全文获取类型
收费全文 | 367篇 |
免费 | 8篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 8篇 |
大气科学 | 29篇 |
地球物理 | 93篇 |
地质学 | 116篇 |
海洋学 | 30篇 |
天文学 | 68篇 |
综合类 | 3篇 |
自然地理 | 32篇 |
出版年
2022年 | 3篇 |
2021年 | 4篇 |
2020年 | 5篇 |
2019年 | 3篇 |
2018年 | 5篇 |
2017年 | 5篇 |
2016年 | 8篇 |
2015年 | 2篇 |
2014年 | 6篇 |
2013年 | 19篇 |
2012年 | 18篇 |
2011年 | 13篇 |
2010年 | 11篇 |
2009年 | 18篇 |
2008年 | 29篇 |
2007年 | 17篇 |
2006年 | 14篇 |
2005年 | 14篇 |
2004年 | 17篇 |
2003年 | 11篇 |
2002年 | 19篇 |
2001年 | 16篇 |
2000年 | 6篇 |
1999年 | 9篇 |
1998年 | 11篇 |
1997年 | 2篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 8篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1975年 | 3篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1970年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有379条查询结果,搜索用时 46 毫秒
71.
Terry M. Hume Ton Snelder Mark Weatherhead Rick Liefting 《Ocean & Coastal Management》2007,50(11-12):905-929
A new approach to the classification of estuaries is described. The estuary environment classification (EEC) is based on a hierarchical view of the abiotic components that comprise the environments of estuaries. The EEC postulates that climate, oceanic, riverine and catchment factors ‘control’ a hierarchy of processes and broadly determine the physical and biological characteristics of estuaries. The classification differentiates estuaries at four levels of detail. Level 1 differentiates global scale variation based on differences in climatic and oceanic processes, which are discriminated by the factors: latitude, oceanic basins and large landmasses. Level 2 differentiates variation in estuary hydrodynamic processes, which are discriminated by estuary basin morphometry, river and oceanic forcing. Level 3 differentiates variation among estuaries that are due to catchment processes, which are discriminated by catchment geology and catchment land cover. The approach has been applied to all the estuaries in New Zealand using existing data sources. Estuaries were assigned class membership at each level of the classification by applying criteria in the form of decision rules to the database of assignment characteristics. GIS was then used to map the estuaries with classes being defined by colour at any level of the classification. The resulting map provides a multi-scale spatial framework that is suitable for many environmental or conservation management applications. 相似文献
72.
Methods to identify and subsequently seal surface water loss zones in stream channels were tested by the United States Bureau of Mines at Staub Run, a first-order stream near Frostburg, Maryland, that partially overlies abandoned coal mine workings. Conventional stream gauging was conducted to establish discharge patterns before and after stream sealing. Electromagnetic terrain conductivity surveys were performed within the stream channel to identify zones of increased relative water saturation to depths less than 15 m. Zones of increased conductivity were generally found to be associated with areas exhibiting statistically significant (P 0.05) gauged flow losses. Conversely, zones that exhibited declining conductivity delineated areas where between-station flows were not significantly different. Using this information on potential loss zones, an experimental grouting procedure was applied by injecting an expandable polyurethane grout to a depth less than one meter into the alluvial streambed over a 180-m section of the stream channel. Before grouting, the study section exhibited a 24 I/sec flow loss; first-phase grouting reduced this to a 14 I/sec flow loss; with a second-phase grouting the losses were only 3 I/sec. 相似文献
73.
River ice break‐up is known to have important morphological, ecological and socio‐economic effects on cold‐regions river environments. One of the most persistent effects of the spring break‐up period is the occurrence of high‐water events. A return‐period assessment of maximum annual nominal water depths occurring during the spring break‐up and open‐water season at 28 Water Survey of Canada hydrometric sites over the 1913–2002 time period in the Mackenzie River basin is presented. For the return periods assessed, 13 (14) stations are dominated by peak events occurring during the spring break‐up (open‐water) season. One location is determined to have a mixed signal. A regime classification is proposed to separate ice‐ and open‐water dominated systems. As part of the regime classification procedure, specific characteristics of return‐period patterns including alignment, and difference between the 2 and 10‐year events are used to identify regime types. A dimensionless stage‐discharge plot allows for a contrast of the relative magnitudes of flows required to generate maximum nominal water‐depth events in the different regimes. At sites where discharge during the spring break‐up is approximately one‐quarter or greater than the magnitude of the peak annual discharge, nominal water depths can be expected to exceed those occurring during the peak annual discharge event. Several physical factors (location, basin area, stream order, gradient, river orientation, and climate) are considered to explain the differing regimes and discussed relative to the major sub‐regions of the MRB. Copyright © 2008 John Wiley & Sons, Ltd and Her Majesty the Queen in right of Canada. 相似文献
74.
Prediction of windthrow risk to individual or groups of retained trees in harvested stands requires an improved understanding
of canopy airflow dynamics. Large-eddy simulations were used to simulate wind-tunnel experiments in two and three dimensions
to compare with observations for model validation and to address parameter space considerations for the design of subsequent
retention pattern experiments. The three-dimensional simulations were similar to the observed wind-tunnel data for the statistical
profiles for but there were greater differences in skewness and kurtosis. These results were obtained using a common leaf-area drag formulation
without either skin friction or speed dependent drag that enables scaling with U
0 (ambient wind speed) and h (height of the canopy). This scaling results in a single non-dimensional parameter h/h
c
where h
c
(x, y, z) is the momentum range resulting from the canopy drag. The validity of the model scaling was tested using two-dimensional
simulations. The irrotational component of the flow (potential flow) was found to be important when defining vertical domain
limitations and has significant implications for time dependent flow (i.e. turbulent conditions) when considering retention
pattern design. The sudden onset of drag associated with the isolated stand presents some unexpected challenges. The horizontal
scales of the shearing instabilities were simulated in two dimensions and found to range between 2h for early times to 7h for later times. The early-time horizontal scales are in the range of logical retention pattern scales and as such need to
be taken into account as part of the parameter space, i.e. a range of retention pattern lengths need consideration. 相似文献
75.
Matt?A.?KingEmail author Michael?Bevis Terry?Wilson Bjorn?Johns Frederick?Blume 《Journal of Geodesy》2012,86(1):53-63
We examine the electromagnetic coupling of a GPS antenna–monument pair in terms of its simulated affect on long GPS coordinate
time series. We focus on the Earth and Polar Observing System (POLENET) monument design widely deployed in Antarctica and
Greenland in projects interested particularly in vertical velocities. We base our tests on an absolute robot calibration that
included the top ~0.15 m of the monument and use simulations to assess its effect on site coordinate time series at eight
representative POLENET sites in Antarctica over the period 2000.0–2011.0. We show that the neglect of this calibration would
introduce mean coordinate bias, and most importantly for velocity estimation, coordinate noise which is highly sensitive to
observation geometry and hence site location and observation period. Considering only sub-periods longer than 2.5 years, we
show vertical site velocities may be biased by up to ±0.4 mm/year, and biases up to 0.2 mm/year may persist for observation
spans of 8 years. Changing between uniform and elevation-dependent observation weighting alters the time series but does not
remove the velocity biases, nor does ambiguity fixing. The effect on the horizontal coordinates is negligible. The ambiguities
fixed series spectra show noise between flicker and random walk with near-white noise at the highest frequencies, with mean
spectral indices (frequencies <20 cycles per year) of approximately −1.3 (uniform weighting) and −1.4 (elevation-dependent
weighting). While the results are likely highly monument specific, they highlight the importance of accounting for monument
effects when analysing vertical coordinate time series and velocities for the highest precision and accuracy geophysical studies. 相似文献
76.
The economics of avoiding dangerous climate change. An editorial essay on The Stern Review 总被引:2,自引:0,他引:2
Terry Barker 《Climatic change》2008,89(3-4):173-194
The problem of avoiding dangerous climate change requires analysis from many disciplines. Mainstream economic thinking about the problem has shifted with the Stern Review from a single-discipline focus on cost-benefit analysis to a new inter-disciplinary and multi-disciplinary risk analysis, already evident in the IPCC Third Assessment Report. This shift is more evidence of the failure of the traditional, equilibrium approach in general to provide an adequate understanding of observed behaviour, either at the micro or macro scale. The economics of the Stern Review has been accepted by governments and the public as mainstream economic thinking on climate change, when in some critical respects it represents a radical departure from the traditional treatment. The conclusions regarding economic policy for climate change have shifted from “do little, later” to “take strong action urgently, before it is too late”. This editorial sets out four issues of critical importance to the new conclusions about avoiding dangerous climate change, each of which have been either ignored by the traditional literature or treated in a misleading way that discounts the insights from other disciplines: the complexity of the global energy-economy system (including the poverty and sustainability aspects of development), the ethics of intergenerational equity, the understanding from engineering and history about path dependence and induced technological change, and finally the politics of climate policy. 相似文献
77.
A review of global stratospheric aerosol: Measurements, importance, life cycle, and local stratospheric aerosol 总被引:1,自引:0,他引:1
Stratospheric aerosol, noted after large volcanic eruptions since at least the late 1800s, were first measured in the late 1950s, with the modern continuous record beginning in the 1970s. Stratospheric aerosol, both volcanic and non-volcanic are sulfuric acid droplets with radii (concentrations) on the order of 0.1–0.5 µm (0.5–0.005 cm− 3), increasing by factors of 2–4 (10–103) after large volcanic eruptions. The source of the sulfur for the aerosol is either through direct injection from sulfur-rich volcanic eruptions, or from tropical injection of tropospheric air containing OCS, SO2, and sulfate particles. The life cycle of non-volcanic stratospheric aerosol, consisting of photo-dissociation and oxidation of sulfur source gases, nucleation/condensation in the tropics, transport pole-ward and downward in the global planetary wave driven tropical pump, leads to a quasi steady state relative maximum in particle number concentration at around 20 km in the mid latitudes. Stratospheric aerosol have significant impacts on the Earth's radiation balance for several years following volcanic eruptions. Away from large eruptions, the direct radiation impact is small and well characterized; however, these particles also may play a role in the nucleation of near tropopause cirrus, and thus indirectly affect radiation. Stratospheric aerosol play a larger role in the chemical, particularly ozone, balance of the stratosphere. In the mid latitudes they interact with both nitrous oxides and chlorine reservoirs, thus indirectly affecting ozone. In the polar regions they provide condensation sites for polar stratospheric clouds which then provide the surfaces necessary to convert inactive to active chlorine leading to polar ozone loss. Until the mid 1990s the modern record has been dominated by three large sulfur-rich eruptions: Fuego (1974), El Chichón (1982) and Pinatubo (1991), thus definitive conclusions concerning the trend of non-volcanic stratospheric aerosol could only recently be made. Although anthropogenic emissions of SO2 have changed somewhat over the past 30 years, the measurements during volcanically quiescent periods indicate no long term trend in non-volcanic stratospheric aerosol. 相似文献
78.
Henrik Friis Adrian A. Finch C. Terry Williams John M. Hanchar 《Physics and Chemistry of Minerals》2010,37(6):333-342
The photoluminescence properties of synthetic zircon, ZrSiO4, doped with REE3+ (REE = Pr, Sm, Eu, Gd, Dy, Ho, Er) were investigated using combined excitation and emission spectroscopy. All samples showed
luminescence characteristics of intra-ion energy transitions, similar to other lanthanide-doped materials. However, the relative
intensities were dependent on the energy of excitation and the presence of charge-transfer bands were inferred from excitation
spectra. From the data, we conclude that the lanthanides in zircon occur in more than one type of coordination. Energy transfer
between different lanthanides was observed in some co-doped samples and emissions that were unassigned in previous studies
have been assigned to specific lanthanides based on excitation spectroscopy. 相似文献
79.
Erzsébet Tóth Tamás G. Weiszburg Teresa Jeffries C. Terry Williams András Bartha Éva Bertalan Ildikó Cora 《Chemical Geology》2010,269(3-4):312-328
Samples of glauconite, representing different stages of glauconitisation, as well as different formation environments, were analysed for rare earth elements (REE) and other trace elements using a combination of bulk sample and spatially-resolved in situ techniques. The results indicate that the high-sensitivity, spatially-resolved technique of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) produces values up to two orders of magnitude lower than the bulk sample analyses. This suggests that submicroscopic rare earth element-bearing phases are distributed within the glauconite aggregates comprising the bulk samples. Analytical scanning electron microscopy (ASEM) revealed the presence of micrometre-sized grains of apatite and pore filling precipitates of an unidentified (REE, Ca)-phosphate (approximate composition Ca0.3–0.4(Ce0.4La0.1–0.2Nd0.1)PO4) in some glauconite grains.The inherent REE concentrations of the glauconite aggregates (i.e., glauconite crystallites without accidental mechanical inclusions or authigenic, not layer silicate mineral precipitates) was found to be relatively low (e.g., typically less than 100 ppm), and this value decreased with increasing glauconitisation (smectite–mica transformation through a series of recrystallisation processes). These results suggest that the REEs substitute for Ca in the interlayer space of the layer silicate structure and, therefore, the REE content decreases as Ca is progressively removed from the interlayer (smectite–mica transition).LA-ICP-MS, when combined with electron probe microanalysis (EPMA) or ASEM, offers an opportunity to exclude submicroscopic accessory minerals from glauconite trace element analyses, and so produces reliable trace element data for the respective minerals which host those elements.These results illustrate that accessory minerals are difficult to eliminate from clay samples, and that care needs to be taken in the interpretation of clay mineral REE distributions, irrespective of the aggregation state of the studied clay (i.e., whether finely dispersed within the sedimentary rock, or forming millimetre-sized aggregates). Model calculations showed that authigenic apatite associated with the studied green marine clays tends to have higher REE content than “bioapatites”, the total REE content being above 10 000 ppm. 相似文献