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1.
Soil resources in parts of Tanzania are rapidly being depleted by increased rates of soil erosion and downstream sediment transport, threatening ecosystem health, water and livelihood security in the region. However, incomplete understanding to what effect the dynamics of soil erosion and sediment transport are responding to land-use changes and climatic variability are hindering the actions needed to future-proof Tanzanian land-use practices. Complementary environmental diagnostic tools were applied to reconstruct the rates and sources of sedimentation over time in three Tanzanian river systems that have experienced changing land use and climatic conditions. Detailed historical analysis of sediment deposits revealed drastic changes in sediment yield and source contributions. Quantitative sedimentation reconstruction using radionuclide dating showed a 20-fold increase in sediment yield over the past 120 years. The observed dramatic increase in sediment yield is most likely driven by increasing land-use pressures. Deforestation, cropland expansion and increasing grazing pressures resulted into accelerating rates of sheet erosion. A regime shift after years of progressive soil degradation and convergence of surface flows resulted into a highly incised landscape, where high amounts of eroded soil from throughout the catchment are rapidly transported downstream by strongly connected ephemeral drainage networks. By integrating complementary spatial and temporal evidence bases, this study demonstrated links between land-use change, increased soil erosion and downstream sedimentation. Such evidence can guide stakeholders and policy makers in the design of targeted management interventions to safeguard future soil health and water quality.  相似文献   
2.
利用多源项目获得的补充加密GNSS观测资料计算研究区高空间分辨率的GNSS水平运动速度场和应变率场,采用地震波形资料,通过CAP方法求解震源机制解,在此基础上使用阻尼区域应力反演方法分析川滇地块区域构造应力场的空间分布特征。结合主要断裂的活动特性,综合分析川滇地区的地壳形变特征。结果表明:1)块体浅部的最大主压应力与地表的最大主压应变率由SSE向转变为近SN向,呈现出较好的一致性,GNSS观测至少可反映20 km以内的地壳形变;2)川滇块体南部的东向滑移和顺时针旋转,可能受青藏高原推挤、华南块体阻挡及印度板块与欧亚板块之间北向运动速率自西向东递减而形成的右旋剪切拖拽作用的顺时针力偶的综合影响;3)川滇块体在综合力偶作用下SE向挤出和顺时针旋转的同时,受到走滑逆冲断裂带的吸收转换,使得青藏高原物质SE向挤出有限。  相似文献   
3.
利用耦合了平板海洋模型的全球气候模式进行了大量的格林函数实验,以探究两极地区对于施加在中低纬度海域的热强迫的气候响应。结果表明,北极地区的气候不仅受到距离较近的北太平洋与北大西洋的影响,远离北极的热带太平洋以及南太平洋也对其气候有显著的影响,南极地区的气候则主要是受到邻近的南大洋的影响。通过经验正交函数法的进一步分析发现,北极响应最显著的区域包括波弗特海(Beaufort Sea)、拉普捷夫海(Laptev Sea)以及北极中心区附近;南极地区的响应主要集中在别林斯高晋海(Bellinsgauzen Sea)区域。另外,利用温度归因法对辐射反馈过程和大气能量输运分解发现,北极地区表面温度的响应主要是受到了反照率反馈以及垂直递减率反馈的影响,而南极地区的响应则主要是反照率反馈发挥了作用。  相似文献   
4.
Multiscale simulation of fluvio‐deltaic stratigraphy was used to quantify the elements of the geometry and architectural arrangement of sub‐seismic‐scale fluvial‐to‐shelf sedimentary segments. We conducted numerical experiments of fluvio‐deltaic system evolution by simulating the accommodation‐to‐sediment‐supply (A/S) cycles of varying wavelength and amplitude with the objective to produce synthetic 3‐D stratigraphic records. Post‐processing routines were developed in order to investigate delta lobe architecture in relation to channel‐network evolution throughout A/S cycles, estimate net sediment accumulation rates in 3‐D space, and extract chronostratigraphically constrained lithosomes (or chronosomes) to quantify large‐scale connectivity, that is, the spatial distribution of high net‐to‐gross lithologies. Chronosomes formed under the conditions of channel‐belt aggradation are separated by laterally continuous abandonment surfaces associated with major avulsions and delta‐lobe switches. Chronosomes corresponding to periods in which sea level drops below the inherited shelf break, that is, the youngest portions of the late falling stage systems tract (FSST), form in the virtual absence of major avulsions, owing to the incision in their upstream parts, and thus display purely degradational architecture. Detailed investigation of chronosomes within the late FSST showed that their spatial continuity may be disrupted by higher‐frequency A/S cycles to produce “stranded” sand‐rich bodies encased in shales. Chronosomes formed during early and late falling stage (FSST) demonstrate the highest large‐scale connectivity in their proximal and distal areas, respectively. Lower‐amplitude base level changes, representative of greenhouse periods during which the shelf break is not exposed, increase the magnitude of delta‐lobe switching and favour the development of system‐wide abandonment surfaces, whose expression in real‐world stratigraphy is likely to reflect the intertwined effects of high‐frequency allogenic forcing and differential subsidence.  相似文献   
5.
Climate change is likely to manifest in river flow changes across the globe, which could have wide-ranging consequences for society and the natural environment. A number of previous studies used the UK Climate Projections 2009 (UKCP09) to investigate the potential impacts on river flows in Britain, but these projections were recently updated by the release of UKCP18, thus there is a need to update flow studies. Here, the UKCP18 Regional (12 km) projections are applied using a national-scale grid-based hydrological model, to investigate potential future changes in seasonal mean river flows across Great Britain. Analysis of hydrological model performance using baseline climate model data (1980–2010) shows relatively good agreement with use of observation-based data, particularly after application of a monthly precipitation bias-correction. Analysis of seasonal mean flow changes for two future time-slices (2020–2050 and 2050–2080) suggests large decreases in summer flows across the country (median −45% by 2050–2080), but possible increases in winter flows (median 9% by 2050–2080), especially in the north and west. Information on the potential range of flow changes using the latest projections is necessary to develop appropriate adaptation strategies, and comparisons with previous projections can help update existing plans, although such comparisons are often not straightforward.  相似文献   
6.
When the observation of small headwater catchments in the pre-Alpine Alptal valley (central Switzerland) started in the late 1960s, the researchers were mainly interested in questions related to floods and forest management. Investigations of geomorphological processes in the steep torrent channels followed in the 1980s, along with detailed observations of biogeochemical and ecohydrological processes in individual forest stands. More recently, research in the Alptal has addressed the impacts of climate change on water supply and runoff generation. In this article, we describe, for the first time, the evolution of catchment research at Alptal, and present new analyses of long-term trends and short-term hydrologic behaviour. Hydrometeorological time series from the past 50 years show substantial interannual variability, but only minimal long-term trends, except for the ~2°C increase in mean annual air temperature over the 50-year period, and a corresponding shift towards earlier snowmelt. Similar to previous studies in larger Alpine catchments, the decadal variations in mean annual runoff in Alptal's small research catchments reflect the long-term variability in annual precipitation. In the Alptal valley, the most evident hydrological trends were observed in late spring and are related to the substantial change in the duration of the snow cover. Streamflow and water quality are highly variable within and between hydrological events, suggesting rapid shifts in flow pathways and mixing, as well as changing connectivity of runoff-generating areas. This overview illustrates how catchment research in the Alptal has evolved in response to changing societal concerns and emerging scientific questions.  相似文献   
7.
作为全球煤电装机规模最大且仍在扩张的国家,中国需要慎重评估兑现《巴黎协定》温室气体减排承诺带来的潜在煤电资产搁浅问题。研究运用“上下交互”的碳锁定曲线模型,识别不同产能扩张情景下(无新增、新增200、300和400 GW)的搁浅煤电机组。首先,从“自上而下”角度匡算中国煤电行业2℃温升目标下的碳配额。然后,从“自下而上”角度,根据高精度的燃煤电站信息核算煤电累积CO2排放量。最后基于“上下交互”模式筛选出搁浅燃煤电站,在此基础上运用现金流量法估算其潜在的搁浅价值,并对其关键因素进行敏感性分析。结果表明,在无新增情景下,煤电搁浅资产规模约为0.38万亿元;若继续增加200~400 GW煤电装机,则搁浅价值将较无新增情景增加3.7~8.2倍。因此,建议“十四五”期间应树立煤电规模峰值意识,严控煤电新增产能,避免错过最佳减排时机。  相似文献   
8.
In snowmelt-driven mountain watersheds, the hydrologic connectivity between meteoric waters and stream flow generation varies strongly with the season, reflecting variable connection to soil and groundwater storage within the watershed. This variable connectivity regulates how streamflow generation mechanisms transform the seasonal and elevational variation in oxygen and hydrogen isotopic composition (δ18O and δD) of meteoric precipitation. Thus, water isotopes in stream flow can signal immediate connectivity or more prolonged mixing, especially in high-relief mountainous catchments. We characterized δ18O and δD values in stream water along an elevational gradient in a mountain headwater catchment in southwestern Montana. Stream water isotopic compositions related most strongly to elevation between February and March, exhibiting higher δ18O and δD values with decreasing elevation. These elevational isotopic lapse rates likely reflect increased connection between stream flow and proximal snow-derived water sources heavily subject to elevational isotopic effects. These patterns disappeared during summer sampling, when consistently lower δ18O and δD values of stream water reflected contributions from snowmelt or colder rainfall, despite much higher δ18O and δD values expected in warmer seasonal rainfall. The consistently low isotopic values and absence of a trend with elevation during summer suggest lower connectivity between summer precipitation and stream flow generation as a consequence of drier soils and greater transpiration. As further evidence of intermittent seasonal connectivity between the stream and adjacent groundwaters, we observed a late-winter flush of nitrate into the stream at higher elevations, consistent with increased connection to accumulating mineralized nitrogen in riparian wetlands. This pattern was distinct from mid-summer patterns of nitrate loading at lower elevations that suggested heightened human recreational activity along the stream corridor. These observations provide insights linking stream flow generation and seasonal water storage in high elevation mountainous watersheds. Greater understanding of the connections between surface water, soil water and groundwater in these environments will help predict how the quality and quantity of mountain runoff will respond to changing climate and allow better informed water management decisions.  相似文献   
9.
文中对IPCC第六次评估报告(AR6)第一工作组(WGI)报告的第七章关于地球能量收支、气候反馈和气候敏感度中的重要内容进行了凝练,并简要总结该方面的最新研究成果和结论。评估显示,自工业革命以来,人类活动造成的有效辐射强迫(ERF)为2.72 [1.96~3.48] W/m2,其中,均匀混合温室气体的贡献为3.32 [3.03~3.61] W/m2,气溶胶的贡献为-1.1 [-1.7~-0.4] W/m2。净的气候反馈参数为-1.16 [-1.81~-0.51] W/(m2∙℃),云仍然是气候反馈整体不确定性的最大来源。平衡态气候敏感度(ECS)和瞬态气候响应(TCR)可用于评估全球平均地表气温对强迫的响应,是衡量全球气候响应的有效手段。ECS和TCR的最佳估计分别为3.0 [2.0~5.0]℃和1.8 [1.2~2.4]℃。  相似文献   
10.
Upland river systems in the UK are predicted to be prone to the effects of increased flood magnitudes and frequency, driven by climate change. It is clear from recent events that some headwater catchments can be very sensitive to large floods, activating the full sediment system, with implications for flood risk management further down the catchment. We provide a 15-year record of detailed morphological change on a 500-m reach of upland gravel-bed river, focusing upon the geomorphic response to an extreme event in 2007, and the recovery in the decade following. Through novel application of two-dimensional (2D) hydrodynamic modelling we evaluate the different energy states of pre- and post-flood morphologies of the river reach, exploring how energy state adjusts with recovery following the event. Following the 2007 flood, morphological adjustments resulted in changes to the shear stress population over the reach, resulting in higher shear stresses. Although the proportion of shear stresses in excess of those experienced using the pre-flood digital elevation model (DEM) varied over the recovery period, they remained substantially in excess of those experienced pre-2007, suggesting that there is still potential for enhanced bedload transport and morphological adjustment within the reach. Although volumetric change calculated from DEM differencing does indicate a reduction in erosion and deposition volumes in the decade following the flood, we argue that the system still has not fully recovered to the pre-flood state. We further argue that Thinhope Burn, and other similarly impacted catchments in upland environments, may not recover under the wet climatic phase currently being experienced. Hence systems like Thinhope Burn will continue to deliver large volumes of sediment further down river catchments, providing new challenges for flood risk management into the future.  相似文献   
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