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   373篇
  免费   12篇
  国内免费   9篇
测绘学   13篇
大气科学   38篇
地球物理   111篇
地质学   114篇
海洋学   89篇
天文学   11篇
综合类   6篇
自然地理   12篇
  2022年   5篇
  2021年   4篇
  2020年   7篇
  2019年   12篇
  2018年   16篇
  2017年   15篇
  2016年   25篇
  2015年   15篇
  2014年   19篇
  2013年   30篇
  2012年   24篇
  2011年   24篇
  2010年   26篇
  2009年   20篇
  2008年   23篇
  2007年   19篇
  2006年   14篇
  2005年   22篇
  2004年   8篇
  2003年   10篇
  2002年   10篇
  2001年   4篇
  2000年   4篇
  1998年   4篇
  1996年   1篇
  1995年   2篇
  1992年   3篇
  1989年   1篇
  1988年   2篇
  1987年   1篇
  1986年   3篇
  1985年   2篇
  1984年   1篇
  1983年   1篇
  1982年   1篇
  1981年   1篇
  1977年   1篇
  1975年   1篇
  1970年   1篇
  1958年   1篇
  1955年   1篇
  1951年   4篇
  1950年   1篇
  1949年   2篇
  1948年   3篇
排序方式: 共有394条查询结果,搜索用时 203 毫秒
61.
The purpose of this study was to compare enzymatic biomarker activities in fish caged at two sites, Masan Bay (contaminated) and Haeguemgang (reference). In the present study, ethoxyresorufin O-deethylase (EROD), brain acetyl cholinesterase (bAChE), muscle acetyl cholinesterase (mAChE) and butyryl cholinesterase (mBChE) in caged rockfish (Sebastes schlegeli) were measured 0, 1, 3, 7, 14, 21 and 30 days after caging. The level of CYP1A mRNA and Protein expression was induced higher in Masan Bay at 1, 3, 7, 14 and 30 days after caging. EROD activity in the caged fish was significantly higher in Masan Bay than in Haeguemgang 3 and 7 days after caging, but not at 14 and 30 days after caging. bAChE activity was significantly inhibited at 7 and 14 days after caging in Masan Bay. However, mBChE activity was not significantly inhibited during the experiment. Taken together, the data suggest that the caged fish were exposed, at least transiently, to CYP1A inducers and ChE inhibitors, which is consistent with our previous observations.  相似文献   
62.
Using a new four-channel system for detecting acoustic emissions in a multianvil apparatus, we have assessed the pressure–temperature range for such emissions, as well as the role of dehydration, by deforming samples of extensively serpentinized peridotite. We show that in the absence of dehydration and for samples initially faulted at low pressure, acoustic emissions occurred well outside the expected pressure–temperature field of unassisted brittle failure. Emissions were also detected during and after dehydration of serpentine. Microstructures of post-run specimens revealed fault slip with offsets up to ~ 500 μm, regardless of whether or not dehydration took place. Dehydration appears to effectively stop slip on pre-existing faults and create new ones. Analysis of P-wave travel times from the four sensors confirmed that the acoustic emissions originated within the specimen during fault slip. These observations suggest that earthquakes can be triggered by slip along an existing fault containing serpentine under significantly higher pressure and temperature conditions than previously thought possible without dehydration.  相似文献   
63.
本文介绍了自行开发的解决Diseetor应用问题的计算机图像处理软件系统及关键技术、算法。本系统能依照Disector原理对多层组织细胞的电镜及光镜图像中的目标进行正确的分割,各层之间图像的人工交互及自动配准。针对每个目标的上下层关系实现目标的Disector自动计数及参数计算,并对每个目标进行体数据的提取和三维重建显示,通过切片级表面重建出曲面表面,再借助OpenGL的显示功能把曲面显示出来。使用Disector分析系统对多种粒子(细胞等)进行三维分析,可以简化寻找新出现粒子的过程,克服切片采集过程中的形变,在统计分析之后,立体地观察粒子结构,能够使操作者从繁琐的手工操作中解脱出来。自动统计新出现的粒子。文中同时还给出了用该系统对小白鼠神经细胞个数的Disector分析,肾小球个数统计分析和三维重建显示实例。  相似文献   
64.
Rare earth elements (REEs) of 91 fine-grained bottom sediment samples from five major rivers in Korea (the Han, Keum, and Yeongsan) and China (the Changjiang and Huanghe) were studied to investigate their potential as source indicator for Yellow Sea shelf sediments, this being the first synthetic report on REE trends for bottom sediments of these rivers. The results show distinct differences in REE contents and their upper continental crust (UCC)-normalized patterns: compared to heavy rare earth elements (HREEs), light rare earth elements (LREEs) are highly enriched in Korean river sediments, in contrast to Chinese river sediments that have a characteristic positive Eu anomaly. This phenomenon is observed also in primary source rocks within the river catchments. This suggests that source rock composition is the primary control on the REE signatures of these river sediments, due largely to variations in the levels of chlorite and monazite, which are more abundant in Korean bottom river sediments. Systematic variations in ΣLREE/ΣHREE ratios, and in (La/Yb)–(Gd/Yb)UCC but also (La/Lu)–(La/Y)UCC and (La/Y)–(Gd/Lu)UCC relations have the greatest discriminatory power. These findings are consistent with, but considerably expand on the limited datasets available to date for suspended sediments. Evidently, the REE fingerprints of these river sediments can serve as a useful diagnostic tool for tracing the provenance of sediments in the Yellow Sea, and for reconstructing their dispersal patterns and the circulation system of the modern shelf, as well as the paleoenvironmental record of this and adjoining marginal seas.  相似文献   
65.
Park  Joo Myun  Jung  Hae Kun  Lee  Chung Il  Huh  Sung-Hoi 《Ocean Science Journal》2019,54(1):141-146
Ocean Science Journal - Diel and gastrointestinal changes in relation to the feeding intensity and prey composition of Apogon lineatus were investigated through the analysis of the diet contents of...  相似文献   
66.
67.
Precise, automatic and fast method for vanishing point detection   总被引:1,自引:0,他引:1  
A new automated approach for vanishing point detection in images of urban scenes is described. This method is based on the theorem of Thales. The main contribution of this paper is the automatic and simultaneous detection of all vanishing points of the image, achieved by converting this problem into the detection of circles in a complex cloud of points, in which each point corresponds to a segment and is associated with an uncertainty. This extraction of circles uses a RANSAC method, modified to improve its speed by using accumulation techniques (Hough transform or otherwise). This robust estimation is then refined by least squares error propagation using the individual variances of each segment. The algorithm is robust, its accuracy is optimised and it is entirely automatic. Its successful operation has been tested on a large number of images of varied urban scenes.  相似文献   
68.
Recent studies in the western North Pacific reported a declining standing stock biomass of anchovy (Engraulis japonicus) in the Yellow Sea and a climate-driven southward shift of anchovy catch in Korean waters. We investigated the effects of a warming ocean on the latitudinal shift of anchovy catch by developing and applying individual-based models (IBMs) based on a regional ocean circulation model and an IPCC climate change scenario. Despite the greater uncertainty, our two IBMs projected that, by the 2030s, the strengthened Tsushima warm current in the Korea Strait and the East Sea, driven by global warming, and the subsequent confinement of the relatively cold water masses within the Yellow Sea will decrease larval anchovy biomass in the Yellow Sea, but will increase it in the Korea Strait and the East Sea. The decreasing trend of anchovy biomass in the Yellow Sea was reproduced by our models, but further validation and enhancement of the models is required together with extended ichthyoplankton surveys to understand and reliably project range shifts of anchovy and the impacts such range shifts will have on the marine ecosystems and fisheries in the region.  相似文献   
69.
This paper is situated at the intersections among GIS and geovisualization, critical social theory, and urban studies. It presents an analysis of housing segregation and unequal food and transportation access in Buffalo, New York. We demonstrate how the representation and examination of this socially complex multi-scalar issue benefits from deliberate, reflexive conversation between different critical social-spatial epistemologies. We begin with a relatively simple GIS analysis of spatial segregation and arrive through critical iteration at a more qualitatively nuanced cartogram which moves beyond representations of fixed space to reveal a much more relational situation—a case of “time-space expansion” in which the travel time needed to meet a basic daily need is much greater for the poor and people of color than it is for whiter, more affluent populations. We conclude by infusing this narrative with additional considerations from social theory to show how even a limited visualization such as ours might better critically engage broader social and discursive processes in and across urban space.  相似文献   
70.
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