全文获取类型
收费全文 | 271篇 |
免费 | 41篇 |
国内免费 | 145篇 |
专业分类
测绘学 | 32篇 |
大气科学 | 44篇 |
地球物理 | 49篇 |
地质学 | 218篇 |
海洋学 | 32篇 |
天文学 | 12篇 |
综合类 | 30篇 |
自然地理 | 40篇 |
出版年
2024年 | 9篇 |
2023年 | 15篇 |
2022年 | 11篇 |
2021年 | 16篇 |
2020年 | 8篇 |
2019年 | 34篇 |
2018年 | 26篇 |
2017年 | 9篇 |
2016年 | 21篇 |
2015年 | 15篇 |
2014年 | 25篇 |
2013年 | 11篇 |
2012年 | 11篇 |
2011年 | 6篇 |
2010年 | 25篇 |
2009年 | 5篇 |
2008年 | 7篇 |
2007年 | 8篇 |
2006年 | 7篇 |
2005年 | 7篇 |
2004年 | 3篇 |
2003年 | 13篇 |
2002年 | 6篇 |
2001年 | 29篇 |
2000年 | 17篇 |
1999年 | 15篇 |
1998年 | 9篇 |
1997年 | 8篇 |
1996年 | 5篇 |
1995年 | 10篇 |
1994年 | 9篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 12篇 |
1987年 | 4篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1965年 | 1篇 |
1964年 | 3篇 |
1959年 | 1篇 |
1958年 | 3篇 |
1957年 | 2篇 |
1936年 | 1篇 |
1933年 | 2篇 |
排序方式: 共有457条查询结果,搜索用时 635 毫秒
11.
The thermal strati?cation of the lakes impedes the transfer of atmospheric oxygen into the lower layers of the lake. In lakes which are af fected by diverse anthropogenic in?uences, the increasing organic matter amounts lead to a sharp decrease in hypolimnetic oxygen amounts, aided by thermal strati?cation,and anaerobic conditions arise. The determination of hypolimnetic oxygen demand(HOD) and areal hypolimnetic oxygen demand(AHOD) and their monitoring represent an integrated approach to investigate the oxygenation of lakes, the nutrient conditions, and the physicochemical dynamics. In this study, two lakes dif fering by size and af fected by dif ferent anthropogenic sources, are investigated in this respect. At?rst, bathymetric studies were conducted to determine the depth, surface area, and volume relationships.Then, based on monitoring studies conducted in 2013 and 2014, the thermal strati?cation dynamics and layer properties were established using the relative thermal resistance to mixing(RTRM) index based on temperature and density pro?les. Following this, the oxygen depletion rates were determined by oxygen and temperature pro?ling in the hypolimnion. For the years of 2013 and 2014, the AHOD values for the Borabey Pond which is far from anthropogenic in?uences, were found to be 0.848 and 0.569 g O 2/(m·d), respectively.The AHOD values for the Porsuk Reservoir which was overburdened for years by industrial and domestic pollution were found to be 4.263 and 5.099 g O 2/(m·d), larger than its counterpart by almost sevenfold. The HOD and AHOD monitoring can be considered to a valuable tool for assessing the ecological and chemical status of lakes within Annex 5 of the Water Framework Directive and as an integrated approach to assess and monitor the status of lakes. 相似文献
12.
Pedro S.B.REYES Mauricio E.VALAREZO Jenry CóRDOVA Fran?ois A.MICHAUD Camilo ZAPATA 《山地科学学报》2018,15(5):966-975
The longitudinal profile of a river channel can be described in function of mathematical expressions. The logarithmic fit is the most used method to describe the relative equilibrium of a channel elevation profile. Rivers showing zones of high channel gradient and convex-upward profiles can be evaluated in function of the offset distance with respect to the logarithmic curve. The Jama River profile has been constructed using differential GPS data for the downstream reach and 4-m-grid DEM data base for the remaining headward profile. The resulting longitudinal profile shows a prominent knickpoint of about 80 m in elevation characterized by sharp local convexity. The offset distance in vertical direction from the logarithmic plot is interpreted as the successive accumulation of multiple uplift episodes associated with the Jama Fault System activity. The horizontal offset is suggested to represent the remaining retreated distance for the upstream propagation of the Jama knickpoint. The highly resistant Cretaceous rocks outcropping along the Jama knickpoint reach acts as an inflection point between two subprofiles that show well-fitted logarithmic curves, thereby representing a temporary partitioned equilibrium along the Jama River profile. 相似文献
13.
Ashley P. GUMSLEY Kevin R. CHAMBERLAIN Wouter BLEEKER Ulf S?DERLUND Michiel O. DE KOCK Tobias C. KAMPMANN Emilie R. LARSSON Andrey BEKKER 《《地质学报》英文版》2016,90(Z1):67-68
正The Neoarchaean to Palaeoproterozoic Transvaal Supergroup of the Kaapvaal Craton,southern Africa,is one of the best-preserved and most complete stratigraphic records across a critical in juncture in the Earth’s history. 相似文献
14.
正The Neotethyan ophiolites exposed in SE Anatolia–Syria occur along two,ENE-WSW-trending,sub-parallel belts(Fig.1).The ophiolites and ophiolitic mélanges in the southern belt include the Cretaceous K?z?lda?(Hatay), 相似文献
15.
SHAN Xin YU Xinghe Peter ?CLIFT LI Yalong JIN Lin SU Dongxu DU Yonghui ZHOU Jinsong HAN Xiaoqin 《《地质学报》英文版》2018,92(1):268-285
16.
Volcanism along the northwest boundary of the Arabian Plate found in the Gaziantep Basin, southeast Turkey, is of Miocene age and is of alkaline and calc-alkaline basic composition. The rare earth element data for both compositional series indicates spinel–peridotite source areas. The rare earth and trace elements of the alkaline lavas originate from a highly primitive and slightly contaminated asthenospheric mantle; those of the calc-alkaline lavas originate from a highly heterogeneous, asthenospheric, and lithospheric mantle source. Partial melting and magmatic differentiation processes played a role in the formation of the petrological features of these volcanics. These rocks form two groups on the basis of their ~(87) Sr/~(86) Sr and ~(143) Nd/~(144) Nd isotopic compositions in addition to their classifications based on their chemical compositions(alkaline and calc-alkaline). These isotopic differences indicate a dissimilar parental magma. Therefore, high Nd isotope samples imply a previously formed and highly primitive mantle whereas low Nd isotope samples may indicate comparable partial melting of an enriched heterogeneous shallow mantle. Other isotopic changes that do not conform to the chemical features of these lavas are partly related to the various tectonic events of the region, such as the Dead Sea Fault System and the Bitlis Suture Zone. 相似文献
17.
Yong Chen Jing Duan Junling An Huizhi Liu Ulrich G?rsdorf Franz H.Berger 《大气和海洋科学快报》2021,14(5):24-29
卫星估雨精度的不确定性受到当地降雨类型和像元内降雨非均匀性影响,而结合这两个关键因素开展半干旱草原卫星估雨的研究有限.2009年夏,我们在中国锡林郭勒半干旱草原用多部微雨雷达和雨量计构建了9 km卫星像元降雨观测网,观测了像元内降雨非均匀性(空间变异系数CV),并评估了卫星估雨精度.结果表明:(1)CV值受像元内平均降雨量,降雨类型,降雨云面积及移向等影响,如高Cv值的降雨过程大多为平均降雨量小,对流性降雨过程,降雨云边缘像元CV值较高;(2)TRMM 3B42V7卫星估雨产品适用性较好,CMORPH和PERSIANN次之,但TRMM 3B42V7易在半干旱草原湖泊处高估降雨. 相似文献
18.
19.
早元古地球也许要比现代有一个更热的地幔和一个大洋板块表面上更少滞留的时间。该更热的地幔可能导致变成更薄的大洋板块。年青的洋底具有低负浮力,因此消减带会产生低的拉动板片力。如果板块越薄,其影响就越大,因为当它们下沉到地幔时热 相似文献
20.
加拿大魁北克省奥蒂什盆地和米斯泰西尼盆地所采取的标本经岩石、Gandclfi-X射线衍射和扫描式电子探针分析已证实: (1)水化含铀矿物组合显示出每个研究过的主要岩性的特性。特别是硅铅铀矿和杂磷铅铀矿的柱状和放射状多晶集合体,已经在塔克瓦第一区段的帕帕斯克瓦斯蒂组砾石砂岩标本内以及拉克安迪卡特第三区段的安迪卡托组砾石砂岩标本内发现。 相似文献