全文获取类型
| 收费全文 | 115篇 |
| 免费 | 12篇 |
| 国内免费 | 22篇 |
专业分类
| 测绘学 | 12篇 |
| 大气科学 | 2篇 |
| 地球物理 | 16篇 |
| 地质学 | 27篇 |
| 海洋学 | 71篇 |
| 天文学 | 12篇 |
| 综合类 | 4篇 |
| 自然地理 | 5篇 |
出版年
| 2023年 | 4篇 |
| 2022年 | 4篇 |
| 2021年 | 3篇 |
| 2020年 | 4篇 |
| 2019年 | 3篇 |
| 2018年 | 3篇 |
| 2017年 | 3篇 |
| 2016年 | 1篇 |
| 2015年 | 7篇 |
| 2014年 | 4篇 |
| 2013年 | 6篇 |
| 2012年 | 5篇 |
| 2011年 | 3篇 |
| 2010年 | 10篇 |
| 2009年 | 9篇 |
| 2008年 | 7篇 |
| 2007年 | 17篇 |
| 2006年 | 4篇 |
| 2005年 | 2篇 |
| 2004年 | 5篇 |
| 2003年 | 4篇 |
| 2002年 | 8篇 |
| 2001年 | 10篇 |
| 2000年 | 5篇 |
| 1999年 | 4篇 |
| 1998年 | 4篇 |
| 1997年 | 3篇 |
| 1996年 | 3篇 |
| 1994年 | 3篇 |
| 1981年 | 1篇 |
排序方式： 共有149条查询结果，搜索用时 624 毫秒
21.
Captive longfin eels (Anguilla dieffenbachii) were exposed to the vertebrate pesticide sodium fluoroacetate (1080) in the water column and through the ingestion of cereal pellet baits or possum muscle and gut tissue that contained 1080 residue. No mortality or unusual behaviour (in comparison with the controls) occurred in eels that were exposed to 1080. However, significantly greater weight loss occurred in eels exposed to 1080 compared with those eels that were not. No residue was detected in tissues of eels exposed to 1080 cereal baits through ingestion and direct (dermal and respiratory) absorption, or through direct absorption only. Low concentrations of 1080 were detected in muscle tissue of eels that consumed contaminated possum muscle (x = 0.0174 μg/g) or gut (x = 0.0306 μg/g) tissue. The primary factors affecting the concentration of 1080 detected in eel tissue included the dose of 1080 (mg/kg) that each eel" receiveddate="and number of days since the eel last fed on contaminated tissue. Based on the 1080 concentrations measured in eels in this study, the risk of acute poisoning to humans from eating contaminated eel flesh is considered extremely low. Even so, national and international perceptions and food safety standards have the potential to limit eel exports and/or close an eel fishery if 1080 residue was discovered in tissue. 相似文献
22.
In this paper, the relationships between paleo-precipitation and the regional influence of El Nino Southern Oscillation (ENSO)
in South America are assessed from a high-resolution calendar varve-thickness record. Two short laminated sediment cores (53
and 61 cm length) from Lago Puyehue (40° S) are analysed by continuous varve measurements through the last 600 years. The
calendar varve years are determined by the occurrence of graded planktonic-rich layers. The annual sediment accumulation rates
are reconstructed by using the standard varve-counting methods on thin sections. The 1980–2000 varve-thickness record is interpreted
in terms of climate through correlation with limnological and local monthly instrumental climate databases. The comparison
between the standardized varve thickness with the instrumental records reveals a strong correlation (r = 0.75, р = 0.07) between the total varve thickness and the austral autumn/winter precipitation. We argue that strong austral winter
winds and precipitation are the forcing factors for the seasonal turn-over and phytoplankton increase in the lake sediments.
During strong El Nino events the precipitation and the winds decrease abnormally, hence reducing the thickness of the biogenic
sediments deposited after the winter turn-over. Our results show one significant regional maximum peak of winter precipitation
(>900 mm) in the mid 20th century and a significant period with lower winter precipitation (<400 mm) before the 15th century,
i.e., the late Medieval Warm Period. The first peak in the mid 20th century is confirmed by the regional precipitation database.
The influence of ENSO cycles over the last 600 years is assessed by spectral analysis in Fagel et al. (2007). The possible influence of the regional volcanism and/or the seismic activity on the local climate record is also discussed.
This is the sixth in a series of eight papers published in this special issue dedicated to the 17,900 year multi-proxy lacustrine record of
Lago Puyehue, Chilean Lake District. The papers in this special issue were collected by M. De Batist, N. Fagel, M. -F. Loutre
and E. Chapron. 相似文献
23.
本文的目的是评估光子计数探测器对CT成像的性能的影响,我们对一款基于碲锌镉(CZT)的光子计数探测器进行了性能测试,并搭建一个成像平台。首先对探测器系统进行能量增益的校正以及坏像素点校正,以减少探测器响应的不均匀性对CT成像的影响。然后对探测器进行能量-阈值标定,以确定探测器的工作能量阈值。最终搭建成像系统,对X光能量分别大于36和45keV的数据,获得了模体的重建结果,并对结果进行了分析。 相似文献
24.
基于常规计数型TDC设计思想,通过FPGA芯片的内部PLL延迟相位技术和内部资源构建延迟链改进常规计数型TDC,时间间隔测量精度可达200 ps。该方法对激光测距、三维激光扫描仪、绝对重力仪等仪器中精密时间测量系统的研究具有实际意义。 相似文献
25.
Pixel counting is probably the most popular way to estimate class areas from satellite-derived maps. It involves determining the number of pixels allocated to a specific thematic class and multiplying it by the pixel area. In the presence of asymmetric classification errors, the pixel counting estimator is biased. The overarching objective of this article is to define the applicability conditions of pixel counting so that the estimates are below a user-defined accuracy target. By reasoning in terms of landscape fragmentation and spatial resolution, the proposed framework decouples the resolution bias and the classifier bias from the overall classification bias. The consequence is that prior to any classification, part of the tolerated bias is already committed due to the choice of the spatial resolution of the imagery. How much classification bias is affordable depends on the joint interaction of spatial resolution and fragmentation. The method was implemented over South Africa for cropland mapping, demonstrating its operational applicability. Particular attention was paid to modeling a realistic sensor's spatial response by explicitly accounting for the effect of its point spread function. The diagnostic capabilities offered by this framework have multiple potential domains of application such as guiding users in their choice of imagery and providing guidelines for space agencies to elaborate the design specifications of future instruments. 相似文献
26.
27.
28.
海岸线是分形领域最传统的研究课题 ,但是在目前的海岸线研究中却忽略了一个重要且根本性的问题 ,那就是海岸线分维数不同计算方法之间是否存在着一定的差异 ,根据不同计算方法计算所得的分维数之间是否具有可比性。在概述海岸线分维数计算方法的基础上 ,分析了它们之间的异同 ,并进行了实证研究。指出 :使用量规法、网格法计算所得海岸线分维数结果之间存在着客观的差异 ,文中利用量规法计算所得的海岸线分维数结果大于使用网格法计算所得的海岸线分维数结果。 相似文献
29.