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   79657篇
  免费   8922篇
  国内免费   4607篇
电工技术   12272篇
技术理论   13篇
综合类   5716篇
化学工业   8908篇
金属工艺   2584篇
机械仪表   3094篇
建筑科学   10285篇
矿业工程   2298篇
能源动力   13001篇
轻工业   2073篇
水利工程   3022篇
石油天然气   6620篇
武器工业   612篇
无线电   5344篇
一般工业技术   7529篇
冶金工业   3594篇
原子能技术   1277篇
自动化技术   4944篇
  2024年   435篇
  2023年   1687篇
  2022年   2774篇
  2021年   3131篇
  2020年   3304篇
  2019年   2944篇
  2018年   2468篇
  2017年   2927篇
  2016年   3263篇
  2015年   3257篇
  2014年   5382篇
  2013年   5106篇
  2012年   5797篇
  2011年   6486篇
  2010年   4923篇
  2009年   4992篇
  2008年   4538篇
  2007年   5047篇
  2006年   4192篇
  2005年   3302篇
  2004年   2720篇
  2003年   2354篇
  2002年   2075篇
  2001年   1775篇
  2000年   1523篇
  1999年   1276篇
  1998年   1011篇
  1997年   794篇
  1996年   747篇
  1995年   561篇
  1994年   466篇
  1993年   336篇
  1992年   262篇
  1991年   227篇
  1990年   189篇
  1989年   165篇
  1988年   126篇
  1987年   95篇
  1986年   65篇
  1985年   98篇
  1984年   83篇
  1983年   50篇
  1982年   71篇
  1981年   34篇
  1980年   47篇
  1979年   25篇
  1978年   13篇
  1977年   11篇
  1959年   5篇
  1951年   12篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
The objective of this paper is to identify and analyse factors that are important for winning acceptance of wind-energy parks on the local level. The developers of wind-energy parks need to know how to manage “social acceptance” at the different stages of planning, realisation and operation. Five case studies in France and Germany focused on factors of success in developing a wind-energy project on a given site and illuminated how policy frameworks influence local acceptance. Our hypothesis is that these factors fall into two categories: institutional conditions, such as economic incentives and regulations; and site-specific conditions (territorial factors), such as the local economy, the local geography, local actors, and the actual on-site planning process (project management).  相似文献   
122.
Current methods in alleviating the wall deposition problem in spray drying emphasize mainly controlling the stickiness of the drying particles and less attention is placed on the properties of the dryer wall. In this experimental study, the effect of wall surface properties on the deposition mechanism has been investigated. Properties considered in classifying different wall materials were surface energy, roughness, and dielectric properties. The model solution contained sucrose, representing low-molecular-weight sugars commonly encountered in spray drying of fruit and vegetable juices. The effect of wall properties on deposition was explored at different drying rates producing particles of different surface rigidity. Larger surface roughness produced higher deposition fluxes for particles with high impact velocity and moisture. Surface energy and surface roughness were found to have no significant effect for dry rigid particles at the middle and bottom elevation of the drying chamber. However, material with lower surface energy (Teflon) exhibited less deposition for rubbery particles at such elevations. Analysis shows that dielectric wall material (Teflon) tends to enhance deposition of dry particles because of attrition at the surface. Higher wall temperature was found to produce slightly more deposition. The results of this work give a general indication of the effect of wall material on the deposition problem and provide the fundamental understanding for further studies along this line. Proper selection of dryer wall material will provide potential alternatives for reducing the deposition problem.  相似文献   
123.
依据基准面旋回原理和方法,综合利用哈得逊地区的钻井、测井、地震以及地球化学资料,在研究区下石炭统识别出1个Ⅰ型和3个Ⅱ型层序界面,将哈得逊地区下石炭统划分为3个中期基准面旋回:SC1、SC2、SC3,对应于早石炭世海侵的3个海进-海退旋回.SC1旋回以滨岸砂坝沉积为主,而SC2、SC3旋回发育潮坪沉积体系.研究认为,SC1旋回滨岸砂岩及SC2下降半旋回的潮间带薄层砂岩为有利储集砂体,是地层-岩性型油气藏的重点勘探目标.  相似文献   
124.
Recent technological advances have made it possible to support long lifetime and large volume streaming data transmissions in sensor networks. A major challenge is to maximize the lifetime of battery-powered sensors to support such transmissions. Battery, as the power provider of the sensors, therefore emerges as the key factor for achieving high performance in such applications. Recent study in battery technology reveals that the behavior of battery discharging is more complex than we used to think. Battery powered sensors might waste a huge amount of energy if we do not carefully schedule and budget their discharging. In this paper we study the effect of battery behavior on routing for streaming data transmissions in wireless sensor networks. We first give an on-line computable energy model to mathematically model battery discharge behavior. We show that the model can capture and describe battery behavior accurately at low computational complexity and thus is suitable for on-line battery capacity computation. Based on this battery model we then present a battery-aware routing (BAR) protocol to schedule the routing in wireless sensor networks. The routing protocol is sensitive to the battery status of routing nodes and avoids energy loss. We use the battery data from actual sensors to evaluate the performance of our protocol. The results show that the battery-aware protocol proposed in this paper performs well and can save a significant amount of energy compared to existing routing protocols for streaming data transmissions. Network lifetime is also prolonged with maximum data throughput. As far as we know, this is the first work considering battery-awareness with an accurate analytical on-line computable battery model in sensor network routing. We believe the battery model can be used to explore other energy efficient schemes for wireless networks as well.  相似文献   
125.
Non-pinched, minimum energy solutions are important class of distillation designs that offer the potential advantage of a better trade-off between capital investment and operating costs. In this paper, two important tasks associated with non-pinched distillation designs are studied. Thus the novel contributions of this work to the literature are
(1) A comprehensive methodology for finding non-pinched minimum energy designs.
(2) Understanding of the reasons for the existence of non-pinched distillation designs.
It is shown that the recent shortest stripping line distance approach of Lucia et al. [Lucia, A., Amale, A. and Taylor, R., 2007, Distillation pinch points and more. Comput Chem Eng, available on-line] is capable of systematically and reliably finding non-pinched, minimum energy distillation designs. In addition, we provide an understanding of the reasons behind the existence of non-pinched designs, which include trajectories that follow unstable branches of a pinch point curve in azeotropic systems, the inherent looping structure of trajectories in hydrocarbon separations, and the presence of ancillary constraints in multi-unit processes like extraction/distillation. Several distillation examples are studied and many numerical results and geometric illustrations are presented that show the shortest stripping line distance methodology is indeed a powerful and systematic tool for computing non-pinched, minimum energy designs and that support the underlying reason we provide for the existence of non-pinched designs.  相似文献   
126.
苏北-南黄海盆地构造演化   总被引:13,自引:1,他引:12       下载免费PDF全文
杨琦  陈红宇 《石油实验地质》2003,25(Z1):562-565
苏北及南黄海盆地是由多期、多类盆地叠加的复合残留盆地,地质概况基本相似,成因演化近同,自元古界下扬子板块形成后,主要经历了古-中生代地台、中生代前陆盆地、走滑拉分盆地时期以及新生代断陷、坳陷盆地时期.在古生代-中生代发展过程中是一个整体,晚白垩世盆地演化出现分化,发育伸展盆地群,形成一系列叠置在中、古生代盆地之上的箕状断陷,箕状断陷的发育及分布明显受中-古生界内部先存逆冲断裂的控制.  相似文献   
127.
To meet Turkey’s growing energy demand, the installed electric power capacity of 27.8 GW in 2001 has to be doubled by 2010 and increased fourfold by 2020. The difference between Turkey’s total primary energy supply (TPES) of from its own sources and total final consumption (TFC) is projected grow from 1 quad (1.06–2.06) in 1999 to 5.71 quads (2.79–8.5) in 2020 (1 QUAD=293.071 TWh). Turkey’s limited amount of fossil fuels has a present average ratio of proved reserves of 97.38 quads to production rate of 3.2 quads yr−1 of about 30 years. Turkey’s reliance on fossil fuel-based energy systems to meet the growing demand is most likely to exacerbate the issues of energy insecurity, national environmental degradation, and global climate change in increasing proportions. Economically-feasible renewable energy potential in Turkey is estimated at a total of ca. 1.69 quads yr−1 (495.4 TWh yr−1) with the potential for 0.67 quads yr−1 (196.7 TWh yr−1) of biomass energy, 0.42 quads yr−1 (124 TWh yr−1) of hydropower, 0.35 quads yr−1 (102.3 TWh yr−1) of solar energy, 0.17 quads yr−1 (50 TWh yr−1) of wind energy, and 0.08 quads yr−1 (22.4 TWh yr−1) of geothermal energy. Pursuit and implementation of sustainability-based energy policy could provide about 90 and 35% of Turkey’s total energy supply and consumption projected in 2010, respectively. Utilization of renewable energy technologies for electricity generation would necessitate about 23.2 Mha (29.8%) of Turkey’s land resources.  相似文献   
128.
本文以中国铝业河南分公司电解厂85kA中间点式下料预焙槽为研究对象,通过6个月的低温电解实验,改善“四低一高”(低电解温度、低分子比、低氧化铝浓度、低效应系数和高极距)技术条件,优化工艺技术条件配置,降低分子比和电解温度,维护炉膛的规整,维护电解槽工作电压的稳定,规范员工作业标准,达到提高电流效率、降低电耗的节能效果。  相似文献   
129.
氧气合理利用决策支持系统和空分装置操作仿真系统   总被引:4,自引:0,他引:4  
童莉葛  王立  张延平  李化治  高远 《钢铁》2003,38(3):53-56
分析了钢铁企业空分系统能源管理的特点 ,并开发出降低空分能耗的应用软件 :氧气合理利用决策支持系统和空分装置操作仿真系统。前者可为决策者提供全面的辅助决策信息和决策支持以降低氧气放散 ,实现氧气的合理利用 ;后者既可实现空分装置运行操作的仿真 ,也可实现空分装置的仿真实验和仿真操作 ,为实施空分装置的节能优化运行提供技术支持  相似文献   
130.
介绍了基于西门子楼宇自控系统的空调计费系统的软硬件设计和具体实现.该系统的特点是借助西门子S600系统强大的数据处理和控制能力,采用时间记录和能量测量相结合的方法进行计费,具有实时监测和定时输出报表功能.该系统计量准确、计费合理、安全可靠、性价比高,满足了现代物业管理的需要.  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