全文获取类型
收费全文 | 5061篇 |
免费 | 1004篇 |
国内免费 | 720篇 |
专业分类
测绘学 | 824篇 |
大气科学 | 253篇 |
地球物理 | 861篇 |
地质学 | 1894篇 |
海洋学 | 177篇 |
天文学 | 94篇 |
综合类 | 1130篇 |
自然地理 | 1552篇 |
出版年
2024年 | 10篇 |
2023年 | 65篇 |
2022年 | 188篇 |
2021年 | 194篇 |
2020年 | 208篇 |
2019年 | 224篇 |
2018年 | 181篇 |
2017年 | 256篇 |
2016年 | 237篇 |
2015年 | 271篇 |
2014年 | 352篇 |
2013年 | 324篇 |
2012年 | 403篇 |
2011年 | 451篇 |
2010年 | 373篇 |
2009年 | 272篇 |
2008年 | 282篇 |
2007年 | 314篇 |
2006年 | 329篇 |
2005年 | 297篇 |
2004年 | 285篇 |
2003年 | 236篇 |
2002年 | 167篇 |
2001年 | 172篇 |
2000年 | 119篇 |
1999年 | 116篇 |
1998年 | 80篇 |
1997年 | 92篇 |
1996年 | 52篇 |
1995年 | 60篇 |
1994年 | 49篇 |
1993年 | 28篇 |
1992年 | 23篇 |
1991年 | 16篇 |
1990年 | 11篇 |
1989年 | 11篇 |
1988年 | 12篇 |
1987年 | 8篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1979年 | 1篇 |
排序方式: 共有6785条查询结果,搜索用时 171 毫秒
11.
12.
M. A. Smith 《第四纪科学杂志》2009,24(7):747-760
Puritjarra rock shelter provides a long record of late Quaternary vegetation in the Australian arid zone. Analysis of the sedimentary history of this rock shelter is combined with reanalysis of charcoal and phytolith records to provide a first‐order picture of changing landscapes in western Central Australia. These show a landscape responding to increasing aridity from 45 ka with deflation of clay‐rich red palaeosols (<45 ka) and sharp declines in grassland and other vegetation at 40–36 ka, and at the beginning of the Last Glacial Maximum (LGM) (24 ka). Vegetation in the catchment of the rock shelter recovered after 15 ka with expansion of both acacia woodland and spinifex grasslands, registering stronger summer rainfall in the interior of the continent. By 8.3 ka re‐vegetation of local palaeosols and dunes had choked off sediment supply to the rock shelter and the character of the sediments changed abruptly. Poaceae values peaked at 5.8 ka, suggesting the early–mid Holocene climatic optimum in Central Australia is bracketed between 8.3 and 5.8 ka. Local vegetation was disrupted in the late Holocene with a sharp decline in Poaceae at 3.8 ka, coinciding with an abrupt intensification of ENSO. Local grasslands recovered over the next two millennia and by 1.5 ka the modern vegetation appears to have become established. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
13.
倪万魁 《地球科学与环境学报》1996,(3)
本文根据大量的调查资料,采用多指标评判打分法对铜川市区滑坡逐一进行了危险性综合评价,旨在为该区滑坡的预测与防治提供可靠的依据。 相似文献
14.
松辽盆地中生代沉积基准面变化研究 总被引:6,自引:0,他引:6
利用地质资料研究来恢复沉积基准面变化。首先根据沉积物的分布规律、沉积构造、古生物组合及古生态、自生矿物和波基面等特征来获得古水深,然后利用对地层做脱水压实校正获得沉积物原始厚度。对湖盆地区古水深和沉积物原始厚度累加起来就可得到沉积基准面变化曲线。沉积基准面变化曲线为在松辽盆地中进行地层对比提供了依据。 相似文献
15.
16.
17.
18.
Variables related to urban park awareness are identified and methods for relaxing assumptions of perfect information in park use models are discussed. Park awareness is related to park characteristics (age and degree of development of the park), population characteristics (race, age, length of residence, recreation participation), and distance. Park attributes are stronger predictors of both park awareness and use than is distance. These findings parallel similar research on the cognitive aspects of shopping decisions. 相似文献
19.
Results of a single group participating in an international experiment are analyzed. The experiment served to verify computational predictions of the ground-motion variations due to near-surface geological effects at a site established for that purpose by the California Department of Conservation. Based on an acceleration record at a rock location, and geotechnical model of medium, records at the other locations of a nearby sedimentary deposit were predicted. A 2-D finite-difference sensitivity analysis suggested that the lateral wave-propagation effects are negligibly small, and locally 1-D computations are sufficient for the present site. Those computations are compared with observations not available to the authors during the blind prediction. Peak accelerations, peak velocities and RMS accelerations were predicted with errors less than 159%, 114% and 62%, respectively. Maxima of the response spectra were fitted within a factor of 2. The predicted and observed Husid's plots (i.e., the normalized cumulative plots of the acceleration squared) have the correlation coefficients 0.98. The detected misfits do not show any simple relation to the instrument location, component, frequency, or time. 相似文献
20.