全文获取类型
收费全文 | 4399篇 |
免费 | 719篇 |
国内免费 | 667篇 |
专业分类
测绘学 | 44篇 |
大气科学 | 288篇 |
地球物理 | 1954篇 |
地质学 | 1426篇 |
海洋学 | 644篇 |
天文学 | 584篇 |
综合类 | 340篇 |
自然地理 | 505篇 |
出版年
2024年 | 12篇 |
2023年 | 41篇 |
2022年 | 116篇 |
2021年 | 142篇 |
2020年 | 141篇 |
2019年 | 142篇 |
2018年 | 141篇 |
2017年 | 151篇 |
2016年 | 137篇 |
2015年 | 144篇 |
2014年 | 209篇 |
2013年 | 220篇 |
2012年 | 195篇 |
2011年 | 179篇 |
2010年 | 199篇 |
2009年 | 345篇 |
2008年 | 331篇 |
2007年 | 315篇 |
2006年 | 276篇 |
2005年 | 251篇 |
2004年 | 238篇 |
2003年 | 226篇 |
2002年 | 164篇 |
2001年 | 151篇 |
2000年 | 228篇 |
1999年 | 189篇 |
1998年 | 173篇 |
1997年 | 135篇 |
1996年 | 124篇 |
1995年 | 98篇 |
1994年 | 79篇 |
1993年 | 63篇 |
1992年 | 65篇 |
1991年 | 44篇 |
1990年 | 20篇 |
1989年 | 26篇 |
1988年 | 13篇 |
1987年 | 14篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1979年 | 7篇 |
1978年 | 2篇 |
1954年 | 3篇 |
排序方式: 共有5785条查询结果,搜索用时 375 毫秒
371.
采用西藏测震台网记录的2008年1月—2018年12月谢通门区域定位地震,系统分析该区M_L1.5以上地震频度变化及与附近强震的对应关系,发现地震台站建设密度对谢通门地震窗监控能力影响较大,故从2008—2011年和2012年7月—2018年12月2个时段予以分析。分析发现,2012年7月开始,谢通门地震窗小震活动水平在每月20次范围内随机波动,当超过20次以上(含20次)即异常高值出现或结束后1.5年内,在半径100 km以内具有发生M_S 5.0以上地震的可能,在半径1 000 km以内具有发生M_S 6.5以上强震的可能。 相似文献
372.
373.
The possible influences of the increasing anthropogenic emissions in India on tropospheric ozone and OH 总被引:2,自引:0,他引:2
A 3-D chemical transport model (OSLO CTM2) is used to investigate the influences of the increasing anthropogenic emission in India. The model is capable of reproducing the observational results of the INDOEX experiment and the measurements in summer over India well. The model results show that when NOx and CO emissions in India are doubled, ozone concentration increases, and global average OH decreases a little. Under the effects of the Indian summer monsoon, NOx and CO in India are efficiently transported into the middle and upper troposphere by the upward current and the convective activities so that the NOx, CO, and ozone in the middle and upper troposphere significantly increase with the increasing NOx and CO emissions. These increases extensively influence a part of Asia, Africa, and Europe, and persist from June to September. 相似文献
374.
375.
北淮阳及其邻接区地壳稳定性研究 总被引:1,自引:1,他引:0
运用多学科、多技术相结合的研究方法,从现今构造应力场特征、现代地壳形变特征、主干断裂构造以及区域断裂活动性分析、新构造运动、地震活动、数值模拟等方面入手,对北淮阳及其邻接区地壳稳定性进行了全面而系统的研究,指出本区地震活动受走滑活动断裂控制,中、强地震集中于区内东南部和西北部NW向与NE向断裂交汇处;第四纪无大规模差异升降运动;数值模拟等综合分析表明,信阳地区的区域构造稳定性高,现代地壳形变量小,应力平缓,地震活动少且弱。 相似文献
376.
The heating of the solar corona has been a fundamental astrophysical issue for over sixty years. Over the last decade in particular, space-based solar observatories (Yohkoh, SOHO and TRACE) have revealed the complex and often subtle magnetic-field and plasma interactions throughout the solar atmosphere in unprecedented detail. It is now established that any energy release mechanism is magnetic in origin - the challenge posed is to determine what specific heat input is dominating in a given coronal feature throughout the solar cycle. This review outlines a range of possible magnetohydrodynamic (MHD) coronal heating theories, including MHD wave dissipation and MHD reconnection as well as the accumulating observational evidence for quasi-periodic oscillations and small-scale energy bursts occurring in the corona. Also, we describe current attempts to interpret plasma temperature, density and velocity diagnostics in the light of specific localised energy release. The progress in these investigations expected from future solar missions (Solar-B, STEREO, SDO and Solar Orbiter) is also assessed.Received: 6 February 2003, Published online: 14 November 2003
Correspondence to: R. W. Walsh 相似文献
377.
Groundwater surveys were performed by detailed(around 300 sites) grid-analysis of water temperature, pH, redox potential, electrical conductivity, 222Rn, alkalinity and by calculating the pCO2, throughout the Ciampino and Marino towns in the Alban Hills quiescent volcano (Central Italy). Following several episodes of dangerous CO2 exhalation from soils during the last 20 years and earlier ashistorically recorded, the work aimed at assessing the Natural Gas Hazard (NGH) including the indoor-Rn hazard. The NGH was defined as the probability of an area to become a site of poisonous peri-volcanic gas exhalations from soils to the lower atmosphere (comprising buildings). CO2 was found to be a ``carrier' for the other poisonous minor and in trace components (HsS, CH4, 222Rn, etc.). This assessment was performed by extrapolating in the aquifer CO2 and 222Rn conditions, and discriminating sectors where future CO2 flux in soils as well as indoor-Rn measurements have to be noted. A preliminary indoor-Rn survey was performed at about 200 sites. The highest values were found in the highest pCO2 and high 222Rn values in groundwater. This indicates convection and enhanced permeability in certain sectors of the main aquifer, i.e., along the bordering faults and inside the gas-trap of the Ciampino Horst., where ``continuous gas-phase micro-macro seepage mechanism' is invoked to explain the high peri-volcanic gases flux. 相似文献
378.
379.
380.