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   63280篇
  免费   4977篇
  国内免费   2798篇
电工技术   3393篇
技术理论   6篇
综合类   4196篇
化学工业   10698篇
金属工艺   3987篇
机械仪表   3923篇
建筑科学   4856篇
矿业工程   2236篇
能源动力   2033篇
轻工业   3573篇
水利工程   1105篇
石油天然气   4630篇
武器工业   466篇
无线电   6598篇
一般工业技术   7363篇
冶金工业   3392篇
原子能技术   775篇
自动化技术   7825篇
  2024年   257篇
  2023年   1012篇
  2022年   1779篇
  2021年   2540篇
  2020年   1890篇
  2019年   1716篇
  2018年   1878篇
  2017年   2098篇
  2016年   1876篇
  2015年   2433篇
  2014年   3089篇
  2013年   3583篇
  2012年   3744篇
  2011年   4110篇
  2010年   3755篇
  2009年   3373篇
  2008年   3326篇
  2007年   3287篇
  2006年   3272篇
  2005年   2830篇
  2004年   2084篇
  2003年   2191篇
  2002年   2502篇
  2001年   2114篇
  2000年   1648篇
  1999年   1736篇
  1998年   1276篇
  1997年   1077篇
  1996年   1112篇
  1995年   858篇
  1994年   635篇
  1993年   470篇
  1992年   369篇
  1991年   276篇
  1990年   208篇
  1989年   167篇
  1988年   153篇
  1987年   88篇
  1986年   69篇
  1985年   37篇
  1984年   38篇
  1983年   27篇
  1982年   25篇
  1981年   14篇
  1980年   22篇
  1979年   4篇
  1978年   2篇
  1977年   2篇
  1974年   1篇
  1951年   2篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
Floor heave of a roadway is a dynamic phenomenon that often happens in the roadways of coal mines. It seriously affects safe production in the coal mine. Floor heave has long been one of the most difficult problems to be resolved during coal mining. An analysis of floor heave in the soft rock surrounding the roadway, and the factors influencing it, allowed the deformation mechanism in the west wing double track haulage roadway of the Tingnan Coal Mine to be deduced. Three types of floor heave are observed there: intumescent floor heave, extrusion and mobility floor heave, and compound floor heave. Control measures are proposed that have been adopted during a recent repair engineering project. Control of the floor heave in the west wing track haulage roadway was demonstrated. The reliability and rationality of a combined support technology including floor anchors, an inverted arch, and anchoring of both sides was verified by mine pressure data and the field observations. Waterproofing measures were also undertaken to assist in the control of floor heave.  相似文献   
942.
施高萍  郭晓梅  陈红亮 《水力发电》2012,38(1):84-86,90
结合浙江省某更新改造泵站,在三维湍流Navier-Stokes控制方程的基础上,采用标准k-ε模型和SIMPLEC算法,对不同叶片安装角的轴流泵内部全流道流场进行了数值模拟,分析讨论了不同安装角下的叶片静压分布图、叶片相对速度分布图,对轴流泵的扬程进行了预测,最后给出了该轴流泵合适的叶片安装角。  相似文献   
943.
蒲石河抽水蓄能电站下库蓄水对下游的影响   总被引:1,自引:0,他引:1  
为了确保蒲石河抽水蓄能电站工程按期投产发电,保证水库及电站初期蓄水和发电运行安全,就不同蓄水方案对下游各业用水部门的影响进行了分析。下游各行业用水的调查分析,为尽可能减轻水库初期蓄水影响,制定切实可行的电站初期下闸蓄水方案提供了技术支撑。  相似文献   
944.
蒲石河工程下水库大坝顶部混凝土护栏位于坝顶临空边沿,钢筋绑扎和模板支立作业难度大,施工时存在安全隐患。为此,蒲石河工程设计了移动台车栏板辅助浇筑系统并成功应用。实践表明,作业台车设计可靠、安全稳定、操作简便、定位准确、移动方便,保障了施工人员人身安全,节约了成本,加快了工期,提高了模板支立质量,值得类似工程借鉴并推广使用。  相似文献   
945.
简要介绍了蒲石河抽水蓄能电站南瑞SSJ-3000计算机监控系统的设计原则、系统结构与功能以及系统特点,该监控运行稳定可靠,完成了各种运行工况的任务要求,能适应大型抽水蓄能机组启停频繁、工况复杂的特点,功能达到设计要求,满足电站的监控要求。  相似文献   
946.
Hydrological Changes of the Irtysh River and the Possible Causes   总被引:2,自引:1,他引:1  
Hydrological changes of the Irtysh River were analyzed concerning the changes of annual runoff and its distribution features within a year measured by coefficient of variation and concentration degree. Abrupt changes were detected by the heuristic segmentation method. Possible causes of the hydrological changes were investigated considering climate changes and human activities (especially the reservoir operation). The Mann-Kendall method was applied to estimate whether the temperature and precipitation was changed. The increased precipitation in winter may increase the runoff of April. The increased temperature and the decreased precipitation in the flood season may decrease the runoff. At the middle reaches, the impact of the reservoirs at the upper reaches is significant and may be the main factor leading to the abrupt decreases in annual runoff and its intra-annual variability and concentration. The increased water surface area of the reservoirs aggravates the evaporation and leads to annual runoff reduction. The reservoirs regulate runoff by storing water in the flood season and releasing water in the dry season. While at the lower reaches, the annual runoff remained steady and its intra-annual variation and concentration were reduced gradually because the impact of the reservoirs is relative small and the climatic impact may be more relevant.  相似文献   
947.
An ecophysiological experiment was conducted to examine the biochemical effects of acidified seawater containing elevated concentration of CO(2) (C(CO2) 0.08, 0.20, 0.50 and 1.00%) on the copepod Centropages tenuiremis. AchE, ATPase, SOD, GPx, GST, GSH level and GSH/GSSG ratio of the copepod were analyzed. The results showed that elevated C(CO2) and the duration of culture time significantly influenced several biochemical indices in C. tenuiremis (ATPase, GPx, GST, GSH and SOD). Furthermore, the principal component analysis results indicated that 72.32% of the overall variance was explained by the first three principal components (GPx, SOD and GSH). Changes in GPx and GSH levels may play a significant role in the antioxidant defense of copepods against seawater acidification. The long-term response of copepods to seawater acidification and the synergistic effects of acidification with other environmental factors, such as temperature, salinity and trace metal need further investigation.  相似文献   
948.
Construction solid waste (CSW), an inescapable by-product of the construction and demolition process, was used as main substrate in a four-stage vertical subsurface flow constructed wetland system to improve phosphorus P removal from domestic wastewater. A 'tidal flow' operation was also employed in the treatment system. Under a hydraulic loading rate (HLR) of 0.76 m3/m2 d for 1st and 3rd stage and HLR of 0.04 m3/m2 d for 2nd and 4th stage of the constructed wetland system respectively and tidal flow operation strategy, average removal efficiencies of 99.4% for P, 95.4% for ammoniacal-nitrogen, 56.5% for total nitrogen and 84.5% for total chemical oxygen demand were achieved during the operation period. The CSW-based constructed wetland system presents excellent P removal performance. The adoption of tidal flow strategy creates the aerobic/anoxic condition intermittently in the treatment system. This can achieve better oxygen transfer and hence lead to more complete nitrification and organic matter removal and enhanced denitrification. Overall, the CSW-based tidal flow constructed wetland system holds great promise for enabling high rate removal of P, ammoniacal-nitrogen and organic matter from domestic wastewater, and transforms CSW from a waste into a useful material.  相似文献   
949.
结合某抽水蓄能电站地下厂房工程,建立全机组段地下厂房与洞室群的耦合地震反应时域数值仿真模型,考虑初始地应力、分部开挖与柔性支护以及岩体的材料弹塑性,分析了厂房混凝土结构的存在对洞室围岩的地震位移、速度、加速度、塑性区等反应特征的影响.结果表明,厂房混凝土结构与围岩的相互作用对洞室围岩的地震反应影响不大,对围岩塑性区的发展起到了一定的约束作用,有利于洞室的安全.  相似文献   
950.
赵立坤  郭书英 《中国水利》2012,(14):25-28,38
水利信息化是实现水利现代化的基础和重要标志。以水管理对象为基础,利用现代信息技术构造数字流域,集中管理流域内的水事问题,是实现流域现代化管理的有效途径。从数字流域体系架构、水管理对象构造及全息化描述、基础平台构建、业务系统的构件化开发、数字功能流域等方面详细介绍了基于水管理对象的数字流域构造技术方法。  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