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   1975篇
  免费   252篇
  国内免费   150篇
测绘学   19篇
大气科学   10篇
地球物理   445篇
地质学   1647篇
海洋学   118篇
天文学   1篇
综合类   63篇
自然地理   74篇
  2023年   7篇
  2022年   26篇
  2021年   35篇
  2020年   39篇
  2019年   42篇
  2018年   30篇
  2017年   41篇
  2016年   73篇
  2015年   73篇
  2014年   93篇
  2013年   64篇
  2012年   50篇
  2011年   69篇
  2010年   75篇
  2009年   168篇
  2008年   224篇
  2007年   187篇
  2006年   204篇
  2005年   136篇
  2004年   115篇
  2003年   78篇
  2002年   71篇
  2001年   48篇
  2000年   50篇
  1999年   42篇
  1998年   45篇
  1997年   42篇
  1996年   41篇
  1995年   44篇
  1994年   36篇
  1993年   29篇
  1992年   25篇
  1991年   9篇
  1990年   11篇
  1989年   6篇
  1988年   11篇
  1987年   5篇
  1986年   2篇
  1985年   6篇
  1984年   9篇
  1983年   3篇
  1982年   7篇
  1981年   4篇
  1980年   1篇
  1954年   1篇
排序方式: 共有2377条查询结果,搜索用时 15 毫秒
231.
为了适应油田地下水动态观测资料的处理,有效地排除干扰,对Weiner滤波方法进行了改进,利用改进后的方法,处理了胜利油田东水-3井的观测资料,结果表明,利用该方法可以较好地消除各种干扰对地下水动态观测的影响。  相似文献   
232.
于军 《江苏地质》2001,25(1):27-32
简要介绍了地下水流面在维实体模型制作系统-GWT3D(V1.00)的实体建模技术及光线跟踪原理,对其绘图所需数据文件结构进行了必要说明,同时阐述了GWT3D的功能与特色,并给出了该软件在这地区绘制地下水流场三维实体模型的一个实用实例。GWT3D是由VisualC 6.O开发的Win32应用程序,采用Outloow98流行的动画工具条风格,能利用通和地下水流模拟软件(如Modfolw等)所提供的网格剖分及水位数据,给制近似逼真的三维地下水流形态,具有动画显示功能和TIF、BMP、GIF3种图像文件存储格式,是一个专业性和实用性较强的计算机图像制作软件。  相似文献   
233.
 This study presents a program for risk management in the contamination of groundwater resulting from leachate in landfills at Mar del Plata (Argentina). The program includes prediction, prevention, monitory observation and mitigation as actions that must be taken prior to, during, and after contamination occurs. This routine aids in the identification of weak points and failures of the program for those who are in charge of making decisions, and will allow better use of limited financial and technical resources based on planning, thus minimizing disconnected determinations. Results of the prediction stage were confirmed through monitoring. The presence of a plume of contamination more than 100 m from the landfill was shown, thus proving that implementation of a monitoring plan to follow the development of the contaminated plume must be implemented, particularly in populated areas which depend on residential wells for their water supply. Received: 8 May 2000 · Accepted: 14 August 2000  相似文献   
234.
The Salí River hydrogeological basin is one of the most productive artesian basins in Argentina. It is located in the southeastern part of the province of Tucumán, northwestern Argentina, and its groundwater resources are developed for water supply and irrigation. The chemical composition of the water is strongly influenced by the interaction with the basinal sediments and by hydrologic characteristics such as the flow pattern and time of residence. Three hydrochemical zones are defined in the study area and the processes that control the chemical composition of the water are manifestly different in each zone. The dissolution of halite, sodium sulphate, and gypsum explains part of the contained Na+, K+, Cl, SO4 2–, and Ca2+, but other processes, such as cation exchange, calcite precipitation, weathering of aluminosilicates, and gas exchange with the atmosphere, also contribute to the water composition. The assessment of contamination indicators, such as pH, dissolved organic matter, dissolved oxygen, phosphate, and nitrate, indicates that the groundwater is suitable for human consumption. However, biological contamination has been detected in samples from some wells, especially those near the Salí River. Electronic Publication  相似文献   
235.
G. Rasula  M. Rasula   《Engineering Geology》2001,60(1-4):351-360
Protection of groundwater already is and will also be in the future, a particularly important environmental, socio-economic, social welfare and political task. The fact that the costs of preventive measures are 10–20 times lower than the funds needed to clean up and revitalize polluted aquifers, as well as the fact that the area to be occupied with transport communications and other infrastructure facilities will aggravate protection, both call for an urgent introduction of modern methods of monitoring and preserving all the existing and potential groundwater resources. The basic principle of groundwater protection against pollution means constant control and preventive measures of protection, namely prevention of incidental and other kinds of pollution. The very construction of communications and all accompanying facilities changes and degrades the existent natural geological environment, and when in use they may become structures in whose immediate surrounds surface and ground waters may be polluted by the toxic and waste substances transported. The experience gained through the following activities: the ‘pilot model’ for groundwater monitoring in the zone of Makis, the investigations and monitoring of critical sites polluted with xylene (CIP, Belgrade, 1994/95), and information on the latest achievements in this field in the world (obtained while working on the study of methodology of hydrogeological investigations needed for groundwater quality monitoring system — Jaroslav Cerni Institute for the Development of Water Resources, Belgrade, 1998), stresses a necessity to obligatory design and construct operational systems for groundwater quality monitoring, particularly in the zones of infrastructure facilities (roads, railway, gas pipelines, oil pipelines), which can be considered as potential linear polluters. In that light, this paper is a contribution to developing hydrogeological investigation methodology for designing and operating a monitoring system in the zones of roads, and its legal and practical incorporation in the technical documents of each project. Besides, an emphasis is put on multidisciplinary approach to system implementation, its full automation, rational management, and effective and optimal measures for groundwater protection.  相似文献   
236.
Monitoring and evaluation of groundwater quality in drinking water protectorates is of particular interest if the uncontrolled entry of pollutants, for example by infiltrating river water, cannot be excluded. A fluorescence spectroscopic method is presented as possible alternative to the conventional expensive hydrochemical investigations. This method uses the information yielded by synchronous fluorescence spectra. After a Fourier transformation of the original spectra and a following discriminant analysis, the samples can be classified in different groups corresponding to the different types of groundwater. The method was tested in the drinking water protectorate of a waterworks of a German metropolis (Halle, Sachsen-Anhalt). We found a prediction rate of about 90% in the investigated case.  相似文献   
237.
灰色系统GM模型在地下水动态异常识别中的应用   总被引:2,自引:1,他引:2  
郭德科 《地震研究》1996,19(1):58-64
本应用灰色系统理论的GM模型对地下水动态资料进行了异常识别,发现在1981年河北宁晋MS5.8级地震、1983年荷泽MS5.9级地震、1985年河北任县MS5.0级地震前,有明显的异常显示,通过选择不同建模数据个数及外推个数,发现对豫01井五日均值资料建模处理,选择2个月的数据10天滑动逐次建模识别的异常较清楚。同时对所建模型的精度进行了分析,证明该方法在本区豫01井、鲁05井资料处理及前兆异常  相似文献   
238.
山西天镇晚白垩世——新恐龙动物君及其地层意义   总被引:1,自引:0,他引:1  
程政武  庞其清 《地球学报》1996,17(Z1):135-139
新发现的山西天镇恐龙动物群是以巨龙类(titanosaurids)和甲龙类(ankylosaurids)为代表,含有鸭嘴龙类及兽脚类化石,其中一具何存较完整的巨龙类骨架(已获骨骼近70%)包括3个甲龙头骨及其头后骨骼.该动物君化石相当丰富,经与蒙古、印度、老挝、加拿大、美国和阿根廷等国晚白垩世恐龙动物君的比较我,实属晚白垩世较为罕见的一新恐龙动物群。由于天镇恐龙动物群的发现不仅将原划归始新世的灰泉堡组的时代归属晚白垩世,而且对白垩系划分和探讨恐龙的分类、演化、迁徒、动物地理区及其绝灭等方面的研究均具有重要意义。  相似文献   
239.
新疆乌什—阿克苏地区下寒武统玉尔吐斯组的小壳化石丰富,已描述了近50属90种,包括1个新属,15个新种。计有软舌螺类、似软舌螺类、单板类、腹足类、骨针类及分类位置未定的化石,还有节肢动物门的高肌虫类。按小壳化石在地层纵向出现的次序及其代表性,可将玉尔吐斯组小壳动物群的比石划分为3个带,即1.Anabarites trisulcatus带;2.Cambroclavus-Aurisella带;3.Adyshevitheca-Xinjiangella带。其中1带可与梅树村阶I.Anabarites-Protohertzina带对比;2—3带大致可与梅树村阶Ⅱ.Paragloborilus-Siphogonuchites带—Ⅲ.Sinosachites-Lapworthella带对比。因Aanbarites trisulcatus的发现,证实玉尔吐斯组的下界可与梅树阶的底界对比;玉尔吐斯组顶部发现的高肌虫有别于筇竹寺阶的高肌虫。前者与大量梅树村期小壳动物共生,可以认为梅树村期已经出现高肌虫的先遣分子。  相似文献   
240.
Groundwater samples collected from both open and bore wells in an area of about 270 km2 from Madras City, India, have been analyzed for major ions (HCO3, Cl, Si, Na, Ca, and Mg) and trace elements (As, Se, B, V, Cr, Fe, Co, Pb, Cu, Zn, Cd, Mn, Ni, Mo, and Ba). The study reveals that the quality of potable water has deteriorated to a large extent. Seawater intrusion into the aquifer has been observed in nearly 50 percent of the study area. The toxic elements (As and Se) have already exceeded the maximum permissible limits of drinking water in almost the entire city. A positive correlation of As and Se with other toxic metals such as V, Cr, Fe, B, etc., indicates that all these elements are anthropogenic in origin. Applying multivariate analysis, the source for trace elements in groundwater has been grouped into two major factors: pollution and mobilization factors. The groundwater in the study area is largely contaminated by organic effluents and reflects the intensity of pollution caused by the overlying soil sediment and rapid infiltration of the pollutants.  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