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   251608篇
  免费   1738篇
  国内免费   278篇
电工技术   4089篇
综合类   99篇
化学工业   40840篇
金属工艺   15226篇
机械仪表   10132篇
建筑科学   4213篇
矿业工程   3770篇
能源动力   3993篇
轻工业   9862篇
水利工程   4116篇
石油天然气   13012篇
武器工业   28篇
无线电   20665篇
一般工业技术   63333篇
冶金工业   32387篇
原子能技术   11152篇
自动化技术   16707篇
  2021年   2899篇
  2019年   2809篇
  2018年   5528篇
  2017年   5780篇
  2016年   6130篇
  2015年   3107篇
  2014年   5405篇
  2013年   10228篇
  2012年   7404篇
  2011年   9065篇
  2010年   7399篇
  2009年   8218篇
  2008年   8286篇
  2007年   7945篇
  2006年   6433篇
  2005年   5628篇
  2004年   5530篇
  2003年   5355篇
  2002年   5177篇
  2001年   4987篇
  2000年   4976篇
  1999年   4295篇
  1998年   7267篇
  1997年   5879篇
  1996年   4461篇
  1995年   3692篇
  1994年   3468篇
  1993年   3668篇
  1992年   3253篇
  1991年   3398篇
  1990年   3511篇
  1989年   3387篇
  1988年   3293篇
  1987年   3287篇
  1986年   3177篇
  1985年   3329篇
  1984年   3274篇
  1983年   3159篇
  1982年   3012篇
  1981年   3055篇
  1980年   3083篇
  1979年   3275篇
  1978年   3495篇
  1977年   3475篇
  1976年   3931篇
  1975年   3212篇
  1974年   3296篇
  1973年   3348篇
  1972年   2989篇
  1971年   2757篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Although tuberculosis is still relatively common in Canada, particularly among recent immigrants, one tends not to consider it very strongly in the absence of definite pulmonary symptoms and in the face of negative smears of expectorated sputum and bronchial washings. We present the case of a young immigrant from Ethiopia who presented with mild constitutional symptoms, bony tenderness of the chest wall, generalized lymphadenopathy, and rib erosions--a set of features which, in the face of smear-negative sputum and bronchial washings, raised a possibility of lymphoma. Eventually, diagnosis of tuberculous lymphadenitis and osteomyelitis was established and the patient responded well to appropriate therapy.  相似文献   
992.
Surface forces nonuniformity within the volume of a capillary system for a given structure has been examined in terms of its effect on a wetting fluid distribution. This approach enables the distribution for a porous body with a uniform structure to be quantified using a specific function for the pore volume size distribution. The surface forces nonuniformity effect is illustrated using a fibrous structure impregnated with molten copper.Institute of Materials Science Problems, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, No. 8(368), pp. 66–69, August, 1993.  相似文献   
993.
994.
Reports an error in the original article by C. J. Brainerd and V. F. Reyna (Psychological Review, 1993[Jan], Vol 100[1], 42–67). On page 56, there were some incorrect data values in the 3rd and 4th columns of Table 4. The amended table is presented. (The following abstract of this article originally appeared in record 1993-17013-001.) Recent experiments have established the surprising fact that age improvements in reasoning are often dissociated from improvements in memory for determinative informational inputs. Fuzzy-trace theory explains this memory-independence effect on the grounds that reasoning operations do not directly access verbatim traces of critical background information but, rather, process gist that was retrieved and edited in parallel with the encoding of such information. This explanation also envisions 2 ways in which children's memory and reasoning might be mutually interfering: (1) memory-to-reasoning interference, a tendency to process verbatim traces of background inputs on both memory probes and reasoning problems that simultaneously improves memory performance and impairs reasoning and (2) reasoning-to-memory interference… (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
995.
In the frame of cylindrical coordinates the Dirichlet outer boundary-value problem is solved on the basis of circular multipoles. A number of multipole-cylindrical fields is calculated.  相似文献   
996.
997.
An in situ NMR study of tert-butanol dehydration in 95 and 85% sulfuric acid did not indicate the formation of tert-butyl cations as active reaction intermediates. Instead, only NMR lines from oxonium ions under the condition of fast exchange with water and the acid were observed. It is most likely that, in the concentrated acid, the active intermediates of this reaction are represented by tert-butyl sulfuric ester which probably is a precursor of invisible tert-butyl carbenium ions representing short-lived excited or transition states.  相似文献   
998.
999.
1000.
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