. Janssens Stefan Reis Gregg Marland Jean-François Soussana Torben R. Christensen Linda Heath Mike Apps Vlady Alexeyev Jingyun Fang Jean-Pierre Gattuso Juan Pablo Guerschman Yao Huang Esteban Jobbagy Daniel Murdiyarso Jian Ni Antonio Nobre Changhui Peng Adrian Walcroft Shao Qiang Wang Yude Pan Guang Sheng Zhou 《Climatic change》2008,88(3-4):209-249
Humans utilise about 40% of the earth’s net primary production (NPP) but the products of this NPP are often managed by different sectors, with timber and forest products managed by the forestry sector and food and fibre products from croplands and grasslands managed by the agricultural sector. Other significant anthropogenic impacts on the global carbon cycle include human utilization of fossil fuels and impacts on less intensively managed systems such as peatlands, wetlands and permafrost. A great deal of knowledge, expertise and data is available within each sector. We describe the contribution of sectoral carbon budgets to our understanding of the global carbon cycle. Whilst many sectors exhibit similarities for carbon budgeting, some key differences arise due to differences in goods and services provided, ecology, management practices used, land-management personnel responsible, policies affecting land management, data types and availability, and the drivers of change. We review the methods and data sources available for assessing sectoral carbon budgets, and describe some of key data limitations and uncertainties for each sector in different regions of the world. We identify the main gaps in our knowledge/data, show that coverage is better for the developed world for most sectors, and suggest how sectoral carbon budgets could be improved in the future. Research priorities include the development of shared protocols through site networks, a move to full carbon accounting within sectors, and the assessment of full greenhouse gas budgets. 相似文献
499.
Jií Svoboda Zbigniew M. Bochenski Vra ulíkov Alena Dohnalov Srka Hladilov Martin Hloek Ivan Hor
ek Martin Ivanov Miroslav Krlík Martin Novk Alexander J.E. Pryor Sandra Szelov Rhiannon E. Stevens Jarosaw Wilczynski Piotr Wojtal 《Geoarchaeology》2011,26(6):838-866
The Dolní Věstonice–Pavlov–Milovice area (Czech Republic) on the slopes of the Pavlov Hills provides an opportunity for correlating the geomorphology of the Dyje River valley with Gravettian settlement patterns. Although the sites vary in size and complexity, they create a regular chain of strategic locations at elevations between 200 m and 240 m asl. In 2009, a road collapsed into deserted cellars inside the village of Milovice and revealed a complex of archaeological layers deep within loess, at an elevation of only 175 m asl. This paper presents an analysis of this atypical archaeological site location and compares the results with the other sites. We argue that this location allowed direct contact with mammoth herds concentrated on the floodplain, while the aquatic environment offered possibilities for gathering plants and fishing. This site represents a new aspect of organized settlement, hunting strategies, and short‐distance human movements during the Gravettian within this area. © 2011 Wiley Periodicals, Inc. 相似文献
500.
A. C. Quillen Ivan Minchev Joss Bland-Hawthorn Misha Haywood 《Monthly notices of the Royal Astronomical Society》2009,397(3):1599-1606
The turbulent diffusion tensor describing the evolution of the mean concentration of a passive scalar is investigated for non-helically forced turbulence in the presence of rotation or a magnetic field. With rotation, the Coriolis force causes a sideways deflection of the flux of mean concentration. Within the magnetohydrodynamics approximation there is no analogous effect from the magnetic field because the effects on the flow do not depend on the sign of the field. Both rotation and magnetic fields tend to suppress turbulent transport, but this suppression is weaker in the direction along the magnetic field. Turbulent transport along the rotation axis is not strongly affected by rotation, except on shorter length-scales, i.e. when the scale of the variation of the mean field becomes comparable with the scale of the energy-carrying eddies. These results are discussed in the context of anisotropic convective energy transport in the Sun. 相似文献