首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   200篇
  免费   18篇
  国内免费   3篇
测绘学   15篇
大气科学   8篇
地球物理   70篇
地质学   68篇
海洋学   12篇
天文学   27篇
自然地理   21篇
  2022年   2篇
  2021年   1篇
  2020年   3篇
  2019年   2篇
  2018年   4篇
  2017年   4篇
  2016年   7篇
  2015年   13篇
  2014年   9篇
  2013年   14篇
  2012年   9篇
  2011年   7篇
  2010年   9篇
  2009年   9篇
  2008年   7篇
  2007年   7篇
  2006年   8篇
  2005年   7篇
  2004年   7篇
  2003年   8篇
  2002年   4篇
  2001年   7篇
  2000年   1篇
  1999年   4篇
  1998年   3篇
  1997年   4篇
  1993年   2篇
  1991年   2篇
  1990年   3篇
  1988年   2篇
  1987年   1篇
  1985年   6篇
  1984年   8篇
  1983年   6篇
  1982年   4篇
  1980年   4篇
  1979年   2篇
  1978年   5篇
  1977年   5篇
  1976年   1篇
  1975年   1篇
  1974年   2篇
  1973年   3篇
  1969年   1篇
  1957年   1篇
  1898年   2篇
排序方式: 共有221条查询结果,搜索用时 15 毫秒
51.
52.
The reef fauna connectivity of the West Indian Ocean (WIO) is one of the least studied globally. Here we use genetic analyses of the grouper Epinephelus merra (Bloch 1793) to determine patterns of connectivity and to identify barriers to dispersal in this WIO marine area. Phylogeographic and population‐level analyses were conducted on cytochrome b sequences and microsatellites (13 loci) from 557 individuals sampled in 15 localities distributed across the West Indian Ocean. Additional samples from the Pacific Ocean were used to benchmark the WIO population structure. The high level of divergence revealed between Indian and Pacific localities (of about 4.5% in sequences) might be the signature of the major tectonic and climatic changes operating at the Plio‐Pleistocene transition, congruently with numerous examples of Indo‐Pacific speciation. In comparison, the E. merra sequences from the Indian Ocean constitute a monophyletic clade with a low average genetic distance (d < 0.5%). However both genetic markers indicated some structure within this ocean. The main structure revealed was the isolation of the Maldives from the WIO localities (a different group signature identified by clustering analysis, great values of differentiation). Both marker types reveal further significant structure within the WIO, mainly the isolation of the Mascarene Islands (significant AMOVA and isolation‐by‐distance patterns) and some patchy structure between the northernmost localities and within the Mozambique Channel. The WIO genetic structure of E. merra appeared congruent with main biogeographic boundaries and oceanographic currents.  相似文献   
53.
54.
麻扎塔格地区地层、地貌及构造变形特征的研究,对于认识塔里木盆地新生代构造演化过程、塔里木—西昆仑的盆山耦合关系、新构造运动对塔里木油气资源分布的影响以及塔克拉玛干沙漠的气候、环境变化都具有重要意义。本文通过卫星照片解译、野外变形观察、剖面实测、地球物理资料解释等手段,对该地区晚新生代的构造特征进行了研究,确定了麻扎塔格构造带为典型的逆冲—褶皱带,并探讨了麻扎塔格逆冲—褶皱带的构造指向、活动时限、隆升速率及缩短速率、东西方向的延伸等问题,取得如下认识:1)麻扎塔格逆冲—褶皱带为西昆仑山前陆褶皱冲断带的前缘部位,和田河气田就是处在逆冲前锋背斜顶部,晚新生代变形作用已明显地改造了塔里木盆地南部及中部的古生代和中生代构造,并促成了和田河气田的形成;2)麻扎塔格山在中新世末(约7 Ma)和中更新世(约780 ka B.P.)经历了两次构造隆升,后一次形成了麻扎塔格逆冲—褶皱带和麻扎塔格山现今的地貌特征;3)估算出麻扎塔格逆冲—褶皱带中更新世以来的隆升速率约为0.26~0.4 mm/a,缩短速率约为0.9 mm/a;4)认为麻扎塔格逆冲—褶皱带向西应与同属西昆仑山前褶皱—冲断带前缘的喀什背斜相连,东端的突然消失可能是由于东段和田河附近存在北东—南西向的走滑断层造成。  相似文献   
55.
Thermal indicators record exhumation of sedimentary units from depths in excess of 6 km over most of the Outer Carpathian fold and thrust belt in Poland. Apatite fission track data, showing cooling ages ranging between 32.1 ± 4.8 and 7.0 ± 0.8 Ma, indicate that exhumation was partially coeval with shortening. However, new thermochronometric information obtained as part of this study allowed us to unravel a previously undetected, post-thrusting exhumation stage. The integration of new field data and structural analysis with low-T thermochronometry suggests that termination of thrusting – at ca. 11 Ma in the area of the present study – was followed by gravity disequilibria within the orogenic wedge. The related extension and denudation phenomena appear to have played a primary role in the recent (< 10 Ma) tectonic evolution of the Western Outer Carpathians, exerting a major control on exhumation processes in this key area of the Alpine–Carpathian mountain system.  相似文献   
56.
Sponsored by National Science & Technology Committee, the cooperation between China Academy of Geoscience and Institute of Geophysics and Tectonics, University Joseph, France conducted a lithospherical experiment using 40 Minititan 3-component and 13 CEIS 1-component seismometers along the road from Gonghe to Yushu in Qinghai Province during 5 months after June, 1998. The interested area is on the north of Bangong- Nujiang fault, the east of Qaidam basin, the south of Center Qilian fault and the west of Longmenshan fault. And the profile across most tectonic parts of Eastern Tibet such as Southern Qilian, Eastern Kunlun fault, Bayan Har terrane, Jinshajiang suture (Figure 1), which is the first seismological profile across Eastern Tibet (Qinghai-Tibet) and will be beneficial on the comparison with the results of its center parts, especially on the understanding of the effect of the thousands-kilometer-faraway collision between Eurasia Plate and Indian Plate on the uplifting of south and north part of Eastern Kunlun fault, and on the thickening of crust and the feature of deep structure of Qilian mountain on the north of Tibet Plateau.  相似文献   
57.
The conversion of secondary lead orthophosphate [PbHPO4] into chloropyromorphite [Pb5(PO4)3Cl] in ca. 10?1 M NaCl solutions has been investigated at 25°C. From the composition of the supernatant solutions, the solubility product constant for Pb5(PO4)3Cl has been calculated to be 10?84.4±0.1, corresponding to ΔG?° of ?906.2 kcal mol?1. The solution equilibria and phase relationships in the system PbCl2-PbO-P2O8-H2O are discussed along with the geological implications.  相似文献   
58.
59.
The Malvern howardite contains glass, probably formed by impact on the surface of a parent body. This achondrite also contains a large xenolith, a breccia in breccia. A mineralogical and chemical study of the stone has been carried out by means of electron microprobe and neutron activation analysis.Individual mineral and bulk compositions show the eucritic character of the xenolith. Most of the stone results from mechanical mixing of possibly related rocks, with glass derived by total or partial melting. Foreign components seem to be present as well.  相似文献   
60.
Adsorption studies with sediment from the Bay of Quinte (Lake Ontario) indicate that the adsorption isotherm for sulfate concentration greater than 20 mg/l can be described by a Langmuir-type equation. The accompanying changes in δ34S of the solutions range from +0.9 to +6.0‰ indicating enrichment of32S in the sediments. The corresponding isotopic fractionation between the adsorbed sulfate and the sulfate remaining in solution ranges from ?10 to ?24‰, the larger fractionations being associated with low sulfate concentrations. The adsorbed sulfate is shown to significantly afftect the isotopic composition of the sediment in contact with the sulfate-bearing solution. The desorption of adsorbed sulfate is considered a possible mechanism for enriching natural freshwaters with32S.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号