全文获取类型
收费全文 | 2655篇 |
免费 | 343篇 |
国内免费 | 421篇 |
专业分类
测绘学 | 237篇 |
大气科学 | 336篇 |
地球物理 | 725篇 |
地质学 | 1149篇 |
海洋学 | 371篇 |
天文学 | 126篇 |
综合类 | 171篇 |
自然地理 | 304篇 |
出版年
2024年 | 18篇 |
2023年 | 53篇 |
2022年 | 120篇 |
2021年 | 135篇 |
2020年 | 124篇 |
2019年 | 121篇 |
2018年 | 155篇 |
2017年 | 131篇 |
2016年 | 136篇 |
2015年 | 131篇 |
2014年 | 161篇 |
2013年 | 140篇 |
2012年 | 134篇 |
2011年 | 165篇 |
2010年 | 143篇 |
2009年 | 149篇 |
2008年 | 125篇 |
2007年 | 114篇 |
2006年 | 92篇 |
2005年 | 80篇 |
2004年 | 77篇 |
2003年 | 83篇 |
2002年 | 119篇 |
2001年 | 105篇 |
2000年 | 77篇 |
1999年 | 53篇 |
1998年 | 72篇 |
1997年 | 67篇 |
1996年 | 39篇 |
1995年 | 48篇 |
1994年 | 33篇 |
1993年 | 33篇 |
1992年 | 36篇 |
1991年 | 19篇 |
1990年 | 11篇 |
1989年 | 18篇 |
1988年 | 10篇 |
1987年 | 9篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1980年 | 10篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1973年 | 3篇 |
排序方式: 共有3419条查询结果,搜索用时 15 毫秒
51.
52.
53.
54.
航磁ΔT解析信号确定线性构造隐伏形态的算法及阿尔金的应用 总被引:2,自引:0,他引:2
本文研究了模拟线性地质构造具有普遍意义的有限延深薄板状体ΔT的解析信号强度与其几何参数之间的超定方程关系,运用奇异值分解和广义逆技术求解超定方程,获得了高精度的理论反演方法,同时给出了定性解释板状体产状的辅助方法。对阿尔金地区隐伏断裂形态的反演结果,为西藏地体的“北推东移”提供了定量化的地球物理解释证据。文章还勾画了阿尔金与塔里木的深部界线。 相似文献
55.
A detailed investigation of the fluvial geochemistry of the Han River system allows to estimate the rates of chemical weathering and the consumption of CO2. The Han River drains approximately 26,000 km2 and is the largest river system in South Korea in terms of both water discharge and total river length. It consists of two major tributaries: the North Han River (NHR) and the South Han River (SHR). Distinct differences in basin lithology (silicate vs. carbonate) between the NHR and SHR provide a good natural laboratory in which to examine weathering processes and the influence of basin geology on water quality. The concentrations of major elements and the Sr isotopic compositions were obtained from 58 samples collected in both summer and winter along the Han River system in both 2000 and 2006. The concentrations of dissolved loads differed considerably between the NHR and SHR; compared with the SHR, the NHR had much lower total dissolved solids (TDS), Sr, and major ion concentrations but a higher Si concentration and 87Sr/86Sr ratio. A forward model showed that the dissolved loads in the NHR came primarily from silicate weathering (55 ± 11%), with a relatively small portion from carbonates (30 ± 14%), whereas the main contribution to the dissolved loads in the SHR was carbonate weathering (82 ± 3%), with only 11 ± 4% from silicates. These results are consistent with the different lithologies of the two drainage basins: silicate rocks in the NHR versus carbonate rocks in the SHR. Sulfuric acid derived from sulfide dissolution in coal-containing sedimentary strata has played an important role in carbonate weathering in the SHR basin, unlike in the NHR basin. The silicate weathering rate (SWR) was similar between the NHR and SHR basins, but the rate of CO2 consumption in the SHR basin was lower than in the NHR basin due to an important role of sulfuric acid derived from pyrite oxidation. 相似文献
56.
塔里木盆地的高分辨率环境记录对于理解西部干旱乃至全球变化至关重要.湖泊沉积物的磁学参数能够记录沉积环境和古气候信息.罗布泊地区是受西风影响的典型区域.本文选取罗布泊Ls2孔7.1Ma以来长度达1050.6m的沉积物进行详细的岩石磁学与环境磁学研究.结果表明,磁铁矿和赤铁矿是沉积物中主要载磁矿物.钻孔底部和上部的沉积物磁铁矿含量相对较高,中部强磁性矿物浓度降低导致赤铁矿占主导.磁性矿物以PSD (pseudo-single-domain)颗粒为主,并含有极少量的SP(super-paramagnetic)颗粒.罗布泊Ls2孔的S-ratio比值表明,7.1~5.6Ma气候为相对较干旱和相对较湿润交替出现,5.6~3.6Ma干旱化加剧,3.60~0.74Ma有所缓和,0.74~OMa干旱化最为强烈,其中5.1Ma和3.6Ma是两个明显的转折点.多磁学参数表明,晚中、上新世以来罗布泊地区的磁性矿物含量的变化,可以反映罗布泊地区气候渐进式的干旱化过程. 相似文献
57.
C.-H. Liao C.-L. Chang C.-Y. Su P.-T. Chiueh 《International Journal of Environmental Science and Technology》2013,10(6):1275-1286
Urban areas are the main sources of greenhouse gas (GHG) emissions. Previous studies have identified the effectiveness of better urban design on mitigating climate change and land-use patterns in cities as important factors in reducing GHG by local governments. However, studies documenting the link between land-use and GHG emissions are scant. Therefore, this study explores the driving forces of land-use change and GHG emission increments in urban areas and investigates their correlations. The study area, Xinzhuang, is a satellite city of Taipei that has rapidly urbanized in the past few decades. Twenty-one potential variables were selected to determine the driving forces of land-use change and GHG emission increments by binomial logistic regression based on the investigation data of national land use in 1996 and 2007. The correlation of land-use change and GHG increments was examined by Spearman rank-order analysis. Results of logistic regression analysis identified that population and its increasing density rate are main driving forces on both land-use change and GHG increments. The Spearman rank correlation matrix indicates that fluctuating urbanization level is significantly correlated with the increase of total GHG emissions, the emissions of residence, commerce, and transportation sectors in neighborhoods; and the emissions of residence and transportation sectors seem closely connected to current urbanization level. The findings suggest that relationships among land-use, urbanization, and GHG emissions in urban areas vary greatly according to residence and transportation characteristics. Land-based mitigation may provide the most viable mechanism for reducing GHG emissions through residence and transportation sectors. 相似文献
58.
This paper is an extension of the earlier one dealing with kyanite in which the best fitting value of the oxygen ligand distance for Cr3+ is adopted to study the spectroscopic properties of Cr3+ ions doped at the two possible Al sites in the other two polymorphs of the aluminosilicate group (Al2O3 · SiO2), namely, andalusite and sillimanite. The superposition model and the crystal field analysis package recently developed for 3d ions doped at arbitrary low symmetry sites in crystals are used to predict energy levels and statevectors within the whole 3d
3 configuration. Then the values of the ground state zerofield splitting for Cr3+ ions at each Al sites in the two crystals are obtained. The splittings of the lower excited states 2
E and 4
T
2 as well as the admixture of 4
T
2 into 2
E have also been predicted. Comparison of our results with the available experimental data enable us to correlate the optical and EPR Spectroscopic properties with the substitutional Cr3+ sites. The conclusion is that in andalusite and sillimanite only the Al sites with nearly-octahedral six-fold coordination seem to be occupied by Cr3+ ions. 相似文献
59.
60.
采用共轭剪节理应力反演方法,恢复了邯郸-峰峰矿区晚古生代以来的3期古构造应力场,进而探讨了煤田构造的演化历史,将其分为4大阶段:①中生代早期近NS向挤压,煤系后期改造初动期;②中生代晚期SE-NW向挤压,奠定煤田构造格架的基础;③中生代末至古近纪NW-SE向拉张,煤田构造格架定型;④新近纪以来近东西向拉张,煤田构造的现代活动. 相似文献