全文获取类型
收费全文 | 725篇 |
免费 | 163篇 |
国内免费 | 352篇 |
专业分类
测绘学 | 82篇 |
大气科学 | 194篇 |
地球物理 | 139篇 |
地质学 | 483篇 |
海洋学 | 152篇 |
天文学 | 39篇 |
综合类 | 91篇 |
自然地理 | 60篇 |
出版年
2024年 | 13篇 |
2023年 | 48篇 |
2022年 | 43篇 |
2021年 | 49篇 |
2020年 | 30篇 |
2019年 | 37篇 |
2018年 | 41篇 |
2017年 | 38篇 |
2016年 | 33篇 |
2015年 | 51篇 |
2014年 | 63篇 |
2013年 | 62篇 |
2012年 | 45篇 |
2011年 | 50篇 |
2010年 | 52篇 |
2009年 | 33篇 |
2008年 | 39篇 |
2007年 | 39篇 |
2006年 | 40篇 |
2005年 | 45篇 |
2004年 | 39篇 |
2003年 | 25篇 |
2002年 | 36篇 |
2001年 | 35篇 |
2000年 | 44篇 |
1999年 | 38篇 |
1998年 | 28篇 |
1997年 | 24篇 |
1996年 | 23篇 |
1995年 | 19篇 |
1994年 | 10篇 |
1993年 | 4篇 |
1992年 | 7篇 |
1991年 | 17篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1964年 | 1篇 |
1960年 | 1篇 |
排序方式: 共有1240条查询结果,搜索用时 15 毫秒
91.
Zhao-Hua Xie Hong Dai Jian-Ming Hao Lei-Ming Du Xiong Zhang Physics Department Yunnan Normal University Kunming Yunnan Astrophysics Center Yunnan University Kunming Graduate School of Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2007,(2)
The physics behind the spectral energy distribution (SED) of blazars remains open. We assembled 36 blazars to tackle the factors that control their SED. Now, many blazar spec- tra have the "double hump" feature in the radio and far-IR frequencies. For these a parameter, , is created to characterize the behavior of the SED. We found a significant correlation be- tween the broad-line luminosity (LBLR) and . Because LBLR is an indicator of the accreting power of the source in blazars, we derived a linear correlation, ∝ M˙1/3.18, which suggests that the SED of blazars may depend on the accretion rate, like that of BL Lac objects. We also found a significant correlation between ■ and for a sample of 11 blazars (out of one of 36) with available black hole masses. This implies the Eddington accretion ratio may influence the shape of the SED of blazars. 相似文献
92.
为改变目前GPS观测数据邮递的数据传递方式,研究用公用电话网进行GPS观测数据传递的传输技术。通过实验以及联调证明此项传输技术不仅传输速度高,而且传输准确,使用方便,系统功能强,还可服务于工程监测、自然灾害防御、地震前兆监测等需数据通信的领域 相似文献
93.
94.
<正>The northeast Tibetan plateau contains important information on the northeastward growth of the Tibetan plateau.It is bounded by the Ordos Block to the east,the Alxa Block to the north,and the Tibetan Plateau to thesouth(inset in Fig.1;Tapponnier et al.,2001),and has undergone complex intracontinental deformation during the Cenozoic.In this region,the northeast-convex arcuate structures developed northeastward,and are composed of 相似文献
95.
<正>Unlike traditional resources,mud shale has the characteristics of low porosity,low permeability,small pore structure,nanoscale pore as the main body.The microscopic pore structures of mud shale can not only influence the occurrence state of shale gas and gas content,but also influence the hydrocarbon expulsion efficiency of source rocks,which makes the study of shale gas reservoir 相似文献
96.
Simulation of the Direct Radiative Effect of Mineral Dust and Sea Salt Aerosols in a Doubled Carbon Dioxide Climate 下载免费PDF全文
The authors examine the equilibrium climatic response to the direct radiative effect(DRE)of mineral dust and sea salt aerosols in a doubled-CO2climate with two-way coupling of aerosol-climate interactions.In response to the drier and windier conditions,dust emissions increase by 26%in the Sahara Desert and by 18%on the global scale relative to present day.Sea salt emissions increase in high latitudes(60°)but decrease in middle latitudes(30°–60°)of both hemispheres due to the poleward shift of westerlies,leading to a 3%decrease in global emissions.The burdens of dust and sea salt increase by 31%and 7%respectively,because reductions in rainfall over the tropical oceans increase the lifetime of particles in the warmer climate.The higher aerosol loading in the doubled-CO2climate reinforces aerosol DRE by0.2 W m 2,leading to an additional cooling of 0.1°C at the surface compared with the climatic effects of aerosols in present day.The additional cooling from changes in natural aerosols compensates for up to 15%of the regional warming induced by doubled CO2. 相似文献
97.
WANG Donghai DUAN Yihong LIU Ying LIANG Zhaoming LIU Chongjian ZHAO Yanfeng ZHANG Yuwei YIN Jinfang WANG Hong 《Acta Meteorologica Sinica》2013,27(5):601-625
A mixed rain-snow storm associated with a strong burst of cold air and development of an extratropical cyclone occurred over North China from 3 to 5 November 2012.This early snowfall event was characterized by a dramatic drop in temperature,strong winds,high precipitation intensity,broad spatial extent,and coexistence of multi-phase precipitating hydrometeors.This study investigates the multi-scale interactions between the large-scale circulation background and the synoptic-scale weather systems associated with the storm.The results are as follows.(1) The Arctic Oscillation (AO) had been in its negative phase long before the event,leading to southward advection of cold air into North China in advance of the storm.(2)The large-scale atmospheric circulation experienced a decreased number of long waves upstream of North China prior to the storm,resulting in reduced wave velocity and an almost stagnant low pressure system (extratropical cyclone) over North China.(3) An Ω-shaped blocking high over East Asia and the western Pacific obstructed the eastward movement of an upstream trough,allowing the corresponding surface cyclone to stabilize and persist over Beijing and its neighboring areas.This blocking high was a major factor in making this event a historically most severe precipitation event in autumn in Beijing for the past 60 years.(4) Baroclinic instability at lower levels gave rise to rapid development of the cyclone under the classical "second type" development mechanism for extratropical cyclones.(5) Moisture originated from the Yellow Sea entered the slowly-moving cyclone in a steady stream,creating fairly favorable water vapor supply for the heavy rainfall-snowfall,especially during the later stage of the cyclone development.(6) Moisture transport and frontal lifting triggered low-level instability and updrafts.Intensification of the front enhanced the vertical wind shear,causing conditional symmetric instability (CSI) to expand upward within the unstable lower troposphere,and to eventually gear into the CSI region of the upper troposphere,which facilitated the upward development of low-level updrafts. 相似文献
98.
99.
近年来,某些经济海藻藻体色型的变异,已引起有关海藻遗传育种工作者的兴趣和注意。Van der Meer(1977—1979)对江(?)几种色型突变体的遗传规律做了比较系统的研究;Mlura用条斑紫菜的几种色型突变体进行了大量的杂交试验,分析了遗传型与表现型之间的关系;Kikuchi(1979)对几种紫菜突变体所含的藻胆素进行了分析研究;Migitita(1983)通过栽培试验,对几种不同色型紫菜突变体的生长和抗病等特性,进行了比较分析。海带叶片色泽是重要的经济性状之一,对商品等级率有直接影响。在长期的栽培实践中,人们早已发现,培养条件对海带叶片色泽有重要影响。 相似文献
100.
Chen Cao Hong Wu Jian-Ling Wang Cai-Na Hao Zu-Gan Deng Xiao-Yang Xia Zhen-Long Zou National Astronomical Observatories Chinese Academy of Sciences Beijing Graduate School of Chinese Academy of Sciences Beijing College of Physical Sciences Graduate School of Chinese Academy of Sciences Beijing Department of Physics Tianjin Normal University Tianjin 《中国天文和天体物理学报》2006,6(2):197-209
We selected a sample of luminous infrared galaxies by cross-identification of the Faint Source Catalogue (FSC) and Point Source Catalogue (PSC) of the IRAS Survey with the Second Data Release of the SDSS. The size of our sample is 1267 for FSC and 427 for PSC by using the 2σ significance level cross-section. The "likelihood ratio" method is used to estimate the individual's reliability and for defining two more reliable subsamples (908 for FSC and 356 for PSC). A catalog of infrared, optical and radio data is compiled and will be used in further work. Some statistical results show that luminous infrared galaxies are quite different from ultra-luminous infrared galaxies. The AGN fractions of galaxies at different infrared luminosities and the radio-infrared correlations are consistent with the previous studies. 相似文献