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   41313篇
  免费   19474篇
  国内免费   44649篇
测绘学   4710篇
大气科学   21975篇
地球物理   13270篇
地质学   38514篇
海洋学   17690篇
天文学   848篇
综合类   4920篇
自然地理   3509篇
  2024年   276篇
  2023年   626篇
  2022年   1071篇
  2021年   1502篇
  2020年   2482篇
  2019年   5774篇
  2018年   5860篇
  2017年   5556篇
  2016年   5677篇
  2015年   5176篇
  2014年   4656篇
  2013年   5339篇
  2012年   5199篇
  2011年   5010篇
  2010年   4983篇
  2009年   4280篇
  2008年   3649篇
  2007年   3554篇
  2006年   3298篇
  2005年   2969篇
  2004年   3139篇
  2003年   2700篇
  2002年   2503篇
  2001年   2254篇
  2000年   1802篇
  1999年   1648篇
  1998年   1684篇
  1997年   1739篇
  1996年   1345篇
  1995年   1311篇
  1994年   1176篇
  1993年   1147篇
  1992年   975篇
  1991年   732篇
  1990年   696篇
  1989年   577篇
  1988年   492篇
  1987年   390篇
  1986年   315篇
  1985年   248篇
  1984年   283篇
  1983年   182篇
  1982年   209篇
  1981年   150篇
  1980年   111篇
  1979年   119篇
  1978年   52篇
  1977年   44篇
  1971年   53篇
  1970年   44篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
Some studies have been made on the variation of primary productivity in the Central South ChinaSea. This paper studies comprehensively the characteristics of chlorophyll a distributions in time andspace and the primary productivity, as well their relations to the environmental factors.Materals and methods During the comprehensive investigation in the Central South China Sea from September 1983 toDecember 1984, the distributions of chlorophyll a and primary productivity were studied. Figure 1shows the sampling stations and their range of investigation.  相似文献   
192.
A new kind of nematocyst, heteromorphore, and three new types of nematocysts, microbasic spino-mastigophore, microbasic undulata-mastigophore, microbasic laevis-mastigophore, are described from medusae of the Xiamen Harbour and discussed by comparison with the results of other research workers.  相似文献   
193.
By combining the singularity distributions method in mathematical-physical equation with the phenomenon of water surface oscillation, two kinds of wave diffraction model of gap breakwater are recommended for preliminary port planning and designing.  相似文献   
194.
195.
In October and November of 1977 and September and October of 1978,a quantitative survey of benthic animals was conducted in the East China Sea Continental Shelf and its adjacent waters(26°00'-34°00'N,124°00'-129°00'E,water depth 39-1550m),where 307 stations were dredged and 1200 samples collected.  相似文献   
196.
FORMATION MECHANISM AND DEVELOPMENTAL CONDITIONS OF TIDAL CURRENT RIDGES   总被引:1,自引:0,他引:1  
This paper discusses mainly the formation mechanism and developmental conditions of tidal current ridges. The tidal current velocities of 1-3.5 knots and the supply of abundant loose sediments are the prerequisites for the formation of the tidal current ridges. The hydrodynamic mechanism is similar to that of straight rivers. In the trough between two ridges the tidal current moves forward in the form of two helical flows. The two flows converge and sink in the centre of the trough, and erode the trough deeply; they diverge and rise on the two sides of the trough, and accumulate the ridges. When the supply material and relief come to the dynamic equilibrium, the development of ridges keeps steady.  相似文献   
197.
In this paper, the morphogenesis, stratigraphic sequences and dates of the coral reefs in the middle and north parts of the South China Sea are discussed, the position of the distributary regions of Cenozoic coral reefs in plate tectonics, the relationships of coral-reef evolutionary characteristics and dates with sea-basin spreading. Neogene sea-water transgression and Quaternary global climate-eustatic fluctuation are expounded and proved, and the latitudinal variation of the distribution of coral reefs in various geologic times are summed up.  相似文献   
198.
Pseudopleuronectes yokamae (Günther) is one of the most important economic fish species in the genus living specially in the northwest Pacific, and is distributed in the southern area of the far east sea of Russia, Japan, Korea, the Huanghai Sea, the Bohai Sea and the northern area of the East China Sea. Usually they live in nearshore waters of these areas as geographic subpopulations. P. yokamae in the Sheath Bay belongs to a local group of the Huanghai-Bohai Sea subpopulation and is distributed in the mouth and adjacent waters of the bay all the year round, and the catch of its spawning group has important economic value in the area. In this paper the fishery biology features of spawning group of P. yokamae in the Sheath Bay is systematically studied to give biology evidence for proper utilization and the multiplification of its resources.  相似文献   
199.
Sand dabs, an important commercial flatfish in the Bohai Sea, has recently decreased gradually in biomass, resulting from overfishing and marine pollution. Artificial culture and multiplication of sand dabs are essential and practical in China. The present paper examines the food habitof this fish to provide detailed information for its culture and multiplication.  相似文献   
200.
夏季东海西部表层海水中的pCO2及海-气界面通量   总被引:10,自引:0,他引:10  
根据2001年夏季长江口及东海西部海域表层海水pCO  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