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171.
This paper aims to present the critical top tension for static equilibrium configurations of a steel catenary riser(SCR) by using the finite element method. The critical top tension is the minimum top tension that can maintain the equilibrium of the SCR. If the top tension is smaller than the critical value, the equilibrium of the SCR does not exist. If the top tension is larger than the critical value, there are two possible equilibrium configurations. These two configurations exhibit the nonlinear large displacement. The configuration with the smaller displacement is stable, while the one with larger displacement is unstable. The numerical results show that the increases in the riser's vertical distances, horizontal offsets, riser's weights, internal flow velocities, and current velocities increase the critical top tensions of the SCR. In addition, the parametric studies are also performed in order to investigate the limit states for the analysis and design of the SCR.  相似文献   
172.
During the last decade, the widely distributed shrublands in northern China have shown significant signs of recovery from desertification, the result of widespread conservation practices. However, to support the current efforts in conservation, more knowledge is needed on surface energy partitioning and its biophysical controls. Using eddy‐covariance measurements made over a semi‐arid shrubland in northwest China in 2012, we examined how surface energy‐balance components vary on diurnal and seasonal scales, and how biophysical factors control bulk surface parameters and energy exchange. Sensible heat flux (H) exceeded latent heat flux (λE) during most of the year, resulting in an annual Bowen ratio (β, i.e. H/λE) of 2.0. λE exceeded H only in mid‐summer when frequent rainfall co‐occurred with the seasonal peak in leaf area index (LAI). Evapotranspiration reached a daily maximum of 3.3 mm day?1, and summed to 283 mm yr?1. The evaporative fraction (EF, i.e. λE/Rn), Priestley–Taylor coefficient (α), surface conductance (gs) and decoupling coefficient (Ω) were all positively correlated with soil water content (SWC) and LAI. The direct enhancement of λE by high vapour pressure deficit (VPD) was buffered by a concurrent suppression of gs. The gs played a direct role in controlling EF and α by mediating the effects of LAI, SWC and VPD. Our results highlight the importance of adaptive plant responses to water scarcity in regulating ecosystem energy partitioning, and suggest an important role for revegetation in the reversal of desertification in semi‐arid areas. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
173.
The Budyko framework characterizes landscape water cycles as a function of climate. We used this framework to identify regions with contrasting hydroclimatic change during the past 50 years in Sweden. This analysis revealed three distinct regions: the mountains, the forests, and the areas with agriculture. Each region responded markedly different to recent climate and anthropogenic changes, and within each region, we identified the most sensitive subregions. These results highlight the need for regional differentiation in climate change adaptation strategies to protect vulnerable ecosystems and freshwater resources. Further, the Budyko curve moved systematically towards its water and energy limits, indicating augmentation of the water cycle driven by changing vegetation, climate and human interactions. This finding challenges the steady state assumption of the Budyko curve and therefore its ability to predict future water cycles. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
174.
175.
中国南海夏季风强、弱年多尺度相互作用能量学特征   总被引:1,自引:0,他引:1  
杨悦  徐邦琪  何金海 《气象学报》2016,74(4):556-571
中国南海夏季风为东亚季风的主要系统之一,其具有多重尺度特征,除季节平均环流场外,低频(季节内振荡)和高频(天气尺度)扰动也十分活跃,各尺度系统存在明显的年际变化。该研究使用ERA-Interim和NCEP/NCAR两套再分析资料,从季风平均动能(MKE)诊断的角度出发,探讨了1979-2010年中国南海夏季风环流年际变化的能量来源及其和扰动场的相互作用过程。结果表明:中国南海夏季风对流活跃年份,中国南海南部(12°N以南)及中南半岛一带为季风平均动能显著增强区,此与南亚季风区西风急流的增强并向东延伸有关;中国南海北部(12°N以北)及西太平洋为气旋性环流盘踞,季风槽加深。中国南海南部季风平均动能增强的能量源自于扰动动量通量与平均环流的相互作用,强季风年,平均环流失去较少的动能给扰动场(亦即平均环流保留较多的动能)。通过进一步探讨高频(<10 d)及低频(10-90 d)扰动场与平均环流不同分量的(散度、涡度、风垂直切变)相互作用过程,发现季风平均动能的增长主要来自于<10 d扰动与季风平均散度和涡度的相互作用。中国南海北部季风槽区季风平均动能的维持来自于大气热源和平均上升运动的相互作用,但同时有较多的季风平均动能向扰动动能转换,有利于扰动的成长。因此,强季风年,中国南海北部热带气旋生成数目增多,夏季北传的季节内振荡也增强,导致中国南部沿海及华南地区出现较多的灾害天气。   相似文献   
176.
A detailed study of long-term variability of winds using 30 years of data from the European Centre for Medium-range Weather Forecasts global reanalysis (ERA-Interim) over the Indian Ocean has been carried out by partitioning the Indian Ocean into six zones based on local wind extrema. The trend of mean annual wind speed averaged over each zone shows a significant increase in the equatorial region, the Southern Ocean, and the southern part of the trade winds. This indicates that the Southern Ocean winds and the southeast trade winds are becoming stronger. However, the trend for the Bay of Bengal is negative, which might be caused by a weakening of the monsoon winds and northeast trade winds. Maximum interannual variability occurs in the Arabian Sea due to monsoon activity; a minimum is observed in the subtropical region because of the divergence of winds. Wind speed variations in all zones are weakly correlated with the Dipole Mode Index (DMI). However, the equatorial Indian Ocean, the southern part of the trade winds, and subtropical zones show a relatively strong positive correlation with the Southern Oscillation Index (SOI), indicating that the SOI has a zonal influence on wind speed in the Indian Ocean. Monsoon winds have a decreasing trend in the northern Indian Ocean, indicating monsoon weakening, and an increasing trend in the equatorial region because of enhancement of the westerlies. The negative trend observed during the non-monsoon period could be a result of weakening of the northeast trade winds over the past few decades. The mean flux of kinetic energy of wind (FKEW) reaches a minimum of about 100?W?m?2 in the equatorial region and a maximum of about 1500?W?m?2 in the Southern Ocean. The seasonal variability of FKEW is large, about 1600?W?m?2, along the coast of Somalia in the northern Indian Ocean. The maximum monthly variability of the FKEW field averaged over each zone occurs during boreal summer. During the onset and withdrawal of monsoon, FKEW is as low as 50?W?m?2. The Southern Ocean has a large variation of about 1280?W?m?2 because of strong westerlies throughout the year.  相似文献   
177.
India's growing role in the global climate debate makes it imperative to analyse emission reduction policies and strategies across a range of GHGs, especially for under-researched non-CO2 gases. Hydrofluorocarbons' (HFCs) usage in cooling equipment and subsequent emissions are expected to increase dramatically in India with the phase-out of hydrochlorofluorocarbons (HCFCs) as coolants in air-conditioning equipment. We focus on the residential air-conditioning sector in India and analyse a suite of HFC and alternative coolant gas scenarios for understanding the implications for GHG emissions from this sector within an integrated assessment modelling framework. We find that, if unabated, HFC410A emissions will contribute to 36% of the total global warming impact from the residential air-conditioner sector in India in 2050, irrespective of the future economic growth trajectory, and the remaining 64% is from energy to power residential air-conditioners. A move towards more efficient, low global warming potential (GWP) alternative refrigerants will significantly reduce the cumulative global warming footprint of this sector by 37% during the period 2010–2050, due to gains both from energy efficiency as well as low GWP alternatives. Best practices for reducing direct emissions are important, but only of limited utility, and if a sustainable lifestyle is adopted by consumers with lower floorspace, low GWP refrigerants, and higher building envelope efficiencies, cumulative emissions during 2010–2050 can be reduced by 46% compared to the Reference scenario.

Policy relevance

Our analysis has important implications for Indian climate policy. We highlight that the Indian government's amendment proposal to the Montreal Protocol is a strong signal to the Indian market that the transition away from high GWP refrigerants towards low/zero GWP alternatives will happen sooner or later. The Bureau of Energy Efficiency should extend building energy conservation code policy to residential buildings immediately, and the government should mandate it. Government authorities should set guidelines and mandate reporting of data related to air-conditioner coolant recharge frequency and recovery of scrapped air-conditioner units. For contentious issues like flammability where there is no consensus within the industry, the government needs to undertake an independent technical assessment that can provide unbiased and reliable information to the market.  相似文献   

178.
This article illustrates the main difficulties encountered in the preparation of GHG emission projections and climate change mitigation policies and measures (P&M) for Kazakhstan. Difficulties in representing the system with an economic model have been overcome by representing the energy system with a technical-economic growth model (MARKAL-TIMES) based on the stock of existing plants, transformation processes, and end-use devices. GHG emission scenarios depend mainly on the pace of transition in Kazakhstan from a planned economy to a market economy. Three scenarios are portrayed: an incomplete transition, a fast and successful one, and even more advanced participation in global climate change mitigation, including participation in some emission trading schemes. If the transition to a market economy is completed by 2020, P&M already adopted may reduce emissions of CO2 from combustion by about 85 MtCO2 by 2030 – 17% of the emissions in the baseline (WOM) scenario. One-third of these reductions are likely to be obtained from the demand sectors, and two-thirds from the supply sectors. If every tonne of CO2 not emitted is valued up to US$10 in 2020 and $20 in 2030, additional P&M may further reduce emissions by 110 MtCO2 by 2030.  相似文献   
179.
利用常规地面气象站多时次气象要素和天气现象观测资料,以及武汉、宜昌和恩施的探空资料,对1998—2014年湖北地区冻雨天气的主要环流背景进行了分析,归纳了冻雨发生发展过程的气象要素和大气层结特征,给出了基于正负能量面积的冻雨发生定量化判断方法。结果表明:乌山阻高型和贝湖阻高型是导致湖北省出现冻雨天气的两种主要天气形势;2005年和2月是冻雨主要发生的年份和月份;共存在3种典型的气温层结演变特征,其中"暖雨-冻雨-固态"的气温层结演变最易导致持续时间长、影响范围大的冻雨天气;基于正负能量面积的冻雨判定方法为:3层层结时,正能量面积(A_(SP))小于80℃·hPa,负能量面积(A_(SN))小于400℃·hPa,且正负能量关系为(5.71A_(SP)-257.14)≤A_(SN)≤(6.25A_(SP)+200);2层层结时,ASP为350~650℃·hPa,A_(SN)为200~400℃·hPa,且正负能量关系为(A_(SP)-350)≤A_(SN)≤(ASP-100)。  相似文献   
180.
地壳运动驱动力的探讨——核能与地球演化   总被引:1,自引:0,他引:1  
马学昌 《地质学报》2016,90(1):24-36
本文综合核物理、天文和地质学的最新研究成果,推导出在45亿年前太阳系的全部原始类地行星及其某些卫星(包括地球及月球)上,发生过大规模的、持续的铀、钚链式核裂变,释出了巨大的热能,熔化了整个原始星球。新星球的物质发生了重力分异作用、形成了按密度划分的圈层结构。地球中心是内地核,在高压下压成了固态。铀、钚下沉到内地核顶部停留,继续发生链式核裂变,但改变不了内地核的固态性质。从此处产生的核裂变能,主要以热对流的形式外导。直到前45亿年以后,铀的链式核裂变停止了,只剩下钚的链式核裂变,生成的热能减少了,地球开始冷凝。当熔浆表面温度下降到700~800℃时,较轻的花岗岩质岩浆首先凝固成薄层。它很脆弱、经不起大风浪和潮汐力的冲击,破碎成小块,随着下面对流的玄武岩质熔浆汇集起来,形成大片飘浮物,后来就成为大陸;小片的便成为岛屿。温度逐渐下降,地幔冷凝成固体。温度下降至100℃以下,大气中的水蒸气冷凝成水,下落汇集在地表低凹处,便有了海洋和湖泊。所以海洋底主要分布着玄武岩。从内地核顶部不断产生的核能以"地幔柱"的形式穿过固体地幔,上升至地壳。受坚硬地壳的隔挡、便集中在地壳下构成软流层。当地壳岩石受热软化和可以流动之后,便开始向压力小的方向流动。又受日、月引力和地球自身自转力的作用,软流层的动能又有了增强。这种巨大的能量支配了地壳的升降、褶曲、断裂、变质、岩浆、火山和地震等活动。地球是天体之一,无时不受自然界各种作用力的影响,但支配它演化的主要作用力是核能。本文还简述了核能、核素与太阳系星体演化的关系。  相似文献   
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