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   342895篇
  免费   31569篇
  国内免费   11375篇
电工技术   21373篇
技术理论   10篇
综合类   22045篇
化学工业   48288篇
金属工艺   20009篇
机械仪表   20101篇
建筑科学   23167篇
矿业工程   8232篇
能源动力   9297篇
轻工业   23860篇
水利工程   7380篇
石油天然气   12522篇
武器工业   2677篇
无线电   42436篇
一般工业技术   45003篇
冶金工业   13825篇
原子能技术   3443篇
自动化技术   62171篇
  2025年   249篇
  2024年   5289篇
  2023年   5061篇
  2022年   8385篇
  2021年   11488篇
  2020年   9012篇
  2019年   7261篇
  2018年   21039篇
  2017年   21388篇
  2016年   17293篇
  2015年   11589篇
  2014年   14192篇
  2013年   16983篇
  2012年   21962篇
  2011年   29260篇
  2010年   26335篇
  2009年   22751篇
  2008年   23741篇
  2007年   23924篇
  2006年   15237篇
  2005年   13165篇
  2004年   9377篇
  2003年   8078篇
  2002年   7309篇
  2001年   6020篇
  2000年   5188篇
  1999年   4446篇
  1998年   3421篇
  1997年   2877篇
  1996年   2637篇
  1995年   2195篇
  1994年   1757篇
  1993年   1283篇
  1992年   1024篇
  1991年   784篇
  1990年   618篇
  1989年   504篇
  1988年   406篇
  1987年   283篇
  1986年   245篇
  1985年   180篇
  1984年   136篇
  1983年   100篇
  1982年   102篇
  1981年   100篇
  1980年   93篇
  1979年   59篇
  1976年   64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 15 毫秒
1.
This study was undertaken to develop a modified atmosphere package to control microbial growth in ready‐to‐eat (RTE) products stored at ambient temperature. Ethanol and/or limonene associated with modified atmosphere (CO2 : O2 : N2 = 30% : 5% : 65%) was used to inhibit the growth of total air‐borne microorganisms and Escherichia coli in RTE products stored at 25°C. The results indicated that 0.05% ethanol vapour in the headspace was effective to inhibit the growth of air‐borne microorganisms and E. coli at 25°C for 72 h in a model study, and the effectiveness was related to ethanol content. Both 73 ppm limonene and 0.05% ethanol vapour enhanced the bacteriostatic effect of modified atmosphere in RTE sushi roll products, and no off‐flavour was detected using this formulated gas; however, no significant inhibitory effect was observed for RTE cold noodle products. This study concludes that combinations of carbon dioxide, ethanol or limonene vapours are effective to inhibit microbial growth in RTE food at ambient temperature, and the outcome may be due to the hurdle effect. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
2.
A new and interesting Pd-oxide-Al/sub 0.3/Ga/sub 0.7/As MOS hydrogen sensor has been fabricated and studied. The steady-state and transient responses with different hydrogen concentrations has been measured at various temperatures. Based on the large Schottky barrier height and presence of oxide layer, the studied device exhibits a high hydrogen detection sensitivity and wide temperature operating regime. The studied device exhibits the low-leakage current and obvious current changes when exposed to hydrogen-contained gas. Even at room temperature, a very high hydrogen detection sensitivity of 155.9 is obtained when a 9090 ppm H/sub 2//air gas is introduced. Furthermore, when exposed to hydrogen-contained gas at 95/spl deg/C, both the forward and reverse currents are substantially increased with increased hydrogen concentration. In other words, the studied device can be used as a hydrogen sensor under the applied bidirectional bias. Under the applied voltage of 0.35 V and 9090 ppm H/sub 2//air hydrogen ambient, a fast adsorption response time about 10 s is found. The transient and steady-state characteristics of hydrogen adsorption are also investigated.  相似文献   
3.
4.
The purpose of this paper is to evaluate two methods of assessing the productivity and quality impact of Computer Aided Software Engineering (CASE) and Fourth Generation Language (4GL) technologies: (1) by the retrospective method; and (2) the cross-sectional method. Both methods involve the use of questionnaire surveys. Developers' perceptions depend on the context in which they are expressed and this includes expectations about the effectiveness of a given software product. Consequently, it is generally not reliable to base inferences about the relative merits of CASE and 4GLs on a cross-sectional comparison of two separate samples of users. The retrospective method that requires each respondent to directly compare different products is shown to be more reliable. However, there may be scope to employ cross-sectional comparisons of the findings from different samples where both sets of respondents use the same reference point for their judgements, and where numerical rather than verbal rating scales are used to measure perceptions.  相似文献   
5.
本文用计算机数字模拟方法研究了电活性分子多层Z型L-B膜修饰电极的循环伏安行为。计算了电极与修饰L-B膜分子第一层之间的电荷转移速度常数K_o,L-B膜分子层间的电荷转移速度常数k_i;对峰电位差△E_p及阳极峰面积Q的影响,以及在不同条件下各层分子的氧化态分数随扫描时间的变化。为研究和设计电活性分子修饰电极的实际体系提供了大量数据和信息。  相似文献   
6.
7.
本文提出新型布线算法,集李氏迷宫法与线搜索法的长处为一体,以饱和带法进行动态排序,以线搜索法确定借孔位置,然后用李氏法进行单层布线,获得最佳路径,从而达到线型好,布通率高的效果。  相似文献   
8.
9.
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   
10.
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