全文获取类型
收费全文 | 2414篇 |
免费 | 359篇 |
国内免费 | 886篇 |
专业分类
测绘学 | 327篇 |
大气科学 | 61篇 |
地球物理 | 531篇 |
地质学 | 1981篇 |
海洋学 | 200篇 |
天文学 | 107篇 |
综合类 | 261篇 |
自然地理 | 191篇 |
出版年
2024年 | 13篇 |
2023年 | 42篇 |
2022年 | 81篇 |
2021年 | 108篇 |
2020年 | 89篇 |
2019年 | 123篇 |
2018年 | 81篇 |
2017年 | 104篇 |
2016年 | 108篇 |
2015年 | 95篇 |
2014年 | 145篇 |
2013年 | 183篇 |
2012年 | 139篇 |
2011年 | 153篇 |
2010年 | 126篇 |
2009年 | 179篇 |
2008年 | 190篇 |
2007年 | 188篇 |
2006年 | 179篇 |
2005年 | 130篇 |
2004年 | 143篇 |
2003年 | 132篇 |
2002年 | 110篇 |
2001年 | 110篇 |
2000年 | 105篇 |
1999年 | 93篇 |
1998年 | 67篇 |
1997年 | 74篇 |
1996年 | 57篇 |
1995年 | 52篇 |
1994年 | 59篇 |
1993年 | 53篇 |
1992年 | 31篇 |
1991年 | 27篇 |
1990年 | 28篇 |
1989年 | 20篇 |
1988年 | 11篇 |
1987年 | 14篇 |
1986年 | 8篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有3659条查询结果,搜索用时 15 毫秒
31.
Daoyong ZHANG Xiangliang PAN Shuimu LIAO Chenglin HUANG Jingmei ZHANG 《中国地球化学学报》2006,25(B08):133-133
Low molecular weight organic acids (LMWOAs) are important components of root exudates. They play an important role in immobilizing and remobilizing contaminants in rhizospheric soil. Effects of four LMWOAs on the sorption and desorption behavior of p-chlorophenol by yellow earth was studied in batch mode. The results showed that the previous application of LMWOAs to enhanced adsorption capacity of p-chlorophenol of the soil in the order of maleic acid〉malic acid〉oxalic acid〉citric acid. However, when LMWOAs were applied to soil where p-chlorophenol had been previously adsorbed, substantial p-chlorophenol was desorbed from soil by oxalic acid, whereas citric acid, malic acid and maleic acid didn't desorb as much p-chlorophenol from soil as deionized water. 相似文献
32.
Yongqing JIN Xiaojuan WANG Chengxiao ZHANG Julia LU Qingbo DUAN 《中国地球化学学报》2006,25(B08):239-240
Effects of mercury on ecosystems and human health are well documented. Human activities have significant impacts on transport, transformation, and fate of mercury in the natural environment. In this study, a gold mining area (Tongchuan), an urban area (Xi'an), and a historical site (Qinshihuan Tomb) in Shaanxi Province, China, was chosen to study the effects of human activities on the transport, transformation, and fate of mercury in the area. Samples of atmospheric precipitate, soil, sediment, pomegranate, corn and those from wells and the rivers that flow through or flow by the city and from the mining area were collected. The EPA methods were used for sample preparation and analysis of these samples. These methods combine acid digestion, chemical reduction, purge and trap with Cold Vapor Atomic Fluorescence Spectrometry (CVAFS). Preliminary results showed high total mercury concentrations in the water samples collected from a river in Tongguan County. The total mercury concentrations ranged from 133 to 188 ng/L in the water samples collected from the rivers flowing through Xi'an City. The amount of total mercury in the soil/sediment samples which were collected in the vicinity of Xi'an ranged from 31.8 to 83.2 ng/g. The total mercury concentrations in the samples of atmospheric precipitate (including rain and snow collected from Sep. 2005 to Jan. 2006) ranged from 106-298 ng/L. 相似文献
33.
Integrated, in situ textural, chemical and electron microprobe age analysis of monazite grains in a migmatitic metapelitic gneiss from the western Musgrave Block, central Australia has identified evidence for multiple events of growth and recrystallisation during poly-metamorphism in the Mesoproterozoic. Garnet + sillimanite-bearing metapelite underwent partial melting and segregation to palaeosome and leucosome during metamorphism between 1330 and 1296 Ma, with monazite grains in leucosome recording crystallisation at 1300 Ma. Monazite breakdown during melting is inferred to have occurred in the palaeosome. During a subsequent granulite facies event at 1200 Ma, deformation and metamorphism of leucosome and palaeosome resulted in partial disturbance of ages and potential minor growth on 1300 Ma monazite in leucosome. Growth of new, high-Y (+HREE) monazite in palaeosome domains occurred during garnet breakdown in the presence of sillimanite to cordierite and spinel, as a result of post-peak isothermal decompression. Diffusive enrichment of resorbed garnet rims in Y + HREE suggests garnet breakdown occurred slower than volume diffusion of REE. Monazite in both palaeosome and leucosome were subsequently partially to penetratively recrystallised during a retrogression event that is suggested to have occurred at 1150–1130 Ma. The intensity of recrystallisation and disturbance of ages appears linked to proximity to retrogressed garnet porphyroblasts and their occurrence in the relatively reactive or ‘fertile’ local environments provided by the palaeosome/mesosome volumes, which caused localised changes in retrogressive fluids towards compositions more aggressive to monazite. Like reaction textures, it is apparent that domainal equilibrium and reaction may control or at least strongly influence monazite REE and U–Th–Pb chemistry and hence ages. 相似文献
34.
To estimate static and seismic active earth pressure (Pad) on a rigid retaining wall, numerical analyses using different step sizes have been carried out in this paper, based on the
modified Culmann line method by considering Coulomb’s planar rupture surface. Equivalent pseudo-static seismic forces are
considered in the analysis. A new concept of modified unit weight by considering ground surcharge is introduced under static
and seismic conditions. By numerical analysis, area of soil (A) has been estimated to obtain the ratio of A/A0 where A0 is θh2, θ is the angle between retaining structure and ground surface and h is the vertical height of the wall. This ratio remains constant for a particular type of soil and has been used to estimate
the maximum active earth pressure using force diagram. Results are provided in tabular form for easy calculation of the coefficient
of static and seismic active earth pressure. Present results by considering the new technique, compares well with the results
obtained by earlier researchers. 相似文献
35.
36.
华南地区晚二叠和晚三叠世煤中稀土元素特征研究 总被引:2,自引:0,他引:2
在华南地区贵州六盘水、江西乐平、露庆和湖北黄石矿区晚二叠和晚三叠世煤层的稀土元素ICP—MS分析数据的基础上,系统研究了研究区煤中稀土元素的含萤分布特征、赋存特征、配分模式以及地质控制因素。含量分布表明晚二叠世稀土元素含量总体高于晚三叠世;煤中稀土元素与灰分成正相关关系,部分煤样品由于有富稀土元素的重矿物组合的存在而出现稀土元素的异常高值;同一矿区、同一时代煤中稀土元素的配分模式具有一定的相似性,而不同地区同一时代和同一地区不同时代煤中稀土元素的配分模式具有较大差异;煤的沉积环境,煤中无机矿物组成以及海水的影响是控制煤中稀土元素含量和配分模式的主要地质因素。 相似文献
37.
N. Takafuji K. Fujino T. Nagai Y. Seto D. Hamane 《Physics and Chemistry of Minerals》2006,33(10):651-654
High-pressure and temperature experiments (28–62 GPa, and 1,490–2,000 K, corresponding to approximately 770–1,500 km depth in the mantle) have been conducted on a MgCO3 + SiO2 mixture using a laser-heated diamond anvil cell combined with analytical transmission electron microscope observation of the product phases to constrain the fate of carbonates carried on the subducting basalt into the lower mantle. At these conditions, the decarbonation reaction MgCO3 (magnesite) + SiO2 (stishovite) → MgSiO3 (perovskite) + CO2 (solid) has been recognized. This indicates that above reaction takes place as a candidate for decarbonation of the carbonated subducting mid ocean ridge basalts in the Earth’s lower mantle. 相似文献
38.
39.
粉喷桩技术加固软土地基 总被引:3,自引:0,他引:3
简介了水泥粉体喷射搅拌加固软土地基的工作机理,结合沪蓉高速公路(沪宁段)地基处理实践,论述了粉喷桩加固软土地基的计算方法.采用粉喷桩加固软基,可加快路堤填土速率,铺筑路面后的工后沉降量能得到有效地控制,保证了工程质量. 相似文献
40.