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   45224篇
  免费   5142篇
  国内免费   3990篇
电工技术   4169篇
技术理论   2篇
综合类   7335篇
化学工业   2014篇
金属工艺   973篇
机械仪表   3405篇
建筑科学   2901篇
矿业工程   936篇
能源动力   1077篇
轻工业   2496篇
水利工程   1096篇
石油天然气   1033篇
武器工业   562篇
无线电   6794篇
一般工业技术   4001篇
冶金工业   990篇
原子能技术   608篇
自动化技术   13964篇
  2024年   220篇
  2023年   631篇
  2022年   1110篇
  2021年   1211篇
  2020年   1227篇
  2019年   1076篇
  2018年   1109篇
  2017年   1338篇
  2016年   1484篇
  2015年   1621篇
  2014年   2538篇
  2013年   2735篇
  2012年   3238篇
  2011年   3514篇
  2010年   2695篇
  2009年   2863篇
  2008年   3008篇
  2007年   3505篇
  2006年   3068篇
  2005年   2736篇
  2004年   2273篇
  2003年   1867篇
  2002年   1503篇
  2001年   1305篇
  2000年   1091篇
  1999年   910篇
  1998年   718篇
  1997年   637篇
  1996年   580篇
  1995年   494篇
  1994年   431篇
  1993年   310篇
  1992年   268篇
  1991年   228篇
  1990年   205篇
  1989年   177篇
  1988年   119篇
  1987年   68篇
  1986年   40篇
  1985年   36篇
  1984年   30篇
  1983年   33篇
  1982年   24篇
  1981年   12篇
  1980年   16篇
  1979年   10篇
  1978年   6篇
  1977年   6篇
  1976年   8篇
  1965年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
常彦勋 《通信学报》1994,15(1):62-65
本文讨论了M序列的自相关性,并证明了:当0<|t-2^n-1|≤[n-1/2]时,|CM(t)|≤2^n-1。  相似文献   
72.
介绍了KJ19型煤矿安全监控系统组成、功能及使用效果。  相似文献   
73.
关于Vague集的模糊熵及其构造   总被引:17,自引:3,他引:14  
本文分析了Vague集的性质,给出了将Vague集变换为Fuzzy集的转换函数,并讨论了其性质。分析了关于Vague集的模糊熵的直观特性,在此基础上我们给出了Vague集的模糊熵的定义。最后给出了一个关于Vague集的模糊熵的构造方法。  相似文献   
74.
AN EXTENDED MODELING OF TIDE-WAVE MOTION   总被引:1,自引:1,他引:0  
1 . INTRODUCTIONTostudythemotionofthetide waves,theshallowwaterequations ,i.e .theverticalintergra tionofthecontinuityequationandmomentumequa tion ,isconsideredasthegoverningequations.Byaboveequationstwoequationsrelatedtothehorizon talfluxofthetide currentsa…  相似文献   
75.
国内现行规范、标准是以极限变形值作为土钉支护结构水平位移安全监测报警值 ,但没有反映工程进度影响 ,不便指导工程实践。提出“过程控制”概念 ,以反正切函数为基本形式 ,基于历史经验建立“安全时程曲线”控制模型 ,要求施工过程中实测水平位移始终处在“安全时程曲线”之下 ,以确保最终变形在某一适当的阈值之内 ,已有实测结果可以为施工方案调整提供依据。通过实际案例 ,检验模型的可行性 ,表明过程控制模型较极限变形策略更具可操作性  相似文献   
76.
1 Introduction The calling dwell time characteristic is critical for the user network planning and deployment, e.g., global system for mobile communications (GSM), as well as the next generation wireless multimedia networks, such as, the currently standar…  相似文献   
77.
Linear Modulated Frequency (LMF) Costas Stepped Frequency Radar (SFR) signal is introduced. Its ambiguity function is derived and analyzed in detail and its feasibility is validated in theory. The scheme of the proposed signal processing is also presented. The results of theoretic analysis and simulation show that, by using the proposed signal and increasing the bandwidth of the total stepped frequency, the ambiguity sidelobe is well suppressed and the range-velocity coupling in the stepped frequency radar is also greatly weakened.  相似文献   
78.
Electroconsolidation® is a process for densifying complex-shaped parts by using electrically conductive particulate solids as a pressure-transmitting medium. The part is immersed in a bed of the particulate medium contained in a die chamber. Sintering temperature is achieved by resistive heating of the medium while applying compaction pressure. The process is capable of ultrahigh temperatures and short cycle times and offers the potential for low processing costs.

Control of the process and selection of process conditions require knowledge of the temperatures within the die. Temperature gradients exist because of the high heating rate and because of variations of density and electrical resistivity of the medium due to the presence of the part. Direct measurement of temperature with thermocouples or other conventional means is impractical because of the high temperatures, high currents, and high pressures that are involved. Therefore, a computer model was developed to predict temperature as a function of time and applied voltage for any location in the die. The computer model is composed of three parts: a geometrical model to approximate the density and resistivity variations in the medium, a finite-element model to calculate the rate of resistive heating within each element, and a finite-difference model to calculate the temperature distribution based on solution of the heat-transfer equations. Predicted temperatures have been shown to be in excellent agreement with measurements, and numerical simulation provided encouraging consistency and reasonably accurate predictions of temperature profiles within the die. The model demonstrated the feasibility of a new process to achieve simultaneous application of pressure and heat to powder densification in Electroconsolidation.  相似文献   
79.
小浪底水电厂位于多泥沙的黄河干流上,水轮机活动导叶会因磨损过大而严重漏水,在水轮机的设计上必须考虑这个因素;同时,为适应混水发电,小浪底水电厂机组采用了筒阀。文中介绍了筒阀的结构特点、功能及控制原理等,并对其在现场的实际应用情况进行了分析。  相似文献   
80.
A cook has to prepare n cakes using an oven with two racks. According to the recipe, the i-th cake has to be baked for exactly a i minutes. Cakes to be cooked are taken from a table and carried to the oven, and once cooked are carried back to the table by means of a trolley that can carry two cakes at a time. What is the minimum number q * of round trips required of the cook? This problem has application to the operation scheduling of transportation systems and to material cutting. A different problem arises according to whether the cook accepts or not to stay near the oven for awhile with the trolley. If the trolley cannot be idle at the oven, an optimum schedule with no oven idle-time always exists: consequently, the trolley schedule is trivial, and the problem is transformed into a set packing. For this case, we propose and test a heuristic method which generates all of the promising columns of the set packing, and solves the resulting problem by branch-and-bound. Instead, if the trolley can be idle at the oven for a limited amount of time, a problem arises to find an optimal schedule of the trolley: in this case we show how to use a scaling technique in order to obtain a very good feasible solution by the method above.  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