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   11569篇
  免费   830篇
  国内免费   233篇
测绘学   455篇
大气科学   1091篇
地球物理   3440篇
地质学   4227篇
海洋学   796篇
天文学   1510篇
综合类   213篇
自然地理   900篇
  2022年   37篇
  2021年   88篇
  2020年   92篇
  2019年   135篇
  2018年   605篇
  2017年   525篇
  2016年   480篇
  2015年   323篇
  2014年   305篇
  2013年   526篇
  2012年   887篇
  2011年   759篇
  2010年   408篇
  2009年   514篇
  2008年   458篇
  2007年   405篇
  2006年   395篇
  2005年   1071篇
  2004年   1103篇
  2003年   837篇
  2002年   387篇
  2001年   190篇
  2000年   188篇
  1999年   117篇
  1998年   120篇
  1997年   100篇
  1996年   96篇
  1995年   84篇
  1994年   93篇
  1993年   75篇
  1992年   87篇
  1991年   74篇
  1990年   63篇
  1989年   55篇
  1988年   55篇
  1987年   57篇
  1986年   55篇
  1985年   68篇
  1984年   64篇
  1983年   79篇
  1982年   57篇
  1981年   66篇
  1980年   58篇
  1979年   70篇
  1978年   53篇
  1977年   38篇
  1976年   33篇
  1975年   30篇
  1974年   27篇
  1973年   33篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
103.
Solid-phase microextraction (SPME) is a simple, sensitive and less destructive method for the determination of dimethylsulfide (DMS) in seawater. Combined with detection by gas chromatography-mass spectrometry (GC-MS), the method had sufficient sensitivity (minimum detectable concentration of DMS was 0.05 nM), and practical levels of reproducibility (relative standard deviation ≤7%) and linearity (r 2 > 0.995) over a wide concentration range (0.5 to 910 nM). The protocol developed was applied to a Sagami Bay water sample to determine concentrations of DMS and DMSP, and in situ DMSP-lyase activity.  相似文献   
104.
Eddy Shedding from the Kuroshio Bend at Luzon Strait   总被引:16,自引:1,他引:16  
TOPEX/POSEDIENT-ERS satellite altimeter data along with the mean state from the Parallel Ocean Climate Model result have been used to investigate the variation of Kuroshio intrusion and eddy shedding at Luzon Strait during 1992–2001. The Kuroshio penetrates into the South China Sea and forms a bend. The Kuroshio bend varies with time, periodically shedding anticyclonic eddies. Criteria of eddy shedding are identified: 1) When the shedding event occurs, there are usually two centers of high Sea Surface Height (SSH) together with negative geostrophic vorticity in the Kuroshio Bend (KB) area. 2) Between the two centers of high SSH there usually exists positive geostrophic vorticity. These criteria have been used to determine the eddy shedding times and locations. The most frequent eddy shedding intervals are 70, 80 and 90 days. In both the winter and summer monsoon period, the most frequent locations are 119.5°E and 120°E, which means that the seasonal variation of eddy shedding location is unclear.  相似文献   
105.
The importance of macrophytes as food sources for estuarine nekton is unclear. Previous carbon isotope investigations in the macrophyte-dominated, freshwater-deprived Kariega Estuary showed that the bivalveSolen cylindraceusdid not utilize the dominant estuarine macrophytes found within the estuary as a primary food source. This finding prompted questions as to what the nekton of this estuary utilize as primary energy sources. δ13C analyses of the principal autochthonous and allochthonous primary carbon sources, as well as the dominant invertebrate and fish species, indicate that there are two main carbon pathways within the Kariega Estuary. The littoral community, which incorporates the majority of crustaceans, gobies, mullet and a sparid, utilizes δ13C enriched primary food sources namelySpartina maritima,Zosteracapensis and epiphytes. The channel fauna, which includes the zooplankton, zooplanktivorous and piscivorous fish, utilizes a primary food source depleted in δ13C, which is most likely a mixture of phytoplankton, terrestrial plant debris and C4macrophyte detritus. The C3saltmarsh macrophytesSarcocornia perennisandChenolea diffusa, as well as benthic microalgae, appear to be less important as primary food sources to the nekton of the Kariega Estuary.  相似文献   
106.
107.
This paper outlines the structure of the institutions involved in scientific and technological development in France. It points to new trends in French marine policy, and gives details of the country's offshore petroleum technology and nodule mining.  相似文献   
108.
109.
Nutrient deprivation or dietary restriction (DR) confers protection against ageing and stress in many animals and induced lysosomal autophagy is part of this mechanism. The effects of dietary restriction on the toxicity of copper and the polycyclic aromatic hydrocarbon phenanthrene have been investigated in the common marine mussel Mytilus edulis. The findings show that DR-induced autophagy facilitates the recovery of the digestive gland (i.e., molluscan liver analogue) from cell injury caused by both copper and phenanthrene. It is inferred that DR-induced autophagy and lysosomal proteolysis results in improved cellular "housekeeping" through the more efficient removal of oxidatively and pollutant damaged proteins (e.g., protein carbonyls, protein adducts, etc.) and that this contributes to stress resistance.  相似文献   
110.
In this paper we analyze seismic regime and earthquake depth distribution and correlation of seismicity and mud volcanism in the Azerbaijan and the Caspian Sea region. For the present region we have calculated accurate source locations, seismic activity, earthquake repetition and released earthquake energy parameters. It is shown that the active tectonic processes in the region are concentrated within the thick sedimentary cover that we consider as a general source of contemporary stress and a main structural element responsible for the origin of regional earthquakes. The correlation of seismicity and mud volcanism is of paragenetic character.  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