全文获取类型
收费全文 | 1849篇 |
免费 | 425篇 |
国内免费 | 867篇 |
专业分类
测绘学 | 8篇 |
大气科学 | 129篇 |
地球物理 | 239篇 |
地质学 | 2072篇 |
海洋学 | 16篇 |
天文学 | 1篇 |
综合类 | 83篇 |
自然地理 | 593篇 |
出版年
2024年 | 14篇 |
2023年 | 42篇 |
2022年 | 101篇 |
2021年 | 84篇 |
2020年 | 90篇 |
2019年 | 112篇 |
2018年 | 115篇 |
2017年 | 106篇 |
2016年 | 121篇 |
2015年 | 110篇 |
2014年 | 131篇 |
2013年 | 139篇 |
2012年 | 143篇 |
2011年 | 124篇 |
2010年 | 100篇 |
2009年 | 144篇 |
2008年 | 138篇 |
2007年 | 138篇 |
2006年 | 143篇 |
2005年 | 139篇 |
2004年 | 144篇 |
2003年 | 104篇 |
2002年 | 117篇 |
2001年 | 83篇 |
2000年 | 83篇 |
1999年 | 83篇 |
1998年 | 66篇 |
1997年 | 52篇 |
1996年 | 31篇 |
1995年 | 37篇 |
1994年 | 28篇 |
1993年 | 28篇 |
1992年 | 20篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 1篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有3141条查询结果,搜索用时 46 毫秒
781.
在地理信息系统ArcGIS环境下,结合1987-2001年的水文资料,用Spatial Analyst、Hydrologic Modeling等扩展模块,对祁连山中段北坡大野口河流域和海潮坝河流域的景观格局与水文特征进行比较分析,结果表明:大野口河流域的景观组分以低海拔的草地和乔木林占优势,草地所占面积最大,整个景观较为破碎;海潮坝河流域的景观组分以高海拔的裸地和灌丛占优势,裸地所占面积最大,景观破碎化程度相对较低。大野口河流域的蒸散发占降水量的61%,流域径流系数为0.39;而海潮坝河流域的蒸散发占降水量的41%,流域径流系数为0.59。研究表明,导致两流域生态水文效应相差较大的主要原因是两流域不同的景观格局。 相似文献
782.
The Renard igneous bodies were discovered in late 2001 as part of a regional diamond exploration program launched by Ashton Mining of Canada and SOQUEM. Nine bodies have been discovered within a 2-km-diameter area, and are comprised of root zone to lower diatreme facies rocks including kimberlitic breccia, olivine macrocrystic hypabyssal material, and brecciated country rock with minor amounts of kimberlitic material. Many mineralogical and petrographic features are common to both kimberlite and melnoite, and strict assignment of the rocks as kimberlite is not possible with these criteria alone. Whole rock trace element compositions suggest a closer affinity to Group I kimberlite, with derivation from a garnet-bearing mantle. Exceptions to conventional classification of the rocks along petrographic or mineralogical lines may be due in part to assimilation of felsic country rock into the Renard magmas at the time of emplacement. The Renard magmas were emplaced into northeastern Laurentia at 630 Ma, when the supercontinent was undergoing a change from convergent margin magmatism to rifting, the latter being associated ultimately with the opening of the Iapetus ocean. 相似文献
783.
784.
785.
南天山南缘晚泥盆世构造事件的^40Ar/^39Ar定年证据及其意义 总被引:2,自引:1,他引:2
南天山南缘前陆褶皱冲断带在独库公路范围内出露于铁力买提达坂一带,其构造岩片主体向南逆掩于塔里木盆地之上,构造样式以双向逆冲为特征。相关韧性剪切带中白云母矿物~(40)Ar/~(39)Ar同位素测年获坪年龄368±1Ma和等时线年龄368±6Ma。结合区域构造分析,这条作为南天山中央地块南部构造边界的大型复合式构造带,主要形成发育时限为晚泥盆世-早石炭世,并在二叠纪重新活动。前者可能是是南天山洋盆向北俯冲于伊犁地块之下的构造变形过程的痕迹,后者则可能是由伊犁-塔里木复合地体与北天山地块在晚石炭世-早二叠世发生碰撞而导致的构造变形。 相似文献
786.
Geochronological studies of mafic-ultramafic intrusions occurrence in the northern Dabie zone (NDZ) suggest that these pyroxenite-gabbro intrusions formed 120—130 Ma ago should be post-collisional magmatic rocks[1—4]. These mafic-ultramafic rocks provid… 相似文献
787.
788.
南天山库车秋里塔格褶皱带三维构造分析 总被引:17,自引:3,他引:17
笔者利用库车秋里塔格地区3000km的二维地震反射资料,结合地表构造测量成果,分段叙述秋里塔格褶皱带的构造几何学和运动学性质,说明构造交汇部位断层和褶皱的叠加过渡关系,并通过二维构造剖面的组合,建立秋里塔格褶皱带的三维构造几何模型。研究发现秋里塔格褶皱带为浅部断层传播褶皱与深部断层转折褶皱叠加形成的复合型背斜带,深部台阶状逆断层的叠加作用、叠加断层位移量的转换、断层断坡高度的变化造成地表背斜沿走向发生变化,笔者通过测量断层叠加方式、断层位移量转换、断层断坡高度,说明秋里塔格褶皱带背斜叠加、扭曲、分叉现象的构造机理,并且给出了秋里塔格褶皱带断层的滑移量。 相似文献
789.
大别山沙村和椒子岩基性-超基性岩锆石U-Pb定年、元素和碳氧同位素地球化学研究 总被引:13,自引:2,他引:13
对大别山北部沙村和椒子岩基性 -超基性岩进行了锆石U Pb定年、全岩主量和微量元素分析 ,全岩和单矿物氧同位素分析以及全岩碳含量及其同位素组成的测定。结果表明 ,这些基性 -超基性岩表现出强烈的轻稀土富集 ,高场强元素 (Nb ,Zr和Ti)负异常以及Pb和Ba正异常。锆石U Pb年龄指示了早白垩世 (12 2~ 12 8Ma)的岩浆结晶年龄 ,但是在 10 5~ 116Ma期间受到了热液蚀变。全岩和单矿物氧同位素比值变化较大 (全岩 :1.1‰~ 6 .6‰ ,单斜辉石 :3.85‰~5 .7‰ ,斜长石 :2 .8‰~ 7.3‰ ,锆石 :3.85‰~ 6 .0 4‰ ) ,大多数锆石具有与正常地幔锆石 ((5 .3±0 .3)‰ )不同的δ18O值 ,部分样品矿物对之间保存了氧同位素平衡分馏 ,而部分样品则表现出明显的氧同位素不平衡分馏 ,指示它们受到了岩浆期后亚固相水 -岩相互作用的扰动。全岩碳含量和同位素组成具有较大的变化范围 ,分别为 0 .0 3%~ 0 .18% ,δ13 C值为 - 2 7.0‰~ - 5 .8‰。将这些中生代基性 -超基性岩的元素和同位素数据与大别 -苏鲁榴辉岩比较后发现 ,它们之间具有较为一致的地球化学特征 ,因此可能具有一定的成因联系。这些榴辉岩的原岩为基性火成岩 ,对应于扬子板块北缘与新元古代裂谷构造有关的岩浆活动。古老富集岩石圈地幔及其上覆地壳部分 相似文献
790.
Ice-distal Upper Miocene marine strata from inland Antarctica 总被引:2,自引:0,他引:2
ABSTRACT Glacimarine strata of the Battye Glacier Formation (≈ 130 m thick), Pagodroma Group, exposed in the Amery Oasis of East Antarctica, provide a record of Late Miocene palaeoenvironmental conditions in an ice‐distal setting. The formation overlies the Amery Erosion Surface (≈ 300 m to ≈ 270 m above sea level) that formed during an advance of the Lambert Glacier into Prydz Bay (ODP Site 739), at least 750 km further north than today. Two lithological members: a grey and muddier Lower Member and a brown, sand‐rich Upper Member, reflect variation in proximity to the terminus of the Lambert Glacier. Ice‐distal, glacimarine, diatom‐bearing mud (up to 12% biogenic silica) and in situ articulated molluscs occur in the Lower Member. The Battye Glacier Formation is significant because of its inland location, which indicates that ice‐distal marine conditions existed 250 km inland from the current Amery Ice Shelf edge. Similar Neogene strata are known on land only from the Pliocene Sørsdal Formation in the Vestfold Hills, near the Antarctic coast. Three stratigraphic intervals of diatom‐bearing mud are recognized from glacially reworked clasts and from in situ strata informally referred to as the McLeod Beds and ‘Bed A’. The diatom‐bearing mud also contains sponge spicules and minor silicoflagellates and ebridians. Marine diatom biostratigraphy constrains the age of the beds to between 10·7 and 9·0 Ma (late Miocene). Abundant benthic diatoms suggest deposition within shallow euphotic waters. The high abundance of intercalary valves of Eucampia antarctica from an interval of the McLeod Beds suggests that there was less winter sea‐ice than in Prydz Bay today. It is unlikely that sea‐ice was perennial because the presence of Thalassionema spp. and Stellarima stellaris (Roper) Hasle et Sims suggests that summer sea‐surface temperatures were too warm (> 0°C and > 3°C respectively). The palaeoclimate at the time of deposition appears to have been analogous to that in modern fjords of East Greenland (e.g. Kangerdlugssuaq Fjord), which is consistent with the depositional model proposed previously for the Pagodroma Group. The three diatom‐bearing mud intervals were deposited in the Amery Oasis, ≈ 250 km inland of the current Amery Ice Shelf edge, when the East Antarctic Ice Sheet was reduced in size relative to today. 相似文献