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   262284篇
  免费   2958篇
  国内免费   545篇
电工技术   4771篇
综合类   321篇
化学工业   42477篇
金属工艺   10221篇
机械仪表   7985篇
建筑科学   5957篇
矿业工程   1453篇
能源动力   5700篇
轻工业   26381篇
水利工程   2669篇
石油天然气   5247篇
武器工业   33篇
无线电   27332篇
一般工业技术   48386篇
冶金工业   50878篇
原子能技术   6286篇
自动化技术   19690篇
  2021年   2251篇
  2019年   2167篇
  2018年   3714篇
  2017年   3647篇
  2016年   3929篇
  2015年   2414篇
  2014年   4188篇
  2013年   10961篇
  2012年   6625篇
  2011年   9000篇
  2010年   7065篇
  2009年   7807篇
  2008年   8229篇
  2007年   8373篇
  2006年   7464篇
  2005年   6686篇
  2004年   6350篇
  2003年   6174篇
  2002年   6267篇
  2001年   6161篇
  2000年   5948篇
  1999年   5841篇
  1998年   14518篇
  1997年   10157篇
  1996年   7788篇
  1995年   5967篇
  1994年   5278篇
  1993年   5207篇
  1992年   3985篇
  1991年   3696篇
  1990年   3897篇
  1989年   3786篇
  1988年   3566篇
  1987年   3136篇
  1986年   3149篇
  1985年   3611篇
  1984年   3400篇
  1983年   3075篇
  1982年   2907篇
  1981年   3017篇
  1980年   2906篇
  1979年   2774篇
  1978年   2819篇
  1977年   3198篇
  1976年   4149篇
  1975年   2476篇
  1974年   2347篇
  1973年   2483篇
  1972年   2048篇
  1971年   1929篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The mechanism responsible for the +G(z)-induced loss of consciousness (G-LOC) experienced by fighter pilots is investigated. The nature of a G-LOC episode is described formcases of rapid onset. Evidence suggests that the G-LOC mechanism might be closely related to the mechanism for sleep. A theory of G-LOC that treats it as a protective physiological mechanism is proposed.  相似文献   
992.
993.
We present a patient with continuous melena, diagnosed as rectal varices bleeding. She had a history of esophageal varices, which was treated by endoscopic ligation therapy. Eight years after the treatment of esophageal varices, the continuous melena began. Colonoscopic examination showed that the melena was caused by rectal varices, which were so severe that they could not be treated by either endoscopic sclerotherapy or surgical devascularization. Taking into considering the overall risk of treating rectal varices, we chose the approach of double balloon-occluded embolotherapy (DBOE) with 5% ethanolamine oleate with iopamodol as a liquid embolic material. DBOE is one of the interventional radiology techniques (Morita et al., Acta Hepatol Jpn 1994;35:109-120), but in this case was a completely new and novel clinical procedure for rectal varices. After the DBOE therapy, the condition of rectal varices was markedly improved. Thus, DBOE might be a new tool for treating inoperable rectal varices.  相似文献   
994.
The stabilizing free energy of beta-trypsin was determined by hydrogen ion titration. In the pH range from 3.0 to 7.0, the change in free energy difference for the stabilization of the native protein relative to the unfolded one (delta delta G0 titration) was 9.51 +/- 0.06 kcal/mol. An isoelectric point of 10.0 was determined, allowing us to calculate the Tanford and Kirkwood electrostatic factor w. This factor presented a nonlinear behavior and indicated more than one type of titratable carboxyl groups in beta-trypsin. In fact, one class of carboxyl group with a pK = 3.91 +/- 0.01 and another one with a pK = 4.63 +/- 0.03 were also found by hydrogen ion titration of the protein in the folded state.  相似文献   
995.
An investigation into a system linking a computer solid modeler to an active stereo imaging inspection station is presented. Given the computer solid model of a surface, a projected pattern can be encoded so that the reflections from the object's surface exhibit a uniformly simple pattern when the object's surface and the modeled surface are identical. Research concerning the method of generating projection patterns, as well as the sensitivity of the system, is discussed. A prototype system consisting of a computer graphics workstation; a flexible projector, and a machine vision system was used to inspect two different manufactured parts  相似文献   
996.
997.
998.
999.
1000.
The experience of our 16 patients treated for membranous duodenal stenosis is reported. Their treatment and course was analysed in a retrospective study. Eight patients were operated on within the first 16 days of life and in the remaining group surgery was performed at 1 month to 4 y of age. The presenting symptom leading to diagnosis was, in all but one case, non-bile-stained vomiting. Associated malformations were found in all but four patients, mostly morbus Down. The operative procedure performed was a partial excision of the duodenal membrane and a duodenoplasty in 10 patients, a duodenojejunostomy in 5 patients, and a duodenoplasty only in 1 patient. The postoperative course was without lethal complications. One late stricture in an anastomosis occurred. We conclude that in its presentation, duodenal stenosis differs from duodenal atresia, and can often be misinterpreted, resulting in a late diagnosis, and should be reported as a separate entity.  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