全文获取类型
收费全文 | 1808篇 |
免费 | 359篇 |
国内免费 | 400篇 |
专业分类
测绘学 | 105篇 |
大气科学 | 366篇 |
地球物理 | 459篇 |
地质学 | 908篇 |
海洋学 | 245篇 |
天文学 | 82篇 |
综合类 | 173篇 |
自然地理 | 229篇 |
出版年
2024年 | 11篇 |
2023年 | 37篇 |
2022年 | 104篇 |
2021年 | 124篇 |
2020年 | 115篇 |
2019年 | 104篇 |
2018年 | 104篇 |
2017年 | 114篇 |
2016年 | 130篇 |
2015年 | 105篇 |
2014年 | 117篇 |
2013年 | 127篇 |
2012年 | 108篇 |
2011年 | 129篇 |
2010年 | 78篇 |
2009年 | 109篇 |
2008年 | 92篇 |
2007年 | 87篇 |
2006年 | 73篇 |
2005年 | 63篇 |
2004年 | 47篇 |
2003年 | 48篇 |
2002年 | 42篇 |
2001年 | 38篇 |
2000年 | 34篇 |
1999年 | 76篇 |
1998年 | 49篇 |
1997年 | 59篇 |
1996年 | 33篇 |
1995年 | 31篇 |
1994年 | 32篇 |
1993年 | 22篇 |
1992年 | 34篇 |
1991年 | 23篇 |
1990年 | 15篇 |
1989年 | 15篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1971年 | 1篇 |
1958年 | 2篇 |
排序方式: 共有2567条查询结果,搜索用时 15 毫秒
131.
黑洞X射线暂现源的迷你爆发是一类峰值光度较低、持续时间较短的爆发.由于观测数据较少,其物理机制仍不清楚.利用RXTE (Rossi X-ray Timing Explorer)卫星从2001年1月28日到3月14日的数据,研究了黑洞X射线暂现源XTE J1550–564 2001年迷你爆发的X射线能谱特性.发现在本次迷你爆发中, XTE J1550–564的X射线能谱可以用幂律谱很好地拟合.整个爆发的硬度强度图不是标准的q型,而是一直保持在最右侧.此外,还分析了此次爆发谱指数Γ与未吸收的2–10 keV能段的X射线流量F_(2–10 keV)的相关性,发现Γ-F_(2–10 keV)呈反相关关系,且谱指数Γ∈[1.35, 1.72].上述结果表明2001年这次爆发一直处于低/硬态,它的X射线辐射主要来自于辐射低效的吸积模式,如ADAF(Advection-Dominated Accretion Flow). 相似文献
132.
Characteristics of Spatial and Temporal Variations of Monthly Mean Surface Air Temperature over Qinghai-Tibet Plateau 总被引:1,自引:0,他引:1
ZHANG Qianggong KANG Shichang YAN Yuping 《中国地理科学(英文版)》2006,16(4):351-358
1 Introduction The Qinghai-Tibet Plateau, known as the highest plateau with the most complex topography in the world, covers an area of more than 200km2, with a mean elevation of more than 4000m a.s.l. (Ye and Gao, 1979). Surrounded by the Earth’s highest mountains, such as the Himalayas, Pamir, Kunlun Mountains, the plateau plays a significant role in climate change in China even in the world, thus attracted great attention of researchers. Up to now, many achievements have been gained by… 相似文献
133.
1INTRODUCTIONIrrigated ricefieldsarecharacterizedbylargespatialandtemporalvariationsin CH4 emissiontotheatmo-sphere.Accordingly,thereisagreatuncertaintyintheestimate ofCH4 emissionsfromricefields.GreateffortshavebeenmadetoestimatetheCH4 emissionsfromricefieldsandseveralapproacheshavebeendeveloped.TherepresentativemethodsincludetheIPCC(Inter-governmentPanelofClimateChange)region-specificemissionfactormethodandthemodelcalculationmethod.Toimprovethecalculationaccuracy,theIPCCmethodreq… 相似文献
134.
在15万区域地质调查基础上,利用花岗岩等级体制填图方法对天湖花岗岩体进行解体,建立了三个填图单元,归并为一个超单元。对各单元岩石类型、矿物成分、组构及野外接触关系进行了论述。通过岩石化学和地球化学资料论证,该岩体是同一次岩浆熔融事件过程中曾经发生过三次岩浆侵入活动而形成的环状深成岩体。 相似文献
135.
基于栅格叠合的沉积物底质图生成方法 总被引:2,自引:0,他引:2
文章提出了一种基于GIS空间插值和栅格图叠合技术,分析生成沉积物底质图的方法,并以曹妃甸海区为例,以170个海底表层沉积物样的粒度分析结果为依据,应用本文设计的方法生成这一海区的底质分布图,并用预留的20个采样点进行了精度分析和检验,在此基础上比较了不同的空间插值方法对生成的底质图结果的影响.结果显示出这一方法成图速度快、自动化程度高,但也存在对原始数据精度要求高、插值方法带来误差等问题.在借鉴传统底质图生成方法的基础上,运用三维TIN模型对成图结果进行改进,最终形成一种结合地貌要素的栅格叠合的沉积物底质图生成方法. 相似文献
136.
Jungho Nam Jongseong Ryu David Fluharty Chul-hwan Koh Karen Dyson Won Keun Chang Hee-Jung Choi Daeseok Kang Jong Seong Khim Chang-Hee Lee 《Ocean & Coastal Management》2010,53(11):703-710
The history of Korean tidal flat management and the process for designating Coastal Wetland Protected Areas (CWPAs) are described. Korean coastal wetlands have a long history of intensive use through reclamation for agricultural and industrial uses in the 20th century. Recently, the management policy is shifting away from intensive use towards the conservation of wetlands. This shift is caused by increasing public awareness of the value of wetlands and strong institutional support from the government. Since the Wetlands Conservation Act was passed in 1999, a total of twelve CWPAs have been designated through both top-down and bottom-up processes. Three designation paths are classified based on the relevant drivers, namely government-driven designations (seven CWPAs), local community driven designations (three CWPAs), and conflict resolution (trade-offs) driven designation (two CWPAs). The lessons learned from the designation of Korean CWPAs is that diversification of designation process could facilitate voluntary participation of local stakeholders and thereby enhance the chance of successful implementation of wise use strategy of tidal flats. 相似文献
137.
The role of eddies in solute transport and recovery in rock fractures: Implication for groundwater remediation
下载免费PDF全文
![点击此处可从《水文研究》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A better understanding of solute transport and retention mechanism in rock fractures has been challenging due to difficulty in their direct observations in microscale rough‐walled fractures. Six representative troughs in a rough‐walled fracture were selected for microscale observations of eddy formation with increasing flow velocity and its effect on spatiotemporal changes of solute concentration. This experimental study was enabled by a microscale visualization technique of micro particle image velocimetry. With increasing flow velocity (Re ≤ 2.86), no eddies were generated, and solutes along the main streamlines transported rapidly, whereas those near the wall moved slowly. A larger amount of solutes remained trapped at all troughs at Re = 2.86 than Re < 1. For Re = 8.57, weak eddies started to be developed at the troughs on the lee side, which little contributed to overall solute flushing in the fracture. Accordingly, a large of amount of water was needed for solute flushing. The flow condition of 1 < Re < 10, before a full development of eddies, was least favourable in terms of time and amount of remediation fluid required to reach a target concentration. After large eddies were fully developed at troughs on the lee side for Re = 17.13, solutes were substantially reduced by eddies with less amount of water. Fully developed eddies were found to enhance solute transport and recovery, as opposed to a general consensus that eddies trap and delay solutes. Direct inflow into troughs on the stoss side also made a great contribution to solute flushing out of the troughs. This study indicates that fully developed eddies or strong inflows at troughs are highly possible to form for Re > 10 and this flow range could be favourable for efficient remediation. 相似文献
138.
西秦岭北缘断裂带地震活动特征及近期发展趋势 总被引:1,自引:0,他引:1
本文讨论了西秦岭北缘断裂带在青藏高原东北部三次地震活动高潮幕和两次地震活动低潮幕中的作用和特点,以及地震活动的时空强特征和近期发展趋势。 相似文献
139.
贵州长顺代化石炭系中间界线的沉积相研究 总被引:3,自引:3,他引:3
在碳酸盐微相的详细研究基础上,贵州长顺代化下、上石炭统剖面由下至上可分出5个主要沉积相:盆地相、开阔海陆架相、下斜坡相、中斜坡相和上斜坡相,下、上石炭统界线处于连续沉积的中斜坡相内。 相似文献
140.