首页 | 官方网站   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   75535篇
  免费   8075篇
  国内免费   4205篇
工业技术   87815篇
  2024年   497篇
  2023年   1679篇
  2022年   2705篇
  2021年   2950篇
  2020年   3154篇
  2019年   2786篇
  2018年   2354篇
  2017年   2803篇
  2016年   3139篇
  2015年   3085篇
  2014年   5276篇
  2013年   4952篇
  2012年   5514篇
  2011年   6167篇
  2010年   4765篇
  2009年   4824篇
  2008年   4340篇
  2007年   4749篇
  2006年   3791篇
  2005年   2936篇
  2004年   2418篇
  2003年   2095篇
  2002年   1859篇
  2001年   1622篇
  2000年   1362篇
  1999年   1086篇
  1998年   872篇
  1997年   694篇
  1996年   627篇
  1995年   454篇
  1994年   404篇
  1993年   324篇
  1992年   245篇
  1991年   222篇
  1990年   185篇
  1989年   146篇
  1988年   121篇
  1987年   94篇
  1986年   66篇
  1985年   96篇
  1984年   82篇
  1983年   51篇
  1982年   70篇
  1981年   32篇
  1980年   42篇
  1979年   25篇
  1978年   13篇
  1977年   11篇
  1959年   5篇
  1951年   11篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
大同市节水型社会建设的探讨   总被引:1,自引:0,他引:1  
大同市是全国108个比较严重缺水城市之一,人均水资源量不足全国的1/10(全国人均水资源量2231m^3),稍超过全省的1/2(全省人均水资源量388m^3),市中心城区工农业及城市生活用水近20年来靠超采地下水来支撑。文中就大同市水资源供需不平衡的现状,提出大同市节水型社会建设的必要性,及今后水资源开源和节流的措施。  相似文献   
2.
The performance of the energy consumption of an electronic valve and a classical thermostatic valve has been compared when these expansion valves are adopted in a vapour compression plant subjected to a cold store. The main aim is to verify experimentally which type of expansion valve would be preferable from energy point of view when a classical thermostat or a fuzzy logic algorithm are used as the control system for the refrigeration capacity. The fuzzy logic‐based control is able to modulate continuously the compressor speed through an inverter. The results show that with a fuzzy algorithm, the thermostatic expansion valve allows an energy saving of about 8% in comparison with the electronic valve. When on–off control is used, the electric energy consumption obtained both with the electronic valve and with the thermostatic valve is comparable. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
3.
游梁式抽油机间歇供电装置的研制与应用   总被引:1,自引:0,他引:1  
针对游梁抽油机电动机效率低和井场窃电问题,研制了具有节电和防井场窃电功能的游梁抽油机调压+间歇供电装置。该装置通过控制可控硅的导通角实现在电动机做功期调压供电,在电动机发电期不供电。分析了间歇供电对电动机、抽油机和电网的影响;根据现场实测数据分析了该装置的节电效果及现场应用情况。该装置节电效果显著,能防止井场窃电,可用于对游梁抽油机电动机的长期驱动。  相似文献   
4.
用染料激光放大器的横向稳态泵浦理论,对不同的入射光能量选择不同的增益计算方法,研究了双级染料放大器的泵浦能量分配比例、泵浦光总能量和信号光能量大小对激光增益的影响。计算结果表明,对于其他参数确定的放大系统,存在着最佳的泵浦能量分配比例,可获得最大增益输出。通过自编程序的计算,可方便地找出特定系统泵浦能量分配比例的最佳值。  相似文献   
5.
Cs-K混合蒸气中Cs(8D)+K(4S)碰撞能量转移   总被引:3,自引:3,他引:0  
在Cs-K混合蒸气中,两步激发Cs原子到8D态,观察了Cs(8D) K(4S)→Cs(5D) K(4P)碰撞能量合并逆过程(REP,reverse energy pooling)。应用双调制技术探测K(4P)原子发射的荧光,基态K原子密度用光学吸收方法测量。得到了REP速率系数,讨论了其它过程对速率系数的影响.  相似文献   
6.
This paper presents a method to compensate voltage sags with minimum energy injection for a series‐connected voltage restorer using a micro‐SMES. A circuit for extracting the fundamental symmetrical components from sag voltages and a minimum energy injection algorithm is described. Simulations of voltage sag compensation have been carried out using PSCAD/EMTDC for various faults. The simulation results confirm the validity of the proposed method and show the possibility of reducing the size of energy storage devices. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(3): 70–80, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10047  相似文献   
7.
深穿透复合射孔技术在中原油田的应用   总被引:1,自引:0,他引:1  
深穿透复合射孔是一项把射孔与高能气体压裂两种技术有机地结合在一起的综合改造油气层的新技术。重点对它的技术原理,包括设计原理、枪身内火药燃烧气体对射孔孔眼的冲刷作用原理、火药燃烧气体射流的高能气体压裂作用原理等进行了研究与探讨,同时对它的施工工艺、现场应用等方面进行了阐述,经中原油田189口井现场应用证明,其工艺简便,成本低廉,可实现多层跨隔层使用,处理后增产效果显著,投入产出比高,可代替传统的聚能射孔技术,具有广阔的推广和应用价值。  相似文献   
8.
Energy taxation in Sweden is complicated and strongly guides and governs district energy production. Consequently, there is a need for methods for accurate calculation and analysis of effects that different energy tax schemes may have on district energy utilities. Here, a practicable method to analyse influence of such governmental policy measures is demonstrated. The Swedish Government has for some years now been working on a reform of energy taxation, and during this process, several interest groups have expressed their own proposals for improving and developing the system of energy taxation. Together with the present system of taxation, four new alternatives, including the proposed directive of the European Commission, are outlined in the paper. In a case study, an analysis is made of how the different tax alternatives may influence the choice of profitable investments and use of energy carriers in a medium‐sized district‐heating utility. The calculations are made with a linear‐programming model framework. By calculating suitable types and sizes of new investments, if any, and the operation of existing and potential plants, total energy costs are minimized. Results of the analysis include the most profitable investments, which fuel should be used, roughly when during a year plants should be in operation, and at what output. In most scenarios, the most profitable measure is to invest in a waste incineration plant. However, a crucial assumption is, with reference to the new Swedish waste disposal act, a significant income from incinerating refuse. Without this income, different tax schemes result in different technical solutions being most profitable. An investment in cogeneration seems possible in only one scenario. It is also found that particular features of some alternatives seem to oppose both main governmental policy goals, and intentions of the district heating company. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
9.
联产供冷与电力供冷能耗比较分析   总被引:5,自引:0,他引:5       下载免费PDF全文
文中将两种供冷能耗比较分解成用电煤耗差、用热煤耗量、增加产汽用电煤耗量三部分进行分析,按照热量法得出在目前一般情况下联产供冷比电力供冷通常费能和定性定量结论,为全面研究比较热电冷联产与分产的能耗奠定一个基础。  相似文献   
10.
The miscibility and phase behavior of ternary blends containing dimethylpolycarbonate (DMPC), tetramethylpolycarbonate (TMPC) and poly[styrene‐co‐(methyl methacrylate)] copolymer (SMMA) have been explored. Ternary blends containing polystyrene (PS) instead of SMMA were also examined. Blends of DMPC with SMMA copolymers (or PS) did not form miscible blends regardless of methyl methacrylate (MMA) content in copolymers. However, DMPC blends with SMMA (or PS) blends become miscible by adding TMPC. The miscible region of ternary blends is compared with the previously determined miscibility region of binary blends having the same chemical components and compositions. The region where the ternary blends are miscible is much narrower than that of binary blends. Based on lattice fluid theory, the observed phase behavior of ternary blends was analyzed. Even though the term representing the Gibbs free energy change of mixing for certain ternary blends had a negative value, blends were immiscible. It was revealed that a negative value of the Gibbs free energy change of mixing was not a sufficient condition for miscible ternary blends because of the asymmetry in the binary interactions involved in ternary blends. Copyright © 2004 Society of Chemical Industry  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-23

京公网安备 11010802026262号