全文获取类型
收费全文 | 416篇 |
免费 | 85篇 |
国内免费 | 58篇 |
专业分类
测绘学 | 13篇 |
大气科学 | 21篇 |
地球物理 | 220篇 |
地质学 | 170篇 |
海洋学 | 61篇 |
天文学 | 11篇 |
综合类 | 19篇 |
自然地理 | 44篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 6篇 |
2021年 | 14篇 |
2020年 | 19篇 |
2019年 | 18篇 |
2018年 | 12篇 |
2017年 | 16篇 |
2016年 | 16篇 |
2015年 | 13篇 |
2014年 | 17篇 |
2013年 | 42篇 |
2012年 | 15篇 |
2011年 | 24篇 |
2010年 | 20篇 |
2009年 | 33篇 |
2008年 | 23篇 |
2007年 | 34篇 |
2006年 | 27篇 |
2005年 | 29篇 |
2004年 | 23篇 |
2003年 | 22篇 |
2002年 | 27篇 |
2001年 | 16篇 |
2000年 | 14篇 |
1999年 | 13篇 |
1998年 | 13篇 |
1997年 | 12篇 |
1996年 | 7篇 |
1995年 | 8篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1982年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有559条查询结果,搜索用时 406 毫秒
81.
In this study, it was aimed to characterize temporal variations of air pollutants for determining contribution to pollution episodes and to obtain correlations between these pollutants. With this aim we used data analysis for measured sulfur dioxide (SO2), particulate matter (PM, black fume and PM10), nitrogen oxides (NOx), ozone (O3), carbon monoxide (CO), methane (CH4), and non‐methane hydrocarbons (NMHC) recorded in Kocaeli, one of the most industrilizated cities of Turkey. Pollutant concentrations were the results of continuous and semi‐automatic measurements. Semi‐automatic measurements of SO2 and PM (black fume) were enclosing period from 1987 to 2008 whereas continuous monitoring of all pollutants included years of 2007–2009. In the first stage of the study daily, monthly, annual, and seasonal variations of pollution were researched. Annual average concentrations were compared with limits set by Air Quality Protection Regulation (AQPR), Air Quality Evaluation and Management Regulation (AQEMR), World Health Organization (WHO), European Union (EU), and National Ambient Air Quality Standards (USEPA). In the following stage relationships between pollutants such as NO2–O3, NOx–CO, NOx–NMHC, and NOx–SO2 were investigated and correlation coefficients were determined as 0.87, 0.56, 0.51, and 0.69, respectively. R2 values of regression models developed from these correlations were 0.78, 0.56, 0.34, and 0.72, respectively. Vehicle density of the traffic was evaluated with NOx–O3 emissions and decrease was seen in NOx emissions due to decreasing vehicle density at weekends whereas O3 concentrations increased. These correlations enable prediction of the parameters that cannot be measured which is important for providing improvement in early warning systems. 相似文献
82.
83.
84.
85.
海洋沉积地质过程模拟:性质与问题及前景 总被引:3,自引:0,他引:3
高抒 《海洋地质与第四纪地质》2011,(5):1-7
探讨了海洋沉积地质数值模拟的功能问题.地球科学研究以正演方法(以数值模拟为代表)和反演方法(以地层记录分析为代表)的结合为特征.数值模拟作为一种重要的研究工具,具有获得过程和机理分析结果、形成工作假说、指导现场观测和采样的作用.与此同时,在正反演交融中模型本身也得到了提高和完善.在海洋沉积地质领域,数值模拟在沉积物输运... 相似文献
86.
不同深度处的含水介质温度时序资料振幅比或相位滞后能用来计算地下水垂向流速,典型的解析模型是Hatch模型。为了评价Hatch模型的参数灵敏度,采用局部灵敏度分析方法确定该模型的主要影响因子及相关参数与模型响应的依存关系,再由全局灵敏度分析方法评价参数共同作用对模型计算结果的影响。灵敏度分析结果表明:Hatch模型精度的主要影响因子是测点距离(Δz),其次是介质比热容(ρscs)和有效孔隙度(ne),而基准热传导系数(λ0)和热弥散度(β)的影响甚微。基准热传导系数和热弥散度与计算流速呈负相关,其余参数则与之呈正相关。因此在实践中,需保证测点距离的准确性,而对基准热传导系数和热弥散度可取经验值。 相似文献
87.
The characteristics of seismic water level fluctuations of the two Sumatra-Andaman strong earthquakes with magnitude 8.7 and 8.5 on December 26,2004 and March 29, 2005 recorded at Jiaji well, Qionghai, Hainan were analyzed, the features of the infrequent "step" changes of well water level after the two earthquakes were also analyzed and the mechanism of the "step change" of well water level was discussed. Then the high-sample-rate digital observation data of seismically-induced water level fluctuations of the Sumatra-Andaman strong earthquakes with magnitude 8.7 and 8.5 recorded at Nanbin well, Sanya and Tanniu well, Wenchang were analyzed. The results suggest that the dominant period of the seismic well water level fluctuation in all three wells was comparatively accordant, the amplitudes of seismic water level fluctuation of the same earthquake in different wells were clearly different, the time duration of seismic water level fluctuations of different earthquakes at the same well was also clearly different. 相似文献
88.
We review recent studies of the statistics of return intervals (i) in long-term correlated monofractal records and (ii) in
multifractal records in the absence (or presence) of linear long-term correlations. We show that for the monofractal records
which are long-term power-law correlated with exponent γ, the distribution density of the return intervals follows a stretched
exponential with the same exponent γ and the return intervals are long-term correlated, again with the same exponent γ. For
the multifractal record, significant differences in scaling behavior both in the distribuiton and correlation behavior of
return intervals between large events of different magnitudes are demonstrated. In the absence of linear long-term correlations,
the nonlinear correlations contribute strongly to the statistics of the return intervals such that the return intervals become
long-term correlated even though the original data are linearly uncorrelated (i.e., the autocorrelation function vanishes).
The distribution density of the return intervals is mainly described by a power law. 相似文献
89.
Yang XiaoQiang Zhu ZhaoYu Zhang YiNan Li HuaMei Zhou WenJuan Yang Jie 《中国科学D辑(英文版)》2008,51(3):441-450
Directional samples were taken to study rock magnetism and palaeomagnetic records from the Dong- sheng profile, which is 5 m thick and on the northwest edge of the Bose Basin. Mineralogy and rock magnetism of typical samples indicate that coarse granular titanomagnetite, and fine-grained hematite, superparamagnetic maghemite formed by pedogenesis are in the sediment, which has undergone many transformative processes during different stages of pedogenesis. Parallel samples were taken for thermal demagnetization (TH) (0 to 680℃) and alternating field (AF) demagnetization (0 to 80 mT) respectively. Experimental results of these two kinds of demagnetization illustrate that there are two or more magnetic components in the samples. Intensity of NRM decreases by almost 60% to 90% rapidly when the temperature ranges from 100℃ to 350℃, with a steady magnetic component. It is impossible to analyze the magnetic components at high temperature because those fluctuate widely when the temperature is higher than 400℃. Steady magnetic components from 100℃ to 350℃ indicate that the remanence was mainly carried by fine-grained hematite formed by pedogenesis, reflecting a change in the geomagnetic field while the magnetite was being oxidized into hematite by chemical weathering after deposition. The formative age of the sediments cannot be obtained by magnetic methods in this profile. 相似文献
90.
YunFa Miao XiaoMin Fang ZhiChen Song FuLi Wu WenXia Han Shuang Dai ChunHui Song 《中国科学D辑(英文版)》2008,51(8):1089-1098
The Eocene palaeovegetation landscape and palaeoclimate reconstructed from the pollen records in the Jiuquan Basin, northwest
China provide some important information on the early uplift of the Tibetan Plateau and the origin and evolution of the aridification
in northwest China. The records show the arid-semiarid scrubs with open forest palynofloras controlled by the subtropical
high existed in northwest China during the 40.2–33.4 Ma. Four pollen assemblages are found: Nitrariadites-Cheno-podipollis-Pinaceae assemblage (40.2–37.9 Ma) is followed by Chenopodipollis-Nitrariadites assemblage (37.9–34.6 Ma), Pinuspollenites & Abietineaepollenites-Chenopodipollis assemblage (34.6–33.9 Ma), and Chenopodipollis-Nitrariadites assemblage (33.9–33.4 Ma). The percentage of thermophilic types is in anti-correlation with that of the dry types, which
means the palaeoclimate is relatively warm-wet or cold-dry during most of that time. Such aridity may be related to the water
vapor reduction and the planetary wind system movement northward in response to the cooling caused by small-ephemeral ice-sheets.
Supported by the National Key Program for Developing Basic Sciences (Grant No. 2005CB422001), the National Science Foundation
of China (Grant Nos. 40334038, 40421101) and the President Fund of Chinese Academy of Sciences 相似文献