全文获取类型
收费全文 | 13841篇 |
免费 | 3509篇 |
国内免费 | 3385篇 |
专业分类
测绘学 | 515篇 |
大气科学 | 403篇 |
地球物理 | 1521篇 |
地质学 | 10083篇 |
海洋学 | 1450篇 |
天文学 | 5558篇 |
综合类 | 563篇 |
自然地理 | 642篇 |
出版年
2024年 | 41篇 |
2023年 | 114篇 |
2022年 | 376篇 |
2021年 | 500篇 |
2020年 | 531篇 |
2019年 | 598篇 |
2018年 | 505篇 |
2017年 | 489篇 |
2016年 | 574篇 |
2015年 | 625篇 |
2014年 | 939篇 |
2013年 | 965篇 |
2012年 | 1002篇 |
2011年 | 1113篇 |
2010年 | 1130篇 |
2009年 | 1488篇 |
2008年 | 1295篇 |
2007年 | 1207篇 |
2006年 | 1167篇 |
2005年 | 999篇 |
2004年 | 877篇 |
2003年 | 736篇 |
2002年 | 590篇 |
2001年 | 532篇 |
2000年 | 486篇 |
1999年 | 458篇 |
1998年 | 323篇 |
1997年 | 175篇 |
1996年 | 167篇 |
1995年 | 113篇 |
1994年 | 138篇 |
1993年 | 112篇 |
1992年 | 57篇 |
1991年 | 49篇 |
1990年 | 43篇 |
1989年 | 25篇 |
1988年 | 33篇 |
1987年 | 7篇 |
1986年 | 23篇 |
1985年 | 29篇 |
1984年 | 22篇 |
1983年 | 17篇 |
1982年 | 15篇 |
1981年 | 6篇 |
1980年 | 11篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 17篇 |
1877年 | 1篇 |
1875年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
1.
2017年精河MS6.6地震震前,尼勒克、巴伦台和小泉沟台钻孔应变仪记录到显著的应变变化,经现场落实确认,异常是可靠的。根据这3个台的记录资料计算相对应变的变化,结果表明,地震前最大(小)主应变大小和方向分别出现明显加速和急剧偏转变化。此外还发现,相对应变场异常期间主方向与震源机制解P轴方位较为一致。 相似文献
2.
利用鄂尔多斯地块及其周缘1970~2014年的垂直形变速率场资料,借助负位错反演研究该区域长期应变积累。结果表明,地块东北缘山西断陷带中北段年均能量积累增量、剪应力强度都较高,西南缘六盘山断裂与渭河断裂西段次之;山西断陷带中南段至晋陕交界处年均剪应力强度较高且显示一定程度的能量积累;西秦岭构造区尤其西秦岭北缘断裂西段、晋冀蒙交界区也反映一定程度的能量积累特性。 相似文献
3.
采用香港11个GPS测站的观测资料进行1 h、2 h、3 h和4h静态PPP解算,获得4组PPP坐标序列,利用调和分析求取11个测站处8个主要分潮的负荷位移参数(振幅和相位),将其与海潮模型计算的负荷位移参数进行对比,并比较分析PPP反演值与海潮模型值改正海潮负荷信号的效果。结果表明,垂直和水平方向上,不同PPP结果反演8个分潮的负荷位移分别具有约5 mm和7 mm的差异;PPP反演8个分潮垂向负荷位移优于全球海潮模型,但水平方向上的反演效果稍弱。 相似文献
4.
Pinus taiwanensis is a species endemic to China. This study selected four typical plots of Pinus taiwanensis in the natural secondary forest around Macheng City, in order to reveal the characteristics of and the relationships between different diameter classes (determined based on the diameter at breast height or DBH), forest densities and species diversity, as well as the similarities of species diversity of different plots within the community. The result showed that Pinus taiwanensis was the dominant species in the community. The ratio of Pinus taiwanensis trees of diameter class IV reached a peak of 19.46% of the total followed by diameter class VII at 18.92%. The study recorded 156 species of vascular plants from 130 genera of 71 families; Pinus taiwanensis was the dominant species in the community. When the forest density was 1200 trees ha -1 with the largest average diameter of DBH=36.779±4.444 cm, the diversity (Shannon index H'=1.6716) and the evenness (Pielou index E=0.6727) of the tree layer was the highest. When the forest density reached 1525 trees ha -1 with the lowest average diameter of DBH=18.957±5.141 cm, the richness (Dma=5.4308), the diversity (H'=2.9612) and the evenness (E=0.8985) of all shrub layers climbed to the maximum. When the forest density was 1325 trees ha -1, the richness (Dma=5.8132), the diversity (H'=3.0697) and the evenness (E=0.9025) of all herb layers peaked. In terms of vertical structure, the average diversity indexes were herb layer>shrub layer>tree layer. High canopy density weakened light intensity in the community, causing a reduction in the species diversities of herbs and shrubs. The average similarity coefficient between the sample plots was 0.3356, which was at the medium dissimilarity level. External disturbances and improper management were major contributors to the low species diversity of the community. The implementation of scientific management measures is urgently needed to optimize the forest structures of Pinus taiwanensis, create a benign community environment, and promote species diversities and establish a stable forest community structure. 相似文献
5.
《Astroparticle Physics》2002,16(4):183-386
Frequency distributions of local muon densities in high-energy extensive air showers (EAS) are presented as signature of the primary cosmic ray energy spectrum in the knee region. Together with the gross shower variables like shower core position, angle of incidence, and the shower sizes, the KASCADE experiment is able to measure local muon densities for two different muon energy thresholds. The spectra have been reconstructed for various core distances, as well as for particular subsamples, classified on the basis of the shower size ratio Nμ/Ne. The measured density spectra of the total sample exhibit clear kinks reflecting the knee of the primary energy spectrum. While relatively sharp changes of the slopes are observed in the spectrum of EAS with small values of the shower size ratio, no such feature is detected at EAS of large Nμ/Ne ratio in the energy range of 1–10 PeV. Comparing the spectra for various thresholds and core distances with detailed Monte Carlo simulations the validity of EAS simulations is discussed. 相似文献
6.
7.
8.
9.
10.