全文获取类型
收费全文 | 844篇 |
免费 | 143篇 |
国内免费 | 128篇 |
专业分类
测绘学 | 57篇 |
大气科学 | 66篇 |
地球物理 | 280篇 |
地质学 | 425篇 |
海洋学 | 64篇 |
天文学 | 21篇 |
综合类 | 136篇 |
自然地理 | 66篇 |
出版年
2024年 | 2篇 |
2023年 | 14篇 |
2022年 | 46篇 |
2021年 | 53篇 |
2020年 | 40篇 |
2019年 | 46篇 |
2018年 | 47篇 |
2017年 | 43篇 |
2016年 | 56篇 |
2015年 | 42篇 |
2014年 | 59篇 |
2013年 | 43篇 |
2012年 | 61篇 |
2011年 | 54篇 |
2010年 | 37篇 |
2009年 | 40篇 |
2008年 | 45篇 |
2007年 | 39篇 |
2006年 | 27篇 |
2005年 | 20篇 |
2004年 | 23篇 |
2003年 | 20篇 |
2002年 | 21篇 |
2001年 | 19篇 |
2000年 | 23篇 |
1999年 | 37篇 |
1998年 | 22篇 |
1997年 | 33篇 |
1996年 | 24篇 |
1995年 | 15篇 |
1994年 | 12篇 |
1993年 | 11篇 |
1992年 | 5篇 |
1991年 | 8篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1958年 | 3篇 |
排序方式: 共有1115条查询结果,搜索用时 210 毫秒
531.
532.
533.
In accordance with the terms global minerogenic series, regional metallogenic series and ore depositsystem which are put forward here, metallogenic environments at different levels are discussed for theporphyry copper deposit series in China. It is considered that the porphyry copper deposits in China arecontrolled not only by the boundaries of convergent plates but, more importantly, by the boundaries ofintraplate divergent mobile belts and those between continental blocks. Besides, the emplacement ofhypabyssal and supper-hypabyssal calc-alkaline magmas and the temporal-spatial distribution of China'sporphyry copper deposits are governed by the superimposition of fracture systems of the pre-Alpine base-ments. Meso-Cenozoic cover and continental-margin new-born crust. Such a superimposition has also re-sulted in the polycyclicity of the mineralization. 相似文献
534.
535.
长期以来,盆地边缘是砂岩型铀矿找矿与勘探的主要区域。然而,近年在盆地内部也探明了多个铀矿床、矿化点,表明盆地内部同样具有良好的铀矿找矿前景。文章剖析了盆地内部砂岩型铀矿的矿床特征,并据此凝练出“大型中- 酸性火成岩隆起+隆起区翼部深大断裂”的关键控铀成矿要素。结合砂岩型铀矿成矿理论,设计了一套相适应的找矿方法组合。该找矿方法组合可分为2个步骤:① 勘探靶区初筛。根据区域重、磁、放射性、遥感等资料查明盆地内部基底起伏和埋深、识别岩性和划分断裂,将岩性为中- 酸性火成岩且发育断裂的隆起区圈定为潜在勘探靶区。结合含矿目的层产出特征、隆起区翼部坡度和隆起区面积等因素来初筛勘探靶区;② 勘探靶区优选。在初筛的勘探靶区深大断裂位置沿隆起区方向布置并实施钻探。通过对地下水“补- 径- 排”体系、含矿目的层供铀和聚铀能力以及氧化- 还原带发育情况等的评价来优选勘探靶区,为下一步铀矿勘探工作的布置与实施提供有益指导。该方法充分利用区域地球物理数据和公开可下载的资料,可极大地降低勘探成本。着眼于关键控铀成矿要素,优选相适应的地质、地球物理等方法,可有效提高盆地内部砂岩型铀矿找矿与勘探的效率。 相似文献
536.
动态分级法是运用聚类分析原理进行计算机分析的新分级方法。采用动态分级法对鞍山岩溶塌陷环境地质质量进行了分级评价,评价结果合理、可靠。为岩溶塌陷环境地质质量提供了一个很好的评价方法。 相似文献
537.
Study on the transverse structures across Taiwan Strait 总被引:3,自引:0,他引:3
The mountain ranges are almost NE- or NNE-trending in mainland and Taiwan island across the strait. But a number of correspondent
transverse structures across Taiwan Strait have been identified on the basis of morphology, surface structure, deep seismic
survey and gravity field etc. Moreover, it is inferred from the square or/and rectangular shape of the isoseist maps of 8
M≥ 6 earthquakes occurring in the western foothill plain of Taiwan that there is an apparent segmentation of the Taiwan Island
along the N-S orientation. This has been verified from the GPS’s results of the ground motions measured during the Chi-Chi
earthquake in 1999. As a matter of fact, the transverse structures within the Taiwan Island could be correlated with more
salient NW- and EW-trending structures in the mainland of Fujian than in Taiwan. The investigation of the transverse structures
across Taiwan Strait is conducive to realizing the geology within the strait. Hence, the tectonic sketch map of the strait
as well as mainland and island drawn in this context shows NW- and EW-trending structures for the study area. 相似文献
538.
伽师-阿图什震区地壳深部结构特征的探测与研究 总被引:6,自引:0,他引:6
通过对两条测深剖面资料的处理计算和综合研究后发现,研究区壳幔结构具有明显的分层性。不同的地质构造块体在速度结构,构造特征上显示出较大差异。上,下地壳的分界C界面和M界面是具有较大起伏变化的界面,由伽师下方最浅的30.0km(C界面),45.5km(M界面)向西昆仑山区急剧加深至44.0km和70.0km;塔里木块体较高的速度结构意味着地壳结构和对“稳定”的特性;根据伽师地区震源深度大多分布在20-40km这一现象,可以认为,C,M界面的局部隆起,低速异常体和深大断裂的存在对于伽师强震群的孕育和发生具有一定的控制作用。 相似文献
539.
The problem of impact–entrainment relationship is one of the central issues in understanding saltation, a primary aeolian transport mode. By using particle dynamic analyser measurement technology the movement of saltating particles at the very near‐surface level (1 mm above the bed) was detected. The impacting and entrained particles in the same impact–entrainment process were identified and the speeds, angle with respect to the horizontal, and energy of the impacting and entrained sand cloud were analysed. It was revealed that both the speed and angle of impacting and entrained particles vary widely. The probability distribution of the speed of impacting and entrained particles in the saltating cloud is best described by a Weibull distribution function. The mean impact speed is generally greater than the mean lift‐off speed except for the 0·1–0·2 mm sand whose entrainment is significantly influenced by air drag. Both the impact and lift‐off angles range from 0° to 180°. The mean lift‐off angles range from 39° to 94° while the mean impact angles range from 40° to 78°, much greater than those previously reported. The greater mean lift‐off and especially the mean impact angles are attributed to mid‐air collisions at the very low height, which are difficult to detect by conventional high‐speed photography and are generally ignored in the existing theoretical simulation models. The proportion of backward‐impacting particles also evidences the mid‐air collisions. The impact energy is generally greater than the entrainment energy except for the 0·1–0·2 mm sand. There exists a reasonably good correlation of the mean speed, angle and energy between the impacting and entrained cloud in the impact–entrainment process. The results presented in this paper deserve to be considered in modelling saltation. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
540.
Located at western portion of northern margin of North China craton, the Baotou–Bayan Obo district is one of the most important Fe–REE–Nb and Au metallogenic provinces in China. Presently, about 52 gold deposits and prospects have been discovered, explored and mined, among which Shibaqinhao, Laoyanghao, Houshihua, Saiyinwusu, Wulashan and Donghuofang are the most important ones. All these gold occurrences can be subdivided into three groups (or types) according to its host rocks: (1) hosted by Archean high-grade metamorphic rocks; (2) hosted by Proterozoic sedimentary rocks; (3) hosted by or related to Hercynian alkaline intrusive rocks. The first group contains the Shibaqinhao, Laoyanghao and Houshihua gold deposits. Gold mineralization at these three deposits occurs within Archean amphibolite, gneiss and granulite as gold-bearing quartz veins and veinlet groups containing native gold, electrum, pyrite and chalcopyrite. The Saiyinwusu deposit belongs to the second group, and occurs within Proterozoic sandstone, quartzite and carbonaceous slate as quartz veins and replacement bodies along the fracture zones. Pyrite, marcasite, arsenopyrite, native gold and electrum are identified. The third group includes the Wulashan, Donghuofang and Luchang deposits. Gold mineralization at these three deposits occurs predominantly within the Hercynian alkaline syenite or melagabbro stocks and dyke swarms or along their contacts with Archean metamorphic wall rocks as K-feldspar–quartz veins, dissemination and veinlets. Pyrite, galena, chalcopyrite, native gold and calaverite are major metallic minerals.δ34S value of sulfides (pyrite, galena and pyrrhotite) separates from groups 1 and 2 varies from −4.01‰ to −0.10‰ and −3.01‰ to 2.32‰, respectively. δ34S values of Archean and Proterozoic metamorphic wall rocks for groups 1 and 2 deposits range from −20.2‰ to −17.0‰ and −15.8‰ to −16.2‰, respectively. The values are much lower than their hosted gold deposits. All these pyrite separates from Hercynian alkaline intrusions associated with the gold deposits show positive δ34S values of 1.3‰ to 4.8‰, which is higher than those Precambrian metamorphic wall rocks and their hosted gold deposits. δ34S values of the sulfides (pyrite and galena) from the Donghuofang and Wulashan deposits (group 3) increase systematically from veins (−14.8‰ to −2.4‰) to the Hercynian alkaline igneous wall rocks (2.8‰ to 4.8 ‰). All of these deposits in groups 1, 2 and 3 show relatively radiogenic lead isotopic compositions compared to mantle or lower crust curves. Most lead isotope data of sulfides from the gold ores plot between the Hercynian alkaline intrusions and Precambrian metamorphic wall rocks. Data are interpreted as indicative of a mixing of lead from mantle-derived alkaline magma with lead from Precambrian metamorphic wall rocks.Isotopic age data, geological and geochemical evidence suggest that the ore fluids for the groups 1 and 2 deposits were generated during the emplacement of the Hercynian alkaline syenite and mafic intrusions. The Hercynian alkaline magma may provide heat, volatiles and metals for these groups 1 and 2 deposits. Evolved metamorphic fluids produced by the devolatilization, which circulated the wall rocks, were also progressively involved in the alkaline magmatic hydrothermal system, and may have dominate the ore fluids during late stage of ore-forming processes. Most of these gold deposits hosted by Archean high-grade metamorphic rocks occur at or near the intersections of the NE- and E–W-trending fracture systems. The ore fluid of the group 3 deposits may have resulted from the mixing of Hercynian alkaline magmatic fluids and evolved meteoric waters. The deposits are believed to be products of Hercynian alkaline igneous processes along deep-seated fault zones within Archean terrain. 相似文献