全文获取类型
收费全文 | 209篇 |
免费 | 14篇 |
国内免费 | 32篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 30篇 |
地球物理 | 60篇 |
地质学 | 137篇 |
海洋学 | 5篇 |
天文学 | 2篇 |
综合类 | 1篇 |
自然地理 | 15篇 |
出版年
2021年 | 4篇 |
2019年 | 2篇 |
2015年 | 3篇 |
2014年 | 4篇 |
2013年 | 27篇 |
2012年 | 10篇 |
2011年 | 5篇 |
2010年 | 4篇 |
2009年 | 8篇 |
2008年 | 5篇 |
2007年 | 12篇 |
2006年 | 4篇 |
2005年 | 5篇 |
2003年 | 6篇 |
2002年 | 6篇 |
2001年 | 12篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 9篇 |
1996年 | 21篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1981年 | 2篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1974年 | 1篇 |
1970年 | 2篇 |
1969年 | 1篇 |
1968年 | 2篇 |
1967年 | 1篇 |
1965年 | 2篇 |
1964年 | 1篇 |
1959年 | 1篇 |
1937年 | 1篇 |
1934年 | 2篇 |
1933年 | 4篇 |
1931年 | 1篇 |
1927年 | 3篇 |
1926年 | 7篇 |
1925年 | 2篇 |
1924年 | 6篇 |
排序方式: 共有255条查询结果,搜索用时 15 毫秒
51.
Abstract Mineralogical and geochemical evidence indicates that partial melting and desulphidation have occurred in the Big Bell gold deposit. Decarbonation may also have occurred, to account for the lack of a carbonate alteration halo; this is compatible with the present data, but difficult to test. The Big Bell deposit consists of auriferous sulphide-bearing (‘lode’;) schists with muscovite and K-feldspar, and surrounding biotite schists, all derived by intense premetamorphic alteration of rocks of mafic composition. Assemblages which include cordierite-sillimanite-K-feldspar-garnet-biotite-quartz suggest peak metamorphic conditions of 4–5 kbar, and 650–700° C, based on phase relations, geobaro-meters and garnet-biotite Fe-Mg exchange partitioning. Partial melting occurred at peak metamorphism, particularly in the altered mafic rocks in and around the deposit, and its occurrence may have been essential to the preservation of the deposit. Melting greatly limited the importance of devolatilization reactions, resulting in negligible aqueous fluids and no means of removing appreciable gold. Minor gold loss may have accompanied desulphidation. A diversity of complex metamorphic assemblages occurs around the mine, compared to the assemblages developed regionally; variable bulk rock composition influences this contrast, but there is no evidence of higher metamorphic grades at the mine, nor that this might have been the prime control on the different assemblages in this narrow belt. It is suggested that the Big Bell and Hemlo deposits are the higher metamorphic grade equivalents of the more abundant greenschist facies gold deposits within Archaean greenstone belts. This interpretation is favoured by the host rock setting and geochemical characteristics of Big Bell. Alternative models that suggest that this class of deposit is a new type must account for the absence of high-grade equivalents of the greenschist facies deposits and also the lack of low-grade equivalents of the Big Bell/Hemlo type. Archaean gold deposits in high-grade metamorphic terrains have undergone a series of processes that are not recorded in the more typical gold deposits of the greenschist facies. 相似文献
52.
53.
54.
55.
采用GOES9卫星观测的能量大于2MeV和大于4MeV电子通量和行星际飞船ACE太阳风参数的高时间分辨率资料,以及磁暴指数Dst资料,分析了1998年4-5月期间地球同步轨道电子通量增强事件的时间和能量响应特征及其与行星际太阳风参数、磁暴和亚暴等扰动条件的对应关系.结果表明,地球同步轨道相对论性(MeV)电子通量增强事件有明显的周日变化,中午极大和午夜极小.4月22日和5月5日开始的两次大事件中,能量大于2MeV电子通量中午极大值上升到最大值的时间尺度分别约为4天和1天,中午极大值高于背景水平的持续时间分别为13天(4月22日-5月4日)和16天(5月4日-20日)以上.每次MeV电子通量增强事件的能量范围不完全相同.两次大事件的上升段都对应于磁暴的恢复相,与太阳风动压脉冲、高速流脉冲和负Bz分量关系密切. 相似文献
56.
井间电磁(EM)成像系统的技术目标是实现井间电学特性的直接测量,并提供井间电阻率的二维及三维图像.从1997年开始,胜利油田与美国EMI公司合作,开展了EM技术的应用与研究,主要是通过大型、系统的现场试验,在大井间距的条件下,进一步验证仪器的性能,进行油藏研究的适用性和可行性分析;以系统的现场实测数据为依据,加快成像处理方法和软件的开发;开展穿透金属套管井的EM试验,探讨金属套管条件下的电阻率成像方法。两年来,利用EMI提供的XBH2000型测量系统,对胜利油田典型的低电阻率砂泥岩剖面,成功地进行了3对井、10个井次的试验。试验证明了仪器性能的可靠,取得了测量重复性好、系统完整的井间EM数据.并反演得到电阻率成像,在分析井间油气分布和油层开采动态方面,取得了良好的地质效果. 相似文献
57.
Heterogeneous coarse grained channels are often characterized by local transitions in bed surface roughness. Distinct spatial zones in terms of grain size have been reported, for example sand ribbons and bedload sheets. The transition from areas of finer to coarser grained surface sediment is often abrupt. However, the effects of these transitions on the shape of the velocity profile and associated shear velocity and roughness length estimates have not been investigated in detail in coarse grained channels. This paper therefore examines the combined effects of a sudden change in surface roughness and of superimposed scales of resistancé on the structure of the turbulent boundary layer. Measurements along roughness transitions from smooth to rough beds were conducted in a flume using artificial roughness features and in a natural gravel bed river. Immediately at the transition from a zone of close packed roughness to a rougher section dominated by obstacles superimposed on the more or less uniform roughness surface, boundary shear stress and roughness length increase considerably. Downstream from this transition, velocity profiles become concave upwards. Downstream and upstream sections show significant differences in terms of near bed velocities (deceleration downstream of the transition), velocity gradient and turbulence intensity of the streamwise velocity component. Comparing the mean velocity profiles corresponding to these two different roughness surfaces gives some indication of the proportion of total shear velocity (or shear stress) associated with the pressure drag produced by large and isolated obstacles. 相似文献
58.
P.TEILHARD DE CHARDIN 《地质学报》1931,(1)
Ⅰ. GEOLOGY OF THE SITE The Lower Cambrian fossils here described were first found, insufficiently preserved, by Licent and Teilhard in 1926 at K(?)ntingshih (圪丁石), just along the border of the high limestone range, 50 lis N. of Cbishanhsien (S. Shansi). 相似文献
59.
Marine beds, containing numerous well preserved shells, are actuallyexposed in a broad pit recently open, one mile south from the Hoangho-PaihoMuseum (Race Course Road, Tientsin), in order to get the earth required forthe filling of some pools along the Race Course Road. 相似文献
60.
M. DE VRIES 《水文科学杂志》2013,58(4):543-544
ABSTRACT The paper presents the observed effects on the streamflow of changing a tropical forest in the high rainfall belt of Zambia to agricultural use based on traditional farming methods. Hydrological observations were carried out on four small catchments under their natural conditions first, and later two of them under agricultural use with accompanying deforestation. Simple linear regression analysis of both monthly and annual runoff from the treated catchments on the monthly and annual runoff from undisturbed catchments showed that there was an increase in streamflow as a result of deforestation and subsistence agriculture. It is also shown that the shape of the flood hydrograph was changed as a result of changes in land use. 相似文献