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   5474篇
  免费   282篇
  国内免费   128篇
电工技术   204篇
技术理论   1篇
综合类   526篇
化学工业   403篇
金属工艺   97篇
机械仪表   250篇
建筑科学   577篇
矿业工程   174篇
能源动力   450篇
轻工业   187篇
水利工程   98篇
石油天然气   225篇
武器工业   355篇
无线电   616篇
一般工业技术   386篇
冶金工业   518篇
原子能技术   58篇
自动化技术   759篇
  2023年   50篇
  2022年   76篇
  2021年   108篇
  2020年   101篇
  2019年   122篇
  2018年   91篇
  2017年   90篇
  2016年   136篇
  2015年   149篇
  2014年   312篇
  2013年   363篇
  2012年   293篇
  2011年   462篇
  2010年   335篇
  2009年   311篇
  2008年   310篇
  2007年   409篇
  2006年   345篇
  2005年   300篇
  2004年   216篇
  2003年   231篇
  2002年   189篇
  2001年   126篇
  2000年   111篇
  1999年   105篇
  1998年   75篇
  1997年   53篇
  1996年   65篇
  1995年   54篇
  1994年   42篇
  1993年   29篇
  1992年   35篇
  1991年   19篇
  1990年   21篇
  1989年   9篇
  1988年   8篇
  1987年   13篇
  1986年   12篇
  1985年   7篇
  1984年   18篇
  1983年   10篇
  1982年   7篇
  1980年   5篇
  1966年   4篇
  1965年   7篇
  1963年   6篇
  1960年   5篇
  1958年   4篇
  1955年   3篇
  1954年   5篇
排序方式: 共有5884条查询结果,搜索用时 15 毫秒
1.
郭保玲  乔佳  董久樟  马旭卿  张雪娇 《煤气与热力》2021,(1):10036-10039,10046
研究美国城市燃气管道完整性管理体系(包括完整性管理法规及指南、完整性管理机构及职责以及支撑完整性管理实施的检查手册、开挖呼叫中心及信息化软件),分析完整性管理的成效。完整性管理的成效为:PE管应用不断增长、泄漏率明显下降、开挖损坏率下降。  相似文献   
2.
《工程爆破》2022,(3):79-81
以工程实践为基础,对深孔爆破的成本控制与施工方法、技术的关系进行了探讨。在不规则地形的情况下,有必要通过浅孔爆破进行平台的修正和根底的处理,使深孔台阶爆破处于良性循环中。把握好布孔、验孔、根底处理等主要工艺过程以及防止拒爆,是确保爆破安全、提高爆破质量和有效地控制成本的关键。  相似文献   
3.
Heat pipes and two-phase thermosyphon systems are passive heat transfer systems that employ a two-phase cycle of a working fluid within a completely sealed system. Consequently, heat exchangers based on heat pipes have low thermal resistance and high effective thermal conductivity, which can reach up to the order of (105 W/(m K)). In energy recovery systems where the two streams should be unmixed, such as air-conditioning systems of biological laboratories and operating rooms in hospitals, heat pipe heat exchangers (HPHEs) are recommended. In this study, an experimental and theoretical study was carried out on the thermal performance of an air-to-air HPHE filled with two refrigerants as working fluids, R22 and R407c. The heat pipe heat exchanger used was composed of two rows of copper heat pipes in a staggered manner, with 11 pipes per row. Tests were conducted at different airflow rates of 0.14, 0.18, and 0.22 m3/h, evaporator inlet-air temperatures of 40, 44, and 50°C, filling ratios of 45%, 70%, and 100%, and ratios of heat capacity rate of the evaporator to condenser sections (Ce/Cc) of 1 and 1.5. For HPHE's steady-state operation, a mathematical model for heat-transfer performance was set and solved using MATLAB. Results illustrated that the heat transfer rate was in direct proportion with the evaporator inlet-air temperature and flow rate. The highest HPHE's effectiveness was obtained at a 100% filling ratio and (Ce/Cc) of 1.5. The predicted and experimental values of condenser outlet-air temperature were in good agreement, with a maximum difference of 3%. HPHE's effectiveness was found to increase with the increase in evaporator inlet-air temperature and number of transfer units (NTU) and with the decrease in airflow rate, up to 33% and 20% for refrigerants R22 and R407c, respectively. Refrigerant R22 was the superior of the two refrigerants investigated.  相似文献   
4.
针对新形势下装备维修保障的优化问题,提出一种装备维修仿真系统的体系结构。分析部队维修保障过 程中关键要素之间的关系,阐述装备维修仿真系统的用户需求;以维修时间优化为例建立静态维修的任务分配优化 模型,设计动态维修条件下维修保障的过程模型,并采用层次分析法(analytic hierarchy process,AHP)和逼近理想解 排序法(technique for order preference by similarity to an ideal solution,TOPSIS)对不同维修分队的维修效能进行比较。 基于离散事件仿真库Simpy 实现了仿真系统的数据分析仿真功能,结合某型装备的维修保障数据进行了仿真验证, 仿真结果表明,该系统能为装备维修的流程设计、资源配置与优化等方面提供参考依据。  相似文献   
5.
The heat transfer effectiveness of nanofluids is adversely affected by the delay in convection onset. The lesser effectiveness, when compared to that of base fluid, is observed in a range of nanofluid layer thickness. The heat transfer coefficient of water–Al2O3 nanofluid can be enhanced by sustaining the equilibrium between Rayleigh number, temperature, particle volume fraction, and enclosure aspect ratio. In this paper, the specific correlation of fluid layer thickness and the onset of convection, which can significantly dominate the heat transfer characteristics of nanofluids are investigated using the concept of critical Rayleigh number. The water layer thickness for convection onset is first experimentally assessed for different real-life heat flux densities. It is then performed for Al2O3–water nanofluid for varying volume fractions. With the increase in volume fraction even though thermal conductivity increases, the overall heat transfer enhancement of the nanofluid is reduced. Temperature involved (heat flux density), the volume fraction of the nanofluid used, nanofluid layer thickness (space availability for the cooling system), and mass of the nanoparticle influence heat transfer enhancement. A higher volume fraction may not always result in enhancement of heat transfer as far as nanofluids are concerned.  相似文献   
6.
陶久亮 《兵工自动化》2022,41(3):45-51,55
为满足运载火箭测量系统对火箭各部段分离进行可视化拍摄的需求,提出一种运载火箭摄像装置视场有 效性仿真分析方法。以某型运载火箭发射任务为背景,针对不同的发射窗口,对火箭飞行全过程中摄像装置视场出 现太阳的时段进行统计,并对摄像装置的拍摄任务开展摄像装置视场有效性分析。结果表明:该方法可以为发射窗 口的制定提供依据,在不影响发射任务的前提下最大程度地保障摄像装置的视场有效性,具有较强的工程应用价值。  相似文献   
7.
结合项目当地具体气候条件,综合对比多种空调系统方案,从节能效果、初投资、运行费用等各方面计算分析,找到适合本项目的空调系统节能设计。空调设计从系统架构特点出发,利用备用机组的制冷能力,结合磁悬浮机组部分负荷效率高的优点,实际运行时冷水机组全部运行,主机负载率为70%~80%,磁悬浮主机的COP可达15以上,配合冷却塔优化选型及新型空调末端可将PUE降到1.3以下。  相似文献   
8.
This paper presents part of the work ComEd and Quanta Technology have performed to quantify the locational and temporal value of DER to avoid distribution grid upgrade investments. It focuses on the formulation of a robust and efficient algorithm for DER optimal dispatch on a distribution feeder to mitigate the violation of current and voltage limits using the allocated cost of capacity and locational marginal value of real and reactive DER injection/withdrawal.  相似文献   
9.
This paper offers an overall picture of the importance of Strategic Environmental Assessment (SEA) in Romania and its opportunities and constraints. The role, scope and effectiveness of SEA in Romania are presented in two good practice examples and examined in order to highlight the strengths and weaknesses of the procedure at national and local scale. In practice, the number of SEA procedures is very high due to the legislation in force, and it is increasingly effective in decision-making about programmes and plans. SEA can be viewed as a great opportunity for the implementation of sustainable development in practice. It also continues to be an important procedural and decisional instrument for management and monitoring of socioeconomic development, spatial planning and environmental protection in Romania.  相似文献   
10.
The paper presents the results of an evaluation of the effectiveness of SEA obtained as a result of a survey with the participation of stakeholders. In Poland, several hundred SEAs are conducted annually at the local and regional levels and several at the national level. Although the survey demonstrated that SEA is evaluated as effective or quite effective, the respondents pointed to several irregularities in the non-procedural dimension of effectiveness. The main ones in terms of substantive effectiveness are that SEA is rarely used to help develop plans/programmes and procedures are highly politicised. Moreover, low effectiveness in terms of variant assessment and cumulative impacts and nearly non-existent monitoring of the actual effects of implementing plans/programmes influence substantive effectiveness significantly. The respondents pointed to the problem resulting from the fact that plan-makers are unwilling to take into account the SEA recommended changes. They also emphasised that there are certain attempts to put pressure on SEA consultants to make the conclusions less stringent. Respondents indicate that in Poland the costs associated with conducting SEA often outweigh the profits. The research shows that the society is properly informed about SEA, but public involvement is still low.  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