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   1764篇
  免费   361篇
  国内免费   471篇
测绘学   181篇
大气科学   327篇
地球物理   398篇
地质学   1059篇
海洋学   247篇
天文学   47篇
综合类   126篇
自然地理   211篇
  2024年   12篇
  2023年   30篇
  2022年   69篇
  2021年   99篇
  2020年   60篇
  2019年   77篇
  2018年   73篇
  2017年   81篇
  2016年   110篇
  2015年   98篇
  2014年   107篇
  2013年   136篇
  2012年   84篇
  2011年   102篇
  2010年   105篇
  2009年   117篇
  2008年   121篇
  2007年   94篇
  2006年   91篇
  2005年   96篇
  2004年   82篇
  2003年   94篇
  2002年   162篇
  2001年   98篇
  2000年   88篇
  1999年   59篇
  1998年   31篇
  1997年   42篇
  1996年   31篇
  1995年   22篇
  1994年   24篇
  1993年   22篇
  1992年   13篇
  1991年   10篇
  1990年   8篇
  1989年   12篇
  1988年   7篇
  1987年   5篇
  1986年   5篇
  1985年   2篇
  1984年   4篇
  1981年   3篇
  1980年   1篇
  1979年   1篇
  1978年   1篇
  1977年   1篇
  1976年   2篇
  1964年   1篇
  1963年   1篇
  1958年   1篇
排序方式: 共有2596条查询结果,搜索用时 171 毫秒
831.
碳酸盐岩台内滩是重要的油气勘探目标,但关于台内滩储层的形成与评价研究相对薄弱。以巴麦地区先巴扎区块上石炭统小海子组作为研究碳酸盐岩台内滩的典型实例,“露头-岩心-镜下-测井-地震”五位一体综合分析表明,小海子组发育-蜓-类生屑滩、藻核形石滩、生屑滩、砂屑滩和薄皮鲕粒滩等5种碳酸盐岩台内滩,形成于海侵背景下、内缓坡台地中的微低古隆起环境,受控于构造变形和海平面变化。优质储层受开阔台地浅滩沉积作用和(准)同生期成岩作用控制;纵向上小海子组下亚段的储层物性比上亚段好;平面上Ⅰ类储层自Bt8井沿北东东向至西南向呈条带状展布,与台内古地貌较高区域相对应;Ⅱ类储层主要发育在台内古地貌较低区域,呈零散的片状分布。  相似文献   
832.
介绍了如何获取兴趣点(POI,Point of Interest)的注记范围,解释了为什么需要使用工具“Tiled Labels To Annotation”获取注记范围;介绍了兴趣点拾取的技术流程,以及如何设计数据库表结构和兴趣点拾取Web Service开发等内容;介绍了兴趣点拾取技术在“天地图·泰安”平台上的应用情况,并对以后数据快速更新产生的问题进行了总结。  相似文献   
833.
Late Paleozoic strata in northeastern China are distributed in a zonal pattern around the old-land on the Jiamusi-Mongolia Block.They are composed of active deposits in the regular distributed tectonic lithofacies zones.This indicates that the late Paleozoic strata belong to continental margin deposits.According to the strong conformability of the sedimentary strata in the same continental margin and distinct differences among the three continental margins,three stratigraphical regions of the Jiamusi-Mongolia Stratigraphical Province are recognized along the northern,southern and eastern margins of the Jiamusi-Mongolia Block,named respectively as Xing’an Stratigraphical Region,Inner Mongolia grass--Songhua River Stratigraphical Region and Baoqing--Hunchun Stratigraphical Region.Due to the characteristics of continental margin deposits and active sediments,the strata can be correlated on the level of formation by the methods of analysing the rock association in the same stratigraphic region.Therefore,some revisions of the lithological formations of the late Paleozoic strata in northeastern China have been made,and a new chart of lithostratigraphic correlation has been proposed.Furthermore,the present stratigraphic framework is setting on the International Stratigraphic Chart on the level of stage,after comprehensive researches to lithostratigraphy,biostratigraphy and chronostratigraphy,especially the conodont biostratigraphy and isotopic ages of volcanic rocks obtained in recent years.  相似文献   
834.
??????????????й?????????????????????????VS2010????????PPL??????м??????????????C++11?????C++0x???±???????????????????????????ж????????????з?????????????????????????????????????????????????????????????????????????Ч???  相似文献   
835.
HJ卫星图像水稻种植面积的识别分析   总被引:7,自引:0,他引:7  
 HJ-1A/1B卫星具有较高时空分辨率,是提取水稻等农作物种植面积的潜力数据源。本文以江汉平原腹地的监利县及周边相邻区域为研究区,根据水稻物候历,选取样区水稻生长关键期的多时相HJ-1A/1B卫星数据,利用水稻移栽期的水分信息和生长期的归一化植被指数(NDVI)变化信息,结合陆表水系数(LSWI)、短波红外波段的反射率(RIRS-B2)、差归一化植被指数(DNDVI),构建了HJ卫星数据的水稻种植面积识别方法,提取了研究区2009-2011年水稻种植面积,得到面积精度和样本点精度均不小于90%,Kappa值不小于0.80的结果。  相似文献   
836.
The ecological footprint concept and its calculation models are useful for the measurement of the sustainable level of social and economic development.The ecological security situation of the Three Gorges Reservoir Area(TGRA) was evaluated using this concept in this study.The construction of the Three Gorges Reservoir has led to the change in the ecology and immigration status of TGRA.The ecological footprint method is an important means to study the regional ecological security.Our results suggested that,by excluding the areas for biodiversity conservation(12% of the total land),the ecological footprint per capita was 0.57895 ha,which exceeded the ecological carrying capacity in TGRA.The total ecological deficit was found to be 11,522,193.34 ha,accounting for 95.02% of the ecological carrying capacity.These findings suggested that the ecological security of TGRA was not good.In order to compensate for the ecological deficit,it was essential to introduce natural resources from other regions.  相似文献   
837.
WU Pu  WANG Lily  SHAO Xuemei 《地理学报》2008,18(2):201-210
Having analyzed the tree ring width and maximum latewood density of Pinus den-sata from west Sichuan, we obtained different climate information from tree-ring width and maximum latewood density chronology. The growth of tree ring width was responded princi-pally to the precipitation in current May, which might be influenced by the activity of southwest monsoon, whereas the maximum latewood density reflected summer temperature (June–September). According to the correlation relationship, a transfer function had been used to reconstruct summer temperature for the study area. The explained variance of re-construction is 51% (F=52.099, p<0.0001). In the reconstruction series: before the 1930s, the climate was relatively cold, and relatively warm from 1930 to 1960, this trend was in accor-dance with the cold-warm period of the last 100 years, west Sichuan. Compared with Chengdu, the warming break point in west Sichuan is 3 years ahead of time, indicating that the Tibetan Plateau was more sensitive to temperature change. There was an evident sum-mer warming signal after 1983. Although the last 100-year running average of summer tem-perature in the 1990s was the maximum, the running average of the early 1990s was below the average line and it was cold summer, but summer drought occurred in the late 1990s.  相似文献   
838.
冀北承德地区张营子-六沟走滑断层及其构造意义   总被引:3,自引:0,他引:3  
笔者等运用构造解析的方法,在对冀北承德县一带的研究中鉴别出一条走向为北北西到北西向的右行走滑断层。断层将沿线太古宙古老变质岩、元古宇蓟县系、青白口系右行错断,它也将一个早期形成的短轴背斜构造带右行错断。位移距离沿断层向南南东方向逐渐减小,由15~16km逐渐减小到12~13km。断层截止于平泉—古北口断裂南侧元古宙逆冲岩片前缘,并将逆冲岩片南侧寒武系和奥陶系错动形成右行不对称牵引褶皱。由于断层使下三叠统丁家沟组变形而中三叠统胡杖子组却自西向东稳定延伸,所以笔者等认为断层形成的时代为早三叠世末。该走滑断层的存在表明,燕山板内造山带早期逆冲构造通过一些横向走滑断层的调节,呈板条状向南逆冲的。另外,前人所确定的“承德推覆体”上的元古宇与实际上在中三叠世以前与其东南侧的元古宇是连为一体的,由于北北西向右行走滑断层的错动使它们被右行错开。  相似文献   
839.
The Yangtze River Source Region has an area of 137,704 km2.Its mean annual runoff of 12.52 billion m3,which was recorded by the Chumda Hydrological Station in 1961-2000,accounts for only 0.13 percent of the Yangtze River’s total annual streamflow.The extensive rivers,lakes,wetlands,glaciers,snow fields,and permafrost of the Yangtze River Source Region,as well as the region’s vast alpine grasslands,play a critical role in storing and regulating the flow of water not only in the upper Yangtze River watershed of Qinghai,Sichuan,the Tibet Autonomous Region (TAR) (Tibet) and Yunnan,but also throughout the entire lower Yangtze River basin.Climate change has been the dominant factor in recent fluctuation in the volume of the Yangtze River Source Region’s glacier resources.The Chumda Hydrological Station on the lower Tongtian River has registered a mean annual glacial meltwater of 1.13 billion m3 for the period 1961-2000,makes up 9 percent of the total annual runoff.Glacial meltwater makes up a significant percentage of streamflow in the Yangtze River Source Region,the major rivers of the upper Yangtze River Source Region:the Togto,Dam Chu,Garchu,and Bi Chu (Bu Chu) rivers all originate at large glaciers along the Tanggula Range.Glaciers in the Yangtze River Source Region are typical continental-type glaciers with most glacial meltwater flow occurring June-August;the close correlation between June-August river flows and temperature illustrates the important role of glacial meltwater in feeding rivers.Glaciers in the source region have undergone a long period of rapid ablation beginning in 1993.Examination of flow and temperature data for the 1961-2000 period shows that the annual melting period for glacial ice,snow,and frozen ground in the Yangtze River Source Region now begins earlier because of increasing spring temperatures,resulting in the reduction of summer flood season peak runoffs;meanwhile,increased rates of glacier ablation have resulted in more uneven annual distribution of runoff in the source region.T  相似文献   
840.
The Yarlung Tsangpo Grand Canyon region is located in the frontal zone of the eastern Himalayan syntaxis, where neo-tectonics and seismicity are intensive and closely related to each other. In the region, two sets of fault structures have developed, striking NNE-NE and NWW-NW, respectively. Investigation shows that they differ markedly in terms of scope, property, active times and intensity. The NWW-NW trending faults are large in size, and most are thrust and thrust strike-slip faults, formed in earlier times. The NEE-NE-strike faults are relatively small in size individually, with concentrated distribution, constituting the NNE-trending shear extensional fault zone, which is relatively younger with evident late Quaternary activities. Strong earthquakes occur mainly in the areas or zones of intensive differential movement of the Himalayas, e.g. along the deep and large fault zones around the crustal blocks. Most earthquakes of M≥7.0 are closely related to tectonics, where large-scale Holocene active faults are distributed with complicated fault geometry, or the faults of multiple directions intersect. Among them, earthquakes of M≥7.5 have occurred on the NW and NE-trending faults with a greater strike-slip component in the fault tectonic zones.  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