首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   20378篇
  免费   2479篇
  国内免费   4272篇
测绘学   472篇
大气科学   1361篇
地球物理   2487篇
地质学   6542篇
海洋学   8077篇
天文学   5114篇
综合类   1060篇
自然地理   2016篇
  2024年   51篇
  2023年   199篇
  2022年   611篇
  2021年   616篇
  2020年   645篇
  2019年   695篇
  2018年   626篇
  2017年   621篇
  2016年   637篇
  2015年   718篇
  2014年   1164篇
  2013年   1263篇
  2012年   1040篇
  2011年   1378篇
  2010年   1289篇
  2009年   1792篇
  2008年   1693篇
  2007年   1560篇
  2006年   1486篇
  2005年   1358篇
  2004年   1142篇
  2003年   1030篇
  2002年   901篇
  2001年   756篇
  2000年   683篇
  1999年   639篇
  1998年   468篇
  1997年   329篇
  1996年   271篇
  1995年   239篇
  1994年   237篇
  1993年   209篇
  1992年   152篇
  1991年   112篇
  1990年   85篇
  1989年   92篇
  1988年   45篇
  1987年   30篇
  1986年   29篇
  1985年   53篇
  1984年   46篇
  1983年   33篇
  1982年   28篇
  1981年   29篇
  1980年   12篇
  1979年   3篇
  1978年   11篇
  1977年   15篇
  1954年   2篇
  1875年   1篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Because of its copious and reliable rainfall, Ireland has an abundance of springs. Many of the larger ones issue from the Carboniferous limestone that occurs in over 40% of the country. The spring water is mainly a calcium bicarbonate type with a temperature of about 10°C. In the 18th century, warm and cold springs were developed as spas in various parts of Ireland. The popularity of these springs was short and most were in major decline by 1850. Today only one cold spa at Lisdoonvarna, Co. Clare is still operating. Springs in Ireland were places of religious significance for the pre-Christian Druidic religion. In the Christian period they became holy wells, under the patronage of various saints. Cures for many different ailments were attributed to water from these wells.  相似文献   
992.
白云鄂博稀土矿床中辉钼矿的铼-锇同位素年龄   总被引:16,自引:2,他引:16  
白云鄂博铁稀土矿床的形成年龄一直是个有争论的问题,采自该矿床东采场的辉钼矿样,通过镜下对矿物结构构造的研究,认为辉钼矿是矿区晚期矿脉形成阶段的矿物,它的铼-锇同位素年龄为(439±8)×10^6a。此结果从另一侧面说明该矿床在加里东期有一期成矿作用。  相似文献   
993.
The downhole vertical accelerometer array VSAP near Paducah, KY, consists of three-component accelerometers at the surface, the top of the McNairy Formation (−41 m), and the top of the Paleozoic bedrock (—99 m). The array is at the northern end of the Mississippi Embayment, and it was installed to verify the ground-motion modeling for the site, assuming a significant earthquake in the New Madrid Seismic Zone. Accelerograms from 4.2 and 2.0 mb earthquakes were used to check aspects of the modeling pertaining to linear behavior of the soil column, and to review the soil column models derived by drilling and geotechnical methods and through the use of high-resolution P- and SH-wave seismic refraction in reflection techniques. Results of the study indicate that for the linear case the soil column models derived by the two techniques are equivalent, and that the most important boundary in the soil column, with respect to amplification of the ground motions, is the interface between the limestone bedrock and soil.  相似文献   
994.
The impact of tourism on coastal areas   总被引:5,自引:0,他引:5  
The manifold influences of tourism on coastal areas are analysed from three different angles: (1) The development of seaside tourism including the changes of socio-economic and settlement patterns; (2) its cultural impact on the local population; (3) its environmental aspects. Point 1 is described with the help of a model showing four peripheries in space and time: (I) the North Sea and Baltic coasts since the 18th century; (II) Southern Europe during the 19th century; (III) the North African shores around 1950; (IV) the tropical oceans after 1965. Within every periphery, several phases (pioneer, domestic, international) can be distinguished according to the origin of tourists, the investment, the know-how etc. While the beginning of every phase is dominated from abroad, later-on national actors play an increasing role. This applies also to point 2, which refers mainly to developing countries. As for point 3, mass tourism may result detrimentally on water supply, sensitive coastal landscapes, socio-cultural identity etc. Among the questions to be raised are: How far are industrial societies responsible for any negative impacts of tourism, and what are the chances for, and a general consciousness on, a sustainable tourism development?  相似文献   
995.
The paper is a report of the field campaign undertaken by an international team (Italian, French and Indonesian) a few weeks after the occurrence of a tsunami invading the south-eastern coast of Java (Indonesia) and it complements the results of a concurrent field survey by Asian and USA researchers. The tsunamigenic earthquake occurred on 3 of June 1994 in the Indian Ocean about 200 km south of Java. The tsunami caused severe damage and claimed many victims in some coastal villages. The main purpose of the survey was to measure the inundation and the runup values as well as to ascertain the possible morphological changes caused by the wave attacks. Attention was particularly focussed on the most affected districts, that is Lumajang, Jember and Banyuwangi in Java, although also the districts of Negera, Tebanan and Denpasar in Bali were examined. The most severe damage was observed in the Banyuwangi district, where the villages of Rajekwesi, Pancer and Lampon were almost completely levelled by the violent waves. Most places were hit by three significant waves with documented wave height often exceeding 5 m. The maximum runup value (9.50 m) was measured at Rajekwesi, where also the most impressive erosion phenomena could be found. In contrast, only in one place of the neighbouring island of Bali was there a slight tsunami, the rest of the island being practically unaffected.  相似文献   
996.
—Mining-induced seismicity associated with longwall face operations in the Ostrava- Karviná coal mines, Czech Republic, has been investigated in order to establish the conditions leading to a focal zone generation. The study, based on macroseismic and instrumental observations, proved that seismicity is influenced by natural as well as mining conditions. The first group includes the influence of faults, washouts and red beds, while the second one is represented by shaft and/or crosscut safety pillars and various types of remnant pillars. All the cases discussed show that many focal zones are generated in overstressed strata as a consequence of interaction of natural conditions and/or old workings with the active coal face. Received June 18, 1996, accepted March 10, 1997  相似文献   
997.
黄河上游径流预报的灰色拓扑方法   总被引:5,自引:6,他引:5  
蓝永超  杨文华 《冰川冻土》1997,19(4):308-311
以龙羊峡水库年平均入库流量预报为例,根据灰色系统理论的建模方法,利用龙羊峡水库入库水量代表站唐乃亥水文站的实测径流资料,建立了一个GM(1,1)拓扑预测模型,用于黄河上游径流的长期预报,并取得了较为满意的结果。  相似文献   
998.
This paper expounds the quantitative tectonic indicators and some qualitative indicators of large earthquakes in the coast areas of Fujian, Guangdong, Taiwan and Hainan. The main quantitative indicators include uplift amplitude of the Moho, Quaternary and Late Holocene coasts. The paper also gives a brief account of the research method on quantitative indicators of surface uplifted zones. Taiwan is a famous neotectonic zone and an area of large earthquakes in the world. There is only one large-earthquake area in each of Fujian, Guangdong and Hainan Provinces. Along the coast large earthquake areas there are certainly many remains of crustal activity. Among these remains, coast activity, taking the sea level as the accurate marker horizon, can determine not only the amplitude of coastal elevation and subsidence in a certain period, but also the cycle and rate of positive or negative movements.  相似文献   
999.
渤海盆地现代构造应力场与强震活动   总被引:12,自引:1,他引:12       下载免费PDF全文
渤海位于北华北新生代裂陷盆地的东部,是一个晚第四纪形成的内陆海盆. 渤海盆地活动断裂发育,地震活动强烈,交会于渤海中部的NE向营口——潍坊断裂带北段、庙西北——黄河口——临邑断裂带及NW向北京——蓬莱断裂带是主要的活动构造带,将海区分成4个次级新构造区,成为现代应力场作用的构造基础. 综合研究38个震源机制解和75个井区应力场等资料,以及构造应力场二维数值模拟计算结果表明,渤海及其邻区现代构造应力场的压应力方向为NE60~90,张应力为SN——NW30;以水平和近水平应力作用为主;不同构造区主应力方向存在一定的差异. 现今渤海地区地壳发育以NNE——NE和NW——WNW走向的共轭剪切破裂为特征,是控制地震活动的主要构造.   相似文献   
1000.
田建明  徐徐  谢华章  杨云  丁政 《地震学报》2004,26(4):432-439
通过对江苏地区及南黄海海域历史地震资料特点分析,将研究区历史地震类型分为相对安全类和相对危险类,并对地震类型的统计结果、地理分布特征及构造进行探讨. 结果表明:① 江苏及南黄海地区绝大多数中强以上历史地震类型为相对安全类,仅有13.8%的中强以上历史地震为相对危险类;② 江苏陆地、长江口以东海域和南黄海北部坳陷地区以相对安全类地震为主,苏中沿海南黄海海域地震类型分布较为复杂,相对安全类和相对危险类地震类型比例基本相当;③ 研究区历史地震类型统计结果和空间分布特征与现代地震序列类型实况非常吻合,反映本区地震活动具有继承性的特点.研究结果可以作为江苏省地震应急工作中震后早期趋势判定的参考依据.   相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号