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   233573篇
  免费   1337篇
  国内免费   246篇
电工技术   3938篇
综合类   206篇
化学工业   34686篇
金属工艺   15549篇
机械仪表   10154篇
建筑科学   4259篇
矿业工程   2506篇
能源动力   3323篇
轻工业   10020篇
水利工程   3692篇
石油天然气   9636篇
武器工业   12篇
无线电   20495篇
一般工业技术   55265篇
冶金工业   32763篇
原子能技术   7741篇
自动化技术   20911篇
  2018年   10367篇
  2017年   10918篇
  2016年   7654篇
  2015年   2148篇
  2014年   3048篇
  2013年   6405篇
  2012年   6597篇
  2011年   12648篇
  2010年   11528篇
  2009年   10764篇
  2008年   10817篇
  2007年   12554篇
  2006年   4199篇
  2005年   6794篇
  2004年   5435篇
  2003年   5069篇
  2002年   4072篇
  2001年   3525篇
  2000年   3503篇
  1999年   3234篇
  1998年   7024篇
  1997年   5151篇
  1996年   3835篇
  1995年   2929篇
  1994年   2628篇
  1993年   2744篇
  1992年   2273篇
  1991年   2329篇
  1990年   2410篇
  1989年   2317篇
  1988年   2321篇
  1987年   2192篇
  1986年   2246篇
  1985年   2292篇
  1984年   2207篇
  1983年   2135篇
  1982年   1981篇
  1981年   2194篇
  1980年   2054篇
  1979年   2272篇
  1978年   2431篇
  1977年   2430篇
  1976年   3095篇
  1975年   2244篇
  1974年   2307篇
  1973年   2342篇
  1972年   2155篇
  1971年   1911篇
  1970年   1701篇
  1969年   1687篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Aqueous extracts of the coralline red algaeBossiella orbigniana have been shown to catalyze the enzymatic oxidation of arachidonic acid to a previously unreported ω6 eicosapentaenoic acid product. This unique fatty acid contains a conjugated tetraene with absorption maxima at 293, 306, and 321 nm, and was identified by spectral methods as 5(Z),8(Z),10(E),12(E),14(Z)-eicosapentaenoic acid. The compound was given the trivial name bosseopentaenoic acid. Under experimental conditions, production of bosseopentaenoic acid was linear up to 2 hr and dioxygen was consumed. Bosseopentaenoic acid, along with several other conjugated tetraenes, was also present in the algae endogenously as revealed by a comparison of the ultraviolet (UV) spectra and the high-performance liquid chromatographic (HPLC) pattern of the purified product and the organic extract ofBossiella.  相似文献   
993.
994.
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   
995.
996.
997.
998.
Abstract— The possibility of using specially prepared single crystals as indicators of fatigue damage is outlined. Results are described of an analysis of deformation patterns developed in the single-crystal indicator surface, under fatigue and static loading. It is shown that the density and direction of deformation bands correlate with the number of loading cycles.  相似文献   
999.
Nonparametric detection of a zero-mean random signal in additive noise is considered. The locally optimum detector based on signs and ranks of observations is derived, for good weak-signal detection performance under any specified noise probability density function. This detector is shown to have interesting similarities to the locally optimum detector for random signals. It may also be viewed as a generalization of the locally optimum rank detector for known signals. Examples of the test statistic of the detector are given for some specific noise probability density functions. Asymptotic and finite sample-size performance of the locally optimum rank detector is also considered  相似文献   
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