全文获取类型
收费全文 | 312篇 |
免费 | 61篇 |
国内免费 | 92篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 85篇 |
地球物理 | 77篇 |
地质学 | 170篇 |
海洋学 | 75篇 |
天文学 | 20篇 |
综合类 | 16篇 |
自然地理 | 17篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 10篇 |
2021年 | 13篇 |
2020年 | 9篇 |
2019年 | 12篇 |
2018年 | 18篇 |
2017年 | 15篇 |
2016年 | 14篇 |
2015年 | 13篇 |
2014年 | 22篇 |
2013年 | 28篇 |
2012年 | 15篇 |
2011年 | 19篇 |
2010年 | 20篇 |
2009年 | 19篇 |
2008年 | 11篇 |
2007年 | 19篇 |
2006年 | 14篇 |
2005年 | 19篇 |
2004年 | 19篇 |
2003年 | 13篇 |
2002年 | 12篇 |
2001年 | 7篇 |
2000年 | 10篇 |
1999年 | 11篇 |
1998年 | 12篇 |
1997年 | 15篇 |
1996年 | 8篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 9篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 8篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有465条查询结果,搜索用时 296 毫秒
421.
The effects of a giant offshore dyke, Saemangeum, have been of special interest on both scientific and environmental aspects. Without any rival worldwide with regard to the ample scale and estuarine setting, the Saemangeum dyke and its vicinity (Saemangeum Area) should be an unprecedented experimental site for monitoring the consequence of the estuarine developments with dykes. In order to unravel geologic changes caused by the Saemangeum dyke, we collected a number of surface sediment samples and bathymetric profiles from a full coverage of the Saemangeum Area, and compared topography and sediment phase on the inter-annual (2002–2006, post-construction) and decadal (1982–2002, between pre- and post-construction) timescales. 相似文献
422.
??????????????????Kalman??????????????????????????Kalman?????????????????????????????????????????????????????????????GNSS/INS?????????????????????????????????????????????????????????????????????????????????????????Kalman?????????????? 相似文献
423.
Determination of critical shear stress of non‐cohesive soils using submerged jet test and turbulent kinetic energy
下载免费PDF全文
![点击此处可从《地球表面变化过程与地形》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Laboratory tests using Jet Erosion Testing (JET) apparatus, impinging normally on a horizontal boundary, were conducted to determine the critical shear stress (τc) of non‐cohesive soil samples. A three‐dimensional (3D) SonTek/YSI 16 MHz Micro‐Acoustic Doppler Velocimeter (MicroADV) was used to measure turbulent kinetic energy (TKE) at a radial limit of entrainment in the wall jet zone and the measurements were used to calculate τc of the samples. The results showed that TKE increases exponentially with increasing particle size. The τc from this study were comparable (R2 = 0.8) to the theoretical τc from Shields diagram after bed roughness scale ratio (D/ks), due to the non‐uniform bed conditions, was accounted for. This study demonstrated that JET and TKE can be used to determine τc of non‐cohesive soils. The use of JET and TKE was found to be faster and easier when compared to the conventional approach of using flumes. A relationship of TKE at the onset of incipient motion (TKEc) and samples’ D50 developed in this study can be used to predict τc of non‐cohesive soils under similar non‐uniform conditions. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
424.
Geochemical Distribution of Trace Elements in Groundwater from the North Mara Large‐Scale Gold Mining Area of Tanzania
下载免费PDF全文
![点击此处可从《Ground Water Monitoring & Remediation》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Mwemezi Johaiven Rwiza Kyoung‐Woong Kim Sang‐don Kim 《Ground Water Monitoring & Remediation》2016,36(2):83-93
The influence of large‐scale mining operations on groundwater quality was investigated in this study. Trace element concentrations in groundwater samples from the North Mara mining area of northern Tanzania were analyzed. Statistical analyses for relationships between elemental concentrations in the samples and distance of a sampling site from the mine tailings dam were also conducted. Eleven trace elements (Al, As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) were determined, and averages of Fe and Al concentrations were higher than levels accepted by the Tanzanian drinking water guideline. Levels of Pb in three samples were higher than the World Health Organization (WHO) and United States Environmental Protection Agency (USEPA) drinking water guidelines of 10 and 15 µg/L, respectively. One sample contained a higher As level than the WHO and USEPA guideline of 10 µg/L. The correlation between element concentrations and distance from the mine tailings dam was examined using the hierarchical agglomeration cluster analysis method. A significant difference in the elemental concentration existed depending on the distance from the mine tailings dam. Mann–Whitney U‐test post hoc analysis confirmed a relationship between element concentration and distance of a sampling site from the mine tailings dam. This relationship raises concerns about the increased risks of trace elements to people and ecosystem health. A metal pollution index also suggested a relationship between elemental concentrations in the groundwater and the sampling sites’ proximity from the mine tailings dam. 相似文献
425.
An efficient method for selecting and scaling ground motions matching target response spectrum mean and variance
下载免费PDF全文
![点击此处可从《地震工程与结构动力学》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The purpose of this study is to propose an accurate and efficient method for selecting and scaling ground motions matching target response spectrum mean and variance, which does not require excessive computation and simulation. In the proposed method, a desired number of ground motions are sequentially scaled and selected from a ground motion library without iterations. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
426.
Using synthetic spectra derived from an updated model atmosphere together with a continuum model that includes contributions from haze, cloud and ground, we have re-analyzed the recently published (Geballe et al., 2003, Astrophys. J. 583, L39-L42) high-resolution 3 μm spectrum of Titan which contains newly-detected bands of HCN (in emission) and C2H2 and CH3D (in absorption), in addition to previously detected bands of CH4. In the 3.10-3.54 μm interval the analysis yields strong evidence for the existence of a cloud deck or optically thick haze layer at about the 10 mbar (∼ 100 km) level. The haze must extend well above this altitude in order to mask the strong CH4 lines at 3.20-3.50 μm. These cloud and haze components must be transparent at 2.87-2.92 μm, where analysis of the CH3D spectrum demonstrates that Titan's surface is glimpsed through a second cloud deck at about the 100 mbar (∼ 50 km) level. Through a combination of areal distribution and optical depth this cloud deck has an effective transmittance of ∼ 20%. The spectral shape of Titan's continuum indicates that the higher altitude cloud and haze particles responsible for suppressing the CH4 absorptions have a largely organic make-up. The rotational temperature of the HCN ranges from 140 to 180 K, indicating that the HCN emission occurs over a wide range of altitudes. This emission, remodeled using an improved collisional deactivation rate, implies mesospheric mixing ratio curves that are consistent with previously predictions. The stratospheric and mesospheric C2H2 mixing ratios are ∼10−5, considerably less than previous model predictions (Yung et al., 1984), but approximately consistent with recent observational results. Upper limits to mixing ratios of HC3N and C4H2 are derived from non-detections of those species near 3.0 μm. 相似文献
427.
Li D Dong M Shim WJ Hong SH Oh JR Yim UH Jeung JH Kanan N Kim ES Cho SR 《Marine pollution bulletin》2005,51(8-12):966-974
In order to investigate spatial and temporal distribution of organic pollutants in the Saemangeum Bay, organophosphorus pesticides (10), alkylphenols (8), chlorophenols (2), bisphenol A were analyzed from the surface seawater taken in 2002–2003. Most of the analytes were not detected in all stations except nonylphenol and S-benzyl-O,O-di-isopropyl phosphorothioate (IBP). Concentrations of nonylphenol and IBP ranged from ND to 298 ng/l and from ND to 1840 ng/l, respectively. The high levels of nonylphenol and IBP were found in the estuary areas of Mangyeong and Dongjin River. The levels of nonylphenol and IBP in surface seawater varied through seasons and the high levels of nonylphenol and IBP were in summer season (August). Based on real time monitoring of IBP and on correlation between concentrations of target compounds and contents of salinity in seawater, physical mixing and diffusion of seawater were found to be the major factors that affect the spatial distribution of IBP and nonylphenol in the Saemangeum Bay environment. 相似文献
428.
Element geochemistry and cleaning potential of the No. 11 coal seam from Antaibao mining district 总被引:1,自引:0,他引:1
WANG Wenfeng QIN Yong SONG Dangyu SANG Shuxun JIANG Bo ZHU Yanming & FU Xuehai . College of Resources & Geosciences China University of Mining Technology Xuzhou China . State Key Laboratory of Coal Combustion Huazhong University of Science Technology Wuhan China 《中国科学D辑(英文版)》2005,48(12):2142-2154
It has aroused great attention that the mobilization of potential toxic substance during coal mining, pro- cessing and using has serious negative influence on environment. Clearly, the coal cleaning can be prop-erly applied to removing hazardous elements or re-ducing their concentrations prior to combustion, which also is considered as an economical and effective technique in minimizing some of these problems[1]. Unfortunately, there are fairly few studies on the parti-tioning behavior of trac… 相似文献
429.
Infrared spectra of Jupiter's atmosphere were obtained with the infrared spectrometer (IRS) on the 1.5-m telescope at the Cerro Tololo Inter-American Observatory (CTIO) during the first 2 days of the impacts of the fragments of Comet Shoemaker–Levy 9 (1993e). We monitored 3.51 ± 0.17 μm radiation from the impact areas, undisturbed areas, and auroral regions of Jupiter after the A and E impacts. The strong emission of a portion of the P-branch of the ν3band of CH4was detected on the A impact area 4 hr after the impact. H+3emissions are found to be decreased at the A and E impact sites after 4 hr and 10 hr 50 min of the impacts, respectively, compared with undisturbed areas at the same latitude. The temperatures of the southern H+3aurora were normal within the first several hours following the A and E impacts. 相似文献
430.
Dong-Hwan Hwang Sang Heon Oh Sang Jeong Lee Chansik Park Chris Rizos 《GPS Solutions》2005,9(4):294-311
Due to their complementary features of GPS and INS, the GPS/INS integrated navigation system is increasingly being used for
a variety of commercial and military applications. An attitude determination GPS (ADGPS) receiver, with multiple antennas,
can be more effectively integrated with a low-cost IMU since the receiver gives not only position and velocity data but also
attitude data. This paper proposes a low-cost attitude determination GPS/INS integrated navigation system. The proposed navigation
system comprises an ADGPS receiver, a navigation computer unit (NCU), and a low-cost commercial MEMS IMU. The navigation software
includes a fault detection and isolation (FDI) algorithm for integrity. In order to evaluate the performance of the proposed
navigation system, two flight tests have been performed using a small aircraft. The first flight test confirmed the fundamental
operation of the proposed navigation system and the effectiveness of the FDI algorithm. The second flight test evaluated the
performance of the proposed navigation system and demonstrated the benefit of GPS attitude information in a high dynamic environment.
The flight test results show that the proposed ADGPS/INS integrated navigation unit gives reliable navigation performance
even when anomalous GPS data is provided and gives better navigation performance than a conventional GPS/INS unit. 相似文献