全文获取类型
收费全文 | 557篇 |
免费 | 129篇 |
国内免费 | 125篇 |
专业分类
测绘学 | 63篇 |
大气科学 | 97篇 |
地球物理 | 102篇 |
地质学 | 275篇 |
海洋学 | 160篇 |
天文学 | 1篇 |
综合类 | 46篇 |
自然地理 | 67篇 |
出版年
2024年 | 6篇 |
2023年 | 26篇 |
2022年 | 26篇 |
2021年 | 26篇 |
2020年 | 25篇 |
2019年 | 31篇 |
2018年 | 45篇 |
2017年 | 23篇 |
2016年 | 21篇 |
2015年 | 26篇 |
2014年 | 45篇 |
2013年 | 40篇 |
2012年 | 37篇 |
2011年 | 36篇 |
2010年 | 39篇 |
2009年 | 34篇 |
2008年 | 37篇 |
2007年 | 44篇 |
2006年 | 37篇 |
2005年 | 34篇 |
2004年 | 34篇 |
2003年 | 24篇 |
2002年 | 12篇 |
2001年 | 7篇 |
2000年 | 18篇 |
1999年 | 14篇 |
1998年 | 17篇 |
1997年 | 11篇 |
1996年 | 7篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1987年 | 1篇 |
1982年 | 2篇 |
排序方式: 共有811条查询结果,搜索用时 15 毫秒
131.
In this paper,Changli station in Hebei Province was taken as an example,in which the minute data of geomagnetic Z component was used to analyze the spectral values of its main frequencies during normal time,geomagnetic storm time and low point displacement time interval respectively. After fitting of ten high spectral values to loga-rithmic functions,it is found that,by using same length of data,the spectral values at geomagnetic storm time in-crease apparently compared with those at normal time,especially at the high frequency segment. While low point displacement occurred,the spectral values at high frequency are approximate to those at normal time,but at period above 4 hours they are mostly lower than those at normal time. Comparison of accumulating of some FFT results at low point displacement and normal time shows that,spectral values at periods of 8.5 and 13.7 hours increase at low point displacement time relative to those at normal time. Compared with the images of Ne observed at DE-METER satellite,it is illustrated that the occurrence of geomagnetic low point displacement is well corresponding with the increase of Ne in ionosphere. Finally it was discussed about those spectral features and the occurrence mechanism of geomagnetic low point displacement. 相似文献
132.
53 pollen traps and surface samples were collected in order to detect the characteristics of pollen assemblages and their
relationships with vegetation and climate in 16 forest communities located in 10 mountains in northern China. The results
show that 72% of the pollen taxa (80 taxa) are the same between the traps and the surface samples. The dominant taxa in the
plant communities are consistent with the main pollen taxa in the pollen assemblages at the same sites. In Pinus plant communities, both Pinus pollen influx and concentration are higher, indicating the high pollen productivity and good pollen preservation ability
of Pinus. In Picea and Abies plant communities, Picea and Abies have lower pollen influxes but higher concentrations, suggesting their low pollen productivities but better pollen preservation
abilities. In Betula and Quercus plant communities, Betula and Quercus have higher pollen influxes but lower concentrations, revealing their high pollen productivities but poor pollen preservation
abilities. The study of relationships between pollen and vegetation with discriminant analysis shows that pollen assemblages
from both trap and surface samples can reflect the characteristics of different communities and distinguish different ecological
areas, but surface samples can reflect the dominant components of communities much better than the traps. The study on correlations
between pollen assemblages and climate with DCCA reveals that significant correlations exist between pollen assemblages and
mean temperature of the coldest month (r = 0.84 for trap samples, r = 0.72 for surface samples), and then annual mean precipitation
(r = 0.73 for trap samples, r = 0.71 for surface samples). 相似文献
133.
134.
吉林中部平原区地下水温动态变化影响因素的关联度分析 总被引:6,自引:0,他引:6
以吉林中部平原区为例,分析了孔隙潜水、孔隙承压水以及白垩系孔隙裂隙承压水温度的多年变化特征,并采用灰色关联度分析方法,确定了各含水层地下水温度与地下水埋深、气温、降水量之间的关联性,分析了影响其变化的主要因素。结果表明,对于3组含水层,从20世纪80年代初至2001年的近20年间,地下水温度都有不同程度的上升。对于孔隙潜水和孔隙承压水,地下水温度呈上升变化的本质原因是全球气候逐年变暖,而地下水活动和大气降水的增强起到了促进作用,特别是对孔隙承压水温度的上升作用更加明显;对于白垩系孔隙裂隙承压水,其温度呈上升变化则主要是由该含水层被普遍超采所引起的。 相似文献
135.
136.
绘制隧洞地质展示图是施工过程中客观反映洞室围岩地质条件的有效方法,但由于其表示的信息较简单且采集不便,难以进行深入的空间地质信息分析。应用AutoCAD内嵌语言AutoCAD,编制和于切制横剖面和高程平切面图的程序,供AutoCAD调用。在洞群区,分别在各洞室切制统一的横剖面图和其一高程的平切面图,构成洞群区三维空间地质信息系统的模型,为进一步的空间分析提供依据。 相似文献
137.
138.
徐淮地区镁铁质岩石捕虏体单斜辉石中石榴石和石英的出溶 总被引:7,自引:0,他引:7
徐淮地区早侏罗世侵入杂岩中榴辉岩,石榴辉石岩和单斜辉石岩捕虏体单斜辉石中可以观察丰富的出溶石英针和石榴石,黝帘石及角闪石的出溶叶片,榴辉岩中出溶石英针的绿辉石核部比其边部相对富含FeO和MgO,贫SiO2,Al2O3和CaO。在石榴辉石岩和单斜辉石岩捕虏体中具有出溶石榴石的单斜辉石。从靠近出溶石榴石的一侧向其核部,Al2O3,Na2O和TiO2含量降低,MgO,SiO2和CaO含量增加,单斜辉石中定向石英针的出溶表明曾经存在有超高压条件下(≥25×10^8Pa)稳定的过硅质绿辉石。单斜辉石中出溶石榴石表明温压条件的降低可能是引起出溶的一个主要原因,捕虏体中的矿物组合和岩相学特征表明它们曾经遭受了榴辉岩相和角闪岩相退化变质作用,这与因压力和温度降低引起矿物出溶的结果相吻合。 相似文献
139.
140.