全文获取类型
收费全文 | 56552篇 |
免费 | 2219篇 |
国内免费 | 3250篇 |
专业分类
测绘学 | 1953篇 |
大气科学 | 5015篇 |
地球物理 | 10217篇 |
地质学 | 25725篇 |
海洋学 | 5340篇 |
天文学 | 9658篇 |
综合类 | 1182篇 |
自然地理 | 2931篇 |
出版年
2023年 | 350篇 |
2022年 | 958篇 |
2021年 | 1310篇 |
2020年 | 1170篇 |
2019年 | 1258篇 |
2018年 | 4422篇 |
2017年 | 4030篇 |
2016年 | 3137篇 |
2015年 | 1206篇 |
2014年 | 1677篇 |
2013年 | 2185篇 |
2012年 | 2666篇 |
2011年 | 4400篇 |
2010年 | 3948篇 |
2009年 | 4170篇 |
2008年 | 3471篇 |
2007年 | 4126篇 |
2006年 | 1802篇 |
2005年 | 1313篇 |
2004年 | 1205篇 |
2003年 | 1338篇 |
2002年 | 1273篇 |
2001年 | 964篇 |
2000年 | 767篇 |
1999年 | 692篇 |
1998年 | 597篇 |
1997年 | 623篇 |
1996年 | 505篇 |
1995年 | 509篇 |
1994年 | 461篇 |
1993年 | 360篇 |
1992年 | 364篇 |
1991年 | 286篇 |
1990年 | 281篇 |
1989年 | 288篇 |
1988年 | 231篇 |
1987年 | 240篇 |
1986年 | 224篇 |
1985年 | 244篇 |
1984年 | 235篇 |
1983年 | 229篇 |
1982年 | 225篇 |
1981年 | 206篇 |
1980年 | 202篇 |
1979年 | 204篇 |
1978年 | 171篇 |
1977年 | 155篇 |
1976年 | 150篇 |
1975年 | 157篇 |
1973年 | 179篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
231.
Mass flux and undertow in a surf zone 总被引:1,自引:0,他引:1
I.A. Svendsen 《Coastal Engineering》1984,8(4):347-365
The mass of water carried shoreward by the breaking waves in a surf zone will, in a two-dimensional situation, be compensated by a seaward return flow, the undertow. It is shown that the undertow is driven by the local difference between radiation stress and the set-up pressure gradient which only balance each other in average over the depth. Turbulent shear stresses are required to maintain a steady situation. Comparison with measurements confirms the theoretical results. 相似文献
232.
Cluster analysis is discussed in the context of its application to map various test areas in the sea. By analysing the correspondence of the identified categories to areas with specific hydrological conditions, an attempt is made to relate the types of fine structure to diverse background conditions. With two test areas mapped, a conclusion is made as to the possible application of cluster analysis to this end.Translated by Vladimir A. Puchkin. 相似文献
233.
I. Rychlik 《Ocean Engineering》1996,23(6):447-454
In this note conservative bounds for significant crest height and amplitude obtained from the crossing intensity of a sea are presented. For Gaussian models of a sea level, the Rayleigh approximation for the distributions of amplitude and crest height is proved to provide conservative values for the expected significant wave characteristics. The results are illustrated by examples in which both Gaussian and non-Gaussian models for a sea are considered. 相似文献
234.
The problem of the seasonal variations of temperature and salinity in the intermediate zone located between the West African and the Gulf of Guinea upwellings is considered. The vertical distribution of the phase-amplitude characteristics of the annual and semi-annual variations is examined in good detail and their parameters are defined from the monthly means using the least-squares fit technique. The contribution of isopycnic advection to the formation of seasonal thermohaline variations is studied.Translated by Vladimir A. Puchkin. 相似文献
235.
236.
A. G. Matul T. A. Khusid V. V. Mukhina M. P. Chekhovskaya S. A. Safarova 《Oceanology》2007,47(1):80-90
The study of diatoms and benthic foraminifers from the southeastern shelf of the Laptev Sea shows that their most diverse and abundant recent assemblages populate the peripheral underwater part of the Lena River delta representing the marginal filter of the sea. This area is characterized by an intense interaction between the fresh waters of the Siberian rivers and the basin seawater, the Atlantic one included. Local Late Holocene (~last 2300 years) environments reflect the main regional and global paleoclimatic changes, the Medieval Warm Period (~600–1100 years B.P.) and the Little Ice Age (~100–600 years B.P.) inclusive. In addition, the composition and distribution of planktonic foraminifers implies a strong influence of the Atlantic water during the Holocene optimum ~5100–6200 years B.P. 相似文献
237.
We collected surface water along the 142nd E meridian from Tasmania to Antarctica in December 1999. We measured temperature,
salinity and total chlorophyll a; additionally, we collected suspended particle size fractions and used fluorometric analysis to determine the quantity of
chlorophyll a in each of four cell size classes: picoplankton (<3 μm), two nanoplankton fractions (3–10 μm and 10–20 μm) and microplankton
(> 20 μm). Changes in temperature and salinity show that we crossed 6 water masses separated by 5 fronts. We found low abundance
(<0.2 mg m−3) of chlorophyll in all size classes, with the exception of higher values near the continent (0.2 to 0.4 mg m−3). Lowest chlorophyll values (<0.1 mg m−3) were found in the Polar Frontal Zone (51° to 54°S). Microplankton made up the largest portion of total chlorophyll throughout
most of the region. We conclude that biomass of all phytoplankton fractions, especially pico-and nanoplankton, was constrained
by limiting factors, most probably iron, throughout the region and that ecosystem dynamics within a zone are not circumpolar
but are regionalized within sectors. 相似文献
238.
In a modern statement, the concept of a parametric integral model consists of integration of the energy balance equation (or wind forcing) over the frequency. The angular distribution of the energy and the frequency spectrum are prescribed. The equation is solved by the numerical method taking into consideration the energy advection and its local pumping with the assigned wind field varying in time and space. To calculate the swell waves one can employ the well-known Longuet-Higgins theorem on the invariance of a two-dimensional spectrum. or the ray discrete technique.UDK 551.466.315Translated by Mikhail M. Trufanov. 相似文献
239.
240.