全文获取类型
收费全文 | 6002篇 |
免费 | 834篇 |
国内免费 | 952篇 |
专业分类
测绘学 | 889篇 |
大气科学 | 636篇 |
地球物理 | 708篇 |
地质学 | 2436篇 |
海洋学 | 409篇 |
天文学 | 21篇 |
综合类 | 563篇 |
自然地理 | 2126篇 |
出版年
2024年 | 23篇 |
2023年 | 69篇 |
2022年 | 219篇 |
2021年 | 286篇 |
2020年 | 285篇 |
2019年 | 309篇 |
2018年 | 221篇 |
2017年 | 274篇 |
2016年 | 273篇 |
2015年 | 297篇 |
2014年 | 359篇 |
2013年 | 388篇 |
2012年 | 371篇 |
2011年 | 465篇 |
2010年 | 351篇 |
2009年 | 391篇 |
2008年 | 304篇 |
2007年 | 347篇 |
2006年 | 342篇 |
2005年 | 321篇 |
2004年 | 320篇 |
2003年 | 222篇 |
2002年 | 186篇 |
2001年 | 159篇 |
2000年 | 155篇 |
1999年 | 155篇 |
1998年 | 116篇 |
1997年 | 92篇 |
1996年 | 88篇 |
1995年 | 69篇 |
1994年 | 80篇 |
1993年 | 52篇 |
1992年 | 54篇 |
1991年 | 37篇 |
1990年 | 30篇 |
1989年 | 20篇 |
1988年 | 21篇 |
1987年 | 16篇 |
1986年 | 9篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 2篇 |
排序方式: 共有7788条查询结果,搜索用时 15 毫秒
31.
Comparison of Drags on Fish Cages of Different Shapes 总被引:1,自引:0,他引:1
1 .Introduction Commercial fishfarming in net cages is becoming widespread around the world as an importantsource of food.In PRChina ,mostfishfarmingtakes placeincalmcoastal areas .Fishcages work wellat these sites becausethe environmental forces are usua… 相似文献
32.
Multiple source rock assemblages were deposited in the sedimentary provinces in South China in geologic history,and some of them were destructed by and some survived against multiple tectonic movements.Therefore,multiple sources,mixed sources,and uneven distribution of sources occurred in the marine sedimentary basins in South China during the late stage of hydrocarbon pooling.Epidiagenesis of the marine carbonate reservoirs and its modification to reservoir poroperm characteristics determined the formation and the scale of natural gas pools.The exploration practices show that the large to medium gas fields mainly occur in areas with high-quality reservoirs.Detailed study of the paleo-oil accumulations and typical oil and gas reservoirs reveals that the basins experienced multiphase superimposition and modification,leading to the distribution of the Paleozoic paleo-oil accumulations and bitumen in the peripheral areas.The phenomenon that oil and gas production concentrates in the Sichuan basin indicates that the overall sealing conditions of a basin determine the oil/gas potentials and the scale of oil and gas production.This is a critical factor controlling the accumulation and distribution of gas in the marine sequences in South China.The early oil and gas pools in the Yangtze platform left billions of bitumen in the peripheral areas due to the destruction of seals.Since the Himalayan,"late-generation and late-accumulation" gas pools represented by the gas pools in the Sichuan (四川) basin were formed in the marine sedimentary sequences in South China as a result of the change of the sealing conditions.Current gas discoveries appear to be "paleo-generation and paleo-accumulation" gas pools but actually are "late-generation and late-accumulation" gas pools.These patterns of hydrocarbon pooling clearly depict themselves in western Sichuan basin and Weiyuan (威远)gas field.It is revealed that the gas pools in the Sichuan basin were mainly formed as a result of hydrocarbon phase change (thermal cracking of oil to gas),miscible migration,and dynamic equilibration since the Himalayan.A large number of gas pools were formed in the Himalayan and the gas pools in the marine sequences are characterized by late pooling; this kind of gas fields/pools are controlled by:(1) effectiveness of modification and superimposition of the marine basins,(2) effectiveness of the source rocks,(3) effectiveness of the overall preservation conditions,and (4) effectiveness of plays. 相似文献
33.
34.
35.
Paleocurrent indicator data collected in field work were used to study the early Cenozoic regional paleodrainage patterns in the Hob Xil basin in northern Tibetan plateau. The paleocurrent directions of the Eocene Fenghuoshan Group obviously show that the flows were northward with a unidirectional dispersal pattern. This probably reflects the uplift of the Qiangtang terrain during the initial basin deposition period and indicates that the Tanggula Moutains occurred as topographic highlands at least in the Eocene. Paleoflows of the Oligocene Yaxicuo Group were dominantly oriented to the north and then flowed eastwards during its late deposition. This regional variability of paleodrainage patterns of the Yaxicuo Group is interpreted to record the dispersal style of sediments from transverse rivers to longitudinal river systems. It is inferred that the Oligocene uplift of the Kunlun Mountains obstructed by northward paleoflows and created longitudinal river systems parallel to the orogenic belts. The temporal and spatial changes of the paleodrainage patterns suggest that the northern boundary of the Tibetan plateau during the early Cenozoic was situated in the Hoh Xil area and its uplift has progressed northwards through time. 相似文献
36.
37.
38.
39.
土地资源具有稀缺性和不可再生性,土地供给日渐紧张,拓展土地利用空间、将土地利用由平面趋向立体化发展的趋势日渐成熟。青岛市崂山区将建设用地使用权分层出让,不但垂范了法规政策,对区域经济的发展也具有很大的现实意义。 相似文献
40.
加强地理信息资源建设和开发利用的思考 总被引:1,自引:0,他引:1
地理信息资源的建设和开发利用在准确掌握国情国力、提高管理决策水平、管理社会公共事务、处理经济社会发展等重大问题中将发挥越来越重要的作用。本文在对发改委、测绘、国土、环境保护等部门进行调研的基础上,从我国地理信息的获取和利用现状、地理信息资源建设和开发利用政策法规的制定、产业发展以及国家安全等四个方面进行了研究,并提出了建议。 相似文献