全文获取类型
收费全文 | 39253篇 |
免费 | 6326篇 |
国内免费 | 8600篇 |
专业分类
测绘学 | 3797篇 |
大气科学 | 4725篇 |
地球物理 | 6980篇 |
地质学 | 21857篇 |
海洋学 | 4328篇 |
天文学 | 4395篇 |
综合类 | 2526篇 |
自然地理 | 5571篇 |
出版年
2024年 | 293篇 |
2023年 | 719篇 |
2022年 | 1379篇 |
2021年 | 1621篇 |
2020年 | 1499篇 |
2019年 | 1830篇 |
2018年 | 1305篇 |
2017年 | 1534篇 |
2016年 | 1622篇 |
2015年 | 1795篇 |
2014年 | 2250篇 |
2013年 | 2172篇 |
2012年 | 2289篇 |
2011年 | 2468篇 |
2010年 | 2144篇 |
2009年 | 2705篇 |
2008年 | 2601篇 |
2007年 | 2717篇 |
2006年 | 2609篇 |
2005年 | 2451篇 |
2004年 | 2132篇 |
2003年 | 2032篇 |
2002年 | 1755篇 |
2001年 | 1566篇 |
2000年 | 1535篇 |
1999年 | 1355篇 |
1998年 | 1214篇 |
1997年 | 816篇 |
1996年 | 711篇 |
1995年 | 598篇 |
1994年 | 559篇 |
1993年 | 476篇 |
1992年 | 331篇 |
1991年 | 302篇 |
1990年 | 211篇 |
1989年 | 158篇 |
1988年 | 137篇 |
1987年 | 78篇 |
1986年 | 42篇 |
1985年 | 37篇 |
1984年 | 19篇 |
1983年 | 16篇 |
1982年 | 12篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 5篇 |
1978年 | 14篇 |
1977年 | 7篇 |
1976年 | 4篇 |
1954年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
Carbon and Noble Gas Isotopes in the Tengchong Volcanic Geothermal Area, Yunnan, Southwestern China 总被引:1,自引:0,他引:1
Carbon and noble gas isotope analyses are reported for bubbling gas samples from the Tengchong volcanic geothermal area near the Indo-Eurasian suture zone. All samples contain a resolvable component of mantle-derived 3He. Occurrence of mantle-derived 3He coincides with surface volcanism. However, 3He occurs over a larger geographic areathan do surface volcanics. δ13C values for CO2 and CH4 vary from -33.4‰ to 1.6 ‰ and from -52.8‰ to -2.8‰, respectively. He and C isotope systematics indicate that CO2 and CH4 in the CO2-rich gases originated predominantly from magmatic component mixed with crustal CO2 produced from carbonate. However, breakdown of organic matter and near-surface processes accounts for the CH4 and CO2 in N2-rich gases. 3He/4He ratio distribution pattern suggests that mantle-derived He and heat sources of high-temperature system in central Tengchong originate from a hidden magma reservoir at subsurface. CO2-rich gases with the highest 3He/4He ratio (5.2 Ra) may be representative of the 相似文献
32.
根据鄂温克旗1959—2008年气象历史资料,统一归类,并采用统计预报方法,简要评定预测出鄂温克旗50年来主要气象灾害之一的干旱、洪涝灾害期,为鄂温克旗防范旱涝灾害做参考。 相似文献
33.
S. O. Asamu 《GeoJournal》2004,61(2):183-189
There is a general shortage of potable water in Nigeria, partly through the lack of natural provision and partly because of
rapid urban growth that has largely been unplanned. The paper describes the recent redevelopment of a public water facility
in a run-down area of Ibadan which is part of the Sustainable Ibadan Project. Despite funding from national and international
bodies, the development is strongly based at community level. The local inhabitants feel they have control over their own
water supply through their representatives on the various planning and managing committees. This aims to reduce vandalism
and to increase pride and involvement in the community.
The project is a pilot for other projects around Ibadan, some of which have begun and others are being planned. This paper
describes the administrative structures and management principles that have been employed. It forcefully advocates community-based
planning and management which respects both the environment and the water-users, and involves a major “bottom-up” element.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
34.
F. Z. Feygin N. G. Kleimenova O. A. Pokhotelov M. Parrot K. Prikner K. Mursula J. Kangas T. Pikkarainen 《Annales Geophysicae》2000,18(5):517-522
We analyse long-lasting (several hours) Pc1 pearl pulsations with decreasing, increasing or constant central frequencies. We show that nonstationary pearl events (those with either decreasing or increasing central frequency) are observed simultaneously with increasing auroral magnetic activity at the nightside magnetosphere while the stationary events (constant central frequency) correspond to quiet magnetic conditions. Events with decreasing central frequency are observed mostly in the late morning and daytime whereas events with increasing central frequency appear either early in the morning or in the afternoon. We explain the diurnal distribution of the nonstationary pearl pulsations in terms of proton drifts depending on magnetic activity, and evaluate the magnetospheric electric field based on the variation of the central frequency of pearl pulsations. 相似文献
35.
对黄,东海及其邻近海域马面历年(1974—1986年)渔获量变化与Elnino现象关系并结合捕捞强度进行一些初步分析,总结出渔获量变化规律,为合理开发渔业资源提供有用信息。 相似文献
36.
高峰100号矿体硫、铅同位素特征 总被引:1,自引:0,他引:1
李蘅 《矿物岩石地球化学通报》2001,20(4):334-336
10 0号矿体的成矿物理化学环境为 :成矿温度 30 0± 30℃ ;成矿压力为 84.2× 10 5Pa ;LogfO2 =- 30 .4~- 35 .6 ,LogfCO2 =- 2 .5 5~ +0 .36 ,LogfS2 =- 8.3~ - 11.0 ,pH =4.2~ 4.9。同位素的分析结果 :硫化物的硫同位素为 6 4‰~ 12 .3‰ ,δ3 4 SΣS 值为 6 6~ 13 8;2 0 6Pb 2 0 4Pb值为 17 4 91~ 18 96 0 ,2 0 7Pb 2 0 4Pb值为 15 5 39~15 940 ,2 0 8Pb 2 0 4Pb值为 37 95 7~ 39 4 90。表明 10 0号矿体的硫源是混合硫 ,铅源是两种异常铅混合的结果。 相似文献
37.
ABSTRACTEvapotranspiration (ET) is one of the most important components in the hydrological cycle, and a key variable in hydrological modelling and water resources management. However, understanding the impacts of spatial variability in ET and the appropriate scale at which ET data should be incorporated into hydrological models, particularly at the regional scale, is often overlooked. This is in contrast to dealing with the spatial variability in rainfall data where existing guidance is widely available. This paper assesses the impacts of scale on the estimation of reference ET (ETo) by comparing data from individual weather stations against values derived from three national datasets, at varying resolutions. These include the UK Climate Impacts Programme 50 km climatology (UKCP50), the UK Met Office 5 km climatology (UKMO5) and the regional values published in the Agricultural Climate of England and Wales (ACEW). The national datasets were compared against the individual weather station data and the UKMO5 was shown to provide the best estimate of ETo at a given site. The potential impacts on catchment modelling were then considered by mapping variance in ETo to show how geographical location and catchment size can have a major impact, with small lowland catchments having much higher variance than those with much larger areas or in the uplands. Some important implications for catchment hydrological modelling are highlighted.
Editor D. Koutsoyiannis; Associate editor L. Ruiz 相似文献
38.
降水是干旱区水文循环研究不可缺少的水文要素,为了揭示我国西北地区大气降水的氢氧同位素时空分布特征,合理开展不同尺度水文循环研究和建立对比标准,系统搜集分析了乌鲁木齐、银川、张掖、兰州、平凉、西安和拉萨七个地区多年大气降水的氢氧同位素数据资料。分析结果表明:乌鲁木齐、银川、张掖和兰州四个地区的δ18O值夏半年明显高于冬半年,从全年尺度上来看只是受到了温度效应的影响;而位于关中盆地的西安地区则由于复杂的水汽来源,冬半年表现出受温度效应的控制,夏半年转为雨量效应控制为主。平凉地区δ18O与其它海拔相近地区(如兰州)相比5~9月份均偏负,这与平凉地区较弱的城市热岛效应有关。西北地区大气降水δD和δ18O的变化范围均在全球大气降水的变化范围之内,除平凉和拉萨外,其它几个地区大气降水线方程的斜率和截距均小于全球大气降水线,说明这些地区的降水是在干旱环境下经历较强程度的蒸发条件下进行的,且在降水过程中还可能受到了局地二次蒸发凝结等水汽循环的影响。而该区域大气降水的氘盈余(d值)表现出冬半年高、夏半年低的特点,表明冬半年和夏半年水汽来源不同或者水源地的蒸发条件不同。 相似文献
39.
阿巴拉契亚-阿钦塔造山带是北美乃至世界著名的大陆边缘挤压碰撞推覆造山带,是地质学研究的经典地区之一,也是许多经典地学理论和概念的发源地.其中,对地质学影响最大的当属地槽学说.继20世纪60年代由深海钻探带来地学革命之后,由COCORP实施的地震反射剖面和深钻揭示了该造山带的巨大推覆构造.人们惊奇地发现,在巨大推覆体之下... 相似文献
40.