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   88486篇
  免费   1061篇
  国内免费   432篇
电工技术   1179篇
综合类   2333篇
化学工业   12815篇
金属工艺   4909篇
机械仪表   3143篇
建筑科学   2336篇
矿业工程   562篇
能源动力   1335篇
轻工业   4073篇
水利工程   1285篇
石油天然气   348篇
无线电   9482篇
一般工业技术   17118篇
冶金工业   2787篇
原子能技术   466篇
自动化技术   25808篇
  2022年   60篇
  2021年   96篇
  2020年   54篇
  2019年   67篇
  2018年   14500篇
  2017年   13422篇
  2016年   10040篇
  2015年   675篇
  2014年   369篇
  2013年   499篇
  2012年   3304篇
  2011年   9667篇
  2010年   8494篇
  2009年   5794篇
  2008年   7050篇
  2007年   8000篇
  2006年   309篇
  2005年   1417篇
  2004年   1294篇
  2003年   1322篇
  2002年   694篇
  2001年   198篇
  2000年   270篇
  1999年   150篇
  1998年   153篇
  1997年   99篇
  1996年   114篇
  1995年   63篇
  1994年   92篇
  1993年   77篇
  1992年   67篇
  1991年   97篇
  1990年   52篇
  1989年   77篇
  1988年   74篇
  1986年   73篇
  1985年   57篇
  1984年   53篇
  1983年   57篇
  1982年   60篇
  1981年   47篇
  1980年   42篇
  1979年   41篇
  1978年   41篇
  1968年   46篇
  1967年   40篇
  1966年   43篇
  1965年   44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
1.
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   
2.
3.
4.
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   
5.
This paper describes the dielectric breakdown characteristics of oil and oil‐impregnated paper for very fast transient (VFT) voltages. Blumlein circuits generate VFT voltages of 60 and 300 ns in a pulse width that simulates disconnecting switching surges in gas‐insulated switch gears. We measured the breakdown voltages of needle‐to‐plane, plane‐to‐plane oil gaps and several pieces of paper between plane electrodes for VFT and lightning impulse voltages. The measured data were formulated in V‐t characteristics and Weibull probability distributions. The inclination n of V‐t characteristics of insulating paper is 150, which is less than n = 13.7 of the plane‐to‐plane oil gap in the VFT time range. The shape parameters of Weibull distribution obtained in this study show that the scattering of breakdown voltages of paper is much less than that of oil. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(4): 16–24, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10043  相似文献   
6.
7.
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   
8.
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   
9.
Nanocrystalline LaFeO3 is prepared by the dehydration of coprecipitated lanthanum and iron(III) hydroxides. It is shown that the behavior of the samples during heating and the size distribution of LaFeO3 nanocrystals can be considerably different depending on the scheme used for coprecipitation of lanthanum and iron hydroxides; independently of the method employed for coprecipitation of the initial compounds, sintering of the samples at 950°C leads to the formation of lanthanum orthoferrite crystals up to 100 nm in size.  相似文献   
10.
Functionalized polyanilines containing biphenyl, terphenyl, carbazole, anthracene, and 4-n-hexylphenyl moieties were synthesized though the reaction of polyaniline in emeraldine base form with sodium salt of corresponding vinylketoaromatics with quantitative yields. Polymers were characterized with Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, and thermogravimetry. The emission characteristics of these polymers in N-methyl-2-pyrrolidone solution were examined. The functionalized polyanilines exhibited an intense green emission.  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