全文获取类型
收费全文 | 11576篇 |
免费 | 2920篇 |
国内免费 | 622篇 |
专业分类
测绘学 | 185篇 |
大气科学 | 68篇 |
地球物理 | 11215篇 |
地质学 | 1960篇 |
海洋学 | 261篇 |
天文学 | 26篇 |
综合类 | 959篇 |
自然地理 | 444篇 |
出版年
2024年 | 9篇 |
2023年 | 97篇 |
2022年 | 268篇 |
2021年 | 424篇 |
2020年 | 382篇 |
2019年 | 430篇 |
2018年 | 434篇 |
2017年 | 426篇 |
2016年 | 309篇 |
2015年 | 485篇 |
2014年 | 611篇 |
2013年 | 625篇 |
2012年 | 572篇 |
2011年 | 677篇 |
2010年 | 600篇 |
2009年 | 845篇 |
2008年 | 621篇 |
2007年 | 693篇 |
2006年 | 667篇 |
2005年 | 672篇 |
2004年 | 599篇 |
2003年 | 592篇 |
2002年 | 480篇 |
2001年 | 447篇 |
2000年 | 416篇 |
1999年 | 355篇 |
1998年 | 357篇 |
1997年 | 339篇 |
1996年 | 355篇 |
1995年 | 299篇 |
1994年 | 287篇 |
1993年 | 221篇 |
1992年 | 181篇 |
1991年 | 96篇 |
1990年 | 76篇 |
1989年 | 52篇 |
1988年 | 45篇 |
1987年 | 16篇 |
1986年 | 15篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 15篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1954年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 23 毫秒
51.
Observations of the Labrador Sea eddy field 总被引:2,自引:0,他引:2
Jonathan M. Lilly Peter B. RhinesFriedrich Schott Kara LavenderJohn Lazier Uwe SendEric D’Asaro 《Progress in Oceanography》2003,59(1):75-176
This paper is an observational study of small-scale coherent eddies in the Labrador Sea, a region of dense water formation thought to be of considerable importance to the North Atlantic overturning circulation. Numerical studies of deep convection emphasize coherent eddies as a mechanism for the lateral transport of heat, yet their small size has hindered observational progress. A large part of this paper is therefore devoted to developing new methods for identifying and describing coherent eddies in two observational platforms, current meter moorings and satellite altimetry. Details of the current and water mass structure of individual eddy events, as they are swept past by an advecting flow, can then be extracted from the mooring data. A transition is seen during mid-1997, with long-lived boundary current eddies dominating the central Labrador Sea year-round after this time, and convectively formed eddies similar to those seen in deep convection modeling studies apparent prior to this time. The TOPEX / Poseidon altimeter covers the Labrador Sea with a loose “net” of observations, through which coherent eddies can seem to appear and disappear. By concentrating on locating and describing anomalous events in individual altimeter tracks, a portrait of the spatial and temporal variability of the underlying eddy field can be constructed. The altimeter results reveal an annual “pulsation” of energy and of coherent eddies originating during the late fall at a particular location in the boundary current, pinpointing the time and place of the boundary current-type eddy formation. The interannual variability seen at the mooring is reproduced, but the mooring site is found to be within a localized region of greatly enhanced eddy activity. Notably lacking in both the annual cycle and interannual variability is a clear relationship between the eddies or eddy energy and the intensity of wintertime cooling. These eddy observations, as well as hydrographic evidence, suggest an active role for boundary current dynamics in shaping the energetics and water mass properties of the interior region. 相似文献
52.
台湾海峡及其西边地区正常地震动态及危险性特征 总被引:1,自引:2,他引:1
本文从地震的时,空分布特征,区域应力场动态,能量释放方式,b值及震群特征6个方面研究了台湾海峡及其西边地区地震活动的正常动态及异常特征。结果表明,具有前兆意义的变化模式表现为区域地震活动在时间,空间及功能方面的有序性变化,即:(a)地震空间分布由分散转为集中,形成条带或空区;(b)断裂活动由多组转为单一,应力场趋向一致;(display status 相似文献
53.
Carl T.F. Ross 《Ocean Engineering》2006,33(16):2087-2104
The paper presents a conceptual design of an underwater star wars’ system, which will be more difficult to detect by the enemy than a recently proposed ‘surface’ star wars’ system.The paper suggests that for the proposed structures needed for the underwater star wars’ system, the material of construction should be a composite and not a metal, as use of the latter for large deep diving underwater vessels will result in such structures sinking to the bottom of the ocean like stones, due to the fact that they will have no reserve buoyancy. The paper also shows that composites have better sound absorption characteristics, thereby making the underwater structures difficult to detect through sonar equipment. It is proposed that these underwater structures should operate up to a depth of 7.16 miles (11.52 km), as at this depth, all of the oceans’ bottoms can be reached.The author shows that current technology can be used to construct and operate such vessels, but more progress needs to be made with metal matrix and ceramic composites, so that the hulls of underwater missiles and torpedoes can be constructed in these materials. 相似文献
54.
Zooplankton samples from the eastern Mediterranean were collected in April/May 1999 with a multiple opening and closing net (mesh size 333 μm) to examine the distribution and taxonomic composition of mesozooplankton, mainly Calanoida (Copepoda), some years after the onset of the Eastern Mediterranean Transient (EMT), a climatically induced shift in hydrography. The samples from seven stations on a transect from the Ionian Sea to the eastern part of the Levantine Basin were collected at closely spaced vertical intervals from the surface to water depths of 4250 m. Data from January 1987, June 1993, January 1998 and October 2001 from the main site of investigation, south of Crete, were used to describe the temporal evolution before (1987), during (1993) and after (1998–2001) the EMT. The eastern Mediterranean mesozooplankton fauna is dominated by three Calanoida species along the west–east transect, with varying abundances in different depth‐zones: Haloptilus longicornis in the epipelagic zone, Eucalanus monachus in the mesopelagic zone, and Lucicutia longiserrata in the bathypelagic zone. A drastic change in mesozooplankton composition and abundance occurred at the main site during the EMT, whereupon increased abundances of Candacia elongata and L. longiserrata were observed in the bathypelagic zone in the following years; L. longiserrata accounted for 43% of the total mesozooplankton in this zone. The hypothesis is posed that the Mediterranean deep‐sea ecosystem is able to respond quickly to changes in the environment and memorizes these changes over time. We claim that the biological effects of climatically induced changes can be easily monitored in the deep eastern Mediterranean Sea using calanoid copepod key species due to the hydrographically extreme, but ‘simply structured’ ecosystem. 相似文献
55.
Kyung-Il Chang Nelson G. Hogg Moon-Sik Suk Sang-Kyung Byun Young-Gyu Kim Kuh Kim 《Deep Sea Research Part I: Oceanographic Research Papers》2002,49(12)
The Ulleung Basin is one of three deep basins that are contained within the East/Japan Sea. Current meter moorings have been maintained in this basin beginning in 1996. The data from these moorings are used to investigate the mean circulation pattern, variability of deep flows, and volume transports of major water masses in the Ulleung Basin with supporting hydrographic data and help from a high-resolution numerical model. The bottom water within the Ulleung Basin, which must enter through a constricted passage from the north, is found to circulate cyclonically—a pattern that seems prevalent throughout the East Sea. A strong current of about 6 cms−1 on average flows southward over the continental slope off the Korean coast underlying the northward East Korean Warm Current as part of the mean abyssal cyclonic circulation. Volume transports of the northward East Korean Warm Current, and southward flowing East Sea Intermediate Water and East Sea Proper Water are estimated to be 1.4 Sv (1 Sv=10−6 m3 s−1), 0.8 Sv, and 3.0–4.0 Sv, respectively. Deep flow variability involves a wide range of time scales with no apparent seasonal variations, whereas the deep currents in the northern East Sea are known to be strongly seasonal. 相似文献
56.
Risk Assessment for Tuzla Naval Base Breakwater 总被引:5,自引:0,他引:5
Can Elmar BALAS 《中国海洋工程》2003,17(3)
1 .IntroductionTurkeywasstruckbytwomajorearthquakeeventsonAugust 1 7thandNovember 1 2th ,1 999,namedIzmit (Mw=7.4 )andD櫣zce (Mw=7.2 )earthquakes,respectively .ThestationsoperatedbytheGeneralDirectorateofDisasterAffairs,theKandilliObservatoryandEarthquakeResearchInstituteofIstanbulTechnicalUniversitymeasuredatleast 2 7stronggroundmotionsfortheIzmitearthquakewithin 2 0 0kmofthefault.AsignificantsegmentofthefaultrupturedintheareabetweenthewestofGolcukandtheeastofLakeSapanca .Inthesou… 相似文献
57.
1 .IntroductionEpicontinental sea or land could formfromcontinental shelf because of the decreasing sea levelduring Quaternary.There is a large-area shell sand deposit more than ten meters thick in the neriticzone of China .To use the abundant marine shell sandresource as engineering material for ocean engi-neering and port engineeringis veryimportant .Sand (Gred and Bjorn,1999) ,fine sand (Zhangetal .,2002) , mediumand coarse sand (Qiuet al .,1995) ,highly weathered stone ballast (Zhanetal… 相似文献
58.
59.
60.
四川汶川大地震的构造分析 总被引:6,自引:0,他引:6
2008年5月12日在汶川映秀(北纬31.0°,东经103.4°)发生8级大地震,而后发生万余次余震,其最大震级为6.4级.此次地震属主震-余震型地震.通过构造分析认为.汶川大地震是构造地震,主要受龙门山断裂带的强烈活动控制.它是一种板内地震,其动力来源来自印度板块与欧亚板块的碰撞.而成都平原处于稳定地块中,尽管离震中较近,然受地震的影响有限,是比较安全的. 相似文献