首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   444篇
  免费   102篇
  国内免费   162篇
测绘学   6篇
大气科学   187篇
地球物理   106篇
地质学   247篇
海洋学   61篇
天文学   3篇
综合类   22篇
自然地理   76篇
  2024年   3篇
  2023年   8篇
  2022年   21篇
  2021年   24篇
  2020年   20篇
  2019年   27篇
  2018年   35篇
  2017年   20篇
  2016年   19篇
  2015年   22篇
  2014年   35篇
  2013年   40篇
  2012年   38篇
  2011年   47篇
  2010年   32篇
  2009年   25篇
  2008年   35篇
  2007年   29篇
  2006年   27篇
  2005年   19篇
  2004年   18篇
  2003年   21篇
  2002年   18篇
  2001年   15篇
  2000年   19篇
  1999年   17篇
  1998年   9篇
  1997年   18篇
  1996年   10篇
  1995年   9篇
  1994年   7篇
  1993年   3篇
  1992年   2篇
  1991年   2篇
  1990年   3篇
  1989年   1篇
  1988年   4篇
  1985年   4篇
  1983年   1篇
  1954年   1篇
排序方式: 共有708条查询结果,搜索用时 62 毫秒
31.
台西南盆地地质构造特征及油气远景   总被引:7,自引:3,他引:7  
本文从盆地的基本地质特征入手,分析了台西南盆地的地层、沉积、构造特征及油气条件,在进行盆地的定性分析的基础上,对盆地内的次级构造单元进行了类比,对盆地的含油气远景进行了评价,提出了该盆地的油气勘探方向。  相似文献   
32.
西南大西洋阿根廷滑柔鱼,Illex argentinus,巴塔哥尼亚南部群体是重要的经济种类。海洋环境因子在柔鱼资源分布中起着重要的作用。本研究利用基于环境因子的动态产量模型评估2000-2010年的滑柔鱼的资源量。假设海洋环境因子(滑柔鱼产卵场最适宜海表温度占比)影响动态产量模型的参数K,DIC值表明在正态分布和均匀分布下均是基于环境因子的评估模型优于基本的动态产量模型。阿根廷滑柔鱼的最大可持续产量(MSY)在351600吨到685 100吨之间,资源生物量在1322400吨到1 803 000吨之间,其捕捞死亡系数均小于F0.1FMSY,资源处在良好状态,没有遭受过度捕捞。本研究为应用环境因子在柔鱼类的资源评估与管理提中供了科学的参考方法。  相似文献   
33.
西南印度洋63.5°E热液区是在超慢速扩张洋脊发现的首个超镁铁质岩热液系统。对取自该区的热液硫化物样品进行了系统的矿物学和地球化学分析,矿物学分析结果表明:该热液区硫化物为富Fe型高温硫化物,且经历了较深程度的氧化蚀变,大量中间态的Fe氧化物充填在硫化物矿物间的孔隙及内部解理中;这些硫化物相以白铁矿为主,其次是等轴古巴矿和少量铜蓝,缺乏黄铁矿、闪锌矿。据推断,该区的热液成矿作用分为4个阶段:低温白铁矿阶段→高温等轴古巴矿阶段→自形白铁矿阶段→后期海底风化阶段(少量铜蓝以及大量的Fe的羟氧化物)。与之相对应,地球化学分析结果表明这些硫化物的Fe含量较高(31.57%~44.59%),Cu含量次之(0.16%~7.24%),而Zn含量普遍较低(0.01%~0.11%);微量元素较为富集Co(328×10-6~2 400×10-6)和Mn(48.5×10-6~1 730×10-6)。该区硫化物中较高含量的Fe、Co与超镁铁质岩热液系统相似,明显高于镁铁质岩热液系统。独特的热液硫化物矿物学特征和元素组成可能与该区普遍出露的地幔岩、橄榄岩蛇纹石化作用以及拆离断层的广泛发育的环境有关。  相似文献   
34.
The ultraslow-spreading Southwest Indian Ridge(SWIR) to the east of the Melville fracture zone is characterized by very low melt supply and intensive tectonic activity. Due to its weak thermal budget and extremely slow spreading rate, the easternmost SWIR was considered to be devoid of hydrothermal activity until the discovery of the inactive Mt. Jourdanne hydrothermal field(27°51′S, 63°56′E) in 1998. During the COMRA DY115-20 cruise in2009, two additional hydrothermal fields(i.e., the Tiancheng(27°51′S, 63°55′E) and Tianzuo(27°57′S, 63°32′E)fields) were discovered. Further detailed investigations of these two hydrothermal sites were conducted by Chinese manned submersible Jiaolong in 2014–2015. The Tiancheng filed can be characterized as a lowtemperature(up to 13.2°C) diffuse flow hydrothermal field, and is hosted by fractured basalts with hydrothermal fauna widespread on the seafloor. The Tianzuo hydrothermal field is an inactive sulfide field, which is hosted by ultramafic rocks and controlled by detachment fault. The discovery of the three hydrothermal fields around Segment #11 which receives more melt than the regional average, provided evidence for local enhanced magmatism providing heat source to drive hydrothermal circulation. We further imply that hydrothermal activity and sulfide deposits may be rather promising along the easternmost SWIR.  相似文献   
35.
西南岩溶地下水资源开发利用效应与潜力分析   总被引:20,自引:0,他引:20  
西南岩溶地区面积78万km2,地下水系统包括裸露岩溶水系统和覆盖-埋藏型岩溶水系统两大类。由于降水丰富、地下岩溶发育,西南岩溶地下水资源丰富,在43万km2调查区内,具有地下水天然资源量1762.82×108m3/a,岩溶地下水允许开采资源量615.70×108m3/a。近年来,通过开展水文地质调查,在地下河、表层岩溶水和蓄水构造岩溶水打井开采方面均取得重要进展,产生了显著的经济和生态环境效应。但由于西南地区岩溶水开发难度大,区域经济落后,西南岩溶地下水的开发利用程度普遍较低,已开采量为98.32×108m3/a,仅占允许开采量的15.97%,剩余地下水潜力资源量517.38×108m3/a。  相似文献   
36.
The ontogenetic, seasonal, bathymetric and regional variations in the feeding spectrum of 922 specimens of southern blue whiting Micromesistius australis and 512 specimens of hoki Macruronus magellanicus were studied on the Falkland Islands’ shelf (Southwest Atlantic) between November 1999 and April 2003. A total of 49 different prey items were found in the stomach contents of the two species, with the hyperiid Themisto gaudichaudii and Euphausiacea being amongst the most important prey. Although the species composition did not change over fish size, the proportions of individual prey items in their diets did, with an increase in T. gaudichaudii and Euphausiacea with increasing fish size in southern blue whiting. The opposite occurred in hoki. Seasonal variations in the diet were found to mirror the seasonal abundance of prey around the Falkland Islands for the two species. Intra-specific differences in the diet of both predators reflected the distribution of prey, which in turn was determined by the water structure in the two regions sampled, leading to very different diets. In the limited time that the two species occupied the same space there was little or no competition resulting in almost total segregation of their trophic niches in space and time.  相似文献   
37.
In mountainous areas, it is the undulant terrain, various types of geomorphic and land use that make the remote sensing images great metamorphism. Moreover, due to the elevation, there are many areas covered with shadow, clouds and snow that make the images more inaccurate. As a result, it would be very difficult to carry out auto-classification of RS images in these areas. The study took Southwest China as the case study area and the TM images, SPOT images as the basic information sources assisted by the a...  相似文献   
38.
The lower part of the Old Red Sandstone in the Dingle Penisula has been previously assigned to one lithostratigraphic group (Dingle Group) despite marked variations in sedimentary facies. However the apparently oldest non-marine sequence in the northwest of the peninsula has sedimentary and lithological attributes that contrast strongly with those of the late Silurian-early Devonian Dingle Group to the south. This northern sequence, here renamed the Smerwick Group, evolved independently of the Dingle Group in a separate basin of deposition. Field relationships between the two groups in the north of the peninsula are interpreted as indicating that the Smerwick Group overlies, with angular unconformity, a normal Dingle Group succession. Similarly, it is argued that the Smerwick Group overlies, with angular unconformity, the Dingle Group in the northwest of the peninsula, but there the Dingle Group is attenuated, represented only by a conglomerate unit some 10 m thick. In the absence of biostratigraphic evidence the age of the Smerwick Group is poorly constrained. Nevertheless, we propose a tectonic model that suggests that the Smerwick Group evolved within a small extensional half-graben on the northern margin of the Munster Basin. This model accounts for the stratigraphic and structural relationships observed, and implies that the Smerwick Group is of Late Devonian age.  相似文献   
39.
利用1982—2017年华西南部地区冬季气温和NCEP再分析资料以及CFS模式实时预测资料,通过SVD诊断分析,选取影响华西南部地区冬季气温的同期关键区大气环流和前期海温及OLR因子场,建立预测与观测场相结合的组合统计降尺度预测模型。该统计降尺度预测模型对1982—2017年的回报结果显示:与观测场的空间相关系数较CFS模式原始预测结果有显著提高,多年均值从-0.06提升到0.38,最高可达0.85。同时,此降尺度预测模型可较好地回报出华西南区冬季气温的空间分布型。  相似文献   
40.
赣西南下奥陶统樟木曲组笔石带的修正和补充   总被引:2,自引:0,他引:2  
本文在对笔石作系统研究的基础上,对樟木曲组的笔石带进行了补充和修正。由原来的9个笔石带划分为11个笔石带,厘定了各笔石带的范围和笔石群的总体面貌,并逐带与国内外进行了对比。文内还涉及到宁国阶的顶界、上下两层下垂时笔石以及关于肿笔石与心笔石混生的问题。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号