全文获取类型
收费全文 | 375篇 |
免费 | 35篇 |
国内免费 | 62篇 |
专业分类
测绘学 | 29篇 |
大气科学 | 30篇 |
地球物理 | 75篇 |
地质学 | 166篇 |
海洋学 | 44篇 |
天文学 | 4篇 |
综合类 | 27篇 |
自然地理 | 97篇 |
出版年
2023年 | 3篇 |
2022年 | 8篇 |
2021年 | 12篇 |
2020年 | 16篇 |
2019年 | 18篇 |
2018年 | 8篇 |
2017年 | 11篇 |
2016年 | 11篇 |
2015年 | 23篇 |
2014年 | 20篇 |
2013年 | 21篇 |
2012年 | 20篇 |
2011年 | 15篇 |
2010年 | 25篇 |
2009年 | 23篇 |
2008年 | 16篇 |
2007年 | 20篇 |
2006年 | 23篇 |
2005年 | 20篇 |
2004年 | 18篇 |
2003年 | 16篇 |
2002年 | 13篇 |
2001年 | 11篇 |
2000年 | 13篇 |
1999年 | 16篇 |
1998年 | 7篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 8篇 |
1994年 | 9篇 |
1993年 | 10篇 |
1992年 | 9篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1978年 | 1篇 |
排序方式: 共有472条查询结果,搜索用时 31 毫秒
411.
北京地区河流沉积物的金属元素背景值研究 总被引:1,自引:0,他引:1
本文检验,表征了北京地区河流沉积物的金属元素背景值。并应用多元分析法探讨了金属元素背景值的地球化学活动性、相关组合、区域差异等地球化学特征以以环境要素对形成背景值的影响。 相似文献
412.
413.
Study on tidal gravity observations obtained at stations Zhongshan and Changcheng, Antarctic 总被引:1,自引:0,他引:1
Lü Chun-cao 《地震学报(英文版)》2001,14(3):325-332
IntroductionThe purpose of the studies on the tidal gravity observations on the Earth(s surface is to investigate the properties of the deformation and the tidal gravity variations of the Earth under the action of the luni-solar tidal force. These variations relate to the internal structure, shape and the medium(s rheology properties of the Earth (Wahr, 1981; Dehant, 1987). The theoretical studies and observations indicated that the amplitudes and the tidal parameters, including the amplitud… 相似文献
414.
以CRT显示器的特征函数与特征矩阵来描述CRT显示器的输入/输出色度特性;建立了CRT显示器数字驱动输入值与其显示颜色三刺激值之间关系的数学模型。 相似文献
415.
416.
利用加权分担的思想,证明具有2个公共值和1个公共值对的整函数的一个唯一性定理,改进了Brosch G,Alza-hary TC和Yi H X等人的有关结果。 相似文献
417.
南海海水中溶解态铜、铅、锌、镉环境背景值的初步研究 总被引:8,自引:0,他引:8
本文通过对南海海域自然环境中表层海水溶解态Cu、Pb、Zn、Cd的分析,讨论了南海表层海水中重金属含量的分布。根据地理环境特征及表层环流结构将南海表层水域分成北部和南部两个重金属背景值海区,并采用统计学方法对海水中重金属的分布类型进行了态性检验,按分布类型分别确定了Cu、Pb、Zn、Cd的环境背景值。 相似文献
418.
Ecosystem services are premises for human beings to exist and develop in the world, and it is of importance to study effects of land use change on ecosystem functions. Songnen plain, located in Northeast China, is one of the national key bases for agricultural production. Because there were remarkable variations in land use in recent years, it can supply specific foundation for protection and restoration of regional eco-environment to explore changes in its values of ecosystem services. This study aims to qualify long-term changes in land use of Songnen plain from 1980 to 2000, and to explore the impact of land use change on ecosystem services. With 2-period land use data using RS and GIS, this paper analyzed changes in land use and in ecosystem service values using the ecosystem service value coefficients (VC) put forward by Costanza et al. Results showed that from 1980 to 2000, area of rangeland, water area and wetlands and area of cropland decreased, but urban area and unused land increased. Due to cropland's comparatively low VC and comparatively high VC of wetlands and water area, increment in cultivated land could not offset the total decrement in regional ecosystem service values because of the decrease in area of wetlands and water area. Meanwhile, city sprawl has also led to loss of ecological values. Total ecosystem service values of the study area reduced dramatically, from 34,926.10×106$ to 31,744.54×106$ in the period 1980-2000. This represents a 9.11% net decline in annual value of ecosystem services in the study area. 相似文献
419.
Lev L. Petrov Yuri N. Kornakov Irina la. Korotaeva Elena A. Anchutina Luidmila A. Persikova Vera E. Susloparova Irina N. Fedorova Viktor A. Shibanov 《Geostandards and Geoanalytical Research》2004,28(1):89-102
This paper describes the creation of two new reference samples of black shale, SCHS-1 and SLg-1, collected in the Bodaibo Region of Irkutsk District (Siberia, Russia). These samples have been developed as State Standard Samples to meet the requirements of Russia's Normative Documents, so that they can be recognised by the Russian State Certification Agency and included on the State Register of certified reference materials. SCHS-1 was produced from shale of the Khomolkho suite; SLg-1 represents the average composition of the Sukhoy Log gold deposit (within Au mineralisation). The homogeneity was assessed by applying the concept of potential inhomogeneity, and the inhomogeneity uncertainties (σinhom ) for the indicator elements that were estimated experimentally by silicate XRF analysis. It was found that a majority of the indicator elements was characterised by σinhom /Δp < 1/8 (Δp is the permissible certification uncertainty), and so σinhom was neglected for the indicator elements and all other elements that were included in their respective group. The value of σinhom calculated for Fe (σinhom,Fe /Δp > 1 /8) was taken into consideration for the noble metals and their associated elements (e.g., Ag, As, Au, etc.). More than fifty laboratories (thirty-seven from Russia) were involved in the interlaboratory experiment (ILE) to analyse these reference samples. The data obtained from the ILE allowed SCHS-1 and SLg-1 to be certified for, fifty-one and forty-three elements, respectively, as State Standard Samples. 相似文献
420.
Zicheng Peng Tegu ChenBaofu Nie M.John Head Xuexian HeWeijian Zhou 《Quaternary Research》2003,59(3):285-292
We have used correlative analysis between mean December-January-February winter wind velocities, measured at the Xisha Meteorological Observatory (16°50′N, 112°20′E) in the middle of the South China Sea, and mean δ18O data for the corresponding month from Porites lutea coral, collected in Longwan waters (19°20′N, 110°39′E), to obtain a linear equation relating the two datasets. This winter wind velocity for the South China Sea (WMIIscs) can then be correlated to the coral δ18O by the equation WMIIscs = −1.213-1.351 δ18O (‰ PDB), r = −0.60, n = 40, P = 0.01. From this, the calculated WMIIscs-δ18O series from 1944 to 1997 tends to decrease during the 1940s to the 1960s; it increases slightly during the 1970s and then decreases again in the 1980s and 1990s. The calculated decadal mean WMIIscs-δ18O series had a obvious decrease from 5.92 to 4.63 m/s during the period of 1944-1997. The calculated yearly mean WMIIscs-δ18O value is 5.58 m/s from 1944 to 1976 and this decreases to 4.85 m/s from 1977 to 1998. That is the opposite trend to the observed yearly mean SST variation. The yearly mean SST anomaly is −0.27° from 1943 to 1976 and this increases to +0.16° from 1977 to 1998. Spectral analysis used on a 54-year-long calculated WMIIscs-δ18O series produces spectral peaks at 2.4-7 yr, which can be closely correlated with the quasibiennial oscillation band (QBO band, 2-2.4 yr) and the El Ñino southern oscillation band (ENSO band, 3-8 yr). Hence most of the variability of the winter monsoon intensity in the middle of the South China Sea is mainly constrained by changes in the thermal difference between the land and the adjoining sea area, perhaps due to global warming. 相似文献