全文获取类型
收费全文 | 2968篇 |
免费 | 590篇 |
国内免费 | 679篇 |
专业分类
测绘学 | 125篇 |
大气科学 | 613篇 |
地球物理 | 815篇 |
地质学 | 1555篇 |
海洋学 | 325篇 |
天文学 | 186篇 |
综合类 | 276篇 |
自然地理 | 342篇 |
出版年
2024年 | 4篇 |
2023年 | 50篇 |
2022年 | 114篇 |
2021年 | 128篇 |
2020年 | 109篇 |
2019年 | 128篇 |
2018年 | 145篇 |
2017年 | 127篇 |
2016年 | 152篇 |
2015年 | 153篇 |
2014年 | 164篇 |
2013年 | 163篇 |
2012年 | 165篇 |
2011年 | 170篇 |
2010年 | 139篇 |
2009年 | 180篇 |
2008年 | 159篇 |
2007年 | 133篇 |
2006年 | 137篇 |
2005年 | 117篇 |
2004年 | 89篇 |
2003年 | 87篇 |
2002年 | 64篇 |
2001年 | 95篇 |
2000年 | 110篇 |
1999年 | 167篇 |
1998年 | 127篇 |
1997年 | 151篇 |
1996年 | 128篇 |
1995年 | 82篇 |
1994年 | 108篇 |
1993年 | 85篇 |
1992年 | 59篇 |
1991年 | 37篇 |
1990年 | 54篇 |
1989年 | 28篇 |
1988年 | 33篇 |
1987年 | 19篇 |
1986年 | 16篇 |
1985年 | 11篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 13篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1965年 | 1篇 |
1958年 | 5篇 |
排序方式: 共有4237条查询结果,搜索用时 31 毫秒
51.
52.
53.
54.
55.
56.
Microbial community changes in contaminated soils in response to phenanthrene amendment 总被引:4,自引:1,他引:3
S. Y. Zhang Q. F. Wang S. G. Xie Ph.D. 《International Journal of Environmental Science and Technology》2011,8(2):321-330
Leachate and reclaimed wastewater have become the important sources of polycyclic aromatic hydrocarbons in soils. However, the information on bioremediation of leachate and reclaimed wastewater-contaminated soils is still lacking. Identification of changes in microbial structure or of enriched genera related to biodegradation could aid identification of particular organisms or consortia capable of degrading polycyclic aromatic hydrocarbons in these contaminated soils. In this study, terminal restriction fragment length polymorphism, coupled with 16S Ribosomal ribonucleic acid clone library analysis, was applied to investigate the composition of bacterial community in leachate-contaminated soil or grassland soil irrigated reclaimed wastewater and the response to phenanthrene amendment. Results showed that phenanthrene amendment had significant but different impacts on microbial community structure, dependent on soil source. Several greatly enriched terminal restriction fragments with phenanthrene biodegradation were identified. Moreover, genus rhizobacteria, possibly linked to phenanthrene biodegradation, was firstly reported in this study. This work might provide some new insights into bioremediation of polycyclic aromatic hydrocarbons-contaminated soils. 相似文献
57.
Wei-min Ye Zi-yuan Qi Bao Chen Ji Xie Yu Huang Yao-ru Lu Yu-Jun Cui 《Environmental Earth Sciences》2011,64(1):269-276
Karst rocky desertification is a process of land degradation involving serious soil erosion, extensive exposure of basement
rocks. It leads to drastic decrease in soil productivity and formation of a desert-like landscape. In this regard, changes
in climatic conditions are the main origin of the soils degradation. Indeed, soils subjected to successive dry/wet cycling
processes caused by climate change develop swelling and shrinkage deformations which can modify their water retention properties,
thus inducing the degradation of soil–water capacity. The ecological characteristics of cultivation soils in karst areas,
Southwest of China, are extremely easy to be affected by external environmental factors due to its shallow bedding and low
vegetation coverage. Based on the analysis of the climate (precipitation) of this region during the past decades, an experimental
study has been conducted on a cultivated soil obtained from the typical karst area in southwestern China. Firstly, the soil–water
properties have been investigated. The measured soil–water retention curve shows that the air-entry value of the soil is between
50 and 60 kPa, while the residual saturation is about 12%. Based on the experimental results, three identifiable stages of
de-saturation have been defined. Secondly, a special apparatus was developed to investigate the volume change behavior of
the soil with controlled suction cycles. The vapor equilibrium technique was used for the suction control. The obtained results
show that under the effect of dry/wet cycles, (1) the void ratio of the cultivated soil is continuously decreasing, leading
to a gradual soil compaction. (2) The permeability decreases, giving rise to a deterioration of water transfer ability as
well as a deterioration of soil–water retention capacity. It is then obvious that the long-term dry/wet cycling process caused
by the climate change induce a continuously compaction and degradation of the cultivated soil in karst rocky desertification
areas. 相似文献
58.
The glacier area changes in the Qangtang Plateau based on the multi-temporal grid method and its sensitivity to climate change 总被引:2,自引:1,他引:1
Glacier area changes in the Qangtang Plateau are analyzed during 1970-2000 using air photos,relevant photogrammetric maps and satellite images based on the multi-temporal grid method.The results indicate that the melting of glaciers accelerated,only a few of glaciers in an advancing state during 1970-2000 in the whole Qangtang Plateau.However,the glaciers seemed still more stable in the study area than in most areas of western China.We estimate that glacier retreat was likely due to air temperature warming during 1970-2000 in the Qangtang Plateau.Furthermore,the functional model of glacier system is applied to study climate sensitivity of glacier area changes,which indicates that glacier lifespan mainly depends on the heating rate,secondly the precipitation,and precipitation increasing can slow down glacier retreat and make glacier lifespan prolonged. 相似文献
59.
Zhen Tao Quanzhou Gao Wenping Guo Zhengang Wang Yongling Zhang Chenji Xie Xiakun Huang Hongwei Zhong 《山地科学学报》2011,8(5):694-703
A whole year analysis of riverine dissolved organic carbon (DOC) concentrations in the Xijiang River (XJR), South China, showed that the mean riverine DOC concentration (1.24 mg L-1) in the XJR was notably lower than the averaged value (5.75 mg L-1) of the global riverine DOC concentration in several major rivers. There is an inconspicuous monthly fluctuation of the DOC signal in the XJR, but on a semi-yearly time scale, however, the riverine DOC concentration had significant difference between hydrological... 相似文献
60.
从亚高山森林到高山林线,逐渐严酷的生长环境影响了生物量的积累和分配.本研究采用相对生长法和样方收获法估算了藏东南色季拉山急尖长苞冷杉林在禾同海拔(4 190 m,4 270 m和4 326 m)的地上生物量,分析了群落中不同层次地上生物量、各器官生物量及其分配比例随海拔的变化格局.结果表明:1.急尖长苞冷杉群落地上生物量在181~284 t/hm2之间,其中,乔木层在11~-248 t/hm2,灌木层为35~62 t/hm2,草本层为0.9~1.5 t/hm2;2.群落地上生物量随海拔升高急剧降低,降低的平均幅度为73.1 t/(hm2·100 m);3.随海拔升高,群落地上生物量分配到非光合器官(树干和枝条)的比例显著降低,分配到叶的比例呈增加趋势.随海拔的增加,急尖长苞冷杉群落通过增加叶生物量所占比例(高叶寿命)以延长养分在植物体内的存留时间,提高生态系统的养分利用效率,从而适应高海拔地区的低温胁迫环境. 相似文献