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751.
Mapping and monitoring net primary productivity with AVHRR NDVI time-series: statistical equivalence of cumulative vegetation indices 总被引:1,自引:0,他引:1
Carlo Ricotta Giancarlo Avena Alessandra De Palma 《ISPRS Journal of Photogrammetry and Remote Sensing》1999,54(5-6)
In the last two decades, numerous investigators have proposed cumulative vegetation indices (i.e., functions which encode the cumulative effect of NDVI maximum value composite time-series into a single variable) for net primary productivity (NPP) mapping and monitoring on a regional to continental basis. In this paper, we investigate the relationships among three of the most commonly used cumulative vegetation indices, expanding on the definition of equivalence of remotely sensed vegetation indices for decision making. We consider two cumulative vegetation indices as equivalent, if the value of one index is statistically predictable from the value of the other index. Using an annual time-series of broad-scale AVHRR NDVI monthly maximum value composites of the island of Corsica (France), we show that the pairwise linear association among the analysed cumulative vegetation indices shows coefficients of determination (R2) higher than 0.99. That is, knowing the value of one index is statistically equivalent to knowing the value of the other indices for application purposes. 相似文献
752.
植被覆盖度遥感估算方法研究进展 总被引:39,自引:0,他引:39
植被覆盖度是重要的生态环境参数之一,遥感影像能够反映不同空间尺度的植被覆盖信息及其变化趋势,故遥感监测是获取区域植被覆盖度参数的一个重要手段.植被指数是反映地表植被覆盖、生物量等的间接指标,基于植被指数的植被覆盖度遥感估算方法有经验模型法、植被指数法、像元分解模型法及FCD模型制图法(Forest Canopy Density Mapping Model)等,基于决策树分类法和人工神经网络分类法的植被覆盖度遥感估算方法也有了一定的进展.本文综合分析讨论了目前常用的于遥感影像的植被覆盖度常用估算方法,对比分析了它们的优缺点,并对遥感植被覆盖度研究进行了展望. 相似文献
753.
754.
对2005-2007年4-9月安徽省冰雹、雷雨大风等强对流天气日数进行统计,分析了基于探空资料计算的不稳定指标与强对流天气发生的关系。结果表明:K指数、A指数、沙氏指数和对流有效位能、归一化对流有效位能和对流抑制能量这几个指标对于强对流天气指示意义较好。基于此结果,挑选K指数、沙氏指数和对流有效位能针对不同季节划分闽值,建立强对流天气潜势预警指标,并利用中尺度模式MM5的数值预报产品计算该指标,对2005—2010年13个强对流天气过程预报结果进行对比检验表明。MM5模式给出的强对流天气潜势预警产品对大多数过程均能起到预警作用。对其中两次强对流天气过程分析表明,模式具备预报强对流发生潜势的能力,预报结果对强对流天气发生的时间、落区有预警意义。 相似文献
755.
756.
FEATURES AND COMPARISONS OF THE QUASI-BIENNIAL VARIATIONS IN THE ASIA-PACIFIC MONSOON SUBSYSTEMS 总被引:1,自引:0,他引:1
The National Centers for Environmental Prediction (NCEP) reanalysis data, Climate
Diagnostics Center Merged Analysis of Precipitation (CMAP) results, and NOAA Extended Reconstructed
Sea Surface Temperature (SST), have been utilized in this paper to study the quasi-biennial variations in
Asia-Pacific monsoon subsystems and associated SST anomalies (SSTA) and wind anomalies. Four
monsoon indices are computed from NCEP/ National Center for Atmospheric Research (NCAR) reanalysis
to represent the South Asian monsoon (SAM), South China Sea summer monsoon (SCSSM), Western
North Pacific monsoon (WNPM) and East Asian monsoon (EAM), respectively. The quasi-biennial periods
are very significant in Asia-Pacific monsoons (as discovered by power spectrum analysis), and for SAM
and EAM---with moderate effects by El Ni?o-Southern Oscillation (ENSO)---the quasi-biennial periods are
the most important factor. For SCSSM and WNPM (once again due to the effects of ENSO), the
quasi-biennial periods are of secondary durations. There are obvious interdecadal variations in the
quasi-biennial modes of the Asia-Pacific monsoon, so in the negative phase the biennial modes will not be
significant or outstanding. The wind anomalies and SSTA associated with the biennial modes are very
different in the SAM, WNPM and EAM regions. Since the WNPM and SCSSM are very similar in the
biennial modes, they can be combined into one subsystem, called SCS/WNPM. 相似文献
757.
高分辨率统计降尺度数据集NEX-GDDP对中国极端温度指数模拟能力的评估 总被引:2,自引:0,他引:2
利用1986—2005年中国地面气象台站观测的格点化逐日气温资料(CN05.1)评估了高分辨率统计降尺度数据集NASA Earth Exchange/Global Daily Downscaled Projections(NEX-GDDP)中21个全球气候模式对中国极端温度指数的模拟能力。在选用了日最低温度最大值(TNx)、日最高温度最大值(TXx)、暖夜指数(TN90p)和暖昼指数(TX90p)来研究极端温度事件的变化。结果显示:(1)除MRI-CGCM3模拟的日最高温度最大值外,其余模式对4个指数的模拟结果均表现出与观测一致的上升趋势,但模拟结果的平均值相对观测平均低0.26℃/(10 a)(日最低温度最大值)、0.19℃/(10 a)(日最高温度最大值)、2.21%/(10 a)(暖夜指数)、1.04%/(10 a)(暖昼指数)。(2)不同模式对各指数变化趋势空间分布特征的模拟存在较大差别,对日最低温度最大值、日最高温度最大值、暖夜指数和暖昼指数模拟能力最优模式分别为CCSM4、CESM1-BGC、MIROC-ESM-CHEM和bcc-csm1-1。模式模拟的日最低温度最大值和日最高温度最大值气候态平均值与观测值的相关系数在0.97以上。暖夜指数和暖昼指数模拟结果与观测值的标准差比值为0.34—1.58,均方根误差变化为1.6%—3.47%,对这两个指数模拟能力较优的模式分别为MIROC-ESM-CHEM(暖夜指数)和CESM1-BGC(暖昼指数)。(3)综合模式对4个指数在气候态平均值和变化趋势模拟能力的评估结果来看,CanESM2、CESM1-BGC和MIROC-ESM-CHEM显示了相对较高的模拟能力。因此,在利用GDDP-NEX研究未来极端温度事件时,建议将它们作为优选模式。 相似文献
758.
膨胀岩的判别与分类标准 总被引:1,自引:0,他引:1
膨胀岩的判别与分级是膨胀岩研究的重要内容。本文在分析和总结了前人研究成果的基础上,提出了一种以膨胀岩中亲水矿物成分的含量为基础控制指标,以岩块的干燥饱和吸水率、极限膨胀量、极限膨胀力为主要控制指标新的标准。并利用新的标准对文献中的工程实例进行了分析应用。 相似文献
759.
扎布耶盐湖具天然Li2CO3产出,其为微溶矿物,且溶解度随温度升高而降低,其余大多数盐类矿物溶解度均为随温度的升高而升高。不同结构结晶池所产出混盐中Li2O3质量百分数明显不同:露天式为4.06%,MPFS式为2.53%,FPFS式为56.43%。据此,总结出高品位Li2O3混盐制取的基本思路和控制指标:盐田冷冻、日晒,使卤水中Li含量升高至当时水温条件下的饱和点后,不蒸发而升温,卤水中Li饱和后的控制指标为温度。 相似文献
760.
A comparison of geochemical information obtained from two fluvial bed sediment fractions 总被引:3,自引:1,他引:3
Ross. A. Sutherland 《Environmental Geology》2000,39(3-4):330-341
A total of 121 bed sediment samples were collected from a 5.8-km stretch of Manoa Stream, Hawaii. Samples were physically
partitioned into two grain-size fractions, <63 μm and 63–125 μm, acid digested and analyzed by ICP-AES and FAAS. Non-parametric
matched-pair statistical testing and correlation analysis were used to assess differences and strengths of association between
the two fractions for Al, Ba, Cu, Fe, Mn, Ni, Pb, Ti and Zn. Results indicated statistically significant differences between
fractions for all elements except Mn. Concentrations were significantly greater in the <63 μm fraction for Al, Cu, Pb, Ti
and Zn, while Ba, Fe and Ni were higher in the 63–125 μm fraction. Though some elements had statistically significant differences
between fractions (Al, Ba, Fe and Zn) percentage differences were in the range of analytical precision of the instrument and
thus differences were not practically significant. Correlation analysis indicated strong positive associations for all elements
between the two fractions (p<0.0001). Three contamination indices indicated similar degrees of pollution for each size fraction
for four elements having an anthropogenic signal (Ba, Cu, Pb and Zn). The environmental information obtained from the 63–125 μm
fraction was essentially equivalent to that from the <63 μm fraction. In this system it is clear that both bed sediment fractions
indicate anthropogenic enrichment of trace metals, especially Pb, and further supports previous research that has found that
aquatic sediments are critical median for tracing sources of pollution.
Received: 17 August 1998 · Accepted: 30 October 1998 相似文献