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   4148篇
  免费   1071篇
  国内免费   1867篇
测绘学   81篇
大气科学   25篇
地球物理   131篇
地质学   6227篇
海洋学   26篇
综合类   378篇
自然地理   218篇
  2024年   23篇
  2023年   78篇
  2022年   138篇
  2021年   164篇
  2020年   157篇
  2019年   225篇
  2018年   155篇
  2017年   186篇
  2016年   240篇
  2015年   245篇
  2014年   346篇
  2013年   289篇
  2012年   362篇
  2011年   387篇
  2010年   366篇
  2009年   271篇
  2008年   225篇
  2007年   328篇
  2006年   280篇
  2005年   246篇
  2004年   231篇
  2003年   225篇
  2002年   222篇
  2001年   231篇
  2000年   194篇
  1999年   211篇
  1998年   179篇
  1997年   169篇
  1996年   153篇
  1995年   96篇
  1994年   106篇
  1993年   68篇
  1992年   72篇
  1991年   59篇
  1990年   45篇
  1989年   35篇
  1988年   25篇
  1987年   20篇
  1986年   23篇
  1985年   6篇
  1983年   3篇
  1980年   1篇
  1972年   1篇
排序方式: 共有7086条查询结果,搜索用时 62 毫秒
191.
Laguerre  Michel S. 《GeoJournal》2005,64(1):41-49
This paper briefly reviews the sociological literature on the “New” Chinatown phenomenon stressing its structural location vis-à-vis the “Old” Chinatown and the homeland. It defines the New Chinatown as a panethnopolis, that is a global neighborhood with a majority population of Chinese immigrants and of other ethnic groups of mostly Asian descent. It analyzes more particularly the formation, development, and integration of San Francisco’s Richmond District’s New Chinatown into both the city where it is located and the network of transglobal sites to which it belongs. It provides an interpretation of the New Chinatown as a cultural enclave within the context of globalization theory.  相似文献   
192.
金龙山——丘岭金矿区含金矿源为层上泥盆统南羊山组和下石炭统袁家沟组。组成含金矿源层岩石为高频互层的细碎屑岩-碳酸盐岩,其中细砂岩、粉砂岩、碳酸盐岩含成矿流体物性较好.页岩、板岩含成矿流体物性较差,构成屏蔽层。金鸡岭Ⅰ级复式向斜控制着金、砷、锑等异常范围;松枣Ⅱ级复式背斜控制着金的矿化带;金龙山-丘岭金矿Ⅲ级背斜控制着金的矿(化)体;镇安——板岩镇断裂的次级断裂是金矿化体的容矿有利位置。在成矿过程中,构造变形与成矿流体的形成、运移及储集密切相关。其规律是:①原生构造导致成矿流体的初次聚集。②第一期构造变形导致成矿流体的聚集。③第二期构造变形导致成矿流体运移及金矿床形成。此期变形是金的主要成矿期。④第三期构造变形使成矿流体进一步聚集和金矿体的富集。⑤第四期构造变形是石英方解石脉的形成时期。总结出矿床形成模式。据此提出了在4种不同的构造部位找金的方向。  相似文献   
193.
文章介绍区域地质背景、矿区地物化特征,对成矿时代、流体包裹体特征进行初步研究,并指出找矿远景,希望对矿区的矿产勘查具有借鉴和指导意义。  相似文献   
194.
广西南丹地区尾矿分布于大厂、车河、芒场等矿区。尾砂来自以锡石为主的多金属矿床,尾砂中除Sn,Pb,Zn,Ag,Sb的质量分数达到工业指标外,Au亦达到综合利用指标。通过试验证明,对尾矿中的细微粒锡石可采用风力分级选矿、磁选和化学选矿等方法回收;尾砂中的非金属资源可作为填充材料、水泥原料利用,使尾砂型人工矿床充分的资源化。  相似文献   
195.
辽宁省的鞍山、本溪两市为我国重要的钢铁基地,各矿山长期生产遗留的铁尾矿问题越来越引起人们的重视,如污染环境、诱发地质灾害等,如何解决已成为地质、环保、水工界的关注。  相似文献   
196.
Effect of suction on the mechanical behaviour of iron ore rock   总被引:1,自引:0,他引:1  
The effect of suction on the behaviour of iron ore has been studied from both physical and mechanical points of view. The porosity and the suction phenomena have been analysed using different experimental techniques. Uniaxial compressive tests on partially saturated samples have shown that the suction is responsible for strength and cohesion improvement. Considering the theory of partially saturated porous soils of Coussy and Dangla (Mécanique des sols non saturés (2002 edn). Hermès Science: 2002; 390), we have proposed a constitutive law for partially saturated iron ore. The real increase in the apparent cohesion due to the capillary attraction forces is overestimated if the yield function is written in terms of effective stresses. The effect of the capillary cohesion has been modelled with a function in the expression of the apparent cohesion of the yield function. The effect of suction on the mechanical behaviour has been represented in the effective stresses space and in the total stresses space like the Alonso model (Géotechnique 1990; 40 :405–430). Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   
197.
陈世斌 《地理研究》2005,24(6):982-991
休闲旅游作为一种旅游方式和休闲活动内容越来越受到重视,通过对杭州市“最具出游力”人群调查,运用旅游地理学分析方法发现,影响他们进行休闲旅游的因素最重要的是时间因素、交通因素和学习因素,传统观点中的经济因素地位明显下降;同时分析了不同职业、性别和年龄人员中各因素作用的差异。这种实证性的调查分析方法和结论对于休闲旅游理论和杭州市休闲产业的发展都有一定意义。  相似文献   
198.
The aim of this study was to investigate rainfall–groundwater dynamics over space and annual time scales in a hard‐rock aquifer system of India by employing time series, geographic information system and geostatistical modelling techniques. Trends in 43‐year (1965–2007) annual rainfall time series of ten rainfall stations and 16‐year (1991–2006) pre‐monsoon and post‐monsoon groundwater levels of 140 sites were identified by using Mann–Kendall, Spearman rank order correlation and Kendall rank correlation tests. Trends were quantified by Kendall slope method. Furthermore, the study involves novelty of examining homogeneity of pre‐monsoon and post‐monsoon groundwater levels, for the first time, by applying seven tests. Regression analysis between rainfall and post‐monsoon groundwater levels was performed. The pre‐monsoon and post‐monsoon groundwater levels for four periods – 1991–1994, 1995–1998, 1999–2002 and 2003–2006 – were subjected to geographic information system‐based geostatistical modelling. The rainfall showed considerable spatiotemporal variations, with a declining trend at the Mavli rainfall station (p‐value < 0.05). The Levene's tests revealed spatial homogeneity of rainfall at α = 0.05. Regression analyses indicated significant relationships (r2 > 0.5) between groundwater level and rainfall for eight rainfall stations. Non‐homogeneity and declining trends in the groundwater level, attributed to anthropogenic and hydrologic factors, were found at 5–61 more sites in pre‐monsoon compared with post‐monsoon season. The groundwater declining rates in phyllite–schist, gneiss, schist and granite formations were found to be 0.18, 0.26, 0.21 and 0.14 m year?1 and 0.13, 0.19, 0.16 and 0.02 m year?1 during the pre‐monsoon and post‐monsoon seasons, respectively. The geostatistical analyses for four time periods revealed linkages between the rainfall and groundwater levels. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
199.
Yudai is a newly discovered copper deposit associated with a porphyritic quartz diorite, in the Kalatag district of the eastern Tianshan, China. SHRIMP U-Pb dating of zircons from the diorite yielded an age of 432 ± 3 Ma. The diorite is peraluminous (ASI = 0.98–1.10), calc-alkaline to tholeiitic with high Al2O3 of 16.6–17.7 wt% and Mg# of 57.4–67.4. Trace element characteristics of the diorite show it is enriched in Ba, K and Sr, and depleted in Nb, Ta, Ti, with a positive Eu anomaly and high Sr/Y and La/Yb ratios. This diorite has positive εNd(t) values ranging from 6.2 to 8.4 with low initial 87Sr/86Sr ratios of 0.704336 to 0.704450. These geochemical and isotopic characteristics indicate that the adakite-like diorite, associated with the copper mineralization, was emplaced in an island arc setting and resulted from partial melting of subducted oceanic plate in a mantle wedge.  相似文献   
200.
采用电感耦合等离子体质谱法(ICP-MS)测定稀土矿石中的镓,高含量的稀土元素会造成严重的质谱干扰。本文采用聚氨酯泡沫塑料在6 mol/L盐酸介质中吸附样品溶液中的镓后,以0.5 mol/L氯化铵水浴加热解脱30 min,镓的吸附-解脱效率超过99%,稀土元素等干扰物质基本不进入解脱液中,即在富集镓的同时实现了镓与基体元素的高效分离,降低了质谱干扰。本方法检出限低(0.022μg/g),经土壤及水系沉积物标准物质验证,镓的测定值与标准值吻合(绝对偏差为0.38%~4.70%),实际稀土矿石样品的加标回收率为94.1%~100.6%,精密度(RSD)低于4%(n=12),可应用于分析一般地质样品以及稀土矿石中的镓。  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