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   608篇
  免费   85篇
  国内免费   43篇
测绘学   163篇
大气科学   25篇
地球物理   113篇
地质学   260篇
海洋学   40篇
天文学   21篇
综合类   40篇
自然地理   74篇
  2024年   1篇
  2023年   2篇
  2022年   10篇
  2021年   8篇
  2020年   7篇
  2019年   15篇
  2018年   10篇
  2017年   10篇
  2016年   48篇
  2015年   26篇
  2014年   20篇
  2013年   54篇
  2012年   38篇
  2011年   33篇
  2010年   24篇
  2009年   38篇
  2008年   22篇
  2007年   22篇
  2006年   35篇
  2005年   39篇
  2004年   35篇
  2003年   51篇
  2002年   28篇
  2001年   28篇
  2000年   26篇
  1999年   17篇
  1998年   12篇
  1997年   12篇
  1996年   11篇
  1995年   6篇
  1994年   5篇
  1993年   12篇
  1992年   9篇
  1991年   9篇
  1990年   4篇
  1989年   2篇
  1988年   2篇
  1987年   3篇
  1985年   1篇
  1984年   1篇
排序方式: 共有736条查询结果,搜索用时 0 毫秒
61.
Multidisciplinary analysis including paleomagnetic, sedimentologic, sea-level change, luminescence dating and palynologic research was performed on a 25 m long orientated core taken at Rutten, close to Eemian key localities in the Netherlands. The main goal of our research was to test a possible delayed onset of temperate conditions in this region compared to Southern Europe, occurring within the Last Interglacial. The sediments revealed the presence of the paleomagnetic Blake Event in ca. 10 m of lower-deltaic floodbasin sediments that contain a pollen record covering the Eemian. The position of the Blake Event in relation to the pollen stratigraphy concurs with the earlier studied Neumark Nord 2 site. Paleomagnetic correlation to core MD95-2042 off SW Iberia indicates ca. 5 kyr diachroneity between the pollen-based onset of temperate interglacial conditions between northern and southern Europe. The onset of the Eemian in north-western and central Europe (ca. 121.0 ka) post-dates the Marine Isotope Stage 6/5e transition by ca. 10 kyr. In addition, the Rutten data provide evidence for a relatively long duration of the Blake Event of at least 8 kyr. The late onset of the temperate conditions that define the base of the Eemian, imply that NW Europe with the Eemian type area is not the most suited region to define the beginning of the Last Interglacial and Late Pleistocene for global chronostratigraphic use.  相似文献   
62.
Recent field prospecting in the Cretaceous sequences of the lower Narmada valley has led to the discovery of three isolated archosaur teeth from the upper part of marine Cretaceous rocks of the Bagh Group. The specimens were recovered by surface prospecting from an oyster‐bearing green sandstone bed occurring at the top of the Coralline Limestone (Coniacian) from a site near Phutibawri village, Dhar District, Madhya Pradesh, India. Of the three teeth recovered from this horizon, two are identified with abelisaurid dinosaurs and the third one with an indeterminate crocodile. The abelisaurid teeth conform to the premaxillary and maxillary tooth morphology of Majungasaurus and Indosuchus. Earlier reports of abelisaurid dinosaurs from India are from the Upper Cretaceous (Maastrichtian) Lameta Group of Jabalpur, Pisdura (Central India) and Balasinor (Western India) and Upper Cretaceous (Late Maastrichtian) Kallamedu Formation (South India). As no associated age diagnostic fossils are found, the specimens described here are considered to represent pre‐Late to Late Maastrichtian age based on the known ages of the underlying and overlying formations. The new finds, therefore, document stratigraphically the oldest occurrence of abelisaurid dinosaurs known from the Indian subcontinent.  相似文献   
63.
Abstract

Abstract Water balances for a re-vegetated xerophyte shrub (Caragana korshinskii) area were compared to that of a bare surface area by using auto-weighing type lysimeters during the 1990–1995 growing seasons at the southeast Tengger Desert, Shapotou, China. The six-year experiment displayed how major daily water balance components might vary for a bare and a re-vegetated sand dune area. Evapotranspiration from the C. korshinskii lysimeter represented a major part of the water balance. The average annual ET/P ratios varied between 69 and 142%. No seepage was observed for the vegetated lysimeter. For the bare lysimeter, on the other hand, 48 mm or 27% of observed rainfall per year occurred as seepage. These results suggest that re-vegetating large sandy areas with xerophytic shrubs could reduce soil water storage by transpiration. Also, the experimental results indicate that re-vegetating large sandy areas could significantly change groundwater recharge conditions. However, from a viewpoint of desert ecosystem reconstruction, it appears that natural rainfall can sustain xerophytic shrubs such as C. korshinskii which would reduce erosion loss of sand. However, re-vegetation has to be balanced with recharge/groundwater needs of local populations.  相似文献   
64.
This paper describes a GPR study carried out with the aim of evaluating deterioration of concrete floors in a textile factory. In the past, production process waste was spilt onto the floor of the factory. A slow but continuous action from this waste on the concrete caused a significant variation in its porosity that can be detected by studying changes in the GPR reflected pulse. A simple synthetic model was developed in order to obtain information about how the response of the GPR antenna pulse is affected by changes in the porosity of concrete. It should also be taken into account the different conditions of the factory floor at the time of testing, as it had been isolated from the action of waste for many years. The heterogeneous conditions of the floor and the simplicity of the model used did not allow for an accurate estimate of the porosity; however, it was possible to map degraded areas of the floor in relationship to changes in the reflected signal. Core samples taken showed that some areas had concrete porosity of 15% and up to 25%, which is closer to that of sand than to concrete.  相似文献   
65.
青海日月山断裂带是青藏高原东北缘柴达木—祁连活动地块内部的一条NNW走向的右旋走滑兼逆冲断裂。 本文基于ENVI 5.1遥感图像处理平台对研究区高分一号多光谱(分辨率8 m)和全色(分辨率2 m)影像进行融合, 获取了高保真、 高分辨率的卫星遥感影像。 通过多尺度、 多角度、 多层次的构造解译以及对比, 将日月山西支断裂的海晏段划分为德州段(F1-3)和海晏段(F1-4)两个次级段, 同时利用高分辨率Google Earth影像对德州段断错微地貌进行了解译、 分析, 结合对德州段野外地质考察, 进一步验证了影像解译结果。 研究表明: 日月山断裂的德州段由5条次级段落组成(f1, f2, f3, f4, f5), 并且该段断裂晚更新世以来活动性明显, 以右旋走滑为主兼有逆倾滑分量; 断裂在晚更新世以来发生过多期断层活动, 其中全新世断层活动可划分为两期, 最新一期水平位错量为6.5~8.7 m, 第二期水平位错量为12.3~14 m; 晚更新世也可划分出两期活动, 第一期水平位错量为16~20 m, 第二期水平位错量为28.5~47 m。  相似文献   
66.
CHRONOSTRATIGRAPHY,SEDIMENTATION AND EVOLUTION OF THE XIGAZE FOREARC BASIN: IMPLICATIONS FOR DYNAMIC EVOLUTION OF THE YARLUNG ZANGBO SUTURE ZONE1 All埁greCJ,CourtillotV ,TapponnierP ,etal.StructureandevolutionoftheHimalaya Tibetorogenicbelt[J] .Nature,1984 ,30 7:17~ 2 2 . 2 CoulonC ,MaluskiH ,BollingerC ,etal.MesozoicandCenozoicvolcanicrocksfromcentralandsouthernTibet:3 9Ar 40 Ardating ,petrotogicalcharacteristicsandgeodyn…  相似文献   
67.
The Council for Geoscience (CGS, South Africa) has a statutory mandate to carry out regional geochemical mapping in South Africa that needs to be rapidly and accurately analysed. Both simultaneous X-ray fluorescence spectrometry (S-XRF) and a newly developed method using inductively coupled plasma-mass spectrometry (ICP-MS) were employed. Various trace elements that could not previously be analysed by S-XRF can now be analysed by ICP-MS for the regional geochemical mapping programme, e.g., Cd, Mo, Te and Li. Using both techniques, the CGS aims to report element distributions for some fifty elements. To ensure that element concentration levels correlate over map boundaries, quality control measures in the sampling, sample preparation and analyses were of critical importance. This paper aims to discuss the sample preparation and quality control measures as applied to the ∼5500 samples of the Giyani and Tzaneen 1:100000 scale map sheets sampled at a density of one soil sample per km2. ICP-MS batch- and instrumental drift-correction procedures will be discussed. As a final step, geochemical data were overlain over simplified geological maps using geographical information system software. These maps complement existing geological information of South Africa, help in the identification of exploration targets, test exploration models and initiate further geological research.  相似文献   
68.
水面蒸发敏感因素的判断,对于干旱区水资源的规划与利用具有重要指导意义。文章以新疆塔额盆地内的塔城市气象站1981—2010年资料为例,采用敏感系数法对研究区多年月均水面蒸发影响因素进行敏感性分析,并与关联分析法分析的结果对比。结果表明:在塔额盆地内,温度与水汽压二因素对水面蒸发影响最为敏感;基于敏感系数法的敏感因素研究结果与关联分析的结果基本一致,尤其在主要影响因子的判定上。  相似文献   
69.
王雅丽  崔银亮 《云南地质》2010,29(4):438-443
根据遥感构造、含矿岩性地层、岩石蚀变异常等多种遥感地质信息,采用地质异常单元统计预测方法,对毛坪铅锌矿进行多元信息成矿预测,明确了找矿方向。  相似文献   
70.
Concentrations of halogens (fluorine, chlorine, bromine and iodine) were determined in six geochemical reference materials (BHVO‐2, GS‐N, JG‐1, JR‐1, JB‐1b, JB‐2). Halogens were first extracted from powdered samples using a pyrohydrolysis technique, then hydrolysis solutions were analysed by ion chromatography for F and Cl and inductively coupled plasma‐mass spectrometry for Br and I. The detection limits in solutions were 100 μg l?1 for both F and Cl and 10 ng l?1 for Br and I. Considering the extraction procedure, performed on a maximum of 500 mg of sample and producing 100 ml of pyrohydrolysis solution, detection limits in rock samples were 20 mg kg?1 for F and Cl and 2 μg kg?1 for Br and I. The mean analytical errors on the studied composition ranges were estimated at 10 mg kg?1 for F and Cl, 100 μg kg?1 for Br and 25 μg kg?1 for I. The concentration values, based on repeated (generally > 10) sample analysis, were in good agreement generally with published values and narrowed the mean dispersion around mean values. Large dispersions are discussed in terms of samples heterogeneity and contaminations during sample preparation. Basaltic RMs were found to be more suitable for studies of halogen compositions than differentiated rock material, especially granites – the powders of which were heterogeneous in halogens at the 500 mg level.  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