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   359887篇
  免费   27308篇
  国内免费   15637篇
电工技术   21651篇
技术理论   11篇
综合类   23397篇
化学工业   53301篇
金属工艺   21007篇
机械仪表   21255篇
建筑科学   25496篇
矿业工程   9452篇
能源动力   9426篇
轻工业   23655篇
水利工程   7464篇
石油天然气   15487篇
武器工业   2852篇
无线电   41689篇
一般工业技术   45368篇
冶金工业   14463篇
原子能技术   3375篇
自动化技术   63483篇
  2024年   1361篇
  2023年   4566篇
  2022年   8814篇
  2021年   12069篇
  2020年   9144篇
  2019年   7265篇
  2018年   21571篇
  2017年   22060篇
  2016年   17440篇
  2015年   12482篇
  2014年   15135篇
  2013年   17826篇
  2012年   23155篇
  2011年   30175篇
  2010年   27185篇
  2009年   23539篇
  2008年   24376篇
  2007年   24462篇
  2006年   16322篇
  2005年   14350篇
  2004年   10211篇
  2003年   8988篇
  2002年   7981篇
  2001年   6754篇
  2000年   6167篇
  1999年   5609篇
  1998年   4243篇
  1997年   3552篇
  1996年   3292篇
  1995年   2821篇
  1994年   2296篇
  1993年   1574篇
  1992年   1281篇
  1991年   994篇
  1990年   725篇
  1989年   627篇
  1988年   496篇
  1987年   340篇
  1986年   254篇
  1985年   135篇
  1984年   100篇
  1983年   72篇
  1982年   94篇
  1981年   80篇
  1980年   74篇
  1968年   50篇
  1965年   48篇
  1959年   49篇
  1955年   63篇
  1954年   68篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
南化大化肥硝铵库工程 ,于 2 0 0 0年 2月 15日开工 ,2 0 0 0年 10月 10日竣工 ,混凝土杯形基础 ,主体结构为单层、单跨、装配式的排架结构 ,30m预应力折线形屋架 ,大型屋面板 ,氯化聚乙烯防水卷材 ,建筑面积为 162 0m2 。氯化聚乙烯防水卷材是防水新型材料 ,由于防水性能好 ,施工方便 ,近几年得到了广泛的应用 ,在实际操作中往往由于施工人员对操作规程不甚了解 ,或虽有所了解 ,但没有认真对待 ,造成这样那样的质量问题 ,硝铵库作为一个储物库房 ,对防渗漏的要求高 ,那么施工中怎样避免出现渗漏现象 ,确保工程质量呢 ?1 做好施工准备检…  相似文献   
12.
13.
In this paper, a localized MEI method (L-MEI) is developed and combined with the domain decomposition method (DDM) for the simulation of scattering by a concave cylinder. In the L-MEI, the whole domain is decomposed into many subdomains. Different from the conventional MEI method, the MEI coefficients of the L-MEI method in each subdomain are only dependent on the localized metrons that are defined in the subdomain. The localization of metrons has the following advantages: (1) speeding up the calculation of MEI coefficients and saving memory, (2) making the MEI method available for concave structures, and (3) obtaining a band sparse matrix directly without any modification  相似文献   
14.
This study empirically examined the organisational learning effects of the nonfinancial performance information provided by management accounting information systems (MAISs) under advanced manufacturing technology (AMT). In this study, a target costing system and the frequent and quick reporting of information were considered the facilitators of learning. First, we examined the relationships between AMT level and the amount of nonfinancial performance information produced by MAISs. The empirical results showed that there are significant positive relationships between the level of AMT and nonfinancial performance information. With a systems approach, we also proved the impact of the relationships among AMT levels, nonfinancial performance information and learning facilitators on the organisational performance of a firm. The results of our research suggest that under a high level of AMT, for the provision of information to result in an increase of performance through organisational learning, a target costing system must be introduced and a large amount of information should be provided frequently and quickly. The results of this study also showed that although AMT level may be low, fairly well-arranged facilitators and a moderately large amount of information may be necessary for the improvement of performance. In conclusion, effective organisational learning depends on the provision of relevant information as well as efficient learning support mechanisms.  相似文献   
15.
16.
The hot blow forming of magnesium sheet offers significant opportunity for forming complex, lightweight parts for automotive applications. This paper characterizes the elevated-temperature formability of AZ31 magnesium sheet materials and the effect of processing conditions on the performance of these materials. In addition, magnesium sheet application development at General Motors Corporation is reviewed.  相似文献   
17.
Strength of ground ceramics may be affected by residual stress as well as surface flaws induced by grinding. Strength prediction for ground ceramics is convenient for mechanical design of ceramic components. In this article, a numerical procedure based on fracture mechanics was proposed to estimate strength distribution of ground ceramics by considering grinding-induced residual stress. Bending strength and residual stress of ground ceramics were measured for three grinding-conditions. By comparison of simulated results with experimental ones, it was revealed that strength characteristics in experiments were well simulated by using the proposed procedure.  相似文献   
18.
19.
通过2-取代苯并咪唑盐的还原开环反应制备了8个N,N′-不同取代的邻苯二胺,并经1HNMR、IR、MS及元素分析表征,其中5个未见文献报道.这是一条由邻苯二胺和羧酸经2.取代苯并咪唑制取该类化合物的简洁合成路线.  相似文献   
20.
A novel cholesterol‐imprinted polymer (CMIP‐H) was prepared by a hybrid method of covalent imprinting and non‐covalent imprinting. This approach involves the copolymerization of a template‐containing monomer, cholesteryl 2‐hydroxyethyl methacrylate carbonate, and a cross‐linker, followed by hydrolysis to afford a flexible guest‐binding site accompanied with the easy and efficient removal of a ‘sacrificial spacer’. The effect of solvent on the binding capacity of CMIP‐H towards cholesterol was studied, indicating that a good binding capacity towards cholesterol could be achieved in a less‐polar solvent. The binding experiments of CMIP‐H towards a series of structural analogues of cholesterol, including cholesterol acetate, progesterone and stigmasterol, were carried out in hexane. The results showed that CMIP‐H almost did not bind cholesterol acetate at all because the hydrogen‐bonding site is blocked. It exhibited a similar binding towards both cholesterol and stigmasterol, but much higher binding towards progesterone. Copyright © 2005 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