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   12101篇
  免费   3313篇
  国内免费   5104篇
测绘学   332篇
大气科学   4572篇
地球物理   2359篇
地质学   7404篇
海洋学   2461篇
天文学   121篇
综合类   1366篇
自然地理   1903篇
  2024年   69篇
  2023年   202篇
  2022年   407篇
  2021年   525篇
  2020年   499篇
  2019年   597篇
  2018年   556篇
  2017年   636篇
  2016年   625篇
  2015年   709篇
  2014年   902篇
  2013年   901篇
  2012年   951篇
  2011年   972篇
  2010年   872篇
  2009年   961篇
  2008年   956篇
  2007年   1022篇
  2006年   990篇
  2005年   864篇
  2004年   760篇
  2003年   668篇
  2002年   638篇
  2001年   587篇
  2000年   504篇
  1999年   508篇
  1998年   422篇
  1997年   402篇
  1996年   334篇
  1995年   294篇
  1994年   248篇
  1993年   220篇
  1992年   168篇
  1991年   137篇
  1990年   85篇
  1989年   82篇
  1988年   60篇
  1987年   37篇
  1986年   19篇
  1985年   24篇
  1984年   20篇
  1983年   9篇
  1982年   9篇
  1981年   15篇
  1980年   12篇
  1979年   5篇
  1978年   12篇
  1977年   18篇
  1976年   1篇
  1954年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Rupert  Riedl 《Marine Ecology》1980,1(1):3-46
Abstract. The major changes within the concepts of marine ecology are investigated, with the aim to design this new journal's scientific format. Four phases of marine sciences are distinguished: the phase of seafarers, of oceanographic expeditions, of marine stations, and of field research. The changes in the latter two are discussed in detail. The changes are described as occurring along three axes. First, as a movement towards the object; accomplished by fieldwork, scientific diving, remote controlled equipment, and by underwater experimentation. Second, the cooperation between several disciplines that led towards bridging gaps. And lastly, how the discovery of unifying principles in ecology (the development of an ecological theory) led the approach in marine ecology towards increasing complexity.  相似文献   
62.
63.
河口环流和盐水入侵Ⅱ--径流量和海平面上升的影响   总被引:1,自引:0,他引:1  
本文利用本序列上篇论文建立的理想河口数值模式,研究径流量和海平面上升对河口环流和盐水入侵的影响.在径流量增大的情况下,口门内表层向海的流速增大,底层向陆的密度流减弱,滞流点下移.口门外侧向口门的密度流增大,上升流趋于增强.口门内盐水入侵减弱,口外盐度减小、冲淡水扩展范围增大.在口门上游北岸底层盐度下降明显,口门处南岸表层盐度下降明显.径流量变化对盐水入侵影响十分巨大.在海平面上升的情况下,拦门沙区域向陆的密度流增强,滞流点上移,表层向海的流动增大.口门内盐水入侵增强,口外盐度增大,冲淡水扩展范围减小.海平面上升对盐水入侵影响十分明显,北岸底层盐度增大尤为特出.  相似文献   
64.
Recent observations suggest that the annual mean southward transport of the East Sakhalin Current (ESC) is significantly larger than the annual mean Sverdrup transport. Motivated by this observational result, transport of a western boundary current has been investigated using a simple numerical model with a western slope. This transport is defined as the instantaneous barotropic transport integrated from the western boundary to the offshore point where the barotropic velocity vanishes. The model, forced by seasonally varying wind stress, exhibits an annual mean of the western boundary current transport that is larger than that of the Sverdrup transport, as observed. The southward transport from October to March in the model nearly equals the instantaneous Sverdrup transport, while the southward transport from April to September decreases slowly. Although the Sverdrup transport in July vanishes, the southward transport in summer nearly maintains the annual mean Sverdrup transport, because the barotropic Rossby wave cannot intrude on the western slope. This summer transport causes the larger annual mean. Although there are some uncertainties in the estimation of the Sverdrup transport in the Sea of Okhotsk, the seasonal variation of the southward transport in the model is qualitatively similar to the observations.  相似文献   
65.
台湾海峡纽形动物初报   总被引:1,自引:1,他引:1  
孙世春 《海洋科学》1995,19(5):45-48
首次报道台湾海峡产的纽形动物,包括沙栖原细首纽虫、浮游拟脑纽虫、椒状岩田纽虫、中华平裂纽虫和马顿氏潘丁纽虫,共5种。除椒状岩田纽虫在琉球群岛有报道外,均为东海新记录。  相似文献   
66.
本文利用1951~1987年286个网格点太平洋月平均海温场及500hPa月平均位势高度场,分析了春季西北太平洋(不含南海)热带气旋与海温场和大气环流的关系。结果表明:前期太平洋海温场与春季热带气旋生成数有显著的相关,并以前一年夏季和前期冬季更为明显。影响春季热带气旋生成的太平洋海温场主要有两个关键区,一个位于赤道东太平洋,为负相关:一个位于北太平洋中部,为正相关。文中还从海温对大气环流影响的角度出发,分析了春季热带气旋活动特多年与特少年前期及同期500hPa大气环流的特征及两者之间的差异。最后利用逐步回归方法作了春季西北太平洋热带气旋长期趋势预报。  相似文献   
67.
Observations of two small estuaries in Cape Cod, U.S.A. indicate large variations in salinity structure that are forced by variations in along-estuary wind stress. During onshore winds, the estuarine circulation is reduced, and the along-estuary salinity gradient increases as freshwater accumulates. During offshore winds, the surface outflow is enhanced, freshwater is flushed out of the estuary, and the along-estuary salinity gradient becomes weak. Constrictions block the wind-induced flushing, resulting in strong salinity fronts across the constrictions. The residence time of one of the estuaries varies by more than a factor of three in response to variations in wind-induced flushing. The other estuary has little variation of flushing associated with winds, due to a constriction at the mouth that inhibits the wind-induced exchange. The strong influence of winds on the flushing of these estuaries is due in part to their shallow depths, which accentuates the influence of wind stress relative to the effects of the horizontal density gradient. In addition, the residence times of the estuaries are comparable to the time scale of wind forcing, allowing large changes in water properties during wind events.  相似文献   
68.
Samples of O isotopic tracer were mlleMed at Sections P3,P25,PcM-t/2-E and PCM-1/2.w in both the Fast China Sea and the area to the east of the Ryūkyū-gunto during October-November,1991.Analytical results of the δ18O are as follows: (1) In the Kuroshio area,the δ18O isolines are almost parallel to the 200 m isobath.The value of δ18O is negative and reaches minimum mt the main axis of the Kuroshio,and increases on both sides.(2) In the Taiwan Warm Current (TWC) area there is a high δ18O tongue extending to the northeast.(3) In the area near the coast,the distribution of δ18O isoline shows that the Changjiang River runoff diffuses seaward and the land-ocean isotopic effect from the nearshore to the offshore.(4) The values of δ18O are from -1.0×10-3 to -0.5×10-3 in the shelf.(5) There is a low mre of δ18O value(<-1.6×10-3) at the 600 m layer in the Kuroshio area,which is quite in accord with the existence of a low salinity mre (S G 34.30) between the 600 and 800 m layers in the same area.Finally,the mrrelations of the δ18O with the salinity and temperature,the upwelling and so on are discussed.  相似文献   
69.
Ocean current forecasting is still in explorative stage of study. In the study, we face some problems that have not been met before. The solving of these problems has become fundamental premise for realizing the ocean current forecasting. In the present paper are discussed in depth the physical essence for such basic problems as the predictability of ocean current, the predictable currents, the dynamical basis for studying respectively the tidal current and circulation, the necessity of boundary model, the models on regions with different scales and their link. The foundations and plans to solve the problems are demonstrated. Finally a set of operational numerical forecasting system for ocean current is proposed.  相似文献   
70.
赵凯  濮梅娟 《台湾海峡》2005,24(3):370-376
0421号热带风暴“海马(Haima)”于2004年9月13日12:00在浙江省温州市沿海登陆,登陆后迅速减弱为热带低压,20:00在浙江境内消失.本研究采用物理量诊断分析法,探讨该热带风暴登陆前后涡度场、湿焓场变化对其移向和强度的影响.结果表明,该热带风暴登陆后,涡度(ξ)明显减弱.涡度局地变化(ξ/t)值分布显示,风暴移动方向的后方,涡度减弱的趋势比前方涡度增大的趋势更剧烈;风暴有向其外围(ξ/t)正值中心(即涡度增幅最大)移动的趋势.该热带风暴登陆前、后,湿焓都增大,但登陆后湿焓增大趋势已大大减弱;风暴有向湿焓局地变化(E/t)正值中心移动的趋势,即向能量增强最大的方向移动.  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