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991.
992.
Changes in glacial lakes and glaciers of post-1986 in the Poiqu River basin, Nyalam, Xizang (Tibet) 总被引:16,自引:0,他引:16
Glacial lakes and glaciers are sensitive indicators of recent climate change. In the Poiqu River basin of southern Tibet, 60–100 km NW of Mt. Everest, Landsat imagery defines post-1986 changes in the size and distribution of both glacial lakes and glaciers. Total area of glaciers in the 229-km2 drainage area has decreased by 20%. The number of glacial lakes with areas in excess of 0.020 km2 has increased by 11%, and the total area of glacial lakes has increased by 47%. The areas of typical large glacial lakes of the area (Galongco, Gangxico, and Cirenmaco) have increased by 104, 118, and 156%, respectively, and these increases are confirmed by field investigations.Comparing the 1986 data, the area of glaciers in the basin headwaters has decreased by 46.18 km2 to a present total area of 183.12 km2, an annual rate of change of 3.30 km2/year. Trends indicate that the total area of glaciers will continue to decrease and that both the numbers and areas of glacial lakes will continue to increase. Accompanying these trends will be an increased risk of debris flows, formed by entrainment of sediment in glacial-outburst floods and in surges from both failure and avalanche- and landslide-induced overtopping of moraine dams. Based on both the local and world-wide history of catastrophes from flows of these origins, disaster mitigation must be planned and appropriate engineering countermeasures put in place as soon as possible. 相似文献
993.
Spontaneous tidal network formation within a constructed salt marsh: Observations and morphodynamic modelling 总被引:3,自引:1,他引:3
Andrea D'Alpaos Stefano Lanzoni Marco Marani Andrea Bonometto Giovanni Cecconi Andrea Rinaldo 《Geomorphology》2007,91(3-4):186
We have monitored and analyzed, through remote sensing and ancillary field surveys, the rapid (O(1) year) development of a tidal network within a newly established artificial salt marsh in the Venice Lagoon. After the construction of the salt marsh, a network of volunteer creeks established themselves away from an artificially constructed main channel (with mean and maximum annual headward-growth rates of 11 m/yr and 18 m/yr, respectively). The rapid formation of this system of tidal creeks provides a unique opportunity to test the reliability of a model of tidal network initiation and development, previously proposed by the authors. The restored marsh presents the characteristics of a controlled environment analogous to a large-scale field laboratory, as it allows comparison of the morphologic features of real and simulated network structures under the reasonable assumption of neglecting accretion and deposition processes over the timescales of observation. Our results compare favorably with observational evidence, showing that the model proves reasonably capable of reproducing the main features of the actual channel-network patterns. The model reproduces statistical network characteristics of eco-morphodynamic and hydrodynamic relevance and captures the dominant modes of the network-incision process. 相似文献
994.
Diatom and chrysophyte cyst-based reconstructions of the dates of spring and autumn lake-mixing enabled us to estimate spring
(STanom) and autumn (ATanom) temperature anomalies as well as ice-cover of the last ca. 4,000 years in a lake sediment core (Oberer Landschitzsee, 2,076
m a.s.l.) from the southern slopes of the Austrian Central Alps. The two independently inferred temperature anomalies were
significantly correlated. On average, spring and autumn temperatures were lower during the two millennia B.C than during 0–1,300
A.D. Marked spring and autumn temperature minima occurred at about 1,300 and 600 B.C. At about 1,300 A.D, STanom declined again. Spring-temperature anomalies during Roman and Medieval times equaled or slightly exceeded the modern values
and paralleled tree-line and glacier fluctuations. The de-coupling of autumn and spring climates, which began during the Medieval
period, might indicate changes in major circulation modes. It was assumed that the North-Atlantic influence, triggering winter-rain
climate in the Northern Mediterranean, became weaker during Medieval times, resulting in a trend towards warmer autumns and
overall more continental climate conditions in the study area. Four pulses of land use, inferred from indicator pollen, occurred
during (1) the Early to Late Bronze, (2) the transition from Late Bronze to Early Iron Age (Hallstatt), (3) Late Iron Age
(La Tène, Celtic time) to Roman times, and (4) during high to late Medieval times. Climate seemed to be an important, though
complex, trigger of Alpine land use. 相似文献
995.
在厚度为369cm的台错TT-1剖面中,共采取连续样品156个,单样平均厚度仅为2.36cm,使之成为一个理想的进行高分辨率研究的对象。通过对样品的硅藻研究,以及全部样品的孢粉和介形虫化石分析鉴定,本项研究取得了多项创新研究成果。①结合铀系不平衡法获得的准确可靠定年数据,本文重建了西藏台错古湖区自晚更新世晚期以来的古气候、古环境演变。从万年尺度上,台错在>32.60~26.15ka BP间的6.45ka间长期处在潮湿、湿润的环境之中;在26.15~4.50ka BP的21.65ka间,气候则以偏干和寒冷为大背景;在4.50ka BP,沉积记录终断,表明湖泊干枯消失。从百年-千年尺度上,厘定出台错自22.70ka BP以来,经历了明显的寒冷气候事件8起,湿润气候事件3起,以及气候颤动事件2起,从而更加详尽地描述了台错在18.2ka中经历的19个古环境、古环境演变阶段。②首次发现了两种硅藻的新化石种--西藏胸隔藻属新种Mastogloiatibetica Li et Wei和西藏桥弯藻属新种Cymbellataicuonensis Li et Zheng。③首次在西藏境内大量发现了Cyprideis torosa(结节正星介)和C.littoralis(滨海正星介)。本文为全球气候变化研究及青藏高原的古气候、古环境研究,提供了来自高原内部的全新精细记录和科学依据。 相似文献
996.
新疆玛纳斯湖近50年来的变迁 总被引:9,自引:0,他引:9
利用近30年来共8期覆盖新疆玛纳斯湖地区的遥感影像(1972MSS、1976MSS、1989TM、1999ETM、2000CBERS、2001CBERS、2003CBERS和2004CBERS),最新实测的精度达到1 m分辨率的地形等高线数据、野外测量数据,结合20世纪50年代野外实地调查资料等前人研究成果,对玛纳斯湖及周围湖泊演化进行了分析。结果表明:①玛纳斯湖并非迁移湖泊而是古玛纳斯湖群的一部分;玛纳斯湖及周围湖泊自第四纪中期以来一直处于萎缩消亡状态,新构造运动使古玛纳斯湖群萎缩分裂后,残留的各小湖泊在近现代也相继萎缩、消亡;②近50年来湖泊演化可分为两个阶段:湖泊萎缩、干涸的逆向演化阶段(1949-1999/2001)和湖泊恢复的正向演化阶段(1999/2001-至今),人类活动与气候变化的叠加是湖泊演化的主要驱动力。 相似文献
997.
八里张石膏矿位于合肥盆地北缘,赋存于古近系定远组含盐岩系。古近系定远组是安徽重要的陆相含盐建造。文中结合矿区地质背景,着重从沉积相特征的角度,通过对定远组含盐岩系的岩相特征、沉积规律、形成条件以及河湖相沉积特征规律的分析,对矿区的矿床成因也做了初步分析。认为矿区含盐岩系由河湖相沉积组成,属陆相盐湖沉积,同时在盐湖的形成过程中,盐盆受断裂控制。 相似文献
998.
A. Aiuppa W. D’Alessandro S. Gurrieri P. Madonia F. Parello 《Environmental Geology》2007,53(4):903-913
Hydrological and geochemical studies performed on Lake Specchio di Venere on Pantelleria island (Italy) indicate that this
endorheic basin has been formed through upwelling of the water table, and that it is continuously fed by the thermal springs
situated on its shores. The lake is periodically stratified both thermally and in salinity, albeit this stratification is
rather unstable over time, since meteorological events such as strong rain or wind can determine the mixing of its waters.
Periodical analyses of the lake water chemistry show large variations of the salt content due to the yearly evaporation-rain
dilution cycle. These processes are also responsible for the saline stratification during steady meteorological conditions.
The mineralogical characterisation of the bottom sediments shows the almost exclusive presence of neoformation minerals, mainly
carbonates, formed in response to the pH gradient between spring- (pH ≈ 6) and lake-waters (pH ≈ 9). Finally, the CO2 partial pressures in the lake water slightly exceeding the atmospheric one, are due to the large amounts of CO2 brought to the lake through the bubbling free gas phase of the thermal springs. Nevertheless the high pH value of the lake
water, its small volume and its periodical mixing prevent dangerous built up of this gas. 相似文献
999.
基于KJ法的艾比湖流域生态环境综合治理研究 总被引:7,自引:0,他引:7
将系统分析中的KJ法应用于新疆艾比湖流域生态环境的综合治理对策研究中。首先制作了59张包含与艾比湖生态环境治理相关的信息卡片,之后根据信息的亲近性将其分为5个大组,每个组内再进行细分,最后得到艾比湖流域生态环境问题综合治理的结构模型图,从管理体制建设和工程措施两方面归纳提炼出了具体治理对策。应用结果表明,KJ法能够充分体现群体的创造性思维并将之有序化,能很好地应用于包括生态系统在内的各种自然、社会、经济以及复合系统的综合集成研究中。 相似文献
1000.
总结了城市湖泊总无机N及各无机氮素的年际变化和不同水期的年际变化,结果表明:总无机N年际变化呈波浪式;不同水期中,总无机N与NH4^+-N以枯水期为最丰,而NO3^--N及NO2^-N则以平水期为相对最丰。同时分析了水体无机氮素的来源,结果显示汛期水流中营养物的滞留及底泥含氮成分的释放是湖泊水体无机氮素的主要来源,并计算了滞留系数及内源性负荷,分别为0.507、10.3%。此外,拟合分析了水体无机氮素间的关系,总无机N与NH4^+-N有明显正相关关系,相关系数达0.997。 相似文献