全文获取类型
收费全文 | 302篇 |
免费 | 46篇 |
国内免费 | 109篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 1篇 |
地球物理 | 37篇 |
地质学 | 370篇 |
海洋学 | 20篇 |
天文学 | 1篇 |
综合类 | 11篇 |
自然地理 | 14篇 |
出版年
2024年 | 2篇 |
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 18篇 |
2020年 | 13篇 |
2019年 | 11篇 |
2018年 | 15篇 |
2017年 | 10篇 |
2016年 | 13篇 |
2015年 | 10篇 |
2014年 | 17篇 |
2013年 | 13篇 |
2012年 | 21篇 |
2011年 | 16篇 |
2010年 | 22篇 |
2009年 | 27篇 |
2008年 | 15篇 |
2007年 | 24篇 |
2006年 | 28篇 |
2005年 | 29篇 |
2004年 | 25篇 |
2003年 | 20篇 |
2002年 | 26篇 |
2001年 | 16篇 |
2000年 | 11篇 |
1999年 | 11篇 |
1998年 | 9篇 |
1997年 | 9篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
排序方式: 共有457条查询结果,搜索用时 0 毫秒
381.
电感耦合等离子体发射光谱法测定镍矿石中镍铝磷镁钙 总被引:1,自引:4,他引:1
样品用硝酸溶解,氢氟酸助溶,高氯酸冒烟除去氢氟酸,盐酸溶解盐类后,在选定的测量条件下用电感耦合等离子体发射光谱法( ICP - AES)测定镍矿中镍、铝、磷、镁、钙.选择Ni 221.6 nm、Al 396.1nm、P 178.2 nm、Mg 285.2 nm、Ca 393.3 nm分别作为镍、铝、磷、镁、钙的分析线;... 相似文献
382.
蚀变围岩指示元素铝钾锡在党河南山金区域成矿预测中的作用 总被引:1,自引:0,他引:1
偏碱性花岗岩及与金的成矿活动有关的硅化、粘土化蚀变是黑刺沟金矿田规模金矿床存在的地质前提.铝、钾、锡应是黑刺沟金矿田的蚀变围岩指示元素,其更客观地反映了区域内的金的主要成矿远景区;但该元素组合仅适用于干旱荒漠区及部分以机械风化、搬运作用为主的高寒山区等水系沉积物采样粒度较粗的地区. 相似文献
383.
The presence of a weak interlayer has usually an adverse effect on the slope stability. However, the rotational failure mechanism in the conventional upper bound limit analysis cannot rationally describe the sliding of the failure mass along the weak interlayer. Therefore, a new failure mechanism was proposed in this study to evaluate the stability of slopes with weak interlayers using the upper bound limit analysis and the associated factor of safety was determined by the shear strength reduction technique. The new failure mechanism is comprised of rigid blocks undergoing rotational or translational movements, instead of the rotational movement in the conventional failure mechanism. It has also been extended to the stability analysis of slopes in presence of stabilizing piles and pore water pressures. Case studies were carried out on actual slopes with weak interlayers. The proposed rotational–translational failure mechanism was verified by the shear strength reduction finite element method (SSRFEM). Comparisons demonstrate the reliability of limit analysis method with the proposed rotational–translational failure mechanism for slopes with weak interlayers and therefore it can be used as a simple evaluation method for the engineering design. 相似文献
384.
385.
太行山太古宙变质杂岩中富铝片麻岩的变质作用 总被引:15,自引:2,他引:15
太行山太古宙变质杂岩中富铝片麻岩主要分布在湾子岩系的底部,常常与大理岩密切伴生或者以似层状体产于花岗质片麻岩中。依据岩石结构和反应关系将变质作用分为早期、中期和晚期三个阶段。早期矿物组合为Gt(石榴石)+St(十字石)+Pl(斜长石)+Ms(白云母)+Bi(黑云母)+Ru(金红石)+Qz(石英)±K-fs(钾长石);中期矿物组合为Gt+Ged(铝直闪石)+Bi+Pl+Ilm(钛铁矿)+Co(刚玉)+Sil1(毛发状夕线石)+Qz+K-fs±Ms;晚期矿物组合为Hc+K-fs+Sil2(针柱状夕线石)。矿物温度压力计和内部一致性热力学计算结果表明早期矿物组合形成于680℃和0.8GPa左右,刚玉、铝直闪石和毛发状夕线石组合形成于730℃~750℃和0.7GPa左右的很窄的P-T范围内,夕线石和尖晶石矿物组合的形成温度与前一组合相似或略高,压力偏低。在P-T空间上上述矿物组合的演化构成了一条近等温减压(ITD型)的PTt轨迹。 相似文献
386.
Oxygen‐isotope compositions of kyanite, andalusite, prismatic sillimanite and fibrolite from the Proterozoic terrane in the Truchas Mountains, New Mexico differ from one another, suggesting that these minerals did not grow in equilibrium at the Al2SiO5 (AS) polymorph‐invariant point as previously suggested. Instead, oxygen‐isotope temperature estimates indicate that growth of kyanite, andalusite and prismatic sillimanite occurred at c. 575, 615 and 640 °C respectively. Temperature estimates reported in this paper are interpreted as those of growth for the different AS polymorphs, which are not necessarily the same as peak metamorphic temperatures for this terrane. Two distinct temperature estimates of c. 580 °C and c. 700 °C are calculated for most fibrolite samples, with two samples yielding clear evidence of quartz‐fibrolite oxygen‐isotope disequilibrium. These data indicate that locally, and potentially regionally, oxygen‐isotope disequilibrium between quartz and fibrolite may have resulted from rapid fibrolite nucleation. Pressures of mineral growth that were extrapolated from oxygen‐isotope thermometry results and calculated using petrological constraints suggest that kyanite and one generation of fibrolite grew during M1 at 5 kbar, and that andalusite, prismatic sillimanite and a second generation of fibrolite grew during M2 at 3.5 kbar. M1 and M2 therefore represent two distinct metamorphic events that occurred at different crustal levels. The ability of the AS polymorphs to retain δ18O values of crystallization make these minerals ideal to model prograde‐growth histories of mineral assemblages in metamorphic terranes and to understand more clearly the pressure–temperature histories of multiple metamorphic events. 相似文献
387.
通过新一轮找矿工作(2006-2008年)的勘查实践及研究认为:(1)大桥坞火山岩型铀矿床赋矿主岩为火山角砾岩,具两种类型的角砾岩,一种为火山通道相隐爆角砾岩.另一种为火山口相受层间构造控制的透镜状角砾岩;NW向组断裂构造是主控矿构造,矿床各矿带铀矿体的总体走向主要为NW向。(2)普查阶段勘查工程的布设应注重灵活机动原则,随地质认识的加深和变化及时调整工程布置方案。 相似文献
388.
赤铁矿在自然界中广泛存在,具有重要的古地磁学和环境磁学意义。土壤中含有大量的杂质离子和分子,在成土作用过程中,这些杂质离子(主要是Al)会进入到赤铁矿的晶体结构中,形成含铝赤铁矿(Al-Hm)。为了确定不同的形成环境因素对Al-Hm中所含Al成分的影响,本文通过实验室合成了一系列的Al-Hm,并对各组样品的最终Al含量进行了测试。结果显示,最终样品的Al含量与初始溶液中的Al含量呈线性关系,前者随着后者的增加而增加,这说明环境中的初始Al含量是影响赤铁矿中Al替代量的一个最主要因素,它起到了源的作用。另外在弱酸或者弱碱性的常温环境中利于Al进入晶格结构。赤铁矿中Al的替代量可用来指示土壤中相对的富铝化强度。尽管影响赤铁矿中Al替代量的因素很多,但是不同环境中其影响因素存在很大差异,如黄土-古土壤和南方红土,所以赤铁矿中的Al替代量可作为区分不同来源赤铁矿的有利参数,具有重要的环境气候意义。 相似文献
389.
渤海湾西岸众多的埋藏牡蛎礁体内,除正常的牡蛎壳体堆积层外,还广泛地存在一定数量的水平夹层。水平夹层的存在,可能指示了礁体的生长环境发生了变化。文章对组成礁体的正常建礁层和水平夹层中的牡蛎壳体,进行了贝壳年轮和稳定同位素分析研究,对比了水平夹层和正常建礁层中的壳体生长速率和壳体记录的稳定同位素变化范围与幅度,恢复了壳体记录的礁体生长环境,探讨了壳体同位素记录揭示的礁体水平夹层成因。结果表明,相对于相邻正常建礁层中的壳体,水平夹层中的壳体记录的季节性氧同位素变化幅度较小,这主要与壳体生长时期的季节性淡水输入变化较小或(和)年平均气温较低有关。水平夹层中的壳体记录的低温季节相对较多的淡水输入量和高温季节相对较少的淡水输入量, 或(和)由于年平均气温较低而导致的壳体在一年中的生长周期缩短,是造成礁体中水平夹层形成的主要驱动因素。 相似文献
390.
Character of the Si and Al Phases in Coal Gangue and Its Ash 总被引:1,自引:0,他引:1
Abstract: Analysis of the Si and Al phases in coal gangue fuel and its ash is important for use of coal gangue ashes. A comprehensive study by theoretical and experimental analyses with differential thermal analysis, X-ray diffraction and Infrared Spectroscopy has been made in the present article to explore the diagram of the Si and Al phases in coal gangue fuel and its ashes. It is found that kaolinite and quartz are the main phases in coal gangue fuel. The ratio of moles Al2O3 to SiO2 (i.e., Al2O3 (mole) /SiO2 (mole)) is usually no more than 0.5 in most coal gangue fuel and its ashes. The kaolinit at about 984°C releases a large quantity of SiO2, which makes calcine coal gangue more active than coal gangue itself. The relationship between the ratio Al2O3 (mole)/SiO2(mole) and the components of coal gangue ash is analyzed, resulting in a formula to calculate the quantity of each phase. Applying the formula to the testing samples from an electric plant in north China supports the above conclusions. 相似文献