首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   6732篇
  免费   1703篇
  国内免费   2348篇
测绘学   433篇
大气科学   3498篇
地球物理   2458篇
地质学   2527篇
海洋学   902篇
天文学   139篇
综合类   501篇
自然地理   325篇
  2024年   37篇
  2023年   72篇
  2022年   164篇
  2021年   229篇
  2020年   268篇
  2019年   288篇
  2018年   243篇
  2017年   289篇
  2016年   294篇
  2015年   358篇
  2014年   442篇
  2013年   462篇
  2012年   473篇
  2011年   484篇
  2010年   366篇
  2009年   481篇
  2008年   438篇
  2007年   525篇
  2006年   435篇
  2005年   485篇
  2004年   441篇
  2003年   380篇
  2002年   350篇
  2001年   324篇
  2000年   332篇
  1999年   302篇
  1998年   317篇
  1997年   249篇
  1996年   241篇
  1995年   212篇
  1994年   183篇
  1993年   166篇
  1992年   109篇
  1991年   85篇
  1990年   40篇
  1989年   52篇
  1988年   43篇
  1987年   12篇
  1986年   11篇
  1985年   16篇
  1984年   14篇
  1983年   7篇
  1982年   14篇
  1981年   14篇
  1980年   15篇
  1979年   2篇
  1978年   9篇
  1977年   10篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
41.
对渤、黄海14个主要海湾的原始验潮记录进行了分析,从中筛选出水位变化幅度大于或等于50cm的54个假潮个例,着重分析了伴随假潮过程的天气形势,把可能引发假潮的天气形势归纳为4种基本类型。分析结果显示:绝大多数(92%)引发假潮的天气个例都与锋面活动有关;所有个例中低层大气基本上都是弱静力稳定,且都具有较强的垂直风速切变。根据观测事实和稳定度理论分析认为,低层大气的弱静力稳定层结构以及由垂直风速切变引起的剪切不稳定性,是假潮气象学成因的一种必要条件和物理机制。  相似文献   
42.
Temperature data at different layers of the past 45 years were studied and we found adiploe mode in the thermocline layer (DMT): anomalously cold sea temperature off the coast of Sumatra and warm sea temperature in the western Indian Ocean. First, we analyzed the temperature and the temperature anomaly (TA) along the equatorial Indian Ocean in different layers. This shows that stronger cold and warm TA signals appeared at subsurface than at the surface in the tropical Indian O-cean. This result shows that there may be a strong dipole mode pattern in the subsurface tropical Indian Ocean. Secondly we used Empirical Orthogonal Functions (EOF) to analyze the TA at thermocline layer. The first EOF pattern was a dipole mode pattern. Finally we analyzed the correlations between DMT and surface tropical dipole mode (SDM), DMT and Nino 3 SSTA, etc. and these correlations are strong.  相似文献   
43.
Repeated hydrographic casts, mooring time series and satellite sea surface temperature collected during the CANALES experiment (1996–98) are used to describe the thermohaline circulation in the Balearic Channels (western Mediterranean) and to analyze its variability. Mass transports are estimated by inverse calculations. The role played by each channel in the meridional water exchange is clarified: the Ibiza Channel funnels southward cool, saline, northern waters whereas the Mallorca Channel appears as the preferred route for the northward progression of warm, fresh, southern waters. A neat interannual trend is revealed by the continuous decrease of the amount of Western Mediterranean Intermediate Waters (WIW) brought by the Northern Current, reflecting the increase in temperature of the winter mixed layer in the northern Mediterranean that occurred each year between 1996 and 1998. A clear seasonal signal was also seen in the transport of the Northern Current which decreased from 1 to 1.4 Sv in winter to < 0.5 Sv in summer. The current intensified again in fall. A number of mesoscale eddies, from 20 to 70 km in size, most of them anticyclonic vortex eddies were brought by the unstable Northern Current, these eddies strongly perturbed the water exchange in the Ibiza Channel forcing retroflections of northern waters back to the north-east into the Balearic Current. These eddies either stayed stalled for several months in the Gulf of Valencia to the north of the channel, or were slowly funnelled southward through the channel narrows. A decreasing trend was observed in the mesoscale activity of the Northern Current between 1996 and 1998. Conversely, large, anticyclonic eddies, 150-km diameter, progressively invaded the Algerian Basin to the south of the channels in 1997–98 and forcing northward inflows (up to 0.75 Sv) of fresh and warm waters of Atlantic origin (AW) into the Mallorca Channel. The marked interannual differences observed in both northern and southern eddy activity may be linked to the interannual variability of the large scale thermohaline circulation.  相似文献   
44.
东亚冬夏季风对热带印度洋秋季海温异常的响应   总被引:5,自引:0,他引:5  
利用多年的Reynolds月平均海表温度资料和NCEP/NCAR全球大气再分析资料,分析了热带印度洋秋季海表温度距平(SSTA)与后期东亚冬夏季风强度变化的关系。结果表明,热带印度洋秋季SSTA的主要模态是全区一致(USB)型和偶极子(IOD)型,USB型模态主要代表热带印度洋秋季SSTA的长期变化趋势,而IOD型模态主要反映热带印度洋秋季SSTA的年际变化。热带印度洋秋季海温气候变率中既存在着明显的ENSO信号,也有独立于ENSO的变率特征,独立于ENSO的热带印度洋秋季SSTA变化的主要模态仍是USB型和IOD型。前期秋季USB模态与东亚冬季风及东亚副热带夏季风之间为负相关关系;与前期正(负)IOD模态相对应,南海夏季风强度偏弱(强),而东亚副热带夏季风强度偏强(弱)。USB型和IOD型模态对后期东亚冬、夏季风强度变化的影响是独立于ENSO的,但ENSO起到了调节二者相关显著程度的作用。  相似文献   
45.
热带印度洋偶极子发生和演变机制的数值研究   总被引:5,自引:0,他引:5  
对中国科学院大气物理研究所(IAP)大气科学和地球流体力学数值模拟国家重点实验室(LASG)发展的第三代海洋模式(L30T63 OGCM)进行了改进。分析了该模式1959年1月—1998年12月的40a积分结果,以此研究热带印度洋偶极子发生、发展和消亡的物理机制。对数值模拟结果的分析表明,赤道印度洋表面异常东风引起的异常环流结构是偶极子发生、发展的主要动力学原因,其表面异常东风转换为异常西风所引起的异常环流结构调整是偶极子消亡的主要动力学原因;海气界面热通量异常的交换对热带印度洋海表温度距平偶极子模态的形成和演变起着重要的作用;垂直输送作用是热带印度洋次表层海温偶极子模态发生和演变的主要物理机制。  相似文献   
46.
The absorption of anthropogenic CO2 and atmospheric deposition of acidity can both contribute to the acidification of the global ocean. Rainfall pH measurements and chemical compositions monitored on the island of Bermuda since 1980, and a long-term seawater CO2 time-series (1983–2005) in the subtropical North Atlantic Ocean near Bermuda were used to evaluate the influence of acidic deposition on the acidification of oligotrophic waters of the North Atlantic Ocean and coastal waters of the coral reef ecosystem of Bermuda. Since the early 1980's, the average annual wet deposition of acidity at Bermuda was 15 ± 14 mmol m− 2 year− 1, while surface seawater pH decreased by 0.0017 ± 0.0001 pH units each year. The gradual acidification of subtropical gyre waters was primarily due to uptake of anthropogenic CO2. We estimate that direct atmospheric acid deposition contributed 2% to the acidification of surface waters in the subtropical North Atlantic Ocean, although this value likely represents an upper limit. Acidifying deposition had negligible influence on seawater CO2 chemistry of the Bermuda coral reef, with no evident impact on hard coral calcification.  相似文献   
47.
In this study we examine the behavior of the thermohaline circulation, as simulated by the Community Climate System Model version 3 (CCSM3), for several centuries following CO2 stabilization for the SRES B1 and A1B scenarios and for an “overshoot” scenario in which CO2 levels temporarily reach the same level as in the A1B scenario before declining to an ultimate stabilization level that is identical to the B1 case. While we find no evidence for irreversible changes of the thermohaline circulation in the overshoot experiment, the interplay of the different timescales of the temperature response of the surface and interior ocean does lead to a number of differences in the long-term response of the ocean between it and the B1 stabilization scenario where the same GHG levels are approached by different paths. The stronger initial warming and its slow penetration into the deeper ocean, followed by a transient surface cooling in the overshoot scenario leads to lower static stability, deeper mixing, and a more rapid recovery of the thermohaline circulation than in the B1 stabilization scenario. While the overshoot scenario recovers surface conditions (e.g. SST, sea ice extent) very similar to the B1 scenario shortly after reaching the same GHG levels, the additional accumulation of heat in the interior ocean during the period of higher forcing causes the global mean ocean temperature and steric sea level to remain higher than in the B1 stabilization scenario for at least another several centuries.  相似文献   
48.
49.
Several large deployments of neutrally buoyant floats took place within the Antarctic Intermediate (AAIW), North Atlantic Deep Water (NADW), and the Antarctic Bottom Water (AABW) of the South Atlantic in the 1990s and a number of hydrographic sections were occupied as well. Here we use the spatially and temporally averaged velocities measured by these floats, combined with the hydrographic section data and various estimates of regional current transports from moored current meter arrays, to determine the circulation of the three major subthermocline water masses in a zonal strip across the South Atlantic between the latitudes of 19°S and 30°S. We concentrate on this region because the historical literature suggests that it is where the Deep Western Boundary Current containing NADW bifurcates. In support of this notion, we find that a net of about 5 Sv. of the 15–20 Sv that crosses 19°S does continue zonally eastward at least as far as the Mid-Atlantic Ridge. Once across the ridge it takes a circuit to the north along the ridge flanks before returning to the south in the eastern half of the Angola Basin. The data suggest that the NADW then continues on into the Indian Ocean. This scheme is discussed in the context of distributions of dissolved oxygen, silicate and salinity. In spite of the many float-years of data that were collected in the region a surprising result is that their impact on the computed solutions is quite modest. Although the focus is on the NADW we also discuss the circulation for the AAIW and AABW layers.  相似文献   
50.
Anomalous change of the Antarctic sea ice and global sea level change   总被引:3,自引:0,他引:3  
AnomalouschangeoftheAntarcticseaiceandglobalsealevelchange¥XieSimei;ZouBing;WangYiandBaoChenglan(1.NationalMarineEnvironmentF...  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号