全文获取类型
收费全文 | 965篇 |
免费 | 142篇 |
国内免费 | 205篇 |
专业分类
测绘学 | 34篇 |
大气科学 | 186篇 |
地球物理 | 215篇 |
地质学 | 421篇 |
海洋学 | 153篇 |
天文学 | 85篇 |
综合类 | 117篇 |
自然地理 | 101篇 |
出版年
2024年 | 2篇 |
2023年 | 20篇 |
2022年 | 53篇 |
2021年 | 38篇 |
2020年 | 30篇 |
2019年 | 41篇 |
2018年 | 61篇 |
2017年 | 64篇 |
2016年 | 55篇 |
2015年 | 35篇 |
2014年 | 51篇 |
2013年 | 56篇 |
2012年 | 59篇 |
2011年 | 62篇 |
2010年 | 58篇 |
2009年 | 61篇 |
2008年 | 47篇 |
2007年 | 56篇 |
2006年 | 30篇 |
2005年 | 38篇 |
2004年 | 29篇 |
2003年 | 25篇 |
2002年 | 37篇 |
2001年 | 22篇 |
2000年 | 23篇 |
1999年 | 36篇 |
1998年 | 34篇 |
1997年 | 26篇 |
1996年 | 19篇 |
1995年 | 8篇 |
1994年 | 21篇 |
1993年 | 20篇 |
1992年 | 14篇 |
1991年 | 15篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 4篇 |
排序方式: 共有1312条查询结果,搜索用时 0 毫秒
101.
Effects of biochar, cow bone, and eggshell on Pb availability to maize in contaminated soil irrigated with saline water 总被引:2,自引:0,他引:2
Yaser A. Almaroai Adel R. A. Usman Mahtab Ahmad Deok Hyun Moon Ju-Sik Cho Young Kyoo Joo Choong Jeon Sang Soo Lee Yong Sik Ok 《Environmental Earth Sciences》2014,71(3):1289-1296
Toxicity of heavy metals adversely affects environment and human health. Organic materials derived from natural matters or wastes have been applied to soils to reduce the mobility of contaminants such as heavy metals. However, the application of cow bone powder (CB), biochar (BC), and eggshell powder (ES) is rarely investigated for the reduction of Pb bioavailability in soils irrigated with saline water. The objective of this study was to assess the effectiveness of CB, BC, and ES additions as immobilizing substances on Pb bioavailability in shooting range soil irrigated with deionized and saline water. Each additive of CB, BC, and ES at 5 % (w/w) was mixed with soils and then the deionized and saline water were irrigated for 21 days. With deionized water irrigation, the soils treated with CB, BC, and ES exhibited higher pH when compared with saline water irrigation. With saline water irrigation, the electrical conductivity, water-soluble anions, and cations were significantly increased in soils treated with CB, BC, and ES. The water-soluble Pb in soils treated with CB, BC, and ES was significantly decreased with saline water irrigation. On the other hand, the water-soluble Pb in soil treated with CB was increased with deionized water irrigation. Only BC with saline water irrigation decreased the Pb concentration in maize shoots. 相似文献
102.
Liang Wang Yuan-ping Cheng Feng-hua An Hong-xing Zhou Sheng-li Kong Wei Wang 《Natural Hazards》2014,71(1):85-107
The Huaibei coalfield is in the East China Economic Area, which is rich in coal and gas resources. However, hundreds of coal and gas outburst accidents have occurred because of the complex geological structures of the coalfield. Based on theoretical analysis and field statistics, the characteristics of regional geological structures and the coal measure strata evolution in the Huaibei coalfield were researched, and gas resource distribution and gas parameters were statistically analyzed to determine the dominant controlling factors of gas occurrence and gas dynamic disaster. The results indicated that the Huaibei coalfield has undergone complex tectonic evolution, causing obvious differences in gas storage in different blocks of different mining areas, which exhibits a pattern of high amounts of gas in the south and east, and low amounts of gas in the north and west. The coal seam and gas occurrence have a bipolar distribution in the coalfield caused by multiple tectonic movements, and they are deeply buried. Horizontal tectonic stress plays a dominant role in gas outburst, and the thermal evolution and trap effects of magma intrusion increase the possibility and extent of gas outburst. Considering coal seam and gas occurrence characteristics in the coalfield, we propose a new technology for deep coal reservoir reconstruction which combined present underground regional gas control methods and surface well extraction methods. The technology has three effects: developing gas resources, improving coal mining safety level and reducing greenhouse gas emissions, which has been practiced to be effective in coal mines in the Huaibei coalfield. 相似文献
103.
Based on a series of international conferences for establishing HFA2 framework, this paper analyzed key issues of frontier of disaster risk science, integrated disaster prevention and mitigation strategies and integrated disaster risk governance. The future direction of disaster risk science was comprehensively discussed according to the widely discussed Post 2015 Hyogo Framework for Action (HFA2). It was proposed to deepen the cognition of the complexity of disaster system in terms of recognizing the complexity of disaster system from the interaction among various elements of the system, recognizing the complexity of climate change risk from the regional characteristics and formation mechanism of the global climate change and recognizing the complexity of the catastrophe risk from the regional development levels and patterns. Furthermore, it was suggested to make integrated disaster risk reduction strategies and countermeasures from the perspective of the complexity of the disaster system, including the establishment of regional integrated disaster risk governance framework to face climate change, the establishment of integrated disaster risk governance system in multi-spatial scale, the establishment of disaster risk governance financial system integrating the insurance, bonds and lottery, the establishment of consilience mode in integrated risk governance considering multi-stakeholder and the establishment of modeling and simulation platform integrated disaster risk information services and disaster risk reduction strategies. Finally, it was pointed out that the assessment of disaster risk levels for different regions in multi spatial scale can provide robust scientific support for integrated disaster risk governance of the world and regions, industries and enterprises so as to improve response to global change and guarantee a global and regional sustainable development. 相似文献
104.
In this paper, the internal structure of shear band is investigated, and a model of the shear band with an echelon crack structure is developed. The model assumes the shear band to be composed of two conjugate sets of echelon cracks, such that the smaller echelon cracks are embedded in the space of the larger ones. The additional strain induced by the echelon cracks and the anisotropic development of the compliance tensor in the shear band zone are analyzed. The critical crack density at the onset of shear band is obtained by applying the bifurcation condition. Deviating from previous approaches, the new procedure evaluates the thickness of shear band based on the geometrical characteristics of echelon crack arrays and the failure probability of grain boundaries in the longitudinal direction at the onset of shear band. Parametric analysis shows that grain size, internal friction angle, dilation angle, and failure probability of grain boundaries are the dominant factors that account for the shear band thickness. The calculated results are consistent with the experimental data available in the literature. The model soundly explains that the measurements of the shear band thickness are generally scattered, ranging from 4 to 30 (or even more) times the grain size. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
105.
JIANG Guoliang LIU Yun DING Mingyu KONG XiuqinCollege of Marine Life Sciences Ocean University of China Qingdao P. R. China 《中国海洋大学学报(英文版)》2003,2(2):230-232
Oyster shell soil conditioner had significant influence on soil and rhizospheric microorganisms in their biomass, respiratory intensity and nutritional requirement. It could stimulate growth of soil and rhizospheric microorganisms, especially nitrogen-fixers, and intensify soil respiration in proportion to the dose and fertilizing time of the conditioner, leading to the increase in the number of nitrogen fixing bacteria and the decrease in the number of bacteria with special nutrition demands. 相似文献
106.
建(构)筑物因土中孔隙水压力升高而失稳破坏的情形屡见不鲜,常剪应力增孔压试验是相关研究的常用手段,但迄今鲜见考虑施工期开挖卸荷影响的试验研究。为探究初始卸荷对花岗岩残积土增孔压过程力学行为的影响,在常规增孔压试验中增加了初始卸荷阶段,开展了一系列考虑初始卸荷程度和卸荷滞时影响的卸荷-增孔压试验,分析土体变形、屈服和强度特性的初始卸荷效应与卸荷滞时效应,并与常规增孔压试验结果对比以揭示初始应力路径的影响。试验结果表明:增孔压过程的变形发展具有明显的阶段性,土体屈服后因其剪胀潜势和变形迅速而产生负超静孔压增量,有效平均应力转而增大;初始卸荷对增孔压过程土体力学性能具有明显的劣化作用,表现为刚度与屈服强度均随初始卸荷程度的增大而衰减;与被动压缩这种“加荷”式应力路径相比,初始卸荷的不利影响更为显著;土体力学性能的劣化随卸荷滞时的增长而加剧;屈服摩擦角随初始卸荷程度的增大逐渐减小,但始终大于临界状态摩擦角。 相似文献
107.
长期以来,陇山杂岩的归属问题一直存在争议。本文对出露于秦岭-祁连山结合部位的陇山杂岩中石榴黑云斜长片麻岩和石榴斜长角闪岩进行了详细的岩石学、P-T温压计算、独居石和榍石U-Pb年代学研究。通过详细的岩相学观察,石榴黑云斜长片麻岩的变质峰期矿物组合为石榴子石+黑云母+斜长石+石英;石榴斜长角闪岩中则识别出了以石榴子石+单斜辉石+角闪石+斜长石+石英为峰期的变质矿物组合。通过传统温压计计算,石榴黑云斜长片麻岩(样品21LS40)和石榴斜长角闪岩样品(样品21LS42-1)的峰期变质P-T条件分别为700℃、0.72GPa和710℃、0.74GPa。激光剥蚀电感耦合等离子体质谱(LA-ICP-MS) U-Pb数据表明,石榴黑云斜长片麻岩中独居石的206Pb/238U的加权平均年龄为407~435Ma。石榴斜长角闪岩中榍石的下交点年龄分别为410±7Ma、409±5Ma和426±10Ma,榍石中Zr含量温度计的计算结果分别为750℃、751℃和748℃(假定压力为0.7GPa)。本文从变质作用的角度出发,将陇山杂岩与秦岭杂岩进行温压条件和变质时代对比研究,认为陇山杂岩与东秦岭杂岩高压-超高压岩石的最后一期退变质作用和西秦岭天水地区的秦岭杂岩麻粒岩相变质作用类似,可能为北秦岭造山带的西延。 相似文献
108.
Puspanathan Thellen Kumar Jayawardane Vihan Shenal Paul Suvash Chandra Ying Kong Sih Shukla Sanjay Kumar Anggraini Vivi 《Acta Geotechnica》2022,17(12):5441-5464
Acta Geotechnica - Biochar has recently been gaining increasing attention as a stable and sustainable soil amendment material. However, the effect of biochar amendment on the desiccation behaviour... 相似文献
109.
Zhang Qi Liu Qinzhi Lou Yahui Kong Dezhong 《Geotechnical and Geological Engineering》2022,40(6):3147-3168
Geotechnical and Geological Engineering - The trajectory of the actual gas drainage drilling often deviates from the design in the process of gas control drilling construction, resulting in the... 相似文献
110.
Zhao Gaobo Guo Wenbing Kong Lingyun Zhao Yun Shi Qingwen 《Geotechnical and Geological Engineering》2022,40(11):5397-5409
Geotechnical and Geological Engineering - The joint pore pressure inside rock mass significantly affects groundwater bursting. To investigate the couple effect of joint pore pressure and joint... 相似文献