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   139594篇
  免费   13756篇
  国内免费   7844篇
电工技术   9918篇
技术理论   15篇
综合类   10335篇
化学工业   21253篇
金属工艺   7730篇
机械仪表   8829篇
建筑科学   11446篇
矿业工程   4338篇
能源动力   4021篇
轻工业   10549篇
水利工程   3072篇
石油天然气   6994篇
武器工业   1440篇
无线电   17390篇
一般工业技术   15559篇
冶金工业   6092篇
原子能技术   1723篇
自动化技术   20490篇
  2024年   767篇
  2023年   2524篇
  2022年   4921篇
  2021年   6836篇
  2020年   5169篇
  2019年   3976篇
  2018年   4490篇
  2017年   4898篇
  2016年   4470篇
  2015年   6347篇
  2014年   7939篇
  2013年   9143篇
  2012年   10555篇
  2011年   11164篇
  2010年   9650篇
  2009年   9028篇
  2008年   8711篇
  2007年   7911篇
  2006年   7060篇
  2005年   5889篇
  2004年   4111篇
  2003年   3181篇
  2002年   2897篇
  2001年   2438篇
  2000年   2435篇
  1999年   2657篇
  1998年   2119篇
  1997年   1757篇
  1996年   1698篇
  1995年   1414篇
  1994年   1213篇
  1993年   841篇
  1992年   645篇
  1991年   490篇
  1990年   401篇
  1989年   355篇
  1988年   267篇
  1987年   181篇
  1986年   131篇
  1985年   90篇
  1984年   72篇
  1983年   44篇
  1982年   63篇
  1981年   44篇
  1980年   55篇
  1979年   29篇
  1976年   15篇
  1974年   11篇
  1959年   15篇
  1951年   14篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
23.
In this study, it is demonstrated that the incorporation of fluorine can enhance poly-Si/Si interfacial oxide break-up in the poly-Si emitter contacted p+-n shallow junction formation. The annealing temperature for breaking up the poly-Si/Si interfacial oxide has been found to be as low as 900°C. As a result, the junction depth of the BF2-implanted device is much larger than that of the boron-implanted device  相似文献   
24.
25.
The development and test of a PLC control program takes time, increases equipment down-time, and might damage hardware due to program errors. All of these problems can be eliminated if there is a computer simulation system for testing control programs off line. This paper presented a new method, called Direct Sequential Method, for simulating PLCs. This method resolves a ladder logic sequentially by applying a series of logic deductions. This simulation system has been implemented in C and tested successfully.  相似文献   
26.
Recently, Timmermann and Nowak developed algorithms for estimating the means of independent Poisson random variables. The algorithms are based on a multiscale model where certain random variables are assumed to obey a beta-mixture density function. Timmermann and Nowak simplify the density estimation problem by assuming the beta parameters are known and only one mixture parameter is unknown. They use the observed data and the method of moments to estimate the unknown mixture parameter. Taking a different approach, we generate training data from the observed data and compute maximum likelihood estimates of all of the beta-mixture parameters. To assess the improved performance obtained by the proposed modification, we consider a denoising application using Poisson data.  相似文献   
27.
Since most end-of-life electronics equipment contain hazardous materials such as lead solder alloys or lead-impregnated glass, it is important to divert them from landfills. For end-of-life products that are not repairable and do not contain reusable parts, bulk recycling is an alternative to recover base materials. In this paper, we contrast production and recycling planning and distribution decisions, activities, and costs. We reveal that while a traditional production facility connects suppliers and customers, a recycling facility connects both "input" and "output" customers. As a result, decisions in short-term bulk recycling planning include what products to accept, what products to process and reprocess, and what products to carry in inventory. Many recyclers set prices to receive "input" based on experience. For various prices to receive "input", we use a new analytical model to investigate the sensitivity of the short-term bulk recycling planning decisions in products from two different sources: industrial returns versus residential returns. The results of the case study show that different decisions are recommended for the industrial returns versus the residential returns when the total quantity of the incoming products is equal.  相似文献   
28.
In this paper, a new vectorial boundary element method is introduced and applied to the modal analysis of dielectric waveguides with piecewise homogeneous refractive indexes. The procedure, which is free of spurious modes, determines the full field distribution from the longitudinal fields at the refractive index boundaries. Singular kernels are evaluated through series solutions while the electric field discontinuity at corners is accommodated through either a grid refinement technique or a semianalytic approach. Our formalism generates propagation constants and modal field distributions for several representative refractive index profiles with far higher accuracy than standard finite-difference or finite-element procedures.  相似文献   
29.
30.
用差热、热重法对原丝的热性能及由不同预处理方法所引起的PVA纤维的热行为变化进行了研究;并通过模拟脱水条件,用不同升温速率,求出了经不同预处理纤维的脱水反应活化能。结果表明,PVA原丝在230℃有一软化点,三种预处理都不同程度地影响了原丝的热效应变化;纤维在180~340℃主要为脱水反应;原丝及经脱水剂、O_3和O_3综合脱水剂处理的纤维,其脱水反应的表观活化能分别为:164.3kJ/mol,92.9kJ/mol,130.5kJ/mol和117.6kJ/mol。  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