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   59633篇
  免费   697篇
  国内免费   1229篇
电工技术   1034篇
技术理论   2篇
综合类   568篇
化学工业   5887篇
金属工艺   1773篇
机械仪表   3039篇
建筑科学   5107篇
矿业工程   2580篇
能源动力   449篇
轻工业   12074篇
水利工程   1955篇
石油天然气   1341篇
武器工业   201篇
无线电   3444篇
一般工业技术   16601篇
冶金工业   1290篇
原子能技术   547篇
自动化技术   3667篇
  2024年   121篇
  2023年   362篇
  2022年   433篇
  2021年   440篇
  2020年   331篇
  2019年   376篇
  2018年   395篇
  2017年   147篇
  2016年   253篇
  2015年   359篇
  2014年   680篇
  2013年   758篇
  2012年   5338篇
  2011年   6629篇
  2010年   1717篇
  2009年   1080篇
  2008年   4737篇
  2007年   4339篇
  2006年   3915篇
  2005年   3542篇
  2004年   2959篇
  2003年   2656篇
  2002年   2477篇
  2001年   1955篇
  2000年   1784篇
  1999年   1138篇
  1998年   658篇
  1997年   623篇
  1996年   550篇
  1995年   557篇
  1994年   527篇
  1993年   399篇
  1992年   545篇
  1991年   522篇
  1990年   602篇
  1989年   524篇
  1988年   610篇
  1987年   660篇
  1986年   594篇
  1985年   658篇
  1984年   632篇
  1983年   538篇
  1982年   578篇
  1981年   560篇
  1980年   415篇
  1979年   281篇
  1978年   180篇
  1976年   142篇
  1957年   123篇
  1955年   116篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
211.
212.
213.
214.
215.
The number of aerobic bacteria on the skin of pork carcasses was measured at seven different points on the slaughtering line in order to study the hygienic effect of pre-scalding brushing on the contamination level of carcasses. Eighty carcasses were investigated, of which 40 were brushed before scalding and 40 served as controls. Samples were excised from three sites: back, abdomen and ham. The total number of samples was 1368. The cleaning monitoring of the pre-scalding brushing machine and the blackscraping machine was done at the same time. After singeing and blackscraping there were significant differences (P<0·05) between brushed and non-brushed ham sites. After singeing, brushed ham sites had a contamination level of 2·11 (log(10) cm(-2)) and non-brushed ham sites a level of 1·57. After blackscraping the contamination of brushed ham sites was 3·45 (log(10) cm(-2)) and that of non-brushed ham sites 3·26. At the end of the slaughtering line brushed carcasses were more contaminated than those not brushed, although this difference was not significant.  相似文献   
216.
Correction schemes have been implemented to correct for T2 distortions in a multiexcitation RARE (rapid acquisition with relaxation enhancement) sequence where data from multiple echoes and multiple excitations are combined. Computer simulation studies and human imaging studies have been conducted to develop and test the correction procedures. A direct method and an iterative technique have been investigated. The direct technique utilizes Hermitian symmetry of the T2 weighted data and is shown to reduce distortions in T2 weighted images. The iterative scheme begins with an estimation of T2, wherefrom k-space data are computed and compared to the true data to provide error images. The error images are then used to refine iteratively the reconstructed images at a specified echo time. The iterative procedure has been used to improve T1 weighted images acquired through a sequence based on acquisition of two half-plane Fourier samples. These correction techniques should enable a practical implementation of RARE for producing T1 and T2 weighted images comparable to standard spin echo images.  相似文献   
217.
Ionic flow associated with neural activation of the brain produces a magnetic field, called the neuromagnetic field, that can be measured outside the head using a highly sensitive superconducting quantum interference device (SQUID)-based neuromagnetometer. Under certain conditions, the sources producing the neuromagnetic field can be localized from a sampling of the neuromagnetic field. Neuromagnetic measurements alone, however, do not contain sufficient information to visualize brain structure. Thus, it is necessary to combine neuromagnetic localization with an anatomical imaging technique such as magnetic resonance imaging (MRI) to visualize both function and anatomy in vivo. Using experimentally measured human neuromagnetic fields and magnetic resonance images, the authors have developed a technique to register accurately these two modalities and have applied the registration procedure to portray the spatiotemporal distribution of neural activity evoked by auditory stimulation.  相似文献   
218.
Consumer confidence is at its lowest ebb since 1980. Economic growth is at a standstill & unemployment & inflation are both rising. Here's a front-line report from more than three dozen operators who are fending off the recession's dual pressures of slow sales & rising costs. They are using discount pricing, partnering with vendors, setting pay for performance standards & a variety of other recession-beating practices.  相似文献   
219.
Estimation of phase aberrations using correlation processing between neighboring elements in a phased array is explored in the presence of inoperable elements. Using a CORDIC-based implementation of a complex baseband correlator, inactive elements can be identified simultaneous with correlation processing. Following detection of inoperable elements, a simple rerouting of the adaptive beam former is used to eliminate these elements from correlation analysis. Experimental results on a 3.33-MHz, 64-element array system with four contiguous, inactive elements demonstrate the robustness of the simple rerouting method for accurate phase aberration estimation.  相似文献   
220.
This study attempted to identify the major sources of work-related stress among telephone operators, with special emphasis on computer monitoring and telephone surveillance. A cross-sectional random sample of over 700 telephone operators participated in a questionnaire survey (response rate = 88%). The survey included items designed to measure perceived stress, management practices, specific job stressors and monitoring preferences. Call-time pressure items were most strongly linked to job stress by operators, with 70% reporting that difficulty in serving a customer well and still keeping call-time down contributed to their feelings of stress to a large or very large extent. About 55% of operators reported that telephone monitoring contributed to their feelings of job stress. If given the opportunity, 44% of operators stated they would prefer not to be monitored by telephone at all, while 23% stated they would prefer some monitoring; 33% had no preference. The setting of inappropriate individual-call-time objectives, which may be consistently unachievable for some operators and which create conflict between management demands for quantity and quality and also between workers values concerning quality and productivity demands, appears to be the most stress-inducing aspect of the job. In terms of telephone surveillance, the issues of timeliness and specificity of feedback appear to be less important than call-time pressure.  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