全文获取类型
收费全文 | 5356篇 |
免费 | 549篇 |
国内免费 | 164篇 |
专业分类
测绘学 | 250篇 |
大气科学 | 602篇 |
地球物理 | 1969篇 |
地质学 | 2186篇 |
海洋学 | 282篇 |
天文学 | 340篇 |
综合类 | 188篇 |
自然地理 | 252篇 |
出版年
2023年 | 2篇 |
2022年 | 12篇 |
2021年 | 24篇 |
2020年 | 11篇 |
2019年 | 18篇 |
2018年 | 445篇 |
2017年 | 388篇 |
2016年 | 264篇 |
2015年 | 158篇 |
2014年 | 130篇 |
2013年 | 138篇 |
2012年 | 659篇 |
2011年 | 429篇 |
2010年 | 123篇 |
2009年 | 139篇 |
2008年 | 124篇 |
2007年 | 114篇 |
2006年 | 125篇 |
2005年 | 832篇 |
2004年 | 871篇 |
2003年 | 651篇 |
2002年 | 174篇 |
2001年 | 71篇 |
2000年 | 43篇 |
1999年 | 15篇 |
1998年 | 5篇 |
1997年 | 17篇 |
1996年 | 11篇 |
1992年 | 2篇 |
1991年 | 9篇 |
1990年 | 9篇 |
1989年 | 5篇 |
1987年 | 4篇 |
1980年 | 3篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1973年 | 2篇 |
1969年 | 2篇 |
1968年 | 2篇 |
1965年 | 3篇 |
1963年 | 2篇 |
1962年 | 1篇 |
1961年 | 2篇 |
1959年 | 2篇 |
1956年 | 1篇 |
1955年 | 2篇 |
1954年 | 2篇 |
1951年 | 2篇 |
1948年 | 2篇 |
1925年 | 1篇 |
排序方式: 共有6069条查询结果,搜索用时 10 毫秒
391.
Fa-Wu?WangEmail author Ye-Ming?Zhang Zhi-Tao?Huo Tatsunori?Matsumoto Bo-Lin?Huang 《Landslides》2004,1(2):157-162
The Qianjiangping landslide occurred after the first impoundment of the Three Gorges Reservoir in July 2003. Field investigation revealed that failure occurred when the reservoir reached 135 m, but the stability of the affected slope was already reduced by pre-existing bedding-plane shears, quarrying of mudstone from the landslide toe, and previous heavy rain. A possible explanation of the rapid and long runout mechanism of the landslide is that movement on a bedding-plane shear ruptured the calcite cement and rapidly reduced the sandstone strength to residual shear strength. 相似文献
392.
393.
藏南沉错湖泊沉积多指标揭示的2万年以来环境变化 总被引:22,自引:1,他引:22
通过对藏南沉错湖芯TC1孔的研究,分析了TC1孔的粒度、TOC、TN、C/N、Fe/Mn、Sr/Ba以及环境磁学参数等环境代用指标,基本上获得了这一地区2万年以来的环境变化记录。结果显示约19 800~18 000 Cal aBP的温度下降在各指标中具有明显的反映;约16 000 Cal aBP左右,温度在一次跃动上升之后,随即出现急剧下降;约15 200~12 000 Cal aBP,是降温之后的缓慢回升过程;约12 000~9 500 Cal aBP,各种指标均显示湖区环境处于不适宜阶段,特别是11 600~10 400 Cal aBP,湖区环境显著恶化。进入全新世后,湖区环境经历了3次明显的暖期(约9 500~7 600 Cal aBP、约6 800~5 800 Cal aBP、约4 800~3 800 Cal aBP) 和2次冷期(约7 600~6 800 Cal aBP、约5 800~4 800 Cal aBP),呈现出暖干/冷湿的交替规律,具有南亚季风(西南季风) 区气候变化的特征。沉错湖区2万年来的气候环境变化序列中的某些特征时段与格陵兰冰芯记录和青藏高原其他记录相比具有较好的一致性,反映了湖区及藏南地区的气候环境演变特征具有全球性特征。 相似文献
394.
Xiyuan?Chi Pengzhen?He Zhuang?Jiang Xiawei?Yu Fange?Yue Longquan?Wang Bokun?Li Hui?Kang Cheng?Liu Zhouqing?XieEmail author 《Acta Meteorologica Sinica》2018,32(1):14-25
We investigated the acidity and concentrations of water-soluble ions in PM2.5 aerosol samples collected from an urban site in Beijing and a rural site in Gucheng, Hebei Province from November 2016 to January 2017 to gain an insight into the formation of secondary inorganic species. The average SO42–, NO3–, and NH4+ concentrations were 8.3, 12.5, and 14.1 μg m–3, respectively, at the urban site and 14.0, 14.2, and 24.2 μg m–3, respectively, at the rural site. The nitrogen and sulfur oxidation ratios in urban Beijing were correlated with relative humidity (with correlation coefficient r = 0.79 and 0.67, respectively) and the aerosol loadings. Based on a parameterization model, we found that the rate constant of the heterogeneous reactions for SO2 on polluted days was about 10 times higher than that on clear days, suggesting that the heterogeneous reactions in the aerosol water played an essential role in haze events. The ISORROPIA II model was used to predict the aerosol pH, which had a mean (range) of 5.0 (4.9–5.2) and 5.3 (4.6–6.3) at the urban and rural site, respectively. Under the conditions with this predicted pH value, oxidation by dissolved NO2 and the hydrolysis of N2O5 may be the major heterogeneous reactions forming SO42– and NO3– in haze. We also analyzed the sensitivity of the aerosol pH to changes in the concentrations of SO42–, NO3–, and NH4+ under haze conditions. The aerosol pH was more sensitive to the SO42– and NH4+ concentrations with opposing trends, than to the NO3– concentrations. The sensitivity of the pH was relatively weak overall, which was attributed to the buffering effect of NH3 partitioning. 相似文献
396.
Hyung-Il?EumEmail author Alex?J.?Cannon Trevor?Q.?Murdock 《Stochastic Environmental Research and Risk Assessment (SERRA)》2017,31(3):683-703
A number of statistical downscaling methodologies have been introduced to bridge the gap in scale between outputs of climate models and climate information needed to assess potential impacts at local and regional scales. Four statistical downscaling methods [bias-correction/spatial disaggregation (BCSD), bias-correction/constructed analogue (BCCA), multivariate adaptive constructed analogs (MACA), and bias-correction/climate imprint (BCCI)] are applied to downscale the latest climate forecast system reanalysis (CFSR) data to stations for precipitation, maximum temperature, and minimum temperature over South Korea. All methods are calibrated with observational station data for 19 years from 1973 to 1991 and validated for the more recent 19-year period from 1992 to 2010. We construct a comprehensive suite of performance metrics to inter-compare methods, which is comprised of five criteria related to time-series, distribution, multi-day persistence, extremes, and spatial structure. Based on the performance metrics, we employ technique for order of preference by similarity to ideal solution (TOPSIS) and apply 10,000 different weighting combinations to the criteria of performance metrics to identify a robust statistical downscaling method and important criteria. The results show that MACA and BCSD have comparable skill in the time-series related criterion and BCSD outperforms other methods in distribution and extremes related criteria. In addition, MACA and BCCA, which incorporate spatial patterns, show higher skill in the multi-day persistence criterion for temperature, while BCSD shows the highest skill for precipitation. For the spatial structure related criterion, BCCA and MACA outperformed BCSD and BCCI. From the TOPSIS analysis, we found that MACA is the most robust method for all variables in South Korea, and BCCA and BCSD are the second for temperature and precipitation, respectively. We also found that the contribution of the multi-day persistence and spatial structure related criteria are crucial to ranking the skill of statistical downscaling methods. 相似文献
397.
QU Jianjun YAN Muhong DONG Guangrong ZHANG Hongfa ZU Ruiping TUO Wanquan ZHAO Aiguo XlAO Zhenghua LI Fang & YANG Bao Key Laboratory of Desert Desertification Cold Arid Regions Environmental Engineering Research Institute Shapotou Desert Research Experiment Station Chinese Academy of Sciences Lanzhou China 《中国科学D辑(英文版)》2004,47(6):529-539
~~Wind tunnel simulation experiment and investigation on the electrification of sandstorms~~ 相似文献
398.
399.
Anirudh?PradhanEmail author Sudhir?Kumar?Srivastav Mahesh?Kumar?Yadav 《Astrophysics and Space Science》2005,298(3):419-432
Some Bianchi type IX viscous fluid cosmological models are investigated. To get a solution, a supplementary condition between
metric potentials is used. The viscosity coefficient of bulk viscous fluid is assumed to be a power function of mass density,
whereas the coefficient of shear viscosity is considered as proportional to scale of expansion in the model. The cosmological
constant Λ is found to be positive and is a decreasing function of time, which is supported by results from recent supernovae
observations. Some physical and geometric properties of the models are also discussed. 相似文献
400.
Julien?LeutholdEmail author Jonathan?D.?Blundy Richard?A.?Brooker 《Contributions to Mineralogy and Petrology》2015,169(2):12
The 176Lu–176Hf and 147Sm–143Nd decay systems are routinely used to determine garnet (Grt)–whole-rock (WR) ages; however, the 176Lu–176Hf age of garnet is typically older than the 147Sm–143Nd age determined from the same aliquots. Here we present experimental data for Lu3+ and Hf4+ diffusion in garnet as functions of temperature, pressure and oxygen fugacity and show that the diffusivity of Hf4+ in almandine/spessartine garnet is significantly slower than that of Lu3+. The diffusive closure temperature (T C) of Hf4+ is significantly higher than that of Nd3+, and although this property is partly responsible for the observed 176Lu–176Hf and 147Sm–143Nd Grt–WR age discrepancies, the difference between the T C-s of Lu3+ and Hf4+ could lead to apparent Grt–WR 176Lu–176Hf ages that are skewed from the age of Hf4+ closure in garnet. In addition, the slow diffusivity of Hf4+ indicates that the bulk of metamorphic garnets retain a substantial fraction of prograde radiogenic 176Hf throughout peak metamorphic conditions, a phenomenon that further complicates the interpretation of 176Lu–176Hf garnet ages and invalidates the use of analytical T C expressions. We argue that the diffusion of trivalent rare earth elements in garnet becomes much faster when their concentration level falls below a few hundred ppm, as in the experiments of Tirone et al. (Geochim Cosmochim Acta 69: 2385–2398, 2005), and further argue that this low-concentration mechanism is appropriate for modeling the susceptibility of 147Sm–143Nd garnet ages to diffusive resetting. 相似文献