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   8956篇
  免费   1229篇
  国内免费   534篇
电工技术   159篇
技术理论   4篇
综合类   813篇
化学工业   132篇
金属工艺   8篇
机械仪表   34篇
建筑科学   1366篇
矿业工程   121篇
能源动力   415篇
轻工业   53篇
水利工程   6795篇
石油天然气   264篇
武器工业   2篇
无线电   22篇
一般工业技术   108篇
冶金工业   162篇
原子能技术   14篇
自动化技术   247篇
  2024年   19篇
  2023年   179篇
  2022年   355篇
  2021年   357篇
  2020年   394篇
  2019年   383篇
  2018年   322篇
  2017年   397篇
  2016年   404篇
  2015年   376篇
  2014年   503篇
  2013年   488篇
  2012年   690篇
  2011年   802篇
  2010年   529篇
  2009年   474篇
  2008年   469篇
  2007年   544篇
  2006年   547篇
  2005年   463篇
  2004年   382篇
  2003年   280篇
  2002年   248篇
  2001年   190篇
  2000年   164篇
  1999年   153篇
  1998年   92篇
  1997年   91篇
  1996年   93篇
  1995年   53篇
  1994年   77篇
  1993年   48篇
  1992年   41篇
  1991年   13篇
  1990年   10篇
  1989年   48篇
  1988年   9篇
  1987年   11篇
  1986年   9篇
  1985年   8篇
  1984年   1篇
  1983年   1篇
  1959年   1篇
  1951年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Monitoring the water level and volume changes of lakes and reservoirs is essential for deepening our understanding of the temporal and spatial dynamics of water resources in the Yellow River Basin, with a view to better utilizing and managing water resources. In recent years, there have been many studies on monitoring water level and volume changes in inland waters, but they were mainly focused on radar altimetry and the full waveform LiDAR ICESat, which was retired in 2010. Few studies based on the latest photon-counting LiDAR ICESat-2 have been reported. Compared with previous sensors, ICESat-2 has great advantages in footprint size, transmitting frequency, pulse number, etc, but its performance in monitoring water level and volume changes in inland waters has not been fully explored. Here we investigated the spatial distribution of water level and volume changes of 11 lakes and 8 reservoirs in the Yellow River Basin based on ICESat-2 and Google Earth Engine, and analyzed the factors affecting the measurement uncertainties. In-situ validation of lake level in Lake Qinghai indicates that the Root Mean Square Error (RMSE) of our result is only 7 cm after the reference coordinate system conversion. We found that the water level trend of the natural lake shows significant seasonal variations, while the water level trend of the reservoir shows a sharp rise and fall. In addition, precipitation plays a decisive role in the changes in natural lake levels and indirectly affects the artificial control of reservoirs’ water discharges. The uncertainty of water volume change monitoring is mainly affected by water level measurement uncertainty for lakes, while for reservoirs, that is affected by the combination of water level and area measurement uncertainties. The stability of lake level measurement increases with the increase in photon counts. The introduction of ICESat-2 ATL13 Significant Wave Height might lead larger standard deviation in water level measurement. According to the law of propagation of uncertainty, the uncertainty of the water volume change estimation by the combination of ICESat-2 and GEE is less than 9 %.  相似文献   
32.
茅洲河污染来源分析及治理对策研究   总被引:1,自引:0,他引:1  
茅洲河作为深圳、东莞界河,水污染问题一直备受关注。污染来源不明导致上下游治理不同步、治污存在争议问题长期存在。根据现场监测,分析水质现状,核算污染通量,明确了深圳光明新区、宝安区、东莞长安镇对茅洲河的污染贡献分别为27.3%、31.5%、41.2%,并提出了整治对策,为茅洲河水污染治理提供依据。  相似文献   
33.
郭璠颖  朱建裕 《广州化工》2014,(19):124-126
通过调查分析湘江"长株潭"段表层底泥的锌、铜、镉、铬、铅、汞、锰等重金属含量,将底泥样品中重金属的含量分别与土壤环境质量标准、污水排入城市下水道水质标准、以及生活饮用水卫生标准中重金属含量进行比较,从而发现重金属在湘江"长株潭"段的污染严重程度。根据调查结果分析,对湘江"长株潭"段底泥重金属污染问题提出减排含重金属废水,有关部门应关注底泥重金属含量变化,和修复河床表层重金属含量高的底泥等建议。  相似文献   
34.
通过对色曲河流域植被的实地考察,结合基于3S技术的遥感解译技术,对该流域植被的分布特征进行了初步探究。从水平分布、垂直分布、林线与雪线的分布规律等方面分析了色曲河流域植被的分布特征。主要表现在:(1)研究区雪线高度为海拔4800m,林线:阴坡为海拔3600m左右;阳坡在3800m左右;(2)研究区山地垂直自然带谱可分为5个,分别为山地常绿硬叶阔叶林地带、山地暗针叶林带/山地落叶阔叶林地带、高山灌丛草甸带、高山草甸带、高寒荒漠带;(3)水平分布的地域性特征比较明显,主要原因为各地的海拔不同所导致;(4)流域植被随坡向变化的规律比较明显,阳坡植被与阴坡植被具有明显的差异性。  相似文献   
35.
For one week from August 17 to 23, 2016, three consecutive typhoons made landfall in Hokkaido for the first time on record. These typhoons and the front they stimulated brought record-breaking torrential rain over the eastern part of Hokkaido. To investigate the damage to grounds and rivers resulting from this rainfall, the Japan Society of Civil Engineers (JSCE) and the Japanese Geotechnical Society (JGS) formed a disaster research group to conduct an investigation. This report provides the results of the investigation into damage to the grounds of areas along the Tokoro River of the Okhotsk region, Hokkaido, that suffered from this tremendous and diverse disaster. Specifically, the report describes the situation of the levees which were broken and eroded by the overflowing water, the shape of the levee bodies, the levee body soil properties examined by observation of the sections, as well as the occurrence of sand boiling and air blows. The washout of road embankments as well as damage to road bridge mounting fills and abutment backfills were also investigated. The investigation has demonstrated the need to clarify the resistance of the abutment backfills and levee bodies to flowing water as well as the geotechnical predominant factors in order to clarify the mechanisms behind erosion and washout, the need to review new measures that allow for the scale of sand boiling and resultant changes in levee body stability, and the fact that the existing embankments were able to temporarily suppress the flooding water which had spilled over from the river. Furthermore, although it has been identified that the findings of a study on an embankment washout associated with a tsunami can be applied to measures taken against the overflowing water, it has also been found necessary to clarify the predominant geotechnical factors using model tests and to use a more sophisticated analytical approach to establish a geotechnical stability review as soon as possible in order to prevent the levees and embankments from being eroded and washed out due to overflowing water.  相似文献   
36.
采用实证研究方法,以规划响应的演变印证规划的本质。前半部分对珠江三角洲乃至粤港澳大湾区的历版规划进行高度概括梳理凝练,解读了规划演变历史背景,揭示规划响应是一个由局部到整体、层级由低到高的演变过程,既是国家意志体现,亦是经济规律使然,此观点具首创性。后半部分主要阐述《粤港澳大湾区发展规划纲要》的出台及粤港澳三地聚焦科技创新走廊的规划响应,通过描述粤港澳三地在空间上和政策上各自作出的规划响应,以地区的特殊性再次重申“体现国家意志,顺应社会经济发展规律”的规划本质。  相似文献   
37.
房间空调器是中国长江流域地区改善室内热环境的重要措施,然而,在以往的房间空调器的行为研究中,只能通过现场实测、问卷调查等方式获取其使用行为,由于数据获取方式本身所存在的局限性,无法对空调的使用行为进行可靠且深入的挖掘,尤其是对于空调的设置温度。为了研究长江流域地区房间空调器的设置温度行为,包括设置温度的分布、设置温度调节习惯、设置温度与一天中不同时间段的关系、设置温度与室外温度的关系,依托于大数据平台下的房间空调器监测数据,针对长江流域地区的3个典型城市(重庆、武汉、上海)的房间空调器的设置温度习惯,对重庆地区575台房间空调器、武汉地区430台房间空调器、上海地区540台空调器的夏季上万次运行数据、冬季上千次运行数据进行了基本的统计与相关分析,结果表明:空调器的设置温度及其调节习惯在不同城市之间存在一定差异性,夏季用户在一次空调使用过程中存在对较低设置温度(低于26℃)的短时需求情景,同时,设置温度与1 d中的不同时刻以及室外温度也有明显关联。  相似文献   
38.
澳大利亚布罗肯希尔地区是世界上最主要的多金属成矿区之一,仅位于其市内的主铅锌矿体累计开采及探明储量矿石超过2.5亿吨。除此之外,域内还有其他超大型、大型铅锌银金铜多金属矿床、铁矿床、钴矿床、银铅矿床、钨矿床等,小型矿床(点)无数。区域主要出露含矿地层古元古界威利玛超群,是由一套连续的变质程度不同的且多期变形的沉积岩和火山岩形成。位于其内的CUSIN溪矿区成矿地质环境及条件与本区其他矿床基本类似,在勘查中对其矿床(点)地质特征认识分析,发现矿区有热泉型矿床特征,结合区域地质背景、物探及探矿成果,认为本区具有潜在找矿潜力。  相似文献   
39.
蔡瀛  朱国鸣 《城市规划》2006,30(6):9-14
从区域规划目标构建、实施机制设定的角度,以珠江三角洲城镇群协调发展规划为例,探讨如何针对区域发展面临的主要问题,立足于可操作领域,构建目标有所侧重且更为强调实施行动的内容体系;进而阐述如何创新制度,以规划作统筹,以协调为核心,建立长效机制,引导各级政府、部门共同推进规划的实施。  相似文献   
40.
The microbiological quality of water is currently assessed by search for fecal bacteria indicators. There is, however, a body of knowledge demonstrating that bacterial indicators are less resistant to environmental factors than human pathogenic viruses and therefore underestimate the viral risk. As river water is often used as a resource for drinking water production, it is particularly important to obtain a valid estimation of the health hazard, including specific viral risk. This work was conducted to compare the survival of infectious Poliovirus-1 used as a pathogenic virus model to the persistence of, on the one hand, thermotolerant coliforms commonly used as indicators and on the other hand, to somatic coliphages and Poliovirus-1 genome considered as potential indicators. We studied the behavior of infectious Poliovirus-1 and the three (potential) indicators of viral contamination in river water at three different temperatures (4 degrees C,18 degrees C and 25 degrees C). This experiment was performed twice with river water sampled at two different periods, once in winter and once in summer. Our results showed that the survival of thermotolerant coliforms can be 1.5-fold lower than infectious Poliovirus-1. In contrast, under all our experimental conditions, somatic coliphages and Poliovirus-1 genome persisted longer than infectious Poliovirus-1, surviving, respectively, 2-6-fold and about 2-fold longer than infectious Poliovirus-1. According to our results exclusively based on survival capacity, somatic coliphages and viral genome, unlike thermotolerant coliforms appear to be better indicators of viral contamination in river water. Moreover, the disappearance of viral genome is well-correlated to that one of infectious virus irrespective of the conditions tested.  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