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   24724篇
  免费   2330篇
  国内免费   1339篇
电工技术   1855篇
技术理论   5篇
综合类   4005篇
化学工业   2053篇
金属工艺   599篇
机械仪表   1064篇
建筑科学   2658篇
矿业工程   923篇
能源动力   770篇
轻工业   3110篇
水利工程   750篇
石油天然气   926篇
武器工业   245篇
无线电   1790篇
一般工业技术   1971篇
冶金工业   915篇
原子能技术   249篇
自动化技术   4505篇
  2024年   120篇
  2023年   303篇
  2022年   572篇
  2021年   672篇
  2020年   793篇
  2019年   666篇
  2018年   623篇
  2017年   741篇
  2016年   857篇
  2015年   982篇
  2014年   1533篇
  2013年   1551篇
  2012年   1851篇
  2011年   1922篇
  2010年   1401篇
  2009年   1416篇
  2008年   1411篇
  2007年   1669篇
  2006年   1545篇
  2005年   1212篇
  2004年   1015篇
  2003年   916篇
  2002年   750篇
  2001年   566篇
  2000年   537篇
  1999年   405篇
  1998年   379篇
  1997年   318篇
  1996年   295篇
  1995年   234篇
  1994年   233篇
  1993年   141篇
  1992年   165篇
  1991年   118篇
  1990年   99篇
  1989年   78篇
  1988年   62篇
  1987年   42篇
  1986年   27篇
  1985年   25篇
  1984年   17篇
  1983年   11篇
  1982年   8篇
  1981年   10篇
  1980年   6篇
  1978年   7篇
  1964年   10篇
  1961年   6篇
  1960年   8篇
  1955年   13篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
塔里木盆地地热场特征与油气   总被引:2,自引:0,他引:2  
作者在收集了34口井的地温,部分井岩心和能谱测井资料的基础上,对塔里木盆地的地热场进行了研究,编制出盆地地温梯度图和深度分别为1000m、3000m、5000m的地温图。计算出盆地平均地温梯度为19.75℃/km,平均大地热流值为39.19mW/m~2,指出塔里木盆地地热场低于我国中、东部盆地,具“冷盆”性质。叶城凹陷地温梯度小于16℃/km,大地热流值为34.42mW/m~2,是盆内地热场最低之处,与前陆坳陷低地热场之特点一致。作者对塔里木盆地地热场特征进行分析后,得出了塔里木盆地最利于油气两种相态并存的结论。  相似文献   
72.
C/O测井中采用同步测量技术来分析非弹性γ与俘获γ,但在一些MSI C/O测井中发现非弹性γ的一小部分或一大部分超前于非弹性门而进入俘获门,我们把这一问题叫做“错位”。“错位”使得C/O的CI值不正常,测井曲线不合格。这样的仪器不能用来测井。吉林油田测井公司碳氧比维修班成功地解决了C/O仪器“错位”等技术难题,在该油田所使用的CZF90-94-09发生器已测井88口,累计打靶时间230h,并且至今  相似文献   
73.
连续时间广义边值系统被描述为Ex(t)=Ax(t)+Bu(t),V0x(0)+Vrx(T)=v,其中E是奇异方阵,u(t)满足任意次可微,本文讨论了一类连续时间广义边值系统的有关向内和向外边值过程的两个重要概念,并在此基础上给出了能控性和能观性定义和判别准则.  相似文献   
74.
油田开发经济运行质量研究与应用   总被引:1,自引:1,他引:0  
提出了油田开发经济运行质量的研究方法和技术思路。对胜利油区几种典型的油藏类型进行了经济运行质量评价。以老河口油田桩106块为例,提出了提高油田经济运行质量的三条基本途径,取得了较好的实际应用效果。  相似文献   
75.
In a field experiment on a deep pale-yellow sand in a 600 mm per annum rainfall Mediterranean environment of south-western Australia, six levels of phosphorus (P) as superphosphate (O up to 546 kg P ha–1) were applied once only, to the soil surface, before sowing lupins (Lupinus angustifolius). The lupins were grown in a continuous arable cropping rotation with, in successive years, oats (Avena sativa), wheat (Triticum aestivum), lupins. Five such rotations were started in the experiment from 1985 to 1989. The experiment continued until the end of 1990.The relationship between lupin seed (grain) yields and the level of P applied was measured in the year of P application for five successive years (1985 to 1989). The relationship had the same general form but it varied between years, largely due to different maximum yields (yield plateaux) in each year.The residual value of superphosphate applied three years previously was measured for lupins on two occasions (1988 and 1989) relative to superphosphate applied in the current year. The residual values was different in the two years. The superphosphate applied three years previously was about 30% as effective as freshly applied superphosphate in 1988, and 12% as effective in 1989.At each harvest, the relationship between grain yield and the P concentration in the grain differed for different species. However, for each species at each harvest, the relationship was similar regardless of when the P was applied in the previous years. Thus each species had the same internal efficiency of P use curve, and yields varied only with P concentration in tissue.Bicarbonate-extractable soil P was determined on soil samples taken in mid-July of 1989 and 1990. These soil test values were related to grain yields at harvest. The relationship between yield and soil test values had the same general form but varied for different species within years and for each species between years. It also varied for each species within years depending on the year the P was applied.  相似文献   
76.
为了准确地进行市场营销活动、提高营销组合4P的有效性,以顾客价值理论基础构建了旅客市场细分模型,定量描述了旅客对于交通工具的选择行为。  相似文献   
77.
Laura Meraz  Isaac Kornhauser 《Fuel》2003,82(12):1499-1507
Waste combustion is an interesting alternative for waste management and energy recovery. Knowledge of the waste higher heating value (HHV) is important for judging it’s worth as fuel. This work introduces a new equation, based on thermochemical concepts, to calculate HHV from elemental composition. This equation is expressed in terms of mass percentages on a dry basis of carbon (%C), hydrogen (%H), oxygen (%O), nitrogen (%N), and sulfur (%S); the HHV is computed in MJ/kg. The equation is as follows: HHV=(1−(%H2O/100))(−0.3708(%C)−1.1124(%H)+0.1391(%O)−0.3178(%N)−0.1391(%S)). The thermochemical concept on which this expression is based involves a wide applicability. This equation neglects the inorganic carbon, hence it is not very adequate when there is a significant concentration of it. The predictions from this approach were contrasted against those proceeding from equations currently used in combustion technology, and also against bomb calorimeter data. The new equation is clearly competitive with respect to other formulations, and it can be very helpful for presenting a waste HHV value based on different derivation suppositions.  相似文献   
78.
提出的图像信息融合方法用于解决传统方法在空间分辨率等方面的不足。原始图像经过小波变换,分解成子图像,再进行分块处理,高、低分辨率图像根据全局方差准则分别计算融合的权值系数,进行图像融合重建,然后,对图像采用全局法进行信息融合,实验表明,方法切实可行,能使低分辨率图像接近于高分辨率图像。  相似文献   
79.
The authors hypothesize that depressed states evolved to minimize risk in social interactions in which individuals perceive that the ratio of their social value to others, and their social burden on others, is at a critically low level. When this ratio reaches a point where social value and social burden are approaching equivalence, the individual is in danger of exclusion from social contexts that, over the course of evolution, have been critical to fitness. Many features of depressed states can be understood in relation to mechanisms that reduce social risk in such circumstances, including (a) hyper-sensitivity to signals of social threat from others, (b) sending signals to others that reduce social risks, and (c) inhibiting risk-seeking (e.g., confident, acquisitive) behaviors. These features are discussed in terms of psychosocial and neurobiological research on depressive phenomena. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
80.
改革开放使中国经济实现了持续高速的发展。然而,随着改革的不断深入,国有资产面临着在新经济环境下的角色转换,在此过程中由于各种原因每年有数百亿元的国有资产流失,所以,国有资产的保值增值成为现阶段乃至将来一段时间我国政府的重大经济课题。本文对国有资产的历史和现状进行了分析并从多角度提出了一些管理方面的看法。  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