全文获取类型
收费全文 | 1405篇 |
免费 | 161篇 |
国内免费 | 174篇 |
专业分类
测绘学 | 58篇 |
大气科学 | 348篇 |
地球物理 | 208篇 |
地质学 | 140篇 |
海洋学 | 65篇 |
天文学 | 720篇 |
综合类 | 51篇 |
自然地理 | 150篇 |
出版年
2024年 | 3篇 |
2023年 | 18篇 |
2022年 | 18篇 |
2021年 | 30篇 |
2020年 | 25篇 |
2019年 | 29篇 |
2018年 | 28篇 |
2017年 | 27篇 |
2016年 | 25篇 |
2015年 | 46篇 |
2014年 | 57篇 |
2013年 | 66篇 |
2012年 | 68篇 |
2011年 | 53篇 |
2010年 | 49篇 |
2009年 | 83篇 |
2008年 | 82篇 |
2007年 | 90篇 |
2006年 | 81篇 |
2005年 | 87篇 |
2004年 | 57篇 |
2003年 | 73篇 |
2002年 | 79篇 |
2001年 | 59篇 |
2000年 | 95篇 |
1999年 | 88篇 |
1998年 | 51篇 |
1997年 | 37篇 |
1996年 | 37篇 |
1995年 | 47篇 |
1994年 | 41篇 |
1993年 | 16篇 |
1992年 | 16篇 |
1991年 | 14篇 |
1990年 | 10篇 |
1989年 | 14篇 |
1988年 | 12篇 |
1987年 | 10篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1982年 | 4篇 |
1981年 | 3篇 |
排序方式: 共有1740条查询结果,搜索用时 15 毫秒
951.
952.
对1970-1980年1AU附近太阳风的观测资料所进行的分析表明,60%的冕旒相关流和40%的CME相关云的流速都不大于350km/s;80%的流速不大于350km/s的低速风起源于冕旒,且除冕旒和CMEs外,看来还存在别的低速风日冕源区.有关冷风的分析表明,近80%的冷风的流速不大于350km/s,80%的冷风起源于冕旒;也有一小部分冷风既非起源于冕旒,也不起源于CMEs.低速风的11年变化显示,在太阳活动各位相,冕旒总是低速风的主要日冕源区.但是,极大位相时的冕旒宽度很可能大于极小和下降位相. 相似文献
953.
从全波段太阳直射辐射确定大气气溶胶光学厚度 I. 理论 总被引:3,自引:1,他引:3
本文提出了从全波段太阳直射辐射信息确定0.7μm波长大气柱气溶胶光学厚度的一种新方法。数值试验表明,对各类气溶胶谱分布,在水汽含量±0.2cm的误差、臭氧总量±0.1cm的误差、太阳直射辐射的±1%的观测误差以及太阳常数的±2%误差范围内,对小于0.1的0.7μm波长气溶胶光学厚度,它的解误差一般小于0.017,对大于0.1并小于0.6的光学厚度,它的解误差一般小于10%。 相似文献
954.
955.
太阳活动异常与降水和地面气温的关系 总被引:14,自引:0,他引:14
利用1951~2000年太阳10.7 cm射电流量、全国160站观测到的降水和气温距平资料,分析了太阳活动异常对中国夏季、冬季降水和气温的影响。结果表明:太阳活动强的年份,夏季南方、东北少雨,黄河中上游流域、黄淮地区以及长江中上游则多雨;冬季全国均多雨。北方(尤其是东北和新疆)冬季气温偏高,夏季气温偏低。太阳活动弱的年份,夏季华南及黄河以北多雨,而长江流域及以北到黄河中上游夏季则少雨;冬季全国均少雨,北方冬季气温偏低。进一步讨论了中国东北地区夏季降水与太阳活动的密切关系。 相似文献
956.
Space physics is a young discipline in Turkey. Since 1970 various national near-Earth space research activities and several
international collaborations have been conducted in Turkey and some of these are continuing. In May 2004 a four-week Graduate
Course on “Space and Atmospheric Physics I and II” was held at the Tübitak Feza Gürsey Institute in Istanbul, Turkey. This
paper explains the background behind this initiative, and gives an introduction to the topics that were covered during the
course, especially emphasizing how solar-terrestrial physics is applied to space weather. During the course the students,
in parallel with the lectures delivered, performed projects based on the curriculum, and using information available on the
Internet and in the literature. A resumé of their results concerning the well-known “space weather” event at the end of 2003
is given. 相似文献
957.
验算软弱下卧层强度时应注意的问题 总被引:1,自引:0,他引:1
针对《建筑地基基础设计规范》(GB 50007—2002)采用压力扩散角法验算软弱下卧层强度,介绍了工作中容易被忽视的地方,重点分析了扩散角的概念以及应用中对扩散角的取值应注意的问题。 相似文献
958.
Victor U. Chukwuma 《Acta Geophysica》2007,55(4):469-489
A study of the geomagnetic storm of July 13–14, 1982, and its ionospheric response is presented using the low-latitude magnetic
index, Dst, and interpreted using solar wind interplanetary data: proton number density, solar wind flow speed, interplanetary magnetic
field southward component B
Z
, and solar wind dynamic pressure. The F2 region structure response to the geomagnetic storm was studied using foF2 data obtained during the storm from a network of various ionosonde stations. Our results appear to show simultaneous abrupt
depletion of foF2 that occurred at all latitudes in both the East Asian and African/European longitudinal zone during the period: 18:00–19:00
UT on July 13 and is as result of an abrupt increase in the dynamic pressure between 16:00 and 17:00 UT. The dynamic pressure
increased from 3.21 to 28.07 nPa within an hour. The aforementioned abrupt depletion of foF2 simultaneously resulted in an intense negative storm with peak depletion of foF2 at about 19:00 at all the stations in the East Asian longitudinal zone. In the African/European longitudinal zone, this simultaneous
abrupt depletion of foF2 resulted in intense negative storm that occurred simultaneously at the low latitude stations with peak depletion at about
20:00 UT on July 13, while the resulting negative storm at the mid latitude stations recorded peak depletion of foF2 simultaneously at about 2:00 UT on July 14. The present results indicate that most of the stations in the three longitudinal
zones showed some level of simultaneity in the depletion of foF2 between 18:00 UT on July 13 and 2:00 UT on July 14. The depletion of foF2 during the main phase of the storm was especially strongly dependent on the solar wind dynamic pressure. 相似文献
959.
C. Lacombe C. Salem A. Mangeney J.-L. Steinberg M. Maksimovic J. M. Bosqued 《Annales Geophysicae》2000,18(8):852-865
The solar wind properties depend on , the heliomagnetic latitude with respect to the heliospheric current sheet (HCS), more than on the heliographic latitude. We analyse the wind properties observed by Wind at 1 AU during about 2.5 solar rotations in 1995, a period close to the last minimum of solar activity. To determine , we use a model of the HCS which we fit to the magnetic sector boundary crossings observed by Wind. We find that the solar wind properties mainly depend on the modulus ||. But they also depend on a local parameter, the total pressure (magnetic pressure plus electron and proton thermal pressure). Furthermore, whatever the total pressure, we observe that the plasma properties also depend on the time: the latitudinal gradients of the wind speed and of the proton temperature are not the same before and after the closest HCS crossing. This is a consequence of the dynamical stream interactions. In the low pressure wind, at low ||, we find a clear maximum of the density, a clear minimum of the wind speed and of the proton temperature, a weak minimum of the average magnetic field strength, a weak maximum of the average thermal pressure, and a weak maximum of the average factor. This overdense sheet is embedded in a density halo. The latitudinal thickness is about 5° for the overdense sheet, and 20° for the density halo. The HCS is thus wrapped in an overdense sheet surrounded by a halo, even in the non-compressed solar wind. In the high-pressure wind, the plasma properties are less well ordered as functions of the latitude than in the low-pressure wind; the minimum of the average speed is seen before the HCS crossing. The latitudinal thickness of the high-pressure region is about 20°. Our observations are qualitatively consistent with the numerical model of Pizzo for the deformation of the heliospheric current sheet and plasma sheet. 相似文献
960.
为解释著名的G矮星问题,提出银河系化学演化的三成分模型,即由银晕、厚盘和薄盘所构成的演化模型.相邻演化阶段间隔着一个快速坍缩过程.对不同星族成分的演化过程分别进行模拟,并在总体上得到一个太阳附近区域的G矮星丰度分布函数.检验了三种不同的模型:初始富化模型、比例生成模型和坍缩模型.利用最小二乘拟合得到最佳模型的参数.结果表明,太阳附近区域的化学演化受物质交换的影响较小,至少在银河系演化的晚期,可将太阳附近区域看作封闭系统.同时,单位质量中新合成的重元素比例对三种恒星成分可分别近似为常数,其差别则说明不同星族恒星的初始质量函数存在着显著差异. 相似文献