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   27919篇
  免费   1220篇
  国内免费   108篇
电工技术   372篇
综合类   228篇
化学工业   4744篇
金属工艺   620篇
机械仪表   577篇
建筑科学   962篇
矿业工程   93篇
能源动力   928篇
轻工业   3825篇
水利工程   252篇
石油天然气   149篇
武器工业   6篇
无线电   2241篇
一般工业技术   4084篇
冶金工业   6224篇
原子能技术   237篇
自动化技术   3705篇
  2023年   137篇
  2022年   203篇
  2021年   774篇
  2020年   530篇
  2019年   595篇
  2018年   683篇
  2017年   763篇
  2016年   716篇
  2015年   549篇
  2014年   848篇
  2013年   1399篇
  2012年   1247篇
  2011年   1576篇
  2010年   1150篇
  2009年   1199篇
  2008年   1093篇
  2007年   956篇
  2006年   774篇
  2005年   831篇
  2004年   904篇
  2003年   810篇
  2002年   786篇
  2001年   696篇
  2000年   538篇
  1999年   525篇
  1998年   2032篇
  1997年   1319篇
  1996年   904篇
  1995年   595篇
  1994年   471篇
  1993年   528篇
  1992年   212篇
  1991年   277篇
  1990年   226篇
  1989年   191篇
  1988年   205篇
  1987年   157篇
  1986年   165篇
  1985年   179篇
  1984年   129篇
  1983年   90篇
  1982年   116篇
  1981年   120篇
  1980年   114篇
  1979年   91篇
  1978年   72篇
  1977年   138篇
  1976年   224篇
  1975年   81篇
  1973年   49篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
OBJECTIVE: To assess how often the aetiology is established in patients with uveitis, what systemic disease are found and what is the contribution of the internist to the diagnostic process. DESIGN: Retrospective study. SETTING: University Hospital Leiden, the Netherlands. METHOD: From January 1987 to April 1992, 342 patients presented with uveitis. All patients underwent a standard ophthalmological examination. Referral to an internist and individualised laboratory screening followed in patients with recurrent, chronic, bilateral or panuveitis. Recorded were: ophthalmological data, results of laboratory screening, results of analysis by the internist, final diagnosis and presence of systemic disease. RESULTS: 149 (44%) patients were examined by the internist, 18 (5.2%) were seen by another specialist. In 169 (49%) patients a specific diagnosis was made. 74 (22%) had a systemic disease, 74 a primary ocular disease. In 28 (8%) a systemic disease was presumed (5% were HLA-B27 positive, 3% had abnormal laboratory results); 5 (1%) patients had endophthalmitis as a complication of a septic process. CONCLUSION: In approximately 1/3 of the patients with uveitis a systemic disease was found. Examination by the internist tailored to the individual patient is essential in the evaluation of uveitis patients.  相似文献   
63.
64.
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   
65.
66.
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   
67.
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   
68.
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   
69.
Prevalence rates of trauma and posttraumatic stress disorder (PTSD) were estimated from a probability sample of 2,509 adults from 4 cities in Mexico. PTSD was assessed according to Diagnostic and Statistical Manual of Mental Disorders (American Psychiatric Association, 1994) criteria using the Composite International Diagnostic Interview (CIDI; WHO, 1997). Lifetime prevalence of exposure and PTSD were 76% and 11.2%, respectively. Risk for PTSD was highest in Oaxaca (the poorest city), persons of lower socioeconomic status, and women. Conditional risk for PTSD was highest following sexual violence, but nonsexual violence and traumatic bereavement had greater overall impact because of their frequency. Of lifetime cases, 62% became chronic; only 42% received medical or professional care. The research demonstrates the importance of expanding the epidemiologic research base on trauma to include developing countries around the world. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
70.
A digital signal processor-based control system for the permanent magnet-assisted reluctance synchronous machine, with the emphasis on dynamic performance, is proposed. A classical design approach is used to design the current and speed controllers for the machine. The stator current of the machine is controlled in such a way that the current angle in the dq synchronous reference frame is constant. The load-torque is estimated using a state space observer and compensation current based on the estimated load is used to improve the dynamic performance of the drive. The control system design is machine specific as it relies on data from finite-element analysis. Simulated and measured results on a 110-kW power level show that the resulting control system is stable and robust with good dynamic performance  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