全文获取类型
收费全文 | 1381篇 |
免费 | 179篇 |
国内免费 | 245篇 |
专业分类
测绘学 | 23篇 |
大气科学 | 177篇 |
地球物理 | 207篇 |
地质学 | 892篇 |
海洋学 | 159篇 |
天文学 | 7篇 |
综合类 | 90篇 |
自然地理 | 250篇 |
出版年
2024年 | 9篇 |
2023年 | 19篇 |
2022年 | 23篇 |
2021年 | 33篇 |
2020年 | 42篇 |
2019年 | 51篇 |
2018年 | 56篇 |
2017年 | 57篇 |
2016年 | 51篇 |
2015年 | 60篇 |
2014年 | 80篇 |
2013年 | 104篇 |
2012年 | 66篇 |
2011年 | 75篇 |
2010年 | 61篇 |
2009年 | 78篇 |
2008年 | 112篇 |
2007年 | 100篇 |
2006年 | 113篇 |
2005年 | 96篇 |
2004年 | 95篇 |
2003年 | 61篇 |
2002年 | 57篇 |
2001年 | 37篇 |
2000年 | 41篇 |
1999年 | 44篇 |
1998年 | 17篇 |
1997年 | 32篇 |
1996年 | 22篇 |
1995年 | 19篇 |
1994年 | 26篇 |
1993年 | 17篇 |
1992年 | 8篇 |
1991年 | 10篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1978年 | 2篇 |
排序方式: 共有1805条查询结果,搜索用时 13 毫秒
61.
62.
中南部非洲优势矿产资源有金、铜、铁、铬、金刚石,锰、铀、镍、钒、钴、铂、锑的储量也居世界前列。主要的矿产集中分布于前寒武纪地体内,中南部非洲前寒武纪地体的形成演化决定了矿产的种类和主要成矿类型。文章总结了中南部非洲的地质构造演化以及其主要矿产资源的成矿类型和分布规律,并划分成矿区带至三级。探讨了部分主要成矿区带的成矿规律:太古宙的矿产主要与花岗-绿岩地体有关;古元古代的矿产主要分布于陆缘盆地,与岩浆作用有关;中元古代的矿产主要与岩浆作用有关,次为沉积变质作用;新元古代的矿产主要与沉积变质作用有关,次为岩浆作用。 相似文献
63.
An extensive dataset (230 precipitation gauges and 79 stream gauges) was used to analyse rainfall–runoff relationships in 10 subregions of a 482000 km2 area in the south‐eastern USA (Maryland, Virginia, North Carolina, South Carolina and Georgia). The average annual rainfall and runoff for this study area between 1938 and 2005 were 1201 and 439 mm, respectively. Average runoff/rainfall ratios during this period varied between 0·24 in the southernmost Coastal Plain subregion to 0·64 in the Blue Ridge Province. Watershed elevation and relief are the principal determinants governing the conversion of rainfall to runoff. Temporal rainfall variation throughout the south‐eastern USA ranges from ~40% above and below normal while the variation for runoff is higher, from ? 75% to + 100%. In any given year there can exist a ± 25–50% error in predicted runoff deviation using the annual rainfall–runoff regression. Fast Fourier Transform and autoregressive spectral analysis revealed dominant cyclicities for rainfall and runoff between 14 and 17 years. Secondary periodicities were typically between 6–7 and 10–12 years. The inferred cyclicity may be related to ENSO and/or Central North Pacific atmospheric phenomena. Mann–Kendall analyses indicate that there were no consistent statistically significant temporal trends with respect to south‐eastern US rainfall and runoff during the study period. The results of U‐tests similarly indicated that rainfall between 1996 and 2005 was not statistically higher or lower than during earlier in the study period. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
64.
65.
GIS based landslide susceptibility mapping of Tevankarai Ar sub-watershed, Kodaikkanal, India using binary logistic regression analysis 总被引:5,自引:0,他引:5
Landslide susceptibility mapping is the first step in regional hazard management as it helps to understand the spatial distribution of the probability of slope failure in an area.An attempt is made to map the landslide susceptibility in Tevankarai Ar subwatershed,Kodaikkanal,India using binary logistic regression analysis.Geographic Information System is used to prepare the database of the predictor variables and landslide inventory map,which is used to build the spatial model of landslide susceptibility.The model describes the relationship between the dependent variable(presence and absence of landslide) and the independent variables selected for study(predictor variables) by the best fitting function.A forward stepwise logistic regression model using maximum likelihood estimation is used in the regression analysis.An inventory of 84 landslides and cells within a buffer distance of 10m around the landslide is used as the dependent variable.Relief,slope,aspect,plan curvature,profile curvature,land use,soil,topographic wetness index,proximity to roads and proximity to lineaments are taken as independent variables.The constant and the coefficient of the predictor variable retained by the regression model are used to calculate the probability of slope failure and analyze the effect of each predictor variable on landslide occurrence in thestudy area.The model shows that the most significant parameter contributing to landslides is slope.The other significant parameters are profile curvature,soil,road,wetness index and relief.The predictive logistic regression model is validated using temporal validation data-set of known landslide locations and shows an accuracy of 85.29 %. 相似文献
66.
Introduction Dead wood is an important structural and functional component of a forest ecosystem(Fridman and Welheim 2000). Recent studies also indicate that dead wood is important for maintaining both plant and animal diversity in different forest ecosystems (Grove 2001) as it serve as an energy source (Bray and Gorham 1964) and habitat for an array of organisms. Dead wood can also help reduce erosion, increase soil organic matters (McFee and Stone 1966), and suitable conditions for seedli… 相似文献
67.
Extreme rainfall events and associated natural hazards in Alaknanda valley, Indian Himalayan region 总被引:2,自引:0,他引:2
JOSHI Varun KUMAR Kireet 《山地科学学报》2006,3(3):228-236
Introduction The Himalaya is considered to be the youngest mountains on the earth, and is tectonically very active, and hence inherently (geologically) vulnerable to hazards. Extreme rainfall events, landslides, debris flows, torrents and flash floods due… 相似文献
68.
20世纪70年代由于防洪、防凌的需要,黄河两侧修建了南、北展宽区,受防洪的限制,展宽区内群众的经济发展相对落后。小浪底水库建成运用后,南北展宽区失去其防洪作用,该文分析了南北展宽区内经济现状和资源的优劣势,针对如何利用现有条件就资源开发、优势互补等方面提出了设想和建议。 相似文献
69.
70.
《世界地质(英文版)》2016,(4):205-215
Deccan volcanic sequences( DVS) in the central Deccan volcanic province( CDVP) are designated as Sahyadri Group having ~ 500 m thick lava pile associated with multiple sedimentary beds at different stratigraphic levels. In the eastern part of CDVP between the latitude 19 °55 '--20 °25 ' N and the longitudes 78 °15 '--78 °30 ' E,palynological investigation of the intertrappean sedimentary beds at five stratigraphic levels was carried out. The study was basically aimed for tracking the floral and environmental changes across the Deccan transition. The resulting finds indicate that the intertrappean sediments at the lowest stratigraphic level between the earliest lava flows are characterized by presence of marker Maastrichtian palynomorphs- Gabonisporis vigourouxii,Aquilapollenites bengalensis,Azolla cretacea and Farabeipollis associated with triporate and tricolpate pollen grains,phytoliths of Oryzeae of Poaceae family and peridinoid dinoflagellate cysts. The increasing volcanism deteriorated the existing flora as evident by absence of pollen-spores and presence of only structured biodegraded organic matter,fungal spores,acritarchs and algal( Botryococcus) remains in the sediments of higher-up in the sequence. For chronostratigraphic constraints on the lava flows magnetic polarity of the flows bracketing the intertrappean beds was investigated. The results indicated presence of N-R-N-R magnetic polarity in the basal lava pile that are interpreted as representing the magnetochron C30 N to C28 R( Maastrichtian-Paleogene). The floral change begins with the onset of volcanism in the chron C30 N and floral deterioration is observed in C29 N with increasing volcanism and it is only in the chron C28 R( Danian) that some evidence of recovery of flora is recorded. The current study shows that in eastern part of CDVP the post Cretaceous-Paleogene boundary eruptions represent the main phase of eruptions that triggered deterioration of the flora. 相似文献