全文获取类型
收费全文 | 15482篇 |
免费 | 2928篇 |
国内免费 | 3521篇 |
专业分类
测绘学 | 271篇 |
大气科学 | 1050篇 |
地球物理 | 3000篇 |
地质学 | 10855篇 |
海洋学 | 2038篇 |
天文学 | 19篇 |
综合类 | 742篇 |
自然地理 | 3956篇 |
出版年
2024年 | 69篇 |
2023年 | 246篇 |
2022年 | 579篇 |
2021年 | 662篇 |
2020年 | 642篇 |
2019年 | 655篇 |
2018年 | 614篇 |
2017年 | 718篇 |
2016年 | 726篇 |
2015年 | 733篇 |
2014年 | 952篇 |
2013年 | 1108篇 |
2012年 | 979篇 |
2011年 | 1117篇 |
2010年 | 884篇 |
2009年 | 1036篇 |
2008年 | 1052篇 |
2007年 | 1123篇 |
2006年 | 1135篇 |
2005年 | 879篇 |
2004年 | 860篇 |
2003年 | 783篇 |
2002年 | 633篇 |
2001年 | 556篇 |
2000年 | 593篇 |
1999年 | 476篇 |
1998年 | 340篇 |
1997年 | 350篇 |
1996年 | 307篇 |
1995年 | 263篇 |
1994年 | 220篇 |
1993年 | 155篇 |
1992年 | 135篇 |
1991年 | 98篇 |
1990年 | 76篇 |
1989年 | 55篇 |
1988年 | 45篇 |
1987年 | 19篇 |
1986年 | 16篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 1篇 |
1981年 | 10篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
山区年、月平均温度推算方法的研究 总被引:9,自引:0,他引:9
本文提出了山区年、月平均温度空间分布的推算方法,并提供了相应的小地形温度订正值。该方法在福建省沙溪流域山区实际应用的结果表明,能有效地揭示山区年、月平均温度空间分布的宏观与微观变化,效果满意,精度较高。 相似文献
962.
本文使用云南滇西地区、红河断裂带北段1984——1985年由PDR-2数字事件记录仪记录到的84张地震记录图,按文献〔4〕中所述的理论和方法,用直达(?)波资料计算了该区的分区粘性多Q_α值,初步结论是:整个场区内介质粘弹性可用非线性体去近似模拟。Q_α值分布情况为:由云龙、洱源、漾濞三点所成的三角区内,其值约为50±30左右较低,而沿弥渡向北,经下关至剑川所示的整个断裂带上所测Q_α值较高,约在160±30左右。反映了明显的构造差异性。 相似文献
963.
The Hikurangi Margin is a region of oblique subduction with northwest-dipping intermediate depth seismicity extending southwest from the Kermadec system to about 42°S. The current episode of subduction is at least 16–20 Ma old. The plate convergence rate varies along the margin from about 60 mm/a at the south end of the Kermadec Trench to about 45 mm/a at 42°S. The age of the Pacific lithosphere adjacent to the Hikurangi Trench is not known.The margin divides at about latitude 39°S into two quite dissimilar parts. The northern part has experienced andesitic volcanism for about 18 Ma, and back-arc extension in the last 4 Ma that has produced a back-arc basin onshore with high heaflow, thin crust and low upper-mantle seismic velocities. The extension appears to have arisen from a seawards migration of the Hikurangi Trench north of 39°S. Here the plate interface is thought to be currently uncoupled, as geodetic data indicate extension of the fore-arc basin, and historic earthquakes have not exceededM
s=7.South of 39°S there is no volcanism and a back-arc basin has been produced by downward flexure of the lithosphere due to strong coupling with the subducting plate. Heatflow in the basin is normal. Evidence for strong coupling comes from historic earthquakes of up to aboutM
s=8 and high rates of uplift on the southeast coast of the North Island.The reason for this division of the margin is not known but may be related to an inferred increase, from northeast to southwest, in the buoyancy of the Pacific lithosphere. 相似文献
964.
965.
The determination of uranium series disequilibria in fluvial environments is proposed as a method of calculating catchment mass balances. The technique is based on two main principles. Firstly, 234U is more mobile than 238U, especially during the early stages of weathering. Secondly, uranium is far more mobile than either thorium or protactinium. Consequently, teaching during weathering results in the loss of the uranium found in the fresh rock, leaving the two immobile daughters behind. The ratio of uranium carried by sediment to that dissolved, US/UW can, therefore, be determined from river water and sediment isotopic activity ratios. Fluxes of uranium can then be calculated from average concentrations in the water and the associated sediment, from which a sediment yield can be inferred. The Witham catchment in Lincolnshire has been used to test the proposed method. A US/UW ratio of between 5 and 7 is determined and a sediment yield of 2.51 ± 2.12 tonnes yr?1 km?2 is proposed. Although some problems concerning environmental chemistry have arisen, the validity of the approach is confirmed by the close correspondence between the results obtained and those inferred by earlier workers using more conventional methods. 相似文献
966.
The C and H isotopic compositions of the methane in more than 160 gas samples from 10 basins in China are presented in this paper.The natural gases are classified as four types: biogenic gas ,bio-thermocatalytic transitional gas, gas associated with condensate oil ,and coal-type gas. The isotopic compositions of these gases closely related to the depositional basins, the types of organic matter,the stages of thermal evolution and the genetic characteristics of different gas reservoirs.Studies of the C and H isotopic compositions of terrigenous natural gases will provide valua-ble information on the prospecting and development of natural gases of different genetic types. 相似文献
968.
造盆作用及成矿盆地的历史动力综合分类建议 总被引:3,自引:0,他引:3
本文把历史分析方法与动力分析方法两种分折方法结合起来,提出了一个综合的盆地分类方案。按历史动力综合分类,造盆作用及盆地可划分为三大类:大洋壳型、雏陆壳(过渡壳)型及大陆壳型大壳型中可细分为活动区型及稳定区型。雏陆壳型包括前地槽型及地槽前期型。大陆壳型中计有地槽后期型、地台型和地洼型。 相似文献
969.
金沙江-澜沧江-怒江地区是中国重要的贵金属、有色金属成矿远景区之一。金矿类型繁多,主要有:蛇绿混杂岩中的构造蚀变岩型;与中酸性岩浆侵入活动有关的多金属石英脉型;构造破碎带中的微细浸染型;碳酸盐岩层构造裂隙中的混成热液型;与次火山岩有关的热液型;火山热泉型和海底火山喷流沉积-热液改造型。成矿时间集中于中新生代。矿床和矿体主要受线型构造控制。岩浆活动在金的成矿过程中有不同程度影响。金矿基本属浅成、中低温热液型。蚀变作用普遍强烈。成矿物质及热液具多源性。 相似文献
970.
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