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   548026篇
  免费   6306篇
  国内免费   1835篇
电工技术   10451篇
综合类   415篇
化学工业   79801篇
金属工艺   21770篇
机械仪表   17268篇
建筑科学   11560篇
矿业工程   2705篇
能源动力   14840篇
轻工业   39022篇
水利工程   5511篇
石油天然气   9847篇
武器工业   24篇
无线电   68542篇
一般工业技术   109790篇
冶金工业   108429篇
原子能技术   11461篇
自动化技术   44731篇
  2021年   4744篇
  2020年   3634篇
  2019年   4698篇
  2018年   7918篇
  2017年   7884篇
  2016年   8393篇
  2015年   5378篇
  2014年   8955篇
  2013年   25826篇
  2012年   14472篇
  2011年   19544篇
  2010年   15621篇
  2009年   17780篇
  2008年   18357篇
  2007年   18159篇
  2006年   16394篇
  2005年   14855篇
  2004年   14256篇
  2003年   14042篇
  2002年   13389篇
  2001年   13531篇
  2000年   12671篇
  1999年   13447篇
  1998年   35233篇
  1997年   24098篇
  1996年   18608篇
  1995年   13788篇
  1994年   12113篇
  1993年   12058篇
  1992年   8561篇
  1991年   8136篇
  1990年   8039篇
  1989年   7646篇
  1988年   7161篇
  1987年   6136篇
  1986年   6120篇
  1985年   6855篇
  1984年   6216篇
  1983年   5624篇
  1982年   5139篇
  1981年   5340篇
  1980年   4816篇
  1979年   4649篇
  1978年   4609篇
  1977年   5375篇
  1976年   7028篇
  1975年   3968篇
  1974年   3765篇
  1973年   3781篇
  1972年   3208篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Research suggests that schizotypal personality disorder (SPD) is a part of the spectrum of schizophrenia-related illnesses. This article hypothesizes that a deficit in the representation and maintenance of context is a core cognitive disturbance in schizophrenia and that SPD individuals should demonstrate context-processing deficits. To test this hypothesis, the authors administered 3 versions of their AX-CPT task, designed to assess context processing, to 35 healthy controls and 26 individuals with DSM-IV SPD. They also administered working memory and selective attention tasks. SPD individuals displayed context representation deficits similar to those found in schizophrenia but did not show the same additional deficits in context maintenance. Context processing was strongly associated with working memory and selective attention performance in the SPD individuals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
82.
Fifty-eight commercial yogurt products of seven brands (which claimed to include bifidobacteria) were obtained from local stores in Greensboro, North Carolina, USA. These products were examined at 0, 1, 2, 3 and 4 weeks for the viability of bifidobacteria and yogurt starter culture during refrigerated storage at 4°C. Our results showed that bifidobacteria counts were variable, ranging from 0 to 5.5 log cfu/mL. The average yogurt starter culture counts ranged from 5.20 to 8.87 log cfu/mL and 7.51–8.94 log cfu/mL for Lactobacillus delbrueckii spp. bulgaricus and Streptococcus thermophilus , respectively. Of the 58 products tested, only 44 products (76%) contained viable cultures. Viability of bifidobacteria in yogurt samples remained within the same levels during 3 weeks of storage at 4°C; however, the bacterial count started to decline during the fourth week. These results suggest optimal beneficial consumption of yogurt foods with live bifidobacteria should occur within 3 weeks of production. Results obtained from this research could be used by the industry to develop new technologies to ensure consumers receive high-quality products.  相似文献   
83.
84.
 An efficient finite element model is presented for the static and dynamic piezothermoelastic analysis and control of FGM plates under temperature gradient environments using integrated piezoelectric sensor/actuator layers. The properties of an FGM plate are functionally graded in the thickness direction according to a volume fraction power law distribution. A constant displacement-cum-velocity feedback control algorithm that couples the direct and inverse piezoelectric effects is applied to provide active feedback control of the integrated FGM plate in a closed loop system. Numerical results for the static and dynamic control are presented for the FGM plate, which consists of zirconia and aluminum. The effects of the constituent volume fractions and the influence of feedback control gain on the static and dynamic responses of the FGM plates are examined. Received: 13 March 2002 / Accepted: 5 March 2003 The work described in this paper was supported by a grant awarded by the Research Grants Council of the Hong Kong Special Administrative Region, China (Project No. CityU 1024/01E).  相似文献   
85.
86.
In this work it is presented a study on the residence time distribution (RTD) of particles in a co-current pilot-plant spray dryer operated with a rotary atomization system. A nuclear technique is applied to investigate the RTD responses of spray dryers. The methodology is based on the injection of a radioisotope tracer in the feed stream followed by the monitoring of its concentration at the outlet stream. The experiments were performed during the drying of aqueous suspensions of gadolinium oxide. The RTD responses obtained experimentally presented good reproducibility, indicating that the technique applied is well suited to investigating fluid-dynamics of spray dryers. In addition to the experimental investigation, a mathematical model was used to describe the RTD experimental curves.  相似文献   
87.
While Fickian diffusion models are commonly used in other applications, there are few reports of them being applied to the batch drying of a mineral concentrate. Diffusion coefficients estimated from small-scale oven-drying tests were used to predict the drying behavior of a concentrate sample 1 m × 1 m in area and 50 cm deep, with a heated bottom pad. These pilot-scale tests included both daily turning of the sample and turning every three days. The excellent quantitative agreement between the predicted and observed pilot-scale behavior gives a high level of confidence in the model predictions and suggests that a Fickian diffusion model is adequate to predict the behavior of mineral concentrates at the low moisture contents used here.  相似文献   
88.
Support effects form important aspect of hydrodesulfurization (HDS) studies and mixed oxide supports received maximum attention in the last two decades. This review will focus attention on studies on mixed oxide supported Mo and W catalysts. For convenience of discussion, these are divided into Al2O3 containing mixed oxide supports, TiO2 containing mixed oxide supports, ZrO2 containing mixed oxide supports and other mixed oxide supports containing all the rest. TiO2 containing mixed oxides received maximum attention, especially TiO2–Al2O3 supported catalysts. A brief discussion about their prospects for application to ultradeep desulfurization is also included. An overview of the available literature with emphasis on research carried out in our laboratory form the contents of this publication.  相似文献   
89.
The scale along the coordinate axes in the equations of motion hitherto used for an H-maser (in relative units) is shown to depend on Q as the quality factor for an H-maser. This hinders both analysis of the operation of the H-maser and optimization of its parameters. The modified equations of motion proposed here do not have that shortcoming. We determine the atomic flux into the bulb that gives the H-maser the best metrological characteristics.  相似文献   
90.
The damage imposed on SiO x deposited nylon 6 films as a result of abrasion with a cotton cloth and Gelboflex testing was examined by evaluating the rate at which copper plates, which were enveloped by the damaged films, were corroded by H2S. Abrasion with a cotton cloth caused some micro-cracking of the SiO x layer and the permeation rate of H2S approached that of the uncoated nylon 6 film. Damage to the SiO x layer by twisting and crushing progressed gradually with the number of Gelboflex test cycles and correspondingly the corrosion rate of the copper plates increased. Comparison of the corrosion rates of the copper plates kept in the pouches made of various commercial films with those obtained for the damaged SiO x deposited nylon 6 films showed a clear relationship between the H2 permeation rate of the films and the corrosion rate of the copper plates by H2S.  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