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   240757篇
  免费   5076篇
  国内免费   761篇
电工技术   4181篇
综合类   432篇
化学工业   36779篇
金属工艺   9247篇
机械仪表   7096篇
建筑科学   6322篇
矿业工程   1528篇
能源动力   6015篇
轻工业   22776篇
水利工程   2628篇
石油天然气   4204篇
武器工业   19篇
无线电   25406篇
一般工业技术   48885篇
冶金工业   43877篇
原子能技术   5388篇
自动化技术   21811篇
  2021年   2562篇
  2020年   1941篇
  2019年   2258篇
  2018年   3942篇
  2017年   3972篇
  2016年   4225篇
  2015年   3075篇
  2014年   4572篇
  2013年   11920篇
  2012年   7085篇
  2011年   9226篇
  2010年   7454篇
  2009年   8052篇
  2008年   8381篇
  2007年   8330篇
  2006年   6974篇
  2005年   6355篇
  2004年   5868篇
  2003年   5766篇
  2002年   5327篇
  2001年   5278篇
  2000年   5145篇
  1999年   5330篇
  1998年   13424篇
  1997年   9430篇
  1996年   7340篇
  1995年   5329篇
  1994年   4812篇
  1993年   4557篇
  1992年   3485篇
  1991年   3302篇
  1990年   3088篇
  1989年   3160篇
  1988年   3021篇
  1987年   2594篇
  1986年   2477篇
  1985年   3031篇
  1984年   2815篇
  1983年   2573篇
  1982年   2297篇
  1981年   2478篇
  1980年   2273篇
  1979年   2312篇
  1978年   2279篇
  1977年   2616篇
  1976年   3661篇
  1975年   1968篇
  1974年   1872篇
  1973年   1926篇
  1972年   1503篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
971.
972.
The authors have exploited the ideas used in vector quantisation for error recovery of scalar quantised LSFs. The good performance of this method has provided high resistance of the LSFs to channel errors, outperforming other schemes by, possibly, a considerable margin. Better objective and subjective performances were obtained with this new method which obviates the need for more powerful FEC schemes for transmission over noisy channels.<>  相似文献   
973.
Enzyme-linked immunosorbent assay and flow cytometric methods to screen hybridoma culture supernatants for antibodies to bovine neutrophils (surface antigen-specific) were optimized. Sensitivity of the 2 methods was compared. A panel of 14 murine monoclonal antibodies (MAB) to surface antigens of bovine polymorphonuclear neutrophilic leukocytes (neutrophils) was produced by hybridoma technology, and their isotypes were determined by whole-cell ELISA. Monoclonal antibody reactivity with neutrophils, eosinophils, and lymphocytes isolated on phosphate-buffered saline solution and on Ficoll-sodium diatrizoate were compared. Biochemical characterization of antigens recognized by MAB was performed by immunoblot analysis. Neutrophil plasma membranes were isolated on sucrose gradients (20, 32, and 50%) and purified for polypeptide characterization. Neutrophil surface proteins were characterized by external labeling with 125I. The flow cytometric method was proven to be more sensitive and rapid than ELISA to screen hybridoma supernatants. This method allowed light-scatter gating of live neutrophil populations for analysis, which eliminated nonspecific binding of antibodies to contaminating cells and dead neutrophils. The optimal conditions for flow cytometric analyses were 5 x 10(5) neutrophils and 1 micrograms of fluorescein-labeled F(ab')2/assay as the second antibody. The optimal conditions for hybridoma screening by ELISA were neutrophil concentration of 2.5 x 10(5)/well, using a 96-well polystyrene microtitration plate as solid support, and 2,2'-azino-di[3-ethyl-benzthiazoline sulfonate (6)] with H2O2 as the chromatogenic substrate. Tissue culture plates as solid support and 3,3', 5,5'-tetramethyl benzidine, with H2O2 as the chromogenic substrate, were equally as sensitive. Panel MAB reacted differently with neutrophils, eosinophils, and lymphocytes. Isolation of these cells from blood on Ficoll-sodium diatrizoate generally did not alter MAB reactivity. Coomassie blue-stained gels of neutrophil plasma membrane proteins contained about 25 polypeptide bands, 13 of which were major bands. Autoradiography revealed about 11 surface proteins, 5 of which were heavily labeled with 125I. Monoclonal antibody S7G8 identified a 65-kd protein and MAB S8G10 identified 65- and 70-kd proteins. On the basis of molecular weight, MAB S7G8 and S8G10 are comparable to human CD15, CD16, and CD64 molecules. The MAB generated in this study are potential candidates to discern bovine neutrophil function and heterogeneity.  相似文献   
974.
The urinary catheter is one of the most frequently used medical devices and has a long and intriguing history of development. This paper describes the catheter from its simple beginnings through the subtle but important changes it has undergone paralleling the advances in plastics technology witnessed this century. The changes have not been without controversy and the recent association of catheters with tissue toxicity, which has forced the implementation of strict guidelines for their manufacture and use, is described.  相似文献   
975.
976.
Übersicht Der Betriebszustand eines Verteilungsnetzes wird durch die Strombelastung aller Betriebsmittel beschrieben. Mit Hilfe einer statischen Estimationsmethode werden aus einzelnen Messungen und der Kenntnis der Verbrauchsdaten typische Verbraucherkurven (TVK) berechnet, die das elektrische Verhalten verschiedener Verbrauchergruppen widerspiegeln. Auf dieser Basis ist eine betriebsmittelbezogene Lastmodellierung an beliebigen Betriebsmitteln in Abhängigkeit der Verbraucherzusammensetzung unter Berücksichtigung externer Einflüsse wie der Temperatur möglich. Die so gewonnenen Belastungsverläufe erlauben eine Beschreibung des Netzzustands in den Verteilungsnetzen.
Bus load modelling in distribution systems
Contents The operating state of a distribution system is determined by the bus load current. Based on individual substation measurements and the load composition typical load curves are calculated using statistical estimation theory. These typical load curves describe the electrical behaviour of the different load types (e.g. household, storage heating, commerce etc.). As soon as the typical load curves are determined it is possible to calculate the bus load current in any substation taking external influences such as temperature into consideration. The bus load current serve as load models which completely describe the operating state of the distribution system.
  相似文献   
977.
A menu-driven interactive graphics software package has been developed for use as an instructional aid for the electric machines course in the electrical engineering curriculum. The main purpose of this tool is to give the students a clearer understanding of the basics of the operation of rotating electric machines. The animation program was developed for displaying live and rotating diagrams depicting different modes of operation of synchronous generators. Different parts are identified with different colors. The interaction of the magnetic poles on the stator and on the rotor, and the relative spatial positions and time variations of the magnetic and electric quantities are demonstrated through moving images. The software features are described  相似文献   
978.
979.
The mortality rate after traumatic brain injury in children ranges between 2.5% and 21%. Standardized diagnostic procedures and therapeutic strategies for the management of traumatic brain damage are presented in this article. Children with traumatic cerebral lesions have a better clinical outcome than head-injured adults. Optimized medical management and intensive rehabilitation may help to reduce the frequency of mental retardation and physical disability following such injuries in children.  相似文献   
980.
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