全文获取类型
收费全文 | 3844篇 |
免费 | 781篇 |
国内免费 | 905篇 |
专业分类
测绘学 | 219篇 |
大气科学 | 683篇 |
地球物理 | 1058篇 |
地质学 | 1931篇 |
海洋学 | 511篇 |
天文学 | 253篇 |
综合类 | 408篇 |
自然地理 | 467篇 |
出版年
2024年 | 31篇 |
2023年 | 92篇 |
2022年 | 241篇 |
2021年 | 253篇 |
2020年 | 219篇 |
2019年 | 245篇 |
2018年 | 217篇 |
2017年 | 228篇 |
2016年 | 249篇 |
2015年 | 219篇 |
2014年 | 254篇 |
2013年 | 220篇 |
2012年 | 245篇 |
2011年 | 219篇 |
2010年 | 210篇 |
2009年 | 194篇 |
2008年 | 186篇 |
2007年 | 168篇 |
2006年 | 151篇 |
2005年 | 114篇 |
2004年 | 99篇 |
2003年 | 109篇 |
2002年 | 108篇 |
2001年 | 116篇 |
2000年 | 132篇 |
1999年 | 132篇 |
1998年 | 118篇 |
1997年 | 115篇 |
1996年 | 104篇 |
1995年 | 101篇 |
1994年 | 93篇 |
1993年 | 69篇 |
1992年 | 70篇 |
1991年 | 42篇 |
1990年 | 33篇 |
1989年 | 32篇 |
1988年 | 18篇 |
1987年 | 12篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 14篇 |
1983年 | 8篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1958年 | 9篇 |
1954年 | 1篇 |
排序方式: 共有5530条查询结果,搜索用时 15 毫秒
661.
This study deals with the toxic effects of Zn2+, Cu2+, Cd2+ and NH3 on Chinese prawn (Penaeus orientalis). The median lethal concentrations of the toxic matters on Chinese prawn were determined. Cd2+>Cu2+>Zn2+>NH3-Nm is the toxic order of these chemicals to Chinese prawn. The toxic order of concentrated Zn2+ and Cd2+ in tissues and organs of Chinese prawn is in the order. gill>shell+appendage>viscera>muscle. 相似文献
662.
潼峪金矿区发育过冲剪滑型、平移剪张型和平移剪滑型三种不同性质、不同方向成矿断裂,分布在金罗斑背形的不同部位,其形成有先后差异,但变形环境大体相同,具脆-韧性变形特征。空间上一般不超越褶皱主体。三类断裂中,前两者具石英脉型金矿化,后者形成构造蚀变岩型及小规模石英脉型金矿化。矿化差异与断裂产出的褶皱部位及其相应的应力应变条件的不同有关。 相似文献
663.
At Beijing Observatory both astrometric and gravimetric observations are available to study the non-tidal variations in the deflections of the vertical (or non-tidal plumbline variations, PLVs). From repeated gravimetric observations performed in a network around the observatory, the PLVs at Beijing Observatory during the period 1987.0–1996.0 have been calculated. After comparison with the observational residuals (which also contain the PLV components) of the photoelectric astrolabe located at the observatory, the accuracy of the obtained PLV results has been examined. It is shown that, due to the asymmetry of the gravimetric network, the qualities of the two different PLV components are not equal. The longitude component of the PLV at Beijing has been determined successfully, to be of the order of 0.05, with a contribution of about 0.02 in the inter-annual time scale. The result for the latitude PLV component is not good enough to draw a conclusion. Although both techniques are able to measure the PLV, the result of the determination depends very much on the availability of observational data. 相似文献
664.
PENG Runmin ZHAI Yusheng WANG Zhigang & HAN Xuefeng . Key Laboratory of Lithospheric Tectonics Lithoprobing Technology Ministry of Education China University of Geosciences Beijing China . Inner Mongolia Geological Prospecting Institute Ministry of Chemical Industry Hohhot China Correspondences should be addressed to Peng Runmin 《中国科学D辑(英文版)》2005,48(6):822-833
Since the mid-1980s,Tanyaokou large Zn-Cu-Fe sulfides deposit,located at the southwest end of Langshan-Zhaertaishan-Bayan Obo Mesoproterozoic metallogenic belt in the west section of the northern margin of the North China Platform[1?9](Fig.1),has been confirmed to be submarine volcanic exhalative-sedimentary metamorphosed deposit hosted in the miogeosynclinal mud-carbonaceous formation of the Langshan Group(LG)[1],or submarine volcanic exha-lative-deposition-altered deposit[2]or stratabo… 相似文献
665.
韩晓钟 《中国海洋湖沼学报》1992,10(3):231-238
The concentrations of major elements and some trace elements were determined at 8 core locations in Taihu Lake. The chemical composition of the cores was related to the sediment particle size-chronology and location of sampling site.Concentrations of Al, Mg, K, Ca and Na, the major mineral species in the sediments, were generally uniform, with only slight fluctuation influenced by water waves and current. Surface enrichment of Cu, Zn, and Ni at some locations was observed to be greater than that of the sediments accumulated 100 years ago. The enrichment of these elements is attributed to anthropogenic input in recent years. Concentration profiles for Mn and Fe are related to the migration of these elements in the pore water. 相似文献
666.
通过分析与研究建立资源管理和作业动态分配ProRMJS模型,解决了中国地震灾害仿真网格试验系统(CEDAGrid)中网格科学计算平台在初期建设中存在的一些资源管理方面的问题. 针对网格科学计算平台默认各个计算节点均能提供计算服务的问题,ProRMJS通过ldquo;计算池rdquo;这一虚拟组织为调度器分发作业提供支撑;而调度器则根据计算池中各个节点的计算能力和状态,动态分配任务,这样就保证了计算平台的稳定性. 针对默认各个计算节点均能完成任务的问题, ProRMJS通过监控各个节点所负担作业的运行进度和设定作业时间阈值来管理作业运行. 对于各个节点计算能力大小的区别, ProRMJS通过对各个节点计算性能的权值量化,实行按ldquo;需rdquo;分配作业. 对各个节点计算性能的权值量化, ProRMJS是通过综合考虑各个因素对机器计算能力大小的影响后通过加权计算的方式完成的,从而提高了整个计算平台的工作效率. 最后通过实现地震应力触发科学计算实例验证了方案的有效性,为网格技术在地震领域内的进一步应用作了有意义的探索. 相似文献
667.
Constraining the hydrocarbon expulsion history of the coals in Qinshui Basin, North China, from the analysis of fluid inclusions 总被引:1,自引:0,他引:1
Wei Li Zhihuan Zhang Yongcai Yang Liguo Han Minghua Shao 《Journal of Geochemical Exploration》2006,89(1-3):222
From the comprehensive study on the homogenization temperatures and the occurrence of fluid inclusions in the framework minerals of the strata between or above the Carboniferous–Permian coals in the Qinshui basin, Shanxi, three stages are predicted of hydrocarbon expulsion from the coals. Combined with the known history of basin evolution, it is deduced that the expulsion of hydrocarbons happened during the J1 (210–180 Ma), the early K1 (150–130 Ma) and K2E1 (110–60 Ma). In the early stage, the coals produced and discharged coal-generated oils. The average GOI value of four sandstone samples is relatively high, as they have been exposed to high paleo-oil saturation in the strata between or above the coals. The biomarker compositions of oil-bearing fluid inclusions are similar to those of extracts from the coals, and so it is concluded that those oils were derived from the same family of the coals. 相似文献
668.
Hydrodynamic change recorded by diatoms in sediments of Liuxihe Reservoir, southern China 总被引:1,自引:0,他引:1
Diatoms are used widely for paleolimnological studies in lakes, but their use for studying the environmental history of reservoirs
has not been tested extensively. Reservoirs have hydrodynamic characteristics intermediate between those of rivers and lakes.
This study assessed the utility of diatom assemblages as recorders of long-term changes in hydrodynamics and spatial gradients
in Liuxihe Reservoir, an impoundment in southern China. Four sediment cores were collected in the reservoir, from the riverine,
transition and lacustrine zones. Each core was sectioned at 2-cm intervals to investigate the stratigraphic distribution of
accumulated diatoms. Varve counting was used to develop a chronology for one of the cores. The unique characteristics of Liuxihe
Reservoir, including its large size, great depth, long narrow morphology and strong thermal stratification for 10 months of
the year, limit secondary sedimentation processes and preserve the varves, enabling development of an accurate chronology.
Damming profoundly altered the physical environment of the former river, especially in the lacustrine zone, where the change
is clearly illustrated by diatoms in the sediment. Diatom abundance increased as a consequence of nutrient enrichment after
construction of the dam in 1958, but later decreased as the new impoundment stabilized. After damming, relative abundance
of Cyclotella increased along with a simultaneous decrease of Navicula and Achnanthes in the lacustrine zone, most significantly in 1963, when Cyclotella replaced Navicula as the dominant genus. This switch was indicative of a general shift from a lotic to a lentic habitat. A longitudinal gradient
was apparent in the patterns of sedimentation and diatom accumulation at different sites in the reservoir, with diatom abundance
highest in the transition zone. In the long term, water discharge from the reservoir showed a weak, but significant negative
correlation with diatom abundance in the lacustrine zone (r = −0.320, P = 0.03). In summary, diatom assemblages in the Liuxihe Reservoir sediments recorded past changes in hydrodynamics, suggesting
that paleolimnological study of some impoundments is feasible. 相似文献
669.
Observed Impact of the South Asian Summer Monsoon on the Local Meteorology in the Himalayas 总被引:1,自引:1,他引:0 下载免费PDF全文
The South Asian summer monsoon(SASM) is the most important climate system in Asia.Using observational data from the HEST2006(Himalayan Exchange between the Surface and Troposphere 2006) campaign and large-scale grid data,this paper analyzed the SASM impact on local meteorological parameters including radiation,temperature,humidity,and wind in the Himalayas.The SASM experienced one active and one break period during the HEST2006 campaign.The local meteorological parameters exhibit great differences between the active period and the break period of the SASM.The radiation fluxes are greater in the break period than in the active period.The air temperature and specific humidity are lower,but soil temperature and wind speed are higher in the break period than in the active period.Further analysis indicates that the SASM greatly affects the meteorological features of the Himalayan region. 相似文献
670.