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   314250篇
  免费   30364篇
  国内免费   18030篇
电工技术   28043篇
技术理论   11篇
综合类   35050篇
化学工业   32718篇
金属工艺   13231篇
机械仪表   25425篇
建筑科学   36779篇
矿业工程   13053篇
能源动力   12288篇
轻工业   20906篇
水利工程   13273篇
石油天然气   14101篇
武器工业   3833篇
无线电   20273篇
一般工业技术   34545篇
冶金工业   12520篇
原子能技术   4712篇
自动化技术   41883篇
  2024年   1305篇
  2023年   3780篇
  2022年   7506篇
  2021年   8801篇
  2020年   9576篇
  2019年   8124篇
  2018年   7930篇
  2017年   9974篇
  2016年   11474篇
  2015年   12085篇
  2014年   19679篇
  2013年   19266篇
  2012年   23752篇
  2011年   25167篇
  2010年   18781篇
  2009年   19236篇
  2008年   17867篇
  2007年   21768篇
  2006年   18983篇
  2005年   15891篇
  2004年   13272篇
  2003年   11359篇
  2002年   9378篇
  2001年   7769篇
  2000年   6743篇
  1999年   5697篇
  1998年   4647篇
  1997年   3993篇
  1996年   3320篇
  1995年   2870篇
  1994年   2497篇
  1993年   1821篇
  1992年   1669篇
  1991年   1192篇
  1990年   1011篇
  1989年   930篇
  1988年   712篇
  1987年   442篇
  1986年   390篇
  1985年   272篇
  1984年   311篇
  1983年   266篇
  1982年   235篇
  1981年   151篇
  1980年   125篇
  1979年   101篇
  1978年   60篇
  1977年   56篇
  1976年   54篇
  1959年   58篇
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
61.
The purpose of this paper is to extend recent results of Ljung and Priouret to a more general class of regressors.  相似文献   
62.
特征X射线能谱法测定Fe^+注入小麦种子的深度   总被引:5,自引:2,他引:3  
颉红梅  卫增泉 《核技术》1997,20(2):105-108
用110keV Fe^+离子束垂直注入小麦种胚后,在扫描电子显微镜上沿种子纵沟剖面,在不同深度上测量Fe元素被激发出的特征X射线强度分布,结果表明分布呈指数衰减,与晶体中的热扩散分布相类似,并对此进行了讨论。  相似文献   
63.
本文通过焊接试验对奥氏体不锈钢绕带容器环板与绕带焊接工艺进行了研究分析,并得出了合理的焊接方法和工艺参数。  相似文献   
64.
A method was developed to assess the heat insulation performance of intumescent coatings. The method consists of temperature measurements using the bench‐scaled experimental set‐up of a cone calorimeter and finite difference simulation to calculate the effective thermal conductivity dependent on time/temperature. This simulation procedure was also adapted to the small scale test furnace, in which the standard time–temperature curve is applied to a larger sample and thus which provides results relevant for approval. Investigations on temperature and calculated effective thermal conduction were performed on intumescent coatings in both experimental set‐ups using various coating thicknesses. The results correspond to each other as well as showing the limits of transferability between both fire tests. It is shown that bench‐scaled cone calorimeter tests are a valuable tool for assessing and predicting the performance of intumescent coatings in larger tests relevant for approval. The correlation fails for processes at surface temperatures above 750°C, which are not reached in the cone calorimeter, but are attained in the small scale furnace set‐up. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
65.
Power devices with high capability have been developed. 8‐kV/3.5‐kA‐class light‐triggered thyristors have the highest capability among power devices. These devices are used in the Kii Channel HVDC transmission system in Japan. In this paper, we report the extracted problems of conventional testing methods of 8‐kV/3.5‐kA‐class light‐triggered thyristors among manufacturers, and the proposed unified testing methods on the basis of element characteristics and operating conditions in the Kii Channel HVDC system. Furthermore, we propose a figure of merit for power devices for the practical use, and try to extract elements used at the Kii Channel HVDC system with small margins and low withstand capabilities. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(3): 61–70, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10024  相似文献   
66.
We consider a stochastic control problem with linear dynamics with jumps, convex cost criterion, and convex state constraint, in which the control enters the drift, the diffusion, and the jump coefficients. We allow these coefficients to be random, and do not impose any Lp-bounds on the control.

We obtain a stochastic maximum principle for this model that provides both necessary and sufficient conditions of optimality. This is the first version of the stochastic maximum principle that covers the consumption–investment problem in which there are jumps in the price system.  相似文献   

67.
Combined shape and sizing optimization of truss structures   总被引:1,自引:0,他引:1  
 In this paper, an evolutionary optimization method is presented for weight minimum problem of a 3-dimensional truss structure in terms of nodal coordinates and element cross-sectional areas. The structure is subject to stress, local buckling and displacement constraints. Two types of design variables with different natures are optimized separately: (1) a fully stressed design (FSD) and scaling techniques are applied to sizing variables and (2) the evolutionary node shift method is applied to shape variables. Alternating procedure is utilized to couple the two types of variables and to combine the results. The optimum solution is achieved gradually from the initial configuration design. Two typical truss structures are examined to illustrate the validity of the method. Received: 22 October 2001 / Accepted: 04 June 2002 This research work is supported by the National Natural Science Foundation of China under the guarantees no. 10072050 and 10172072, respectively.  相似文献   
68.
The effect of a range of organic additives on the thermal stability of poly(vinyl chloride), both with and without a chloroparaffin extender, was studied using a number of experimental techniques. Of the additives used the best overall balance was provided by pentaerythritol, which increased stability when the extender was present and had no effect when it was absent. The congo red test emerged as the most suitable technique, being consistent and inexpensive and able to screen several additives simultaneously. Isothermal differential thermal analysis correlated with the congo red test but required more expensive equipment, was time-consuming and demanded good mixing of the poly(vinyl chloride) compound to give reproducible results. Thermogravimetry was not sufficiently sensitive and the heat stability test was the least useful of all.  相似文献   
69.
前言银和其他贵金属元素一样,在地壳中比较稀少,按其自然丰度为第67号元素,平均含量仅0.07 ppm。由于地质样品成分非常复杂,为测定其微量银,必须进行严格的化学分离。但是迄今文献中报道的许多分离分法,步骤都相当冗长,一般采用氯化银反  相似文献   
70.
云南省水环境状况及问题分析   总被引:2,自引:0,他引:2  
黄英 《人民长江》2002,33(7):23-24
根据2000年云南省主要河流水质监测评价结果,全省评价河段总长9280km中,水质为Ⅰ-Ⅲ类的河长占76.3%,总体上,云南省内各大水系水质良好,但水污染总体上正在加重,从1985-2000年,Ⅰ类河长年均减少2.3%,V类河长年均增长0.6%,废污水直接排入江河是引起污染的重要原因。水环境问题已成为社会经济可持续发展的关键问题,要切实加强水资源的保护,科学地开发利用水土资源,为了有效地改善水环境的质量,污染控制应从源头开始并采取综合治理措施。  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