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51.
1 INTRODUCTION Guanting Reservoir is located on the Yongding River (a large tributary of the Haihe River) and at the border of Beijing Municipality and Hebei Province. The reservoir receives three tributaries: the Sanggan River with a drainage area of 25,840 km2, the Yanghe River with 16,170 km2, and the Guishui River with 852 km2. The drainage area above the reservoir is 43,402 km2. The reservoir has two arms. The Sanggan River and Yanghe River join the Yongding River at the ups… 相似文献
52.
1 INTRODUCTION Dongting Lake lies south of the middle reach of the Yangtze River in Hunan and Hubei provinces (Fig. 1). On the north side of Dongting Lake, there are the three diversion openings of the Yangtze River named Songzi, Taiping, and Ouchi, and, on the south and west sides, there are the four tributary streams named Xiang, Zi, Yuan, and Li Rivers. The flow of the three diversion openings and the four tributary streams runs into Dongting Lake, and runs out at Chenglingji a… 相似文献
53.
The three-dimensional flow field in a scour hole around different abutments under a clear water regime was experimentally measured in a laboratory flume, using the Acoustic Doppler Velocimeter (ADV). Three types of abutments used in the experiments were vertical-wall (rectangular section), 45° wing-wall (45° polygonal section) and semicircular. The three-dimensional time-averaged velocity components were detected at different vertical planes for vertical-wall abutment and azimuthal planes for wing-wall and semicircular abutments. The velocity components were also measured at different horizontal planes. In the upstream, presentations of flow field through vector plots at vertical / azimuthal and horizontal planes show the existence of a primary vortex associated with the downflow inside the scour hole. On the other hand, in the downstream, the flow field shows a reversed flow near the abutments having a subsequent recovery with a passage of flow as a part of the main flow. The data presented in this p 相似文献
54.
Hubert Hellmann 《洁净——土壤、空气、水》2003,31(2):85-96
A Recent Contamination Trend: Polycylic Aromatic Hydrocarbons (PAHs) in Aquatic and Terrestrial Sediments Concentrations of polycylic aromatic hydrocarbons (PAHs) measured in aquatic sediments of small, medium‐sized or very large inland lakes, of estuaries as well as in terrestrial sediments from Germany, the UK, Finland, and the USA were plotted in 10 trend curves over the period from 1800 to 1990. The segments of the bore cores were dated for their deposition age. For comparability of the results, the trend is preferentially shown by the guide parameter fluoranthene. Until the 19th century, a constant background value of CFluo = 10…50 μg/kg was observed in all regions. Then a steep increase in concentration followed, reaching in the aquatic sediments a maximum in the period 1940 to 1965, while the individual fluoranthene values ranged widely from 90 to 2400 μg/kg. In several regions, a more or less distinct decrease superseded this maximum, although this development did not appear in terrestrial sediments, in one estuary, and in remote forest lakes in Finland. The trend curves reflect the atmospheric deposition of PAHs in airborne dust and in some cases the import through runoff via rivers. Thus, the sediment profiles depict the development of air pollution by pyrogenic contaminants over more than a century. Sediment profiles from rivers can be used only with a high degree of reservation, because of the irregularity and low representativity of the sedimentation. 相似文献
55.
Despite growing evidence for environmental oscillations during the last glacial–interglacial transition from high latitude, terrestrial sites of the North Pacific rim, oxygen-isotopic records of these oscillations remain sparse. The lack of data is due partially to the paucity of lakes that contain carbonate sediment suitable for oxygen-isotopic analysis. We report here the first record of oxygen-isotopic composition in diatom silica (δ18OSi) from a lake in that region. δ18OSi increases gradually from 19.0 to 23.5‰ between 12,340 and 11,000 14C yr B.P., reflecting marked climatic warming at the end of the last glaciation. Around 11,000 14C yr B.P., δ18OSi decreases by 1.7‰, suggesting a temperature decrease of 3.5–8.9 °C at the onset of the Younger Dryas (YD) in southwestern Alaska. Climatic recovery began ca. 10,740 14C yr B.P., as inferred from the increase of δ18OSi to a maximum of 23.9‰ near the end of the YD. Our data reveal that a YD climatic reversal in southwestern coastal areas of Alaska occurred, but the YD climate did not return to full-glacial conditions. 相似文献
56.
WANG Tiefeng Northeast Investigation Design Research Institute China ZHANG Zhi Northeast Investigation Design Research Institute China YI Yue Northeast Investigation. Design Research Institute China 《国际泥沙研究》1997,(3)
I.INTRODUCTIONThePtlmped-storagepoll,erprojectofPushiriverisconsistedofupperreservoir,lobal-erreset'oir.watertransmissionSystemandpotvergeneratingsystem.ThelowerreservoirIviththecatchmentbasinareaof1141kmZisthewatersupplierl-c'hichislocatedonthedownstreamofthePushiriverinthesouthernpactofNortheastChina.Theupperreservoirisabout300-400metershigherthanthelowerresen!oirattheleftsideoftheriverwithcatchmentbasinareaof1.12km2.Thecharacteristicsoftheprojectandreservoirareshottviintablel-l.Ino… 相似文献
57.
XU Jiongxin Professor Institute of Geography Chinese Academy of Sciences Beijing China 《国际泥沙研究》1997,(3)
LINTRODUCTIONThetributariesofmiddleYellowRiverarefamousintheworldforthehighestsuspendedsedimentconcentrationandsedimentyield.Forexample,atWenjiachuanstationofKuyeheRiverthemeasuredhighestsuspendedconcentrationis1700kg/m',andthemeanannualsedimentyieldis25000t/(kln'.a).Theformationofhyperconcentratedflowsandtheirinfluenceonerosionprocessesareofgreatimportancenotonlyfromatheoreticalpointofviewbutalsoforpracticalpurposes.Therefore,scientistsfromChinaandallovertheworldhavedrawntheirintensio… 相似文献
58.
Sediment origin and budget in Sepetiba Bay (Brazil) - an approach based on multielemental analysis 总被引:1,自引:0,他引:1
Sediment origin and transport were determined in a shallow 447 km2 coastal lagoon in Brazil, using the distribution of major elements in bottom and suspended sediments. Applying multivariate
analysis, the sum of normalized concentrations of Ti, Fe, and Al in sediments was selected to trace the terrigenous influence
in bottom sediments, whereas Ca, Si, and K were used as indicators of marine influence. Sepetiba Bay bottom sediments are
dominated by up to 80% terrigenous inputs. The open bay sediments are enriched in P, Mg, K, and Ca because of the intensive
water column primary production. The inner bay forms an independent circulation cell with a predominance of terrigenous sediments.
The results suggest a long residence time for particles in the bay, demonstrated by the magnitude of resuspension flux compared
to the total sediment input to the bay.
Received: 29 May 1996 · Accepted: 17 December 1996 相似文献
59.
腾格里沙漠东南缘降尘粒度特征和沉积速率 总被引:15,自引:9,他引:15
从多年降尘实测资料入手,分析了粉尘粒度特征、沉积速率和时变过程。提出了气象要素相关估测模型.确定0.25mm为本区粉尘沉积粒径上限。周围沙漠是粉尘沉积细砂部分的尘源,粉砂和粘土部分沉积来自一个较大的时空范围,二者几乎各占降尘量的1/2。研究区年平均粉尘沉积速率4358kg/hm2,每年5月的季风转期具有年内最大沉积速率。 相似文献
60.
The circulation of cold, deep water is one of the controlling factors of the Earth's climate. Forty percent of this water
enters the world ocean through the Southwest Pacific as a deep western boundary current (DWBC) flowing northwards at bathyal
to abyssal depths, east of the New Zealand microcontinent. South of latitude 50°S, the DWBC is intimately linked with the
Antarctic circumpolar current (ACC), which is the prominent force for the shallow-water circulation. The Pacific DWBC is presently
the largest single contributor of deep ocean water, and deciphering its evolution is of fundamental importance to understanding
ocean and climate history, and global ocean hydrography. The evolution of the DWBC system, and of related circum-Antarctic
currents, has taken place since 30–25 Ma when plate movements created the first oceanic gaps south of Australia and South
America. The stratigraphic record preserved in sediment drifts of the Southwest Pacific, in eastern New Zealand, is the best
available for deciphering the Neogene history of Southern Ocean water masses, and of the circulation of the ACC, DWBC and
their precursor systems. Major current activity commenced on the New Zealand margin in the late Eocene or early Oligocene
(Hoiho Drift; early ACC) and was widespread by the mid-late Oligocene (Marshall Paraconformity and Weka Pass Limestone drift;
ACC). During the Neogene the eastern South Island continental shelf built seawards by accretion at its outer edge of large
Miocene current drifts up to tens of kilometres long and hundreds of metres thick (Canterbury drifts). Also commencing in
the mid-Cenozoic, but in depths >2000 m, the DWBC emplaced large deep-water sediment drifts. Rates of drift deposition accelerated
considerably in the late Neogene, when climatic change (and particularly glacial sea-level falls) caused the delivery of large
volumes of turbiditic sediment into the path of the DWBC via the Bounty and Hikurangi channels.
Received: 9 August 1995 / Accepted: 15 January 1996 相似文献