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   16865篇
  免费   673篇
  国内免费   223篇
测绘学   471篇
大气科学   1327篇
地球物理   4130篇
地质学   6658篇
海洋学   1441篇
天文学   2806篇
综合类   233篇
自然地理   695篇
  2022年   150篇
  2021年   221篇
  2020年   199篇
  2019年   236篇
  2018年   953篇
  2017年   794篇
  2016年   724篇
  2015年   335篇
  2014年   520篇
  2013年   721篇
  2012年   1090篇
  2011年   973篇
  2010年   668篇
  2009年   771篇
  2008年   691篇
  2007年   682篇
  2006年   616篇
  2005年   1142篇
  2004年   1171篇
  2003年   930篇
  2002年   445篇
  2001年   313篇
  2000年   296篇
  1999年   183篇
  1998年   189篇
  1997年   187篇
  1996年   125篇
  1995年   132篇
  1994年   116篇
  1993年   97篇
  1992年   72篇
  1991年   107篇
  1990年   106篇
  1989年   73篇
  1988年   80篇
  1987年   103篇
  1986年   80篇
  1985年   108篇
  1984年   95篇
  1983年   105篇
  1982年   86篇
  1981年   82篇
  1980年   100篇
  1979年   88篇
  1978年   88篇
  1977年   78篇
  1976年   61篇
  1975年   63篇
  1974年   71篇
  1973年   66篇
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
141.
Long-term Sensor Drift Found in Recovered Argo Profiling Floats   总被引:5,自引:0,他引:5  
We recovered three Argo profiling floats after 2 to 2.5 years of operation, and recalibrated their temperature, conductivity, and pressure sensors. The results demonstrate that these floats exhibited a significant drift in salinity of −0.0074 to −0.0125, primarily due to the conductivity sensor drift. Combined with the recalibration result for another previously recovered float, the indication is that the negative salinity drift increases nearly in proportion to the operating period of floats. The increasing rate is −0.0041 (±0.0015) year−1, which yields a salinity drift of −0.016 (±0.006) for the expected float lifetime of four years. The present result suggests that reducing the float surfacing time would improve the accuracy of the salinity measurements.  相似文献   
142.
143.
The sediment infill over the Paleozoic bedrock in the Bosphorus Strait consists of four sedimentary units which were deposited in the last 26,000 14C years B.P. The stratigraphy of these units suggests that this part of the Bosphorus was a freshwater lake between 26,000 and 5,300 14C years B.P., depositing sands with a freshwater mollusc fauna of Black Sea neo-euxinian affinity (Dreissena rostriformis, Dreissena polymorpha, and Monodacna pontica). The first appearance of euryhaline Mediterranean molluscs (e.g., Ostrea edulis, Mytilus edulis) was observed at 5,300 14C years B.P. in this part of the Bosphorus. Deposition of coarse Mytilus-bank and Ostrea-bank units suggests that the establishment of the present dual-flow regime in the Bosphorus took place at about 4,400 14C years B.P.  相似文献   
144.
X-ray images of sediment core allow recognition of fine-scaled sedimentary structures which traditional epoxy casts or lacquer peels are unable to resolve. The X-ray imaging system SCOPIX has the additional advantage of acquiring high-resolution digital pictures suitable for further analysis by advanced image processing techniques. Because of the frequent presence of both physical and biogenic sedimentary structures in undisturbed sediment cores, two image analysis procedures have been established which simplify the information contained in the images (in term of structures and facies), and allow a quantitative characterization of the observed structures. This form of parametrization of the image structure constitutes an additional source of information for a better interpretation of the physical processes responsible for the generation of the sedimentary structures.  相似文献   
145.
146.
A seamount chain with an approximately WNW trend is observed in the northeastern Ulleung Basin. It has been argued that these seamounts, including two islands called Ulleung and Dok islands, were formed by a hotspot process or by ridge related volcanism. Many geological and geophysical studies have been done for all the seamounts and islands in the chain except Anyongbok Seamount, which is close to the proposed spreading ridge. We first report morphological characteristics, sediment distribution patterns, and the crustal thickness of Anyongbok Seamount using multibeam bathymetry data, seismic reflection profiles, and 3D gravity modeling. The morphology of Anyongbok Seamount shows a cone shaped feature and is characterized by the development of many flank cones and flank rift zones. The estimated surface volume is about 60 km3, and implies that the seamount is smaller than the other seamounts in the chain. No sediments have been observed on the seamount except the lower slope, which is covered by more than 1,000 m of strata. The crustal structure obtained from a 3D gravity modeling (GFR = 3.11, SD 3.82 = mGal) suggests that the seamount was formed around the boundary of the Ulleung Plateau and the Ulleung Basin, and the estimated crustal thickness is about 20 km, which is a little thicker than other nearby seamounts distributed along the northeastern boundary of the Ulleung Basin. This significant crustal thickness also implies that Anyongbok Seamount might not be related to ridge volcanism.  相似文献   
147.
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   
148.
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   
149.
150.
Generalization of the approximation for the autocovariance function of estimate error, used frequently in four-dimensional analysis of the ocean's hydrophysical fields, is suggested for cross-covariance functions. It is shown that the principal properties of the covariance function of error estimate are not then violated. Approximation accuracy is studied through numerical experimentation using the two-dimensional equation for passive admixture transport as an example.Translated by V. Puchkin.  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