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   393949篇
  免费   29225篇
  国内免费   15850篇
电工技术   21315篇
技术理论   45篇
综合类   25513篇
化学工业   66869篇
金属工艺   21538篇
机械仪表   23230篇
建筑科学   29638篇
矿业工程   11829篇
能源动力   10753篇
轻工业   26880篇
水利工程   7197篇
石油天然气   23563篇
武器工业   2806篇
无线电   41343篇
一般工业技术   45363篇
冶金工业   25131篇
原子能技术   3899篇
自动化技术   52112篇
  2024年   1479篇
  2023年   5781篇
  2022年   10302篇
  2021年   14533篇
  2020年   10900篇
  2019年   9150篇
  2018年   10612篇
  2017年   11743篇
  2016年   10975篇
  2015年   14627篇
  2014年   18499篇
  2013年   23277篇
  2012年   24368篇
  2011年   27289篇
  2010年   23917篇
  2009年   22636篇
  2008年   22470篇
  2007年   21496篇
  2006年   21671篇
  2005年   19121篇
  2004年   13165篇
  2003年   11875篇
  2002年   11023篇
  2001年   9585篇
  2000年   9328篇
  1999年   9997篇
  1998年   7756篇
  1997年   6716篇
  1996年   6366篇
  1995年   5362篇
  1994年   4412篇
  1993年   3137篇
  1992年   2573篇
  1991年   1856篇
  1990年   1649篇
  1989年   1387篇
  1988年   1147篇
  1987年   880篇
  1986年   720篇
  1985年   677篇
  1984年   624篇
  1983年   482篇
  1982年   423篇
  1981年   357篇
  1980年   367篇
  1979年   314篇
  1978年   264篇
  1977年   248篇
  1976年   234篇
  1975年   200篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
黄河流域委属大河控制站站网布局分析检验与调整   总被引:4,自引:0,他引:4  
简要论述了黄河流域委属大河控制站的基本情况,通过资料分析,按“直线原则”计算了黄河大河控制站布站数目的上、下限,并调查分析落实了各河段近期和中长期治理开发对水资料的需求,确定各河段测站数目的采用值;对照现有站数,结合测站位置,功能,测验,生活条件等,逐段逐站进行审查,综合评估,决定测站的撤,迁,留,并对密度不足的河段提出了设站意见。  相似文献   
102.
Cif2000平台下的核磁共振测井解谱方法研究   总被引:3,自引:0,他引:3  
王才志  李宁 《测井技术》2002,26(5):360-363
介绍了在Cif2000多井解释平台下的核磁共振解谱方法与编程实现。解谱采用加入平滑因子后在特征矩阵的奇异值分解中截去小的非零奇异值的方法,可以在低信噪比时得到稳定的弛豫谱,在油田实际应用中证明了该方法的有效性。根据该方法在Cif2000平台上编制了完整的解谱处理程序,可以直接用于油田的生产实际。  相似文献   
103.
Assessed the efficiency of the peer review system during 3 National Science Foundation panel meetings held in 1982 and 1983. During these meetings, nearly 200 proposals received almost 1,400 reviews from "insiders" (panel members) and "outsiders" (ad hoc reviewers). Although the ratio of ad hoc time to panelist time was about 2:1, ad hoc reviewers' quantitative ratings had scant independent influence on final proposal ratings. Nevertheless, it may be that ad hoc reviewers provided crucial qualitative information, acting more as expert witnesses than as judges. The outcome of about a third of the proposals (the very good and the very poor) could be reliably predicted by independent panelist assessments that occurred before the panel meetings. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
104.
105.
试论会计电算化系统的内部控制   总被引:6,自引:0,他引:6  
阐述了会计电算化系统产生和发展对内产控制的影响,以及内部控制的实施方法。  相似文献   
106.
The formula and program for calculating the total and negative first harmonic interaction impedance from the data of “large perturbation measurement” are given. This program is a part of the programs for CCTWT design.  相似文献   
107.
Oxygen injection has been proposed and experimentally demonstrated as an effective control measure for limiting the rate of heat release and altering the rate of polymerization in emulsion processes. A detailed mathematical model has been previously developed to describe the system behavior with and without oxygen injection. A simple lab scale apparatus was constructed and run extensively. Only trace quantities of oxygen are needed to inhibit the reaction completely. The facile response makes this method attractive for fast temperature control. However, because of the rapid penetration of dissolved oxygen into the polymer particles, growing radical chains are terminated prematurely, lowering product molecular weights. To minimize this detrimental effect, pulsed oxygen control is used and extensive experimental work was performed to determine the effects of controller set points on molecular weight. Moderate oxygen flows and moderate set point temperatures are found to give the optimal response without significant lowering of the final molecular weight. Injected quantities agree well with the order-of-magnitude sparging calculations needed to completely stop initiation. However, complete agreement between model simulations and experimental results was not reached due to an unmeasured loss of monomer from the reactor. Chain transfer to monomer is found to be important in modeling the polymer molecular weight. It has, however, a negligible effect on the reaction rate.  相似文献   
108.
Intense irradiation (25–40 A/cm2) at intermediate energy (400 keV) has been found to cause “metallisation” of tungsten oxide and titanium niobate crystal surfaces. The possible mechanisms and the likely consequences for high-resolution imaging of clean oxide surfaces are briefly discussed.  相似文献   
109.
New fundamental solutions which automatically satisfy boundary conditions at the interfaces of an elastic plate perfectly bonded to two elastic halfspaces are implemented in a 3-D boundary element method (BEM) for crack problems. The BEM features a new integration scheme for highly singular kernels. The capability is achieved through a part analytic and part numerical integration procedure, such that the analytic part of the integration is similar for all slip/opening variations, ‘Part-through’ elliptic cracks in an elastic plate with traction-free surfaces are analysed and the stress intensity factor (SIF) values along the crack front are found to compare favourably with widely accepted numerically obtained SIF results by Raju and Newman.1  相似文献   
110.
ZnGa2O4纳米晶的制备和结构表征   总被引:2,自引:0,他引:2  
采用喷射共沉淀法制备了ZnGa2O4 纳米晶,XRD、SEM和TEM结构分析结果表明,喷射共沉淀法制备的ZnGa2O4的纳米晶颗粒细小均匀,形状完整,与化学共沉淀法相比,粒子尺寸明显减小,小于10nm,同时ZnO杂相峰消失,分析了喷射共沉淀法的机理,并对实验结果进行了解释。  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