全文获取类型
收费全文 | 324篇 |
免费 | 83篇 |
国内免费 | 156篇 |
专业分类
测绘学 | 35篇 |
大气科学 | 68篇 |
地球物理 | 71篇 |
地质学 | 232篇 |
海洋学 | 71篇 |
天文学 | 2篇 |
综合类 | 56篇 |
自然地理 | 28篇 |
出版年
2024年 | 2篇 |
2023年 | 8篇 |
2022年 | 14篇 |
2021年 | 12篇 |
2020年 | 23篇 |
2019年 | 23篇 |
2018年 | 9篇 |
2017年 | 13篇 |
2016年 | 17篇 |
2015年 | 17篇 |
2014年 | 17篇 |
2013年 | 21篇 |
2012年 | 35篇 |
2011年 | 33篇 |
2010年 | 28篇 |
2009年 | 21篇 |
2008年 | 28篇 |
2007年 | 23篇 |
2006年 | 36篇 |
2005年 | 27篇 |
2004年 | 34篇 |
2003年 | 19篇 |
2002年 | 26篇 |
2001年 | 22篇 |
2000年 | 18篇 |
1999年 | 9篇 |
1998年 | 6篇 |
1997年 | 7篇 |
1996年 | 4篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1986年 | 2篇 |
1984年 | 2篇 |
排序方式: 共有563条查询结果,搜索用时 15 毫秒
221.
222.
南海北部ODP1148站中新世以来的碳酸盐含量变化及其古环境意义 总被引:13,自引:0,他引:13
对南海北部 ODP 114 8站采自孔深 4 6 5 m以上的 170 0个沉积物样品 ,测定了 Ca CO3含量、Ca CO3堆积速率、非钙质堆积速率、浮游有孔虫丰度、粗组分百分含量 (>6 3μm)、浮游有孔虫破壳率和底栖有孔虫在有孔虫全群中的百分含量。碳酸盐百分含量和碳酸盐堆积速率自 2 4 Ma以来的变化呈现逐步下降的趋势 ,但在 2 4 .0~ 15 .8、14 .2~ 11.6、10 .6~ 4 .8和 3.4~ 0 Ma四个时期具有高碳酸盐生产力 ,其中 10 .6~ 4 .8Ma的高生产力与印度洋和太平洋中新世晚期和上新世早期的“生物勃发”相对应。非钙质和碳酸盐两者堆积速率变化趋势在总体上相似 ,反映了陆源物质输入对碳酸盐生产力的影响。 3.4 Ma后非钙质堆积速率的大幅度增长主要与青藏高原和台湾岛的隆起有关 ,它们也是上新世晚期和第四纪 Ca CO3百分含量显著下降的主要原因。 2 4 Ma以来南海北部碳酸盐的保存逐渐变弱 ,而碳酸盐溶解作用逐渐增强 ,在 15 .8~ 14 .2、11.6~ 10 .6和 4 .8~ 3.4 Ma存在 3个显著的碳酸盐溶解事件 ,其中 11.6~ 10 .6 Ma的溶解事件与赤道太平洋和加勒比海的中—晚中新世“碳酸盐崩溃”事件相当 ,说明该事件具更广泛的全球影响 相似文献
223.
This paper, the second part of further analyses of the structure of the typhoon, mainly discusses the distributions of temperature and moisture fields of typhoon No. 7507. The result has shown that the typhoon developed from the warm-core disturbance. The height of maximum warming is highest (300 to 250 hPa) during the mature stage. There is a dry layer capping the typhoon during the initial stage. Once the typhoon rapidly developed, the dry layer was destroyed. A deep saturation layer eventually occurred in the central region of the typhoon. Meanwhile, the dry air from the China main continuously intruded into the outer region in the western and northwestern parts of the typhoon.The initial eyewall of the typhoon sloped outward with increasing height, and then became nearly vertical below 12 km level. This was closely associated with convective activity. The convective instability had been mostly released during the growing stage of the typhoon and stratification rapidly tended to moist neutralization. 相似文献
224.
225.
226.
在人类活动和气候变化的影响下,汾河入黄径流量锐减,加剧了山西省水资源短缺的现状,并引起生态环境的恶化,同时入黄径流量的减少致使黄河干流流量的减少,加剧了黄河中下游的水资源短缺。以汾河流域为研究区,采用水文变异诊断系统分析了汾河流域入黄控制站河津站1956-2012年的径流情势的变化情况,入黄径流有显著下降的趋势,并且在1971年左右发生了突变减少。然后采用多元分析方法,分析造成径流突变减少的影响因子,其径流受到降水量、潜在蒸散发量和人类活动引起的流域属性改变的影响。随后采用Budyko公式分析其敏感性,在相对较长的时间尺度上,气候变化对径流的影响比人类活动更加敏感。最后采用累计斜率法分析上述参数对径流的影响比率,得到径流量受降水量、潜在蒸散发量和流域属性的影响比率分别为16.29%、-4.86%和88.57%。 相似文献
227.
The interdecadal change in the interannual variability of the South China Sea summer monsoon(SCSSM) intensity and its mechanism are investigated in this study. The interannual variability of the low-level circulation of the SCSSM has experienced a significant interdecadal enhancement around the end of the 1980s, which may be attributed to the interdecadal changes in the evolution of the tropical Indo-Pacific sea surface temperature(SST) anomalies and their impacts on the SCSSM. From 1961 to 1989... 相似文献
228.
This paper tests the idea of substituting the atmospheric observations with atmospheric reanalysis when setting up a coupled data assimilation system.The paper focuses on the quantification of the effects on the oceanic analysis resulted from this substitution and designs four different assimilation schemes for such a substitution.A coupled Lorenz96 system is constructed and an ensemble Kalman filter is adopted.The atmospheric reanalysis and oceanic observations are assimilated into the system and the analysis quality is compared to a benchmark experiment where both atmospheric and oceanic observations are assimilated.Four schemes are designed for assimilating the reanalysis and they differ in the generation of the perturbed observation ensemble and the representation of the error covariance matrix.The results show that when the reanalysis is assimilated directly as independent observations,the root-mean-square error increase of oceanic analysis relative to the benchmark is less than 16%in the perfect model framework;in the biased model case,the increase is less than 22%.This result is robust with sufficient ensemble size and reasonable atmospheric observation quality(e.g.,frequency,noisiness,and density).If the observation is overly noisy,infrequent,sparse,or the ensemble size is insufficiently small,the analysis deterioration caused by the substitution is less severe since the analysis quality of the benchmark also deteriorates significantly due to worse observations and undersampling.The results from different assimilation schemes highlight the importance of two factors:accurate representation of the error covariance of the reanalysis and the temporal coherence along each ensemble member,which are crucial for the analysis quality of the substitution experiment. 相似文献
229.
通过对桩端置于含泥圆砾卵石层超短静压预制桩桩底注浆及注浆前后静载试验,分析了桩竖向极限承载力的提高机理。试验表明,桩底注浆可较大幅度地提高以砂卵石为持力层的静压预制桩的竖向承载力。 相似文献
230.