全文获取类型
收费全文 | 22756篇 |
免费 | 3384篇 |
国内免费 | 4129篇 |
专业分类
测绘学 | 1090篇 |
大气科学 | 4048篇 |
地球物理 | 6286篇 |
地质学 | 10065篇 |
海洋学 | 2940篇 |
天文学 | 1508篇 |
综合类 | 1753篇 |
自然地理 | 2579篇 |
出版年
2024年 | 67篇 |
2023年 | 294篇 |
2022年 | 758篇 |
2021年 | 896篇 |
2020年 | 737篇 |
2019年 | 834篇 |
2018年 | 977篇 |
2017年 | 933篇 |
2016年 | 1101篇 |
2015年 | 936篇 |
2014年 | 1091篇 |
2013年 | 1308篇 |
2012年 | 1101篇 |
2011年 | 1223篇 |
2010年 | 1227篇 |
2009年 | 1236篇 |
2008年 | 1037篇 |
2007年 | 1080篇 |
2006年 | 859篇 |
2005年 | 809篇 |
2004年 | 621篇 |
2003年 | 661篇 |
2002年 | 642篇 |
2001年 | 567篇 |
2000年 | 710篇 |
1999年 | 984篇 |
1998年 | 837篇 |
1997年 | 817篇 |
1996年 | 786篇 |
1995年 | 729篇 |
1994年 | 648篇 |
1993年 | 548篇 |
1992年 | 472篇 |
1991年 | 333篇 |
1990年 | 292篇 |
1989年 | 248篇 |
1988年 | 240篇 |
1987年 | 163篇 |
1986年 | 163篇 |
1985年 | 135篇 |
1984年 | 147篇 |
1983年 | 122篇 |
1982年 | 125篇 |
1981年 | 96篇 |
1980年 | 108篇 |
1979年 | 87篇 |
1978年 | 70篇 |
1976年 | 56篇 |
1975年 | 58篇 |
1973年 | 51篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
41.
陈伦炯所著《海国闻见录》是我国十八世纪的地理著作,对我国后世海岸地理、世界地理的研究影响颇大,对今天的海防建设和沿海港口城市的建设也有参考意义. 陈伦炯,字资斋,福建省泉州府同安县(今厦门市同安县)人.生于清朝康熙、雍正年间.父陈昂,曾随靖海侯施琅远征澎湖、台湾.并受施琅之命,“出入东西洋,招访郑氏(郑成功)有无遁匿遗人”[1]历时五载.康熙五年(公元1666年),官至广东副都统.由于他长期“往来外洋,……所至必察其面势,辨其风潮”,因此,“尽识共风潮土浴,地形险易”[2]. 相似文献
42.
Philip B. James 《Icarus》1985,64(2):249-264
The Martian CO2 cycle, which includes the seasonal condensation and subsequent sublimation of up to 30% of the planet's atmosphere, produces meridional winds due to the consequent mass flux of CO2. These winds currently display strong seasonal and hemispheric asymmetries due to the large asymmetries in the distribution of insolation on Mars. It is proposed that asymmetric meridional advection of water vapor on the planet due to these CO2 condensation winds is capable of explaining the observed dessication of Mars' south polar region at the current time. A simple model for water vapor transport is used to verify this hypothesis and to speculate on the effects of changes in orbital parameters on the seasonal water cycle. 相似文献
43.
Hui-Rong Ji Qi-Jun Pu Yi-Hua Yan Yu-Ying Liu Zhi-Jun Chen Cheng-Ming Tan Cong-Ling Cheng De-Bang Lao Shu-Ke Li Zhi-Qiang Wang Min-Hong Yu Jian-Nong Liu Li-Kang Zhang Ji-Yong Gao National Astronomical Observatories Chinese Academy of Sciences Beijing Hebei Semiconductor Research Institute Shijiazhuang 《中国天文和天体物理学报》2005,5(4):433-441
An improved Solar Radio Spectrometer working at 1.10-2.06 GHz with much improved spectral and temporal resolution, has been accomplished by the National Astronomical Observatories and Hebei Semiconductor Research Institute, based on an old spectrometer at 1-2 GHz. The new spectrometer has a spectral resolution of 4 MHz and a temporal resolution of 5ms, with an instantaneous detectable range from 0.02 to 10 times of the quiet Sun flux. It can measure both left and right circular polarization with an accuracy of 10% in degree of polarization. Some results of preliminary observations that could not be recorded by the old spectrometer at 1-2 GHz are presented. 相似文献
44.
Based on the CN and C2 comae isophotes for two comets (1961 IX and 1970 16) given by Rahe et al. and the relevant theory of physical chemistry, we have deduced the distributions of the CN and C2 modecules in the coma, their scale heights and mean lifetimes. The results favour the viewpoint that HCN is the parent of CN, and that C2H2 is the parent of C2. 相似文献
45.
CHEN Bing-lu ZHANG Yun-ni CHEN Xin-geng WANG Zhi-gang YANG Guang-xing 《中国地理科学(英文版)》2001,11(2):155-162
1 HYDROLOGIC FEATURES Lingdingyang Estuary, located at the middle south of Guangdong Province, is a bell-shaped estuary with a north-south direction. Its area is about 2100km2. The north of Qi′ao Island and Inner-Lingding Island, and the south of Humen are grouped as Neilingdingyang Estuary, having an area of 1041km2. Affected by topography, runoff and tide, its dynamic condition is very complicated. Different water areas have different hydrologic features. The topography under … 相似文献
46.
IntroductionThe area of eastern Liaoning is an importantmetal and nonmetal metallogenetic district in China,and the Liaohe group is one of the most importantstrata that hosts Pb, Zn, Au, B and Mg etcstratabound deposits. Up to now many geo1ogistssuch as Z… 相似文献
47.
James F. Kasting 《Astrophysics and Space Science》1996,241(1):3-24
The goal of this conference is to consider whether it is possible within the next few decades to detect Earth-like planets around other stars using telescopes or interferometers on the ground or in space. Implicit in the term “Earth-like” is the idea that such planets might be habitable by Earth-like organisms, or that they might actually be inhabited. Here, I shall address two questions from the standpoint of planetary atmosphere evolution. First, what are the chances that habitable planets exist around other stars? And, second, if inhabited planets exist, what would be the best way to detect them? 相似文献
48.
使用中国科学院紫金山天文台青海站13.7米射电望远镜于1996年12月至1997年1月对富碳拱星IRC 10216和CIT6的CO J=1-0跃迁(115GHz)进行了观测。在观测谱线的基础上得到了IRC 10216的视向速度和膨胀速度分别为一26.1km s~(-1)和14.8km s~(-1),CIT6的视向速度和膨胀速度分别为0.6km s~(-1)和13.8kms~(-1)。并对望远镜的射束及指向精度进行了研究。 相似文献
49.
50.
We present the astrophysical conditions necessary for the ejection of shielded microorganisms from a solar system and the biological conditions involving ultraviolet and ionizing radiations to which they are subjected in space. The radiation dose for both UV and ionizing radiation from the host star, the destination star and interstellar space is calculated for three different micro-organisms. The time of transport and the survival of the micro-organisms are strongly dependent on the composition and thickness of any mantle encasing the micro-organism and on the mass/luminosity ratio of the two stars. The maximum size of grains that can be ejected from the vicinity of one solar mass main sequence and red giant stars ranges from 0.65-0.35µm and 2.1-1.2µm respectively, for a reasonable range of densities. We conclude that unshielded known micro-organisms are immediately killed by ultraviolet radiation, and that an ice mantle does not provide sufficient shielding for either type of star. However, micro-organisms shielded by a carbonaceous thin-film mantle can be ejected from the vicinity of a one solar-mass red-giant star, and such micro-organisms have a high probability of surviving damage from the ultraviolet and ionizing radiations to which they are exposed. 相似文献