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   20593篇
  免费   921篇
  国内免费   30篇
电工技术   171篇
综合类   18篇
化学工业   3976篇
金属工艺   331篇
机械仪表   322篇
建筑科学   634篇
矿业工程   33篇
能源动力   520篇
轻工业   2598篇
水利工程   131篇
石油天然气   44篇
无线电   896篇
一般工业技术   2796篇
冶金工业   6265篇
原子能技术   99篇
自动化技术   2710篇
  2023年   111篇
  2022年   349篇
  2021年   582篇
  2020年   349篇
  2019年   397篇
  2018年   652篇
  2017年   605篇
  2016年   637篇
  2015年   457篇
  2014年   644篇
  2013年   1103篇
  2012年   1033篇
  2011年   1179篇
  2010年   840篇
  2009年   798篇
  2008年   797篇
  2007年   689篇
  2006年   589篇
  2005年   512篇
  2004年   395篇
  2003年   379篇
  2002年   329篇
  2001年   244篇
  2000年   245篇
  1999年   330篇
  1998年   2077篇
  1997年   1176篇
  1996年   852篇
  1995年   463篇
  1994年   420篇
  1993年   425篇
  1992年   95篇
  1991年   126篇
  1990年   119篇
  1989年   123篇
  1988年   113篇
  1987年   108篇
  1986年   98篇
  1985年   87篇
  1984年   51篇
  1983年   57篇
  1982年   73篇
  1981年   83篇
  1980年   82篇
  1979年   30篇
  1978年   40篇
  1977年   147篇
  1976年   267篇
  1975年   26篇
  1973年   26篇
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
61.
Preparation of clean coal by flotation following ultra fine liberation   总被引:1,自引:0,他引:1  
This paper reports the results of current fundamental research at the Department of Process Engineering, University of Miskolc on the processing of clean coal from Mecsek bituminous coal, Southern Hungary. The theoretical possibility of the separation of different petrographic components was proven experimentally and their liberation degree was determined based on the petrographic composition, flotation kinetic study of isolated components (groups of components), scanning electron microscopy and microprobe analyses. The mill with stirred ball media was chosen for the ultra-fine liberation of the coal components. It was revealed that along with the liberation of coal components, their surface oxidation and spontaneous agglomeration, entrapping the mineral impurities take place in ultra-fine grinding. This paper discusses the interfacial phenomena occurring in the ultra-fine grinding process and their influence on the flotation. The concept for the advanced preparation of clean coal was developed, tested and proved. The main steps of this concept are the ultra-fine liberation in the stirred-media mill, the de-agglomeration of flocs spontaneously formed during the ultra-fine grinding and the induced (hydrophobic) flocculation with the following two-step flotation in a flotation column.  相似文献   
62.
An updated version of the semi‐discretization method is presented for periodic systems with a single discrete time delay. The delayed term is approximated as a weighted sum of two neighbouring discrete delayed state values and the transition matrix over a single period is determined. Stability charts are constructed for the damped and delayed Mathieu equation for different time‐period/time‐delay ratios. The convergence of the method is investigated by examples. Stability charts are constructed for 1 and 2 degree of freedom milling models. The codes of the algorithm are also attached in the appendix. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   
63.
64.
A hamster-human hybrid containing only the q arm of chromosome 2 has been used to construct a panel of hybrids bearing reduced regions of chromosome 2 using the technique of irradiation fusion gene transfer. The human chromosome 2 carried the Ecogpt gene and all hybrids were selected using this marker. The integrated Ecogpt gene was localized to the region 2q33-34, resulting in the selective retention of this region in the hybrids. These data were combined with another previously constructed panel of hybrids containing regions of 2q, which were enriched for the region 2q36-37. The combined hybrid panel is useful for the mapping of new markers to defined regions of chromosome 2 and for the cloning of genes located on 2q by a positional strategy.  相似文献   
65.
66.
BCG vaccination     
The author expounds the fairly obscure history of BCG vaccination. Summarises the efficiency of accomplished vaccinations of different geographical areas. He accounts the diversity of results by the distinction of technical and methodical conditions and disparity in virulence of BCG strains. Overviews the Inland and European routine and the risk of possible complications. The favourable position of domestic childhood tuberculosis is due to the effective preventive arrangements. Considering the international and national epidemiology of tuberculosis in adults the administration of BCG vaccine, by chance in modified form, is recommended further on.  相似文献   
67.
Subsequent to the implementation of a severity marker stamp in case notes, an audit was performed in 86 admissions with acute asthma to a specialist centre over a 12 month period. Compared to previous audit the documentation of severity markers was significantly better (PEFR: 52% vs 83% p = 0.001, Respiratory rate: 44% vs 81% p = 0.001, ABG: 72% vs 80% p = 0.04, air entry: 58% vs 86% p = 0.001, speech: 27% vs 86% p = 0.001, exhaustion: 4% vs 86% p = 0.001). In contrast to the previous audit where no patient received FiO2 > 0.35, 66% of the cases in the repeat audit received FiO2 0.60 (p = 0.001). The mean duration of admission was five days and showed highest partial correlation (r = 0.6) to the time in hours for the pulse to fall to 80/min. Multiple linear regression showed that this was the only variable best predicting the duration of admission (R2 = 0.3). Admission pulse rate (p = 0.04) and serum K+ (p = 0.04) best discriminated between patients admitted for over and under five days. Logistic regression identified only the admission pulse as significant in calculating the odds of the patient staying in the hospital for > 5 days.  相似文献   
68.
Fetus-in-fetu is an unusual condition in which a vertebrate fetus is enclosed within the abdomen of another fetus. These occurrences are usually benign. This report describes an instance of malignant recurrence after resection of a fetus-in-fetu.  相似文献   
69.
The past year has seen significant advances in our understanding of the mechanism of RNA movement between the nucleus and the cytoplasm. The emerging view is that proteins bind to and escort RNAs to their proper subcellular location. The discovery of peptide signals that target nuclear export and the identification of novel protein mediators of RNA export are examples of significant recent discoveries.  相似文献   
70.
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