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851.
Keliang ZHAO Xiaoqiang LI Hai XU Xingying ZHOU John DODSON Junchi LIU 《中国科学:地球科学(英文版)》2019,(7):1125-1137
The nature and dynamics of climate change in central Asia since the late Pleistocene are controversial. Moreover,most of the published studies focus mainly on the evolution of moisture conditions, and there have been few attempts to address changes in seasonality. In this study, records of δ13Corg, TOC, TN, C/N and grain size were obtained from lacustrine sediments at Yili Basin, Xinjiang, NW China. Our aim was to reconstruct the trend in seasonality of precipitation from the last glaciation to the Holocene. The organic matter content of the sediments is derived predominantly from terrestrial plants. The δ13Corgvalues vary from-19.4‰ to-24.8‰, indicating that the vegetation was dominated by C_3 plants. Winter-spring precipitation is identified as the factor determining the relative proportions of C_3 and C_4 plants in the region. A negative trend in δ13Corgcorresponding to an increase in the relative abundance of C_3 plants indicate a trend of increasing winter-spring precipitation from the last glaciation to the Holocene. The increased incidence of wintertime storms in the interior of Asia is suggested to result in the increase of winterspring precipitation in the Holocene. 相似文献
852.
《水文科学杂志》2012,57(2):311-324
ABSTRACTIn semi-arid regions, reduced river flows present is a major challenge in water resources management. We present a new standardized contribution of rainfall to runoff index (SCRI) for evaluating changes in rainfall contribution to river flow. We employ the standardized precipitation index (SPI), standardized discharge index (SDI) and SCRI to characterize meteorological drought, hydrological drought and land-use change impacts on river flow, respectively. These indices are applied to the Mond River Basin (Iran), which is regulated by the Salman Farsi and Tangab dams since 2006. A new concept called “mirage water” is proposed that represents the reduced water delivery to downstream areas due to new developments and water withdrawals in headwater tributaries. In particular, mirage water accounts for changes in upstream water consumption between the planning phase and construction/operation life of dams. We recommend that this concept be used for communication with decision-makers and managers to clarify the need for revising dimensions of planned dams. 相似文献
853.
854.
855.
通过专家模型提取1995年、1998年和2000年3个时期遥感影像的水土流失区,结合地理信息系统研究崇仁河流域水土流失时空演变规律。研究结果表明,崇仁河流域水土流失虽然近两年有所改善但仍很严重。原因是研究区月平均气温高,雨量充沛,岩石岩性以紫红、砖红色砂砾岩为主,地层构造不发育,土壤肥力差,植被生长困难,再加上人类活动频繁,以及不合理利用土地资源,使本来就易受侵蚀的土壤流失更迅速。同时,针对本区水土流失的特殊性,提出了合理保持水土的措施。 相似文献
856.
According to the latest International Chronostratigraphic Scheme (ICS, 2000), the Permian in the Middle-Lower Yangtze region of South China can e divided into three series and nine stages relevant to the traditional six stages of South China. From Assellian to Changxingian of Permian, 44 Main age range, the strata are composed of 14 third-order sequences, each of which is 3.14 Ma in average age range. There is one third-order sequence of Zisongian, equivalent to middle and upper Chuanshan Formation or equal to Asselian and two thirds of Sakmarian. There are two third-order sequences, corresponding to Liang-shan Formation or Zhenjiang Formation and upper Chuanshan Formation, which are assigned to Longlingian, coinciding with Artinskian and one third of Sakmarian. In addition, three third-order sequences, equal to Qixia Formation, are attributed to Chhsian, corresponding to Kubergandian and one third of Roadian. Four third-order sequences, comprising Gufeng, Maokou, Yanqiao,Yinping and Wuxue formations, are assigned to Maokouan, equivalent to two thirds of Roadian, Wordian and Capitanian. Two third-order sequences, equal to Longtan Formation or Wujiaping Formation, are included in Wuchiapingian. Other two third-order sequences, corresponding to changxing Formation or Dalong Formation, are assigned to Changhsingian. In brief, these above third-order sequences can be incorporated into 4 sequences sets. 相似文献
857.
在全面收集与系统分析全国水温台网近300口观测井2008年动态的基础上,梳理出井水温的正常年动态与固体潮,并进一步识别与分析2008-05-12汶川MS8.0地震震前、震时及震后的异常变化;归纳出全国井水温动态的正常年动态类型、特征及水温潮汐的基本特征,识别出汶川地震前14口井出现的异常,并分析该异常的形态与时空分布特征;分析125口井的同震响应与震后变化特征,进一步论证利用井水温动态监测地震前兆的可能性与存在的问题,提出把现有的水温观测网进一步改造与升级、开拓地壳热动态与地震活动关系观测与研究的创新思路。 相似文献
858.
Human activities use more than half of accessible freshwater, above all for agriculture. Most approaches for reconciling water conservation with feeding a growing population focus on the cropping sector. However, livestock production is pivotal to agricultural resource use, due to its low resource-use efficiency upstream in the food supply chain. Using a global modelling approach, we quantify the current and future contribution of livestock production, under different demand- and supply-side scenarios, to the consumption of “green” precipitation water infiltrated into the soil and “blue” freshwater withdrawn from rivers, lakes and reservoirs. Currently, cropland feed production accounts for 38% of crop water consumption and grazing involves 29% of total agricultural water consumption (9990 km3 yr−1). Our analysis shows that changes in diets and livestock productivity have substantial implications for future consumption of agricultural blue water (19–36% increase compared to current levels) and green water (26–69% increase), but they can, at best, slow down trends of rising water requirements for decades to come. However, moderate productivity reductions in highly intensive livestock systems are possible without aggravating water scarcity. Productivity gains in developing regions decrease total agricultural water consumption, but lead to expansion of irrigated agriculture, due to the shift from grassland/green water to cropland/blue water resources. While the magnitude of the livestock water footprint gives cause for concern, neither dietary choices nor changes in livestock productivity will solve the water challenge of future food supply, unless accompanied by dedicated water protection policies. 相似文献
859.
Palaeolimnological Development of Lake Njargajavri, Northern Finnish Lapland, in a Changing Holocene Climate and Environment 总被引:1,自引:2,他引:1
Kaarina Sarmaja-Korjonen Marjut Nyman Seija Kultti Minna Väliranta 《Journal of Paleolimnology》2006,35(1):65-81
This study used palaeolimnological approaches to determine how Holocene climatic and environmental changes affected aquatic
assemblages in a subarctic lake. Sediments of the small Lake Njargajavri, in northern Finnish Lapland above the present treeline,
were studied using multi-proxy methods. The palaeolimnological development of the lake was assessed by analyses of chironomids,
Cladocera and diatoms. The lake was formed in the early Holocene and was characterized by prominent erosion and leaching from
poorly developed soils before the establishment of birch forests, resulting in a high pH and trophic state. The lake level
started to lower as early as ca. 10,200 cal. BP. In the resulting shallow basin, rich in aquatic mosses, pH decreased and
a diverse cladoceran and chironomid assemblage developed. It is likely that there was a slight rise in the water level ca.
8000 cal. BP. Later, during the mid-Holocene characterized by low effective moisture detected elsewhere in Fennoscandia, the
lake probably completely dried out; this is manifest as a hiatus in the stratigraphy. The sediment record continues from ca.
5000 cal. BP onwards as the lake formed again due to increased effective moisture. The new lake was characterized by very
low pH. The possible spread of pine to the catchment and the development of heath community may have contributed to the unusually
steep (for northern Fennoscandia) decline in pH via change in soils, together with the natural decrease in leaching of base cations. Furthermore, the change in pH may have been
driven by cooling climate, affecting the balance of dissolved inorganic carbon in the lake. 相似文献
860.
Seismic surveys with sub‐bottom profiler were carried out in the Manfredonia Gulf in the southern Adriatic Sea. Here, a buried surface was recognized on which three valleys, located about 80 km from the shelf edge, were deeply incised. Beneath this surface, a pre‐upper Würm seismic unit (PW) was identified. Above, two seismic units were recognized: the transgressive system tract (TST) and highstand system tract (g2). On the basis of regional correlation with onshore and offshore data, these units and their boundaries were dated and correlated with phases of the last glacial–interglacial cycle. The incised valley system was attributed to the Marine Isotopic Stage (MIS) 2. The TST and g2 units fill the valleys and were attributed to the post‐glacial sea‐level rise and highstand. The incised valleys are anomalous with respect to published models; despite having many characteristics that would have limited the fluvial incision (the lowstand shoreline that remained on the shelf, the low gradient of the shelf, the subsidence that affected the study area since MIS 5), the valleys appear to be deeply incised on the shelf, with valley flanks that can exceed 40 m in height. The model to explain the formation of the valleys comprises enhanced river discharge as the key factor in increasing river energy and promoting erosion across the low gradient shelf. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献