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   41630篇
  免费   2337篇
  国内免费   119篇
电工技术   477篇
综合类   235篇
化学工业   9912篇
金属工艺   778篇
机械仪表   917篇
建筑科学   1494篇
矿业工程   112篇
能源动力   1343篇
轻工业   6820篇
水利工程   361篇
石油天然气   225篇
武器工业   6篇
无线电   2846篇
一般工业技术   6058篇
冶金工业   6827篇
原子能技术   281篇
自动化技术   5394篇
  2024年   76篇
  2023年   260篇
  2022年   998篇
  2021年   1821篇
  2020年   962篇
  2019年   1027篇
  2018年   1177篇
  2017年   1276篇
  2016年   1293篇
  2015年   1025篇
  2014年   1484篇
  2013年   2360篇
  2012年   2118篇
  2011年   2629篇
  2010年   1934篇
  2009年   1975篇
  2008年   1789篇
  2007年   1614篇
  2006年   1270篇
  2005年   1184篇
  2004年   1237篇
  2003年   1127篇
  2002年   1066篇
  2001年   860篇
  2000年   665篇
  1999年   678篇
  1998年   2156篇
  1997年   1450篇
  1996年   1039篇
  1995年   685篇
  1994年   537篇
  1993年   600篇
  1992年   291篇
  1991年   327篇
  1990年   272篇
  1989年   230篇
  1988年   240篇
  1987年   195篇
  1986年   204篇
  1985年   222篇
  1984年   167篇
  1983年   117篇
  1982年   134篇
  1981年   141篇
  1980年   136篇
  1979年   116篇
  1978年   97篇
  1977年   154篇
  1976年   235篇
  1975年   96篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
111.
112.
In this paper we describe the effect of the vicinity of a liquid3He-vacuum interface on the behavior of a vibrating wire viscometer. It was found that in the fluid near the liquid interface the quality factor is lower than in the bulk liquid. We further report on the observation of a doubling of the resonance peak of the wire in a saturated3He-4He mixture. The frequencies and amplitudes of the two peaks strongly depend on the distance between the phase boundary and the vibrating wire; the temperature and the velocity of the phase boundary have no significant influence on the peak frequencies. The observed peak doubling is attributed to the coupling of the vibrating wire with a standing second-sound wave in the dilute phase where the volume of the dilute phase can be regarded as a resonating cavity for second sound.  相似文献   
113.
114.
115.
主要介绍了Honeywell公司TPS系统在直纺涤纶长丝用骤冷风空调装置中的应用。重点说明了该系统的硬件配置和一些复杂控制回路的实施和组态。  相似文献   
116.
Maes  W. de Meyer  K. Dupas  L. 《Electronics letters》1985,21(11):490-491
Classical parameter-extraction programs rely on the minimisation of the relative current deviation. However, since, especially for analogue applications, the slope of the IDS/VDS curve in the saturation region is at least equally important, a new fit strategy has been developed. This new fit strategy extracts a parameter set which optimises the current residual as well as the slope residual at every point.  相似文献   
117.
118.
FILIP (fuzzy intelligent learning information processing) system is designed with the goal to model human information processing. The issues addressed are uncertain knowledge representation and approximate reasoning based on fuzzy set theory, and knowledge acquisition by “being told” or by “learning from examples”. Concepts that can be “learned” by the system can be imprecise (fuzzy), or the knowledge can be incomplete. In the latter case, FILIP uses the concept of similarity to extrapolate the knowledge to cases that were not covered by examples provided by the user. Concepts are stored in the Knowledge Base and employed in intelligent query processing, based on flexible inference that supports approximate matches between the data in the database and the query.

The architecture of FILIP is discussed, the learning algorithm is described, and examples of the system's performance in the knowledge acquisition and querying modes, together with its explanatory capabilities are shown.  相似文献   

119.
BACKGROUND: Xylitol bioproduction from lignocellulosic residues comprises hydrolysis of the hemicellulose, detoxification of the hydrolysate, bioconversion of the xylose, and recovery of xylitol from the fermented hydrolysate. There are relatively few reports on xylitol recovery from fermented media. In the present study, ion‐exchange resins were used to clarify a fermented wheat straw hemicellulosic hydrolysate, which was then vacuum‐concentrated and submitted to cooling in the presence of ethanol for xylitol crystallization. RESULTS: Sequential adsorption into two anion‐exchange resins (A‐860S and A‐500PS) promoted considerable reductions in the content of soluble by‐products (up to 97.5%) and in medium coloration (99.5%). Vacuum concentration led to a dark‐colored viscous solution that inhibited xylitol crystallization. This inhibition could be overcome by mixing the concentrated medium with a commercial xylitol solution. Such a strategy led to xylitol crystals with up to 95.9% purity. The crystallization yield (43.5%) was close to that observed when using commercial xylitol solution (51.4%). CONCLUSION: The experimental data demonstrate the feasibility of using ion‐exchange resins followed by cooling in the presence of ethanol as a strategy to promote the fast recovery and purification of xylitol from hemicellulose‐derived fermentation media. Copyright © 2008 Society of Chemical Industry  相似文献   
120.
From visual data exploration to visual data mining: a survey   总被引:8,自引:0,他引:8  
We survey work on the different uses of graphical mapping and interaction techniques for visual data mining of large data sets represented as table data. Basic terminology related to data mining, data sets, and visualization is introduced. Previous work on information visualization is reviewed in light of different categorizations of techniques and systems. The role of interaction techniques is discussed, in addition to work addressing the question of selecting and evaluating visualization techniques. We review some representative work on the use of information visualization techniques in the context of mining data. This includes both visual data exploration and visually expressing the outcome of specific mining algorithms. We also review recent innovative approaches that attempt to integrate visualization into the DM/KDD process, using it to enhance user interaction and comprehension.  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