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981.
982.
陆相高分辨率层序界面识别的地球化学方法 总被引:8,自引:3,他引:5
粘土矿物、微量元素普遍存在于各种类型的沉积物和沉积岩中,它们对环境的变化敏感,同时它们的沉积分异、组合特征、矿物成分及其含量都从不同的角度记录了形成过程中各种环境因素的变化。这些对恢复古环境,研究陆相湖盆水深变化具有重要的指示意义。通过对东营凹陷胜北断层下降盘沙三段 -沙四上段各层序内部高分辨率层序地层单元中岩石地球化学标型参数的研究发现,在一个高分辨率层序地层单元形成过程中,在古气候驱动下的湖平面变化旋回中,沉积岩中的矿物成分 (主要指粘土矿物和胶结物 )、化学成分 (微量元素 )等皆发生周期性变化。 相似文献
983.
Yuanyuan You Jianyu Liu Yongqiang Zhang Hylke E. Beck Xihui Gu Dongdong Kong 《水文研究》2021,35(10):e14367
Runoff signatures, including low flow, high flow, mean flow and flow variability, have important implications on the environment and society, predominantly through drought, flooding and water resources. Yet, the response of runoff signatures has not been previously investigated at the global scale, and the influencing mechanisms are largely unclear. Hence, this study makes a global assessment of runoff signature responses to the El Niño and La Niña phases using daily streamflow observations from 8217 gauging stations during 1960–2015. Based on the Granger causality test, we found that ~15% of the hydrological stations of multiple runoff signatures show a significant causal relationship with El Niño–southern oscillation (ENSO). The quantiles of all runoff signatures were larger during the El Niño phase than during the La Niña phase, implying that the entire flow distribution tends to shift upward during El Niño and downward during La Niña. In addition, El Niño has different effects on low and high flows: it tends to increase the low and mean flow signatures but reduces the high flow and flow variability signatures. In contrast, La Niña generally reduces all runoff signatures. We highlight that the impacts of ENSO on streamflow signatures are manifested by its effects on precipitation (P), potential evaporation (PET) and leaf area index (LAI) through ENSO-induced atmospheric circulation changes. Overall, our study provides a comprehensive picture of runoff signature responses to ENSO, with valuable insights for water resources management and flood and drought disaster mitigation. 相似文献
984.
Thermal effects of lateral supra‐permafrost water flow around a thermokarst lake on the Qinghai–Tibet Plateau 下载免费PDF全文
Both the inflow and outflow of supra‐permafrost water to lakes play important roles in the hydrologic process of thermokarst lakes. The accompanying thermal effects on the adjacent permafrost are required for assessing their influences on the development of thermokarst lakes. For these purposes, the lake water level, temperature dynamics, and supra‐permafrost water flow of a lake were monitored on the Qinghai‐Tibet Plateau. In addition, the spatial and temporal variation of the active layer thickness and permafrost distribution around the lake were investigated by combining ground penetrating radar, electrical resistivity tomography, and borehole temperature monitoring. The results revealed that the yearly unfrozen supra‐permafrost water flow around the lake lasted approximately 5 months. The temperature and water level measurements during this period indicate that the lake water was recharged by relatively colder supra‐permafrost water from the north‐western lakeshore and was discharged through the eastern lakeshore. This process, accompanied by heat exchange with the underlying permafrost, might cause a directional difference of the active layer thickness and permafrost characteristics around the lake. Specifically, the active layer thickness variation was minimal, and the ice‐rich permafrost was found adjacent to the lakeshore along the recharge groundwater pathways, whereas a deeper active layer and ice‐poor permafrost were observed close to the lakeshore from which the warm lake water was discharged. This study suggests that the lateral flow of warm lake water can be a major driver for the rapid expansion of thermokarst lakes and provides clues for evaluating the relationships between the thermokarst expansion process and climate warming. 相似文献
985.
Water temperature is an important habitat factor in river ecosystems that exhibits the characteristics of continuous change. Dam construction disrupts the continuity of river water temperature and reset it, thus exerting sharp rise/decrease on the characteristics of water temperature change. The effect of a dam on river continuity is directly related to the dam size. To explain this relationship, two rivers in China were selected: one river without reservoirs and one river with cascade reservoirs. Through the analysis of the longitudinal change of water temperature in free-flowing rivers, we found that water temperature changes continuously and steadily in the longitudinal direction. Based on this, a temperature trend hypothesis in river was proposed, and the discontinuity of the water temperature in the reservoir section was evaluated. The results are as follows: (1) In mixed reservoirs, river water temperature remained as continuous as free-flowing rivers. However, the river water temperature had a large discontinuity in the stratified reservoir. (2) Water residence time was used as an indicator of the continuity of reservoir water temperature. (3) Selective withdrawal of stratified reservoirs in January could not remove the discontinuity caused by itself, but it worked in June. 相似文献
986.
提出一种基于极大验后估计(MAP)超分辨率重建算法的新的改进算法.该算法将MAP算法或其他超分辨率重建算法所获得的高分辨率影像引入到MAP算法中,主要思想是基于所求取的分辨率应该与理想的高分辨率影像最大相关的原理.最后采取基于灰度的四参数仿射变换模型的配准算法,采用共轭梯度算法来迭代求解超分辨率重建方程.仿真试验证明,... 相似文献
987.
988.
Shi Yan Wu Qi You Zhou Gang Wang Lei Yang Cheng Peng Ling 《Environmental Earth Sciences》2011,62(5):999-1011
Based on batch experiments conducted on soil samples in the laboratory, the relationship between dielectric constant and water
content based on electrical capacitance measurement was investigated. Factors that may affect the relationship, such as measurement
frequency, electrode array methods, and soil particle sizes, were analyzed. A model fitting the relationship between dielectric
constant and water content was proposed. The results clearly indicate that even with the use of rod-like sensors, the measured
electrical capacitance with 1 kHz frequency can be used to construct a good relationship between dielectric constant and water
content. Although the electrode array methods (parallel or non-parallel electrode pair) and soil particle sizes do affect
the obtained absolute values of dielectric constant to some extent, the relationship between dielectric constant and water
content remains unchanged. A clear characteristic is the increase reduction in the dielectric constant at near saturation
condition, and the low increase speed when water content is small. The proposed modified VG model incorporated this characteristic
into it and fitted the data better than the reported models. These results suggest that the electrical capacitance-based dielectric
constant measurement can be extensively used and would be useful, especially in the situations where parallel sensor requirement
is difficult to satisfy. 相似文献
989.
Cui Hua Huang Xian Xue Tao Wang Roberto De Mascellis Giacomo Mele Quan Gang You Fei Peng Anna Tedeschi 《Environmental Earth Sciences》2011,63(4):701-708
Due to the lack of freshwater, highly saline groundwater was the main irrigation source in the last few decades in the Minqin
Basin, which is in northwest China. The study evaluates the effects of salt accumulation on the soil physical–chemicals properties.
Undisturbed and disturbed soil samples were taken from the experiment site, which was irrigated with saline water at a concentration
of 0.8, 2 and 5 g L−1 (coded later as C08, C2 and C5). Undisturbed soil samples, at depths of 0–45 and 45–60 cm were taken to determine the water retention curve (WRC). Moreover,
in the same place, another set of undisturbed soil samples were taken to determine the porosity and pore-size distribution
(PoSD). From the WRC, the water-holding capacity of the soil was estimated. Disturbed soil samples at depths of 0–20, 0–45,
45–60 and 80–100 cm were taken to determine the index of aggregates stability in water (IC). The electrical conductivity of
the saturated paste (ECe) was determined at depths of 0–30, 30–60 and 60–90 cm, during the irrigation season on C08, C2 and C5 treatments. The results show that the total porosity and the index of aggregates stability in water decrease with the increasing
salinity of irrigation water, and the ECe increases with the increasing salinity of irrigation water especially in the surface soil. The water-holding capacity (WHC)
of soil also increases with the increasing salinity of irrigation water. 相似文献
990.
Zhang L Liu X You L Zhou D Wu H Li L Zhao J Feng J Yu J 《Marine environmental research》2011,72(1-2):33-39
Copper is an important heavy metal contaminant with high ecological risk in the Bohai Sea. In this study, the metabolic responses in the bioindicator, Manila clam (Ruditapes philippinarum), to the environmentally relevant copper exposures were characterized using NMR-based metabolomics. The significant metabolic changes corresponding to copper exposures were related to osmolytes, intermediates of the Krebs cycle and amino acids, such as the increase in homarine, branched chain amino acids and decrease in succinate, alanine and dimethylamine in the copper-exposed clam gills during 96 h exposure period. Overall, Cu may lead to the disturbances in osmotic regulation and energy metabolism in clams during 96 h experimental period. These results demonstrate that NMR-based metabolomics is applicable for the discovery of metabolic biomarkers which could be used to elucidate the toxicological mechanisms of marine heavy metal contaminants. 相似文献