全文获取类型
收费全文 | 3926篇 |
免费 | 648篇 |
国内免费 | 593篇 |
专业分类
测绘学 | 43篇 |
大气科学 | 294篇 |
地球物理 | 1606篇 |
地质学 | 1200篇 |
海洋学 | 652篇 |
天文学 | 583篇 |
综合类 | 323篇 |
自然地理 | 466篇 |
出版年
2024年 | 34篇 |
2023年 | 59篇 |
2022年 | 116篇 |
2021年 | 141篇 |
2020年 | 138篇 |
2019年 | 134篇 |
2018年 | 139篇 |
2017年 | 144篇 |
2016年 | 134篇 |
2015年 | 141篇 |
2014年 | 187篇 |
2013年 | 203篇 |
2012年 | 189篇 |
2011年 | 153篇 |
2010年 | 198篇 |
2009年 | 287篇 |
2008年 | 245篇 |
2007年 | 269篇 |
2006年 | 222篇 |
2005年 | 197篇 |
2004年 | 203篇 |
2003年 | 187篇 |
2002年 | 148篇 |
2001年 | 137篇 |
2000年 | 181篇 |
1999年 | 153篇 |
1998年 | 152篇 |
1997年 | 124篇 |
1996年 | 110篇 |
1995年 | 91篇 |
1994年 | 77篇 |
1993年 | 57篇 |
1992年 | 61篇 |
1991年 | 41篇 |
1990年 | 18篇 |
1989年 | 24篇 |
1988年 | 13篇 |
1987年 | 15篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1979年 | 7篇 |
1978年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有5167条查询结果,搜索用时 15 毫秒
991.
GB 18306—2015《中国地震动参数区划图》发布距今已有十多年,期间,地震资料(尤其是青藏地震区地震资料)发生了较大变化,及时开展相关地震带地震活动性参数研究对重大建设工程抗震设防安全具有重要意义。本文研究补充了600余条地震目录,其中8.0~8.9级地震7次,7.0~7.9级地震35次,并分析了地震资料的完整性:由于历史、地理、人文的原因,喜马拉雅地震带地震遗漏较严重,7级地震直至1897年才基本完整,6级地震直至1950年才基本完整,5级地震直至1980年才基本完整;本文根据8级以上地震密集活动时段划分了地震活动周期,公元1803年以来可以划分出2个活动周期,并对未来地震活动进行了预测;采用多种方案拟合了喜马拉雅地震带的b值和4级以上地震年发生率:b=0.90,v4=162,并与前人的计算结果进行了简单对比。 相似文献
992.
延边东北部地区中生代陆相火山断陷盆地处于吉黑褶皱系延边优地槽褶皱带延边复向斜内;区内中生代以来不同方向的断裂发育,火山活动强烈,岩浆侵入频繁;与中生代火山-岩浆活动有成因联系的金、铜金金属矿床多处,矿化蚀变线索也较多,构成了著名的五凤-小西南岔近东西向火山-岩浆期后低温热液型金、铜多金属成矿带;区内中生代火山-岩浆岩的形成是太平洋板块俯冲作用使大陆边缘拉张活动不断加剧,造成上地幔岩浆上侵的结果;并伴有成矿作用的发生,在岩浆岩体内外接触带的有利部位形成金、金铜或铜金多金属矿床;从远源至近源的成矿分带为Au-Ag→Au-Cu-Ag→Cu-Au-Pb-Zn→Cu(-Mo-Au);成矿作用表现出从低温至高温、从低硫到高硫的变化. 相似文献
993.
994.
Lake Rotoiti in Taupo Volcanic Zone was formed by damming of the drainage system through the floor of Okataina Caldera. Basin sediments are predominantly silt or sand, with mineralogy consistent with derivation from local silicic rocks and airfall tephras. Sandy lithofacies around the shoreline are wave worked deposits. Sand and gravel lithofacies in deeper water and on steep slopes are largely relict or airfall tephras, or both. Profundal sediments are diatomaceous silts. Organic-rich diatomaceous silts also accumulate in near-shore wave-damped zones under weed beds.Short cores penetrated the Tarawera (1886 AD) and Kaharoa (1180 AD) Tephras, identified by their stratigraphic position, geochemistry and mineralogy. Localised slumping is evidenced from secondary tephras interbedded and redeposited within the basin silts. Sedimentation rates in the basins, estimated from the age of bounding tephras, are 0.9 to 4.0 mm y-1, and are highest under the influence of inflowing water from adjacent Lake Rotorua. For several hundred years prior to the Tarawera eruption sediment accumulation rates and the sediment geochemistry remained unchanged; deposition was predominantly biogenic opaline silica with a small terrestrial component. The Tarawera eruption deposited a terrestrial-silica, aluminum-rich primary tephra across the lake, which was followed by reworked tephra from within the catchment, the effects of which were progressively diluted by biogenic opaline silica as conditions stabilised. While the major effects of the eruption have been rapidly absorbed the lake has not returned to pre-eruption background conditions. A new equilibrium has been attained in which Tarawera Tephra continues to be eroded into the lake and is the principal source for a doubling of sedimentation rates following the eruption. High arsenic levels in some diatomaceous silts are attributed to episodic venting of hydrothermal fluids or gases into the water column. 相似文献
995.
本文对太阳活动第21周、22周(1976年—1992年间)97个质子活动区进行统计分析,包括活动区的面积、型别、磁结构、半影纤维等,结果表明:75%的质子耀斑产生于面积为500≤Sp≤3000单位的黑子群中;耀斑爆发前一天及后一天活动区面积有显著减少;质子活动区含δ复杂磁结构的占70%;具有半影旋涡形态的质子活动区中,约77%的耀斑发生在旋涡黑子出现以后。 相似文献
996.
本文讨论了第22太阳活动周的下列重要特点:1.呈现双峰,并在双峰期的槽中又突起孤立的单峰。2.黑子面积峰值滞后相对数峰值的仅占16.67%;黑子面积与相对数同步占58.33%;二者峰值不能对应占25%。3.1986年10月以后,纬度≥30°的有半影的黑子群共出现87群;延迟在峰年期间出现的有53群,占60.92%;对应有M级以上X射线爆发的活动区18个,占20.69%。这一现象与“蝴蝶图”规律不符。 相似文献
997.
K. Urushibara-Yoshino 《Environmental Geology》1996,28(3):154-160
The properties of soils on previously dated sand dunes from Robe to Naracoorte in South Australia were examined. In these
areas younger sand dunes are composed of fresh sand, but older sand dunes are composed of calcarenited sand. The soils on
the sand dunes developed successionally by the age of sand dunes. The soil properties of these sand dunes differ depending
on the ages of the sand dunes. The properties of sand particles in soils are as follows:
(1) On the sand dunes of 4300 years B.P., A/C profile developed (Rendzina). On the sand dunes older than 125 000 years B.P.
and on the plateau of Tertiary limestone, soil profiles of A1/AB/B/C on the sand dunes of 83 000 years B.P. and A1/A3/B1/B2/C (Terra rossa) are well developed.
(2) Within the sand of A/C horizons of the sand dunes with the age of 4300 year B.P., the calcite grain content is about 64%,
and the quartz content is about 35%. Within the B horizons of soils on the dunes from 83 000 years B.P. to 347 000 years B.P.,
the calcite grain content is only 1–2%; however, the quartz grain content is about 92%. In the B2 horizons of soils on the dune of 690 000 years B.P. and on the Tertiary plateau, there are some calcite grains but the quartz
grain content is about 96%.
(3) The average size of quartz grains in the soils on the sand dunes from 4300 B.P. to 347 000 years B.P. is generally smaller,
but the average size of quartz on the sand dunes of 690 000 year B.P. becomes larger and the grains are well rounded. On the
Tertiary limestone plateau, the average quartz size becomes again smaller, and the grains are more rounded.
(4) Fet in B2 horizon of the soil profiles increases clearly corresponding to the age. Iron activity expressed by Feo/Fed also shows a close relation to the chronological sequence. The B horizon of the soil profiles shows a drastic decrease of
Feo/Fed according to the age. Iron crystalinity, (Fed-Feo)/Fet, has a tendency for a positive relation with increasing age.
Received: 1 June 1995 · Accepted: 4 December 1995 相似文献
998.
999.
本文介绍了1991年3月5日一个与3N级光学耀斑伴生的喷泉状爆发日珥。用Hα线观测从开始到结束整个过程共持续约50分钟时间,日珥的最大投影高度15.9万公里,视向速度分布表明,日珥主要以较大的速度向着观测者的运动,最大速度每秒120公里。 相似文献
1000.
The evaluation of eco-environmental susceptibility to human activity in Yulin region 总被引:1,自引:0,他引:1
The eco-environmental susceptibility is to demonstrate the reaction of a ecosystem under the same influences of the human
activity. It comprise many influencing factors which have a complicated relation to the eco-environmental susceptibility.
In this paper, the Analysis of Hierarchy Process (AHP) is used to determine the weight of each factor to the eco-environmental
susceptibility through analyzing the relationship between human activity and environmental deterioration. And the weighted
summation method is used to calculate the eco-environmental susceptibility of different divisions in Yulin region. The result
shows that the loess hilly and gully area is more subjective to deteriorating eco-environment than the desert area because
of the strong human activity and severe soil erosion.
The project is supported by the National Natural Science Foundation of China 相似文献