全文获取类型
收费全文 | 657篇 |
免费 | 139篇 |
国内免费 | 204篇 |
专业分类
测绘学 | 51篇 |
大气科学 | 204篇 |
地球物理 | 180篇 |
地质学 | 356篇 |
海洋学 | 66篇 |
天文学 | 36篇 |
综合类 | 59篇 |
自然地理 | 48篇 |
出版年
2024年 | 4篇 |
2023年 | 11篇 |
2022年 | 23篇 |
2021年 | 40篇 |
2020年 | 32篇 |
2019年 | 31篇 |
2018年 | 37篇 |
2017年 | 32篇 |
2016年 | 47篇 |
2015年 | 47篇 |
2014年 | 34篇 |
2013年 | 41篇 |
2012年 | 43篇 |
2011年 | 36篇 |
2010年 | 35篇 |
2009年 | 31篇 |
2008年 | 21篇 |
2007年 | 44篇 |
2006年 | 25篇 |
2005年 | 21篇 |
2004年 | 19篇 |
2003年 | 21篇 |
2002年 | 17篇 |
2001年 | 18篇 |
2000年 | 31篇 |
1999年 | 46篇 |
1998年 | 37篇 |
1997年 | 35篇 |
1996年 | 21篇 |
1995年 | 18篇 |
1994年 | 15篇 |
1993年 | 18篇 |
1992年 | 11篇 |
1991年 | 8篇 |
1990年 | 6篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 9篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1958年 | 4篇 |
排序方式: 共有1000条查询结果,搜索用时 21 毫秒
941.
针对“蒸发悖论”科学问题,从长江流域实际蒸发量变化的原因着手,探讨实际蒸发量与潜在蒸发量之间的关系。研究结果表明:一般情况下当干燥度指数R<0.8时,实际蒸发量与潜在蒸发量为明显的正相反关系,当0.81.0时,实际蒸发量与潜在蒸发量为明显的互补关系。 相似文献
942.
Hydrology of Dali Lake in central-eastern Inner Mongolia and Holocene East Asian monsoon variability 总被引:12,自引:1,他引:11
Jule Xiao Bin Si Dayou Zhai Shigeru Itoh Zaur Lomtatidze 《Journal of Paleolimnology》2008,40(1):519-528
Lacustrine records from the northern margin of the East Asian monsoon generate a conflicting picture of Holocene monsoonal precipitation change. To seek an integrated view of East Asian monsoon variability during the Holocene, an 8.5-m-long sediment core recovered in the depocenter of Dali Lake in central-eastern Inner Mongolia was analyzed at 1-cm intervals for total organic and inorganic carbon concentrations. The data indicate that Dali Lake reached its highest level during the early Holocene (11,500–7,600 cal yr BP). The middle Holocene (7,600–3,450 cal yr BP) was characterized by dramatic fluctuations in the lake level with three intervals of lower lake stands occurring 6,600–5,850, 5,100–4,850 and 4,450–3,750 cal yr BP, respectively. During the late Holocene (3,450 cal yr BP to present), the lake displayed a general shrinking trend with the lowest levels at three episodes of 3,150–2,650, 1,650–1,150 and 550–200 cal yr BP. We infer that the expansion of the lake during the early Holocene would have resulted from the input of the snow/ice melt, rather than the monsoonal precipitation, in response to the increase in summer solar radiation in the Northern Hemisphere. We also interpret the rise in the lake level since ca. 7,600 cal yr BP as closely related to increased monsoonal precipitation over the lake region resulting from increased temperature and size of the Western Pacific Warm Pool and a westward shifted and strengthened Kuroshio Current in the western Pacific. Moreover, high variability of the East Asian monsoon climate since 7,600 cal yr BP, marked by large fluctuations in the lake level, might have been directly associated with variations in the intensity and frequency of the El Niño-Southern Oscillation (ENSO) events. 相似文献
943.
大比例尺数字地形图的数据质量控制 总被引:11,自引:1,他引:10
数据质量控制是良好的数字地形图质量的重要保证。文中从野外采集数据和地图数字化两个方面分析了影响大比例尺数字地形图数据质量的因素 ,讨论了数据质量控制的方法。 相似文献
944.
利用G分布函数对中国1951-2004年地面台站逐日降水观测资料进行雨日降水量概率分布拟合并定义极端降水事件,在此基础上对极端降水日数与ENSO的关系进行分析研究。结果表明,ENSO对同期的极端降水发生频率在不同地区和不同季节表现出不同的影响作用。总体而言,中国极端降水事件更易发生在厄尔尼诺年的冬春季和拉尼娜年的夏秋季。极端降水在对ENSO强信号的滞后响应上,其发生频率在时空上发生了变化,主要表现为,多数地方更易在ENSO暖位相出现后的半年左右发生极端降水事件。研究表明,ENSO冷暖信号对我国极端降水事件多寡的影响具有不对称性。 相似文献
945.
Platinum has been one of the highly needed mineral resources in China. The geochemical exploration at two survey scales was
applied in telescoping ore targets for the first time in Eastern Yunnan Pt geochemical province that was delineated using
Pt data from flood plain sediments with extra-low sampling density. Our study was based on the delineations and assessments
of both regional and local Pt anomalies using the Pt data by analyzing with C-OES the composite samples with two sampling
densities. The composite samples were obtained by recomposing at two sampling densities the original stream sediment samples
collected by the National Geochemical Mapping Project. Semi-variograms were used to quantitatively describe the variability
of Pt anomalies and further analyze the factors controlling the variability. Pt resource potentials of both the regional Pt
anomalies and the local Pt anomalies in the study area were estimated based on the geochemical block methods, respectively.
It comes to the conclusions as follows. (1) From the regional to local Pt anomaly, the factors controlling their variability
from the deep seated faults-basalts turn into the basalts-branch faults, which suggest that Semi-variograms could identify
the geological factors controlling the variability of the Pt anomalies identified by the Pt data from the stream sediments
with different sampling densities. (2) There exist two types of Pt anomalies in the study area. One is those displaying at
sampling densities, and its average Pt concentration significantly increases with sampling density increasing. The other is
getting weaker and/or disappears with sampling density increasing. This shows that TOTGEMS could gradually eliminate non-ore
anomalies and keep ore anomalies. (3) The average Pt concentration of the local Pt anomaly blocks delineated using Pt data
from stream sediments with sampling density of one composite per 16 km2 is twice as much as that of the regional Pt anomaly blocks delineated using Pt data from stream sediments with sampling density
of one composite per 64 km2. The Pt resource amount of the local Pt anomaly blocks is 60% of the regional anomaly blocks,
but the area of the former is just 35% of the latter, which suggests that the Pt resource amount is mainly concentrated in
its local anomalies, and that TOTGEMS has a good exploration function that efficiently approaches ore targets.
Supported by National High-Tech Research & Development Program of China (863 Program) (Grant No. 2006AA06Z113) and National
Natural Science Foundation of China (Grant No. 40772197) 相似文献
946.
The mixing of seawater/hydrothermal fluid within the large seafloor hydrothermal sulfide deposits plays a key role in the
formation processes of the sulfide deposits. Some issues attract considerable attentions in the study of seafloor hydrothermal
system in recent years, such as the relationships among different types of vent fluids, the characteristics of chemical compositions
and mineral assemblages of the hydrothermal deposits and their governing factors. Combined with the measured data of hydrothermal
fluid in the TAG field, the thermodynamic model of mixing processes of the heated seawater at different temperatures and the
hydrothermal fluid is calculated to understand the precipitation mechanism of anhydrite and the genetic relationships between
the black and white smoker fluids within the TAG mound. The results indicate that the heating of seawater and the mixing of
hydrothermal fluid/seawater are largely responsible for anhydrite precipitation and the temperature of the heated seawater
is not higher than 150°C and the temperature of the end-member hydrothermal fluid is not lower than 400°C. Based on the simulated
results, the evolving patterns of fluids within the TAG deposit are discussed. The mixed fluid of the end-member hydrothermal
fluid and the seawater heated by wall rock undergoes conductive cooling during upflowing within the deposit and forms “White
Smoker” eventually. In addition, the end-member hydrothermal fluid without mixed with seawater, but undergoing conductive
cooling, vents out of the deposit and forms “Black Smoker”.
Supported by China Ocean Mineral Resources Research and Development Association Program (Grant No. DY115-02-1-01) and National
Basic Research Program of China (Grant No. G2000078503) 相似文献
947.
Due to anthropogenic activities, the nutrient loadings of the Changjiang (Yangtze River) are strickly on the rise. The high nutrient concentrations notwithstanding, river water was pCO2 supersaturated in the inner estuary during summer 2003 but decreased quickly in the mid-estuary due to mixing with low pCO2 waters from offshore. In addition, settling of particles in the estuary resulted in better light conditions so that phytoplankton bloomed, driving down pCO2 to ∼200 μatm. In the outer estuary and outside of the bloom area, pCO2 increased again to near or just below saturation. Literature data also reveal that the mainstream of the Changjiang is always supersaturated with respect to CO2 probably because the decomposition of terrestrial organic matter overwhelms the consumption of CO2 due to biological production. 相似文献
948.
Minhan Dai Weidong Zhai Wei-Jun Cai Julie Callahan Bangqin Huang Shaoling Shang Tao Huang Xiaolin Li Zhongming Lu Weifang Chen Zhaozhang Chen 《Continental Shelf Research》2008
We observed a phytoplankton bloom downstream of a large estuarine plume induced by heavy precipitation during a cruise conducted in the Pearl River estuary and the northern South China Sea in May–June 2001. The plume delivered a significant amount of nutrients into the estuary and the adjacent coastal region, and enhanced stratification stimulating a phytoplankton bloom in the region near and offshore of Hong Kong. A several fold increase (0.2–1.8 μg Chl L−1) in biomass (Chl a) was observed during the bloom. During the bloom event, the surface water phytoplankton community structure significantly shifted from a pico-phytoplankton dominated community to one dominated by micro-phytoplankton (>20 μm). In addition to increased Chl a, we observed a significant drawdown of pCO2, biological uptake of dissolved inorganic carbon (DIC) and an associated enhancement of dissolved oxygen and pH, demonstrating enhanced photosynthesis during the bloom. During the bloom, we estimated a net DIC drawdown of 100–150 μmol kg−1 and a TAlk increase of 0–50 μmol kg−1. The mean sea–air CO2 flux at the peak of the bloom was estimated to be as high as ∼−18 mmol m−2 d−1. For an average surface water depth of 5 m, a very high apparent biological CO2 consumption rate of 70–110 mmol m−2 d−1 was estimated. This value is 2–6 times higher than the estimated air–sea exchange rate. 相似文献
949.
综述了构造流体与成矿系统及其动力学的研究进展、趋势, 初步提出构造-流体-成矿系统及其动力学的理论格架与方法体系.突出构造和流体在成矿中的关键作用, 强调多种组成与多重作用过程耦合和套合的整体性及其综合效应, 并以这一理论为指导, 提出将构造-流体-成矿系统及其动力学作为一个整体, 从流体与岩石-构造环境相互作用及构造-流体演化的角度探讨成矿系统的形成过程和动力学特征, 遵循实践→认识→再实践→再认识的循序渐进原则, 在多学科综合研究的基础上, 以宏观整体性认识为指导, 深入解析代表性典型中观成矿系统时-空轨迹的规律性特色本质, 具体指导微观成矿作用过程及机理的研究, 实现研究的系统性、完整性和定量化, 从更广、更深层次上认识构造-流体-成矿系统时-空结构及本质属性. 相似文献
950.