全文获取类型
收费全文 | 74047篇 |
免费 | 1492篇 |
国内免费 | 677篇 |
专业分类
测绘学 | 1799篇 |
大气科学 | 5268篇 |
地球物理 | 14801篇 |
地质学 | 26218篇 |
海洋学 | 6458篇 |
天文学 | 17007篇 |
综合类 | 223篇 |
自然地理 | 4442篇 |
出版年
2022年 | 409篇 |
2021年 | 708篇 |
2020年 | 805篇 |
2019年 | 867篇 |
2018年 | 1943篇 |
2017年 | 1801篇 |
2016年 | 2298篇 |
2015年 | 1363篇 |
2014年 | 2243篇 |
2013年 | 3929篇 |
2012年 | 2357篇 |
2011年 | 3242篇 |
2010年 | 2728篇 |
2009年 | 3659篇 |
2008年 | 3388篇 |
2007年 | 3161篇 |
2006年 | 2980篇 |
2005年 | 2442篇 |
2004年 | 2347篇 |
2003年 | 2209篇 |
2002年 | 2009篇 |
2001年 | 1862篇 |
2000年 | 1800篇 |
1999年 | 1434篇 |
1998年 | 1529篇 |
1997年 | 1427篇 |
1996年 | 1139篇 |
1995年 | 1186篇 |
1994年 | 1012篇 |
1993年 | 920篇 |
1992年 | 890篇 |
1991年 | 786篇 |
1990年 | 889篇 |
1989年 | 768篇 |
1988年 | 687篇 |
1987年 | 858篇 |
1986年 | 696篇 |
1985年 | 916篇 |
1984年 | 989篇 |
1983年 | 928篇 |
1982年 | 884篇 |
1981年 | 773篇 |
1980年 | 716篇 |
1979年 | 643篇 |
1978年 | 640篇 |
1977年 | 599篇 |
1976年 | 576篇 |
1975年 | 536篇 |
1974年 | 531篇 |
1973年 | 500篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
S. B. Dharmadhikari E. Garcia S. Espinoza J. Dominguez J. M. Goris 《Ocean Engineering》1978,5(3):165-180
This paper describes the process of launching and joining of two sections of a product carrier of 30,500 DWT built at Dianca shipyard at Puerto Cabello, Venezuela. The specifications and characteristics of this ship are in line with the market requirements. This paper deals with the problems encountered during the decision of dividing the ship in two halves, use of syncrolift for launching and subsequent joining of two halves in the dry dock. 相似文献
993.
Abstract. New data on the planktonic diatoms from the Gulf of Naples are presented together with those from the literature. Information is given on abundances, seasonal cycles and distributions of 183 taxa, including species, varieties and forms. 相似文献
994.
995.
Wavelet analysis of bathymetric sidescan sonar data for the classification of seafloor sediments in Hopvågen Bay - Norway 总被引:1,自引:0,他引:1
In this paper we examine the use of bathymetric sidescan sonar for automatic classification of seabed sediments. Bathymetric sidescan sonar, here implemented through a small receiver array, retains the advantage of sidescan in speed through illuminating large swaths, but also enables the data gathered to be located spatially. The spatial location allows the image intensity to be corrected for depth and insonification angle, thus improving the use of the sonar for identifying changes in seafloor sediment. In this paper we investigate automatic tools for seabed recognition, using wavelets to analyse the image of Hopvågen Bay in Norway. We use the back-propagation elimination algorithm to determine the most significant wavelet features for discrimination. We show that the features selected present good agreement with the grab sample results in the survey under study and can be used in a classifier to discriminate between different seabed sediments. 相似文献
996.
The riverine mud that escapes retention in the estuaries and enters the Gulf of Papua appears to be transported southeastward, across depth contours, by the prevailing currents in a series of wind-driven events. The mud deposits to the southeast of the rivers, at the mid-shelf region within a depth range of 40–60 m. Mud transported farther eastward is carried down the continental rise. Coarser riverine sediment (silt and sand) is deposited closer inshore. On the outer shelf (depth >60 m) relict carbonate debris dominates. The area of mud has maximum rates of pelagic and benthic productivity in the gulf. 相似文献
997.
998.
The average corrected heat flow in the Wilmington Canyon region, an area of inferred slope instability, is 35 ± 10 mW/m2. This average heat flow is marginally consistent with the 46 ± 9 mW/m2 measured at other North Atlantic sites over 160 m.y. old. High topographic relief causes most of the variability in surface heat flow and may lower the mean surface heat flow. There is no significant difference between the average corrected heat flow of 35 ± 10 mW/m2 in sediment slide areas and the average corrected heat flow of 34 ± 10 mW/m2 in undisturbed sediments. 相似文献
999.
Abstract. Survival and behaviour of the hermatypic coral Diploria strigosa was studied during 6–24 h doses with water-accomodated fractions of chemically dispersed crude oil, and for a subsequent recovery period of 1 month. Experiments utilized a flow-through laboratory dosing procedure and incorporated petroleum hydrocarbon measurements in order to simulate a major but short-term oil spill in shallow subtidal benthic reef environments. Chemically dispersed oil treatments consisted of Arabian Light Crude oil with Corexit 9527 or BP1100WD at 1–20 ppm concentrations of oil.
In general, effects observed were sub-lethal, temporary, and associated with the highest concentrations tested. Responses to the presence of dispersed oil at 20ppm for 24 h included mesenterial filament extrusion, extreme tissue contraction, tentacle retraction and localized tissue rupture. The nature and severity of reactions during the dosing phase varied between colonies and treatments, but colonies typically resumed normal behaviour within 2 h to 4 d of the recovery period. It therefore seems unlikely that observed biological effects would impair long-term viability. 相似文献
In general, effects observed were sub-lethal, temporary, and associated with the highest concentrations tested. Responses to the presence of dispersed oil at 20ppm for 24 h included mesenterial filament extrusion, extreme tissue contraction, tentacle retraction and localized tissue rupture. The nature and severity of reactions during the dosing phase varied between colonies and treatments, but colonies typically resumed normal behaviour within 2 h to 4 d of the recovery period. It therefore seems unlikely that observed biological effects would impair long-term viability. 相似文献
1000.