全文获取类型
收费全文 | 2241篇 |
免费 | 740篇 |
国内免费 | 1471篇 |
专业分类
测绘学 | 60篇 |
大气科学 | 2357篇 |
地球物理 | 385篇 |
地质学 | 604篇 |
海洋学 | 653篇 |
天文学 | 24篇 |
综合类 | 142篇 |
自然地理 | 227篇 |
出版年
2024年 | 19篇 |
2023年 | 49篇 |
2022年 | 77篇 |
2021年 | 101篇 |
2020年 | 115篇 |
2019年 | 132篇 |
2018年 | 120篇 |
2017年 | 143篇 |
2016年 | 141篇 |
2015年 | 155篇 |
2014年 | 193篇 |
2013年 | 239篇 |
2012年 | 195篇 |
2011年 | 194篇 |
2010年 | 157篇 |
2009年 | 222篇 |
2008年 | 212篇 |
2007年 | 220篇 |
2006年 | 186篇 |
2005年 | 199篇 |
2004年 | 179篇 |
2003年 | 145篇 |
2002年 | 145篇 |
2001年 | 121篇 |
2000年 | 114篇 |
1999年 | 87篇 |
1998年 | 100篇 |
1997年 | 95篇 |
1996年 | 77篇 |
1995年 | 64篇 |
1994年 | 63篇 |
1993年 | 45篇 |
1992年 | 32篇 |
1991年 | 35篇 |
1990年 | 9篇 |
1989年 | 11篇 |
1988年 | 9篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 11篇 |
1980年 | 2篇 |
1977年 | 6篇 |
排序方式: 共有4452条查询结果,搜索用时 500 毫秒
991.
本文应用ECOM模式,设计1个控制试验,研究理想河口环流和盐水入侵的动力过程.数值计算结果表明,盐水入侵产生盐度锋面,在锋面处底层存在着向陆的密度流,为保持断面上质量连续,上层的流速趋于增大;近口门附近底层流有偏南分量,表明有横向环流存在.在口门外因斜压和底形的作用,产生明显的上升流.盐水入侵在空间上具有不对称性,高盐水位于北岸的下层.在拦门沙上游出现上下2个相反方向的横向环流,而在口门处只出现1个顺时针方向的横向环流.从动力机制上分析了盐水入侵的空间不对称性和横向环流的产生. 相似文献
992.
993.
Long-Term Variability of North Pacific Subtropical Mode Water in Response to Spin-Up of the Subtropical Gyre 总被引:1,自引:0,他引:1
The Meteorological Research Institute's ocean general circulation model (MRI-OGCM) has been used to investigate the temperature
variability of the North Pacific Subtropical Mode Water (NPSTMW) over a time series longer than 5 years via the spin-up of
the subtropical gyre. Besides an interannual variation, the wintertime sea surface temperature in the area where the NPSTMW
is formed, and the temperature of the NPSTMW itself, both change remarkably in a >5-year time scale. An analysis of heat budgets
showed that the long-term changes in NPSTMW temperature are due mainly to a leading advection of heat by the Kuroshio Extension
and compensating surface heat flux. As a result of a dynamical adjustment to the wind stress fields, the transports of the
Kuroshio and the Kuroshio Extension increased in the mid 1970s with a lag of 3 years after the wind stress curl in the central
North Pacific. The increased heat advection by the Kuroshio Extension induces a warming in the mixed layer in the NPSTMW formation
area, followed by a warming of the NPSTMW itself. Both these warming actions increase the heat release to the atmosphere.
These results imply that the surface heat flux over the Kuroshio Extension area varies in response to the change in the ocean
circulation through the spin-up of the subtropical gyre.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
994.
995.
996.
We have constructed a fine-resolution model with realistic bathymetry to study the spatial and temporal variations of circulation in the Taiwan Strait (TS). The TS model with a resolution of 3~10 km derives its open boundary conditions from a larger-scale model. The QSCAT/NCEP winds and AVHRR SST provide forcing at the sea surface. Because of the high resolution in model grids and forcing, the model achieves a previously unavailable level of agreement with most observations. On biweekly time scales surface-trapped current reversals often lead to Strait transport reversals if the northeasterly wind bursts in winter are sufficiently strong. On seasonal time scales the northward current is the strongest in summer since both summer monsoon and pressure gradient force are northward. The summer northward current appears to be relatively unimpeded by the Changyun Rise (CYR) and bifurcates slightly near the surface. With the arrival of the northeast monsoon in fall, downwind movement of China Coastal Water (CCW) is blocked by the northward current near 25.5°N and 120°E. In winter, the northward current weakens even more as the northeasterly monsoon strengthens. The CCW moves downwind along the western boundary; the CYR blocks part of the CCW and forces a U-shaped flow pattern in the northern Strait. Past studies have failed to reveal an anticyclonic eddy that develops on the northern flank of CYR in winter. On interannual time scales a weakened northeast monsoon during El Niño reduces advection of the cold CCW from the north and enhances intrusion of warm water from the south, resulting in warming in the TS. 相似文献
997.
本文利用NCAR(美国国家大气研究中心)1976年太平洋各层风场资料,计算了0°—50°N,105°E—110°W范围内,7月850hPa,700hPa,500hPa,300hPa,250hPa和200hPa各层上的垂直运动,并与叶笃正等所作的太平洋上空夏季平均环流特征作比较得出:(1)常年Walker环流明显,而E1 Ni(?)o发生年热带西太平洋上升运动减弱,东太平洋空气下沉区变成了强上升区,Walker环流下沉区东移至110°W以东;(2)常年热带西太平洋Hadley环流不明显,沿160°E以东Hadley环流越来越清楚,呈向东递增的趋势,而E1 Ni(?)o年Hadley环流东西变化甚为复杂,Hadley环流的上升支并不在赤道附近,而移至10°N左右,明显较常年偏北,Hadley环流也变成自热带向副热带倾斜的环流圈;(3)E1 Ni(?)o发生年,夏季以淮河为中心的空气上升区变成下沉区,而37°N以北的华北地区仍是上升区,华北多雨,所以出现Ⅰ型降水。 相似文献
998.
WEST: A northern California study of the role of wind-driven transport in the productivity of coastal plankton communities 总被引:1,自引:0,他引:1
J.L. Largier C.A. Lawrence M. Roughan D.M. Kaplan E.P. Dever C.E. Dorman R.M. Kudela S.M. Bollens F.P. Wilkerson R.C. Dugdale L.W. Botsford N. Garfield B. Kuebel Cervantes D. Kora
in 《Deep Sea Research Part II: Topical Studies in Oceanography》2006,53(25-26):2833
The “Wind Events and Shelf Transport” (WEST) program was an interdisciplinary study of coastal upwelling off northern California in 2000–03. WEST was comprised of modeling and field observations. The primary goal of WEST was to better describe and understand the competing influences of wind forcing on planktonic productivity in coastal waters. While increased upwelling-favorable winds lead to increased nutrient supply, they also result in reduced light exposure due to deeper surface mixed layers and increased advective loss of plankton from coastal waters. The key to understanding high levels of productivity, amidst these competing responses to wind forcing, is the temporal and spatial structure of upwelling. Temporal fluctuations and spatial patterns allow strong upwelling that favors nutrient delivery to be juxtaposed with less energetic conditions that favor stratification and plankton blooms. Observations of winds, ocean circulation, nutrients, phytoplankton and zooplankton off Bodega Bay and Point Reyes (38°N) were combined with model studies of winds, circulation and productivity. This overview of the WEST program provides an introduction to the WEST special issue of Deep-Sea Research, including the motivation for WEST, a summary of study components, an integrative synthesis of major research results to-date, and background on conditions during field studies in May–June 2001 (the upwelling period on which this special issue is focused). 相似文献
999.
Martyn S. Stoker Daniel Praeg Berit Oline Hjelstuen Jan Sverre Laberg Tove Nielsen Pat M. Shannon 《Marine and Petroleum Geology》2005,22(9-10):977
A regional correlation of Neogene stratigraphy has been attempted along and across the NW European Atlantic continental margin, between Mid-Norway and SW Ireland. Two unconformity-bounded successions are recognised. These are referred to as the lower and upper Neogene successions, and have been dated as Miocene–early Pliocene and early Pliocene–Holocene, respectively, in age. Their development is interpreted to reflect plate-wide, tectonically driven changes in the sedimentary, oceanographic and latterly climatic evolution of the NE Atlantic region. The lower Neogene succession mainly preserves a record of deep-water sedimentation that indicates an expansion of contourite sediment drifts above submarine unconformities, within this succession, on both sides of the eastern Greenland–Scotland Ridge from the mid-Miocene. This is interpreted to record enhanced deep-water exchange through the Faroe Conduit (deepest part of the Southern Gateway), and can be linked to compressive inversion of the Wyville–Thomson Ridge Complex. Thus, a pervasive, interconnected Arctic–North Atlantic deep-water circulation system is a Neogene phenomenon. The upper Neogene succession records a regional change, at about 4 Ma, in the patterns of contourite sedimentation (submarine erosion, new depocentres) coeval with the onset of rapid seaward-progradation of the continental margin by up to 100 km. This build-out of the shelf and slope is inferred to record a marked increase in sediment supply in response to uplift and tilting of the continental margin. Associated changes in deep-water circulation may be part of an Atlantic-wide reorganisation of ocean bottom currents. Glacial sediments form a major component of the prograding shelf margin (shelf-slope) sediment wedges, but stratigraphic data indicate that the onset of progradation pre-dates significant high-latitude glaciation by at least 1 Ma, and expansive Northern Hemisphere glaciation by at least 3 Ma. 相似文献
1000.
利用50 a的SODA资料对1月(冬季)和7月(夏季)印度洋越赤道经向翻转环流的年际变化进行研究。通过对2类典型年份的合成分析指出:1月份正异常年对应的经向翻转环流偏强,向北的经向热输送增加;7月份正异常年对应的经向翻转环流则偏弱,向南的经向热输送减少;1月份和7月份的负异常年皆与其正异常年相反;越赤道经向翻转环流有明显的年际变化,平均周期在4 a左右;经向翻转环流的年际变化和海面风场的变化密切相关。提出了反映1月和7月此环流年际变化的几个指数。 相似文献