全文获取类型
收费全文 | 3456篇 |
免费 | 986篇 |
国内免费 | 1819篇 |
专业分类
测绘学 | 21篇 |
大气科学 | 78篇 |
地球物理 | 711篇 |
地质学 | 4911篇 |
海洋学 | 63篇 |
天文学 | 96篇 |
综合类 | 209篇 |
自然地理 | 172篇 |
出版年
2024年 | 18篇 |
2023年 | 73篇 |
2022年 | 154篇 |
2021年 | 146篇 |
2020年 | 175篇 |
2019年 | 211篇 |
2018年 | 190篇 |
2017年 | 204篇 |
2016年 | 224篇 |
2015年 | 242篇 |
2014年 | 234篇 |
2013年 | 226篇 |
2012年 | 293篇 |
2011年 | 262篇 |
2010年 | 238篇 |
2009年 | 293篇 |
2008年 | 197篇 |
2007年 | 267篇 |
2006年 | 271篇 |
2005年 | 226篇 |
2004年 | 242篇 |
2003年 | 213篇 |
2002年 | 189篇 |
2001年 | 175篇 |
2000年 | 189篇 |
1999年 | 197篇 |
1998年 | 165篇 |
1997年 | 134篇 |
1996年 | 109篇 |
1995年 | 112篇 |
1994年 | 97篇 |
1993年 | 95篇 |
1992年 | 64篇 |
1991年 | 27篇 |
1990年 | 34篇 |
1989年 | 20篇 |
1988年 | 19篇 |
1987年 | 13篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1979年 | 5篇 |
1954年 | 3篇 |
排序方式: 共有6261条查询结果,搜索用时 15 毫秒
961.
青山洞金矿位于湖南西南部的雪峰弧形构造成矿带上,是该成矿区带近年来新发现的重要金矿床。通过对青山洞金矿床地质特征的研究,分析其矿床成因类型属构造岩浆+变质热液并以充填交代方式形成的韧脆性剪切带型金矿床,具硫化物-自然金矿石建造,工业类型为破碎蚀变岩型。并初步总结了成矿模式并建立了找矿模型,为寻找同类型金矿提供参考和指导。 相似文献
962.
茶棚银矿位于河北省北部坝上草原向山区过渡地带,风成砂覆盖严重,示矿标志不明显,地表找矿难度大;地表矿体断续出露,而深部银矿体主要以隐伏矿体的形式赋存于近南北向展布的构造破碎带中,数量明显增多、品位变富、厚度变大;在这种特殊的景观地质特征下,利用激电中梯扫面,可发现厚覆盖状态下构造矿化蚀变带,利用EH4连续导电率测量可厘定矿化蚀变带的规模、产状并可提供隐爆角砾岩体等深部控矿地质信息,利用可控源音频大地电磁测深的中低阻陡变带和中阻带,特别是陡变带中的转折部位(形态呈耳状部位)可具体定位银矿体的赋存空间。 相似文献
963.
964.
Based on the deformation characteristics of the ductile shear zones in Sumdo (松多) Group, the quartz fabric by EBSD (electron backscatter diffraction), the data of muscovite 40Ar-39Ar geochronology (220-230 Ma) from ductile shear zones and the zircon SHRIMP U-Pb chronology (190 Ma) of granites in Snmdo region, Lhasa (拉萨) terrane is thought to have experienced an important Indosinian orogenic event at 220-230 Ma, which caused the closure of the paleo-Tethys Ocean along the tectonic zone of eclogite and the collision between northern part and southern part of the Lhasa terrane. The zircon SHRIMP U-Pb chronology of 190 Ma for biotite adamellite, with the distributing characteristics of the granite massif intruding in Sumdo Group, indicates that the biotite adamellitc should be the late orogenic or post-orogenic granite resulting from the lndosinian orogenesis. The discovery of Indosinian orogenic belt in Lhasa terrane expansed the southern boundary of lndosinian orogenic belt in Qinghai (青海)-Tibet plateau to Lhasa terrane from Qiangtang (羌塘) terrane, which changed the understanding about the distribution of Indosinian orogenic belt in Qinghai-Tibet plateau and extended the "T" type lndosinian orogenic belt in China. The study is very important for the formation and distribution of paleo-Tethys Ocean in Tibet. The ancient terrane framework and evolution of Qinghai-Tibet plateau need further research. 相似文献
965.
966.
967.
秋里塔格构造带位于库车前陆逆冲带前锋,区域构造位置介于库车坳陷三叠-侏罗系烃源岩生排烃中心与塔北前缘隆起带之间,第三系广泛分布两套膏盐岩层,发育多套储盖组合和复杂的构造样式,石油地质条件非常优越.本文在分析3个区带的变形特征基础上,探讨了盐上层和盐下层的构造成因,认为盐上层的构造成因与盐层的流动性有关,西段变形比东段强烈;盐下层构造成因东、西差异较大,东段与盐层的塑性变形无关,西段则受其影响. 相似文献
968.
苏盖特构造带位于新疆昆仑山弧形推覆体前缘.本文通过研究苏盖特构造带的构造特征,确定了地震反射层的地质属性,认为苏盖特构造带由表层推覆体及下部下第三系-二叠系之间的地层经过3次重复形成的叠瓦状推覆体构成.苏盖特构造带活动始于上新世阿图什组沉积期,定型于更新世.通过研究西昆仑逆冲推覆体及已钻探井的地表油源、储层特征及储盖组合,认为苏盖特构造带具有两套好的油源即石炭-二叠系及侏罗系油源,两套好的储集层即白垩系和下第三系储层,相应地,发育两套储盖组合,具有良好的圈闭及运聚条件,是有利的勘探目标区. 相似文献
969.
O. Vaduvescu M. Birlan A. Tudorica A. Sonka F.N. Pozo A.D. Barr D.J. Asher J. Licandro J.L. Ortiz E. Unda-Sanzana M. Popescu A. Nedelcu D. Dumitru R. Toma I. Comsa C. Vancea D. Vidican C. Opriseanu T. Badescu M. Badea M. Constantinescu 《Planetary and Space Science》2011,59(13):1632-1646
We report on the follow-up and recovery of 100 program NEAs, PHAs and VIs using the ESO/MPG 2.2 m, Swope 1 m and INT 2.5 m telescopes equipped with large field cameras. The 127 fields observed during 11 nights covered 29 square degrees. Using these data, we present the incidental survey work which includes 558 known MBAs and 628 unknown moving objects mostly consistent with MBAs from which 58 objects became official discoveries. We planned the runs using six criteria and four servers which focus mostly on faint and poorly observed objects in need of confirmation, follow-up and recovery. We followed 62 faint NEAs within one month after discovery and we recovered 10 faint NEAs having big uncertainties at their second or later opposition. Using the INT we eliminated four PHA candidates and VIs. We observed in total 1286 moving objects and we reported more than 10,000 positions. All data were reduced by the members of our network in a team effort, and reported promptly to the MPC. The positions of the program NEAs were published in 27 MPC and MPEC references and used to improve their orbits. The O−C residuals for known MBAs and program NEAs are smallest for the ESO/MPG and Swope and about four times larger for the INT whose field is more distorted. For the astrometric reduction, the UCAC-2 catalog is recommended instead of USNO-B1. The incidental survey allowed us to study statistics of the MBA and NEA populations observable today with 1–2 m facilities. We calculate preliminary orbits for all unknown objects, classifying them as official discoveries, later identifications and unknown outstanding objects. The orbital elements a, e, i calculated by FIND_ORB software for the official discoveries and later identified objects are very similar with the published elements which take into account longer observational arcs; thus preliminary orbits were used in statistics for the whole unknown dataset. We present a basic model which can be used to distinguish between MBAs and potential NEAs in any sky survey. Based on three evaluation methods, most of our unknown objects are consistent with MBAs, while up to 16 unknown objects could represent NEO candidates and four represent our best NEO candidates. We assessed the observability of the unknown MBA and NEA populations using 1 and 2 m surveys. Employing a 1 m facility, one can observe today fewer unknown objects than known MBAs and very few new NEOs. Using a 2 m facility, a slightly larger number of unknown than known asteroids could be detected in the main belt. Between 0.1 and 0.8 new NEO candidates per square degree could be discovered using a 2 m telescope. 相似文献
970.
SHRIMP zircon U–Pb geochronological, elemental and Sr–Nd isotopic data from Early Cretaceous mafic dykes in North Dabie orogenic belt elucidate a change of Mesozoic lithospheric mantle in eastern China. The dykes are predominantly dolerite with the major mineral assemblage clinopyroxene + hornblende + plagioclase and yield a SHRIMP zircon U–Pb age of 111.6 ± 5.3 Ma. They have a narrow range of SiO2 from 46.16% to 49.78%, and relative low concentrations of K2O (1.07−2.62%), Na2O (2.45−3.54%), Al2O3 (13.04−14.07%), and P2O5 (0.42−0.55%) but relatively high concentration of MgO (5.94–6.61%) with Mg# 52–54. All the samples are characterized by enrichment of large ion lithophile elements (LILE, e.g., Ba, Th) and high field strength elements (HFSE, e.g., Nb, Ti). (87Sr/86Sr)i ratios from 0.704 to 0.705, εNd values from 3.36 to 4.33 and mantle‐depletion Nd model ages (T2DM) in the range 0.56–0.64 Ga indicate that the magma of the Baiyashan mafic dykes was derived from a young depleted mantle source. This finding is different from previous research on mafic dykes in the age range 120–138 Ma that revealed enrichment of LILE and depletion of HFSE, high initial Sr isotopic ratios and negative εNd, value which represents an old enriched mantle source. Ours is the first report of the existence of Early Cretaceous depleted mantle in eastern China and it implies that changing of enriched mantle to depleted mantle occurred at ca. 112 Ma, associated with back‐arc extension which resulted from the subduction of the Palaeo‐Pacific Plate towards the Asian Continent. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献