全文获取类型
收费全文 | 3233篇 |
免费 | 825篇 |
国内免费 | 1838篇 |
专业分类
测绘学 | 66篇 |
大气科学 | 3034篇 |
地球物理 | 364篇 |
地质学 | 1357篇 |
海洋学 | 532篇 |
天文学 | 14篇 |
综合类 | 168篇 |
自然地理 | 361篇 |
出版年
2024年 | 41篇 |
2023年 | 86篇 |
2022年 | 154篇 |
2021年 | 175篇 |
2020年 | 166篇 |
2019年 | 221篇 |
2018年 | 183篇 |
2017年 | 137篇 |
2016年 | 155篇 |
2015年 | 189篇 |
2014年 | 299篇 |
2013年 | 276篇 |
2012年 | 296篇 |
2011年 | 304篇 |
2010年 | 258篇 |
2009年 | 277篇 |
2008年 | 347篇 |
2007年 | 330篇 |
2006年 | 339篇 |
2005年 | 270篇 |
2004年 | 214篇 |
2003年 | 200篇 |
2002年 | 118篇 |
2001年 | 137篇 |
2000年 | 117篇 |
1999年 | 103篇 |
1998年 | 91篇 |
1997年 | 83篇 |
1996年 | 71篇 |
1995年 | 56篇 |
1994年 | 48篇 |
1993年 | 48篇 |
1992年 | 27篇 |
1991年 | 26篇 |
1990年 | 11篇 |
1989年 | 8篇 |
1988年 | 12篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 3篇 |
排序方式: 共有5896条查询结果,搜索用时 360 毫秒
281.
282.
CHARACTERISTICS OF MESOSCALE FLOOD-MAKING TORRENTIAL RAIN SYSTEM SIMULATED BY HIGH RESOLUTION LIMITED AREA MODEL—NUMERICAL SIMULATION OF A HEAVY RAIN PROCESS DURING MEIYU SEASON IN 1991* 下载免费PDF全文
An experimental work on the transplant of high resolution limited area model(HIRLAM) isfirstly introduced into China.For the implementation,first of all is to adjust a new geographicalcoordination and to remove the instability caused by the Tibetan Plateau,the roof of the world.Then,we have applied this model to simulate a flood-making torrential rain process which occurredin the Changjiang-Huaihe River Valley in July 1991.That revealed the formation,development andmovement of a mesoseale heavy rain system which had made a disastrous flood event in the middleand lower reaches of Changjiang River Valley.The result encourages us to use the HIRLAM for the researches on the Meiyu belt,the salientfeature of precipitation of East Asia,and the numerical prediction of heavy rains in China. 相似文献
283.
Concentrations of Pb, Cd, Cu and Zn have been measured using improved ultraclean procedures in a succession of twenty six snow samples integrating a 40 yr time sequence from 1940 to 1980 which were collected from the walls of a 6 m deep pit at stake D 55 in Adelie Land, East Antarctica. Measured concentrations, which are among the lowest ones ever measured in Antarctic snows, are found not to have significantly increased during the investigated time period, with the possible exception of Pb for which there might have been a significant increase after the mid 1960's. For this last metal, measured concentrations in the 1940's are about 6-fold higher than in Antarctic Holocene ice several thousand years old, which indicates that a large fraction of the anthropogenic increase for Pb probably occurred before the 1940's. 相似文献
284.
An experimental investigation is presented on the batch foam fractionation of the heavy metal cations Pb2+, Cd2+, Cu2+, Sb3+ and As5+ from diluted aqueous solutions with hexamethylenedithiocarbamate (HMDC) as complexing agent and sodiumdodecylsulfate (SDS) as surfactant. Among the considered pH-values of 2,4 and 7 the pH 2 experiments allow a direct application of foam fractionation on acidic extracts from heavy metal contaminated soil. The experiments at pH 2 and pH 4 show better results than those at neutral pH. Although a simple device was used, a maximum enrichment factor of 13.8 and a minimum removal factor of 0.01 have been measured. The flotation with weak organic acids like citric acid (CA) and acetic acid (AA) show about 50–70% smaller enrichment factors than those acidified with hydrochloric acid. The dissolution and mixing of the reacting components as well as the concentration of the detergent and the gaseous volume flow can be regarded as basic parameters of foam fractionation. 相似文献
285.
Heavy rains occur in China frequently, which often bring us floods and serious disasters in the summer half-year. The meso-scale heavy rain parcels (MHRP) in the mid-latitude are usually developed in following cases:I.By the approaching, meeting and / or overlapping of different weather systems, when two or more different rainfall systems are getting to conjugate, some MHRPs could be developed, such as: 1) a new cold/warm front or squall line approaches an old front or squall, even when the old one is somewhat decrepit; 2) at the places where two or more synoptic systems with different characteristics are meeting together, such as the meeting of tropical cyclone with the cold airs coming from the mid- and / or high-latitudes, or the low latitude vortex meeting with the westerly trough; 3) at the intersections of some different weather systems, such as the intersection of drylines, squall lines or fronts moving from different directions; and 4) by the overlapping of rainfall parcels produced continuously 相似文献
286.
287.
利用常规观测资料、卫星云图、雷达、风廓线组网资料对2017年8月8日-9日天津地区局部大暴雨天气进行分析,得到以下结论:A、B两个中尺度雨团先后影响天津,A雨团持续了4个小时,雨强相对较大;B雨团持续了3个小时,雨强相对较小;对应有两个MCS,强降水发生在TBB低值中心偏向温度梯度最大的区域;降水回波的移动路径和强度特征存在差异,A雨团回波为自西北向东南方向移动的带状的高质心降水回波;B雨团回波自西南向东北方向移动,为低质心降水回波带状回波,高质心降水回波雨强高于低质心降水回波。新型探测资料有助于分析中尺度影响系统,判断对流系统的移动方向。用风廓线组网资料对比两个阶段降水的中尺度系统,A雨团为上冷下暖的高低空配置,B雨团降水出现在整层西南气流中,引导风的不同,导致回波的移动方向、天气剧烈程度的不同;变压梯度、温度梯度等环境因素对判断局地对流暴雨发生的环境条件有一定指示性。 相似文献
288.
利用1962—2018年华西地区301个气象台站秋季降水量资料和国家气候中心整理的130项气候系统指数,采用年际增量法建立了华西秋雨预测模型。首先通过相关分析挑选了4个与华西秋雨年际增量前3主模态密切相关的影响因子,进而采用多元线性回归方法进行建模,拟合时段和后报时段分别选为1962—1991年和1992—2018年。华西秋雨年际增量前3主模态累积值的预测模型通过了α=0.01的显著性水平检验,表明该模型具有较高的拟合预测能力。然后用相同的预测因子分别建立华西地区301个气象站点的华西秋雨年际增量预测模型,大部分模型都通过了显著性检验。用PS评分指标对预测效果进行检验,结果显示后报期年平均PS评分达74.5分。从空间分布来看后报期大部分站点的PS评分都超过60分,其中四川盆地南部、贵州东部和湖南西部等地超过80分。与华西各省和国家气候中心发布的近6年秋季降水预测PS评分进行比较,发现模型后报结果有显著优势。总体来看,用年际增量法建立的华西秋雨预测模型具有较高的预测技巧和实际应用价值。 相似文献
289.
"98.7"特大暴雨低涡的螺旋度和动能诊断分析 总被引:49,自引:26,他引:23
“98.7”特大暴雨过程与700hPa低涡切变线的强烈发展以及丰沛的水汽和强垂直运动密切相关。螺旋度的诊断结果揭示,与强暴雨区和切变线低涡相应的是一对符号相反而又紧邻的螺旋度带。它们的垂直结构是一对符号相反而又互伴的螺旋度柱;螺旋度及其诸分量的量级是相同的。这表明,垂直运动的水平切变和水平速度的垂直切变以及水平速度的水平切变对螺旋度有相同大小的员献,也意味着强垂直运动和低空急流对暴雨的发生和发展极其重要。动能的诊断结果显示。强动能区与暴雨区和低涡切变线有很好的对应关系,在中、低空的强动能中心也正是强降雨中心;动能最强的700hPa也是低涡切变线发展最强的层面。强动能及其强梯度区和强螺旋度区基本一致。表明强动能及其强梯度对螺旋度变率及其通量有重要贡献。 相似文献
290.