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   330236篇
  免费   3915篇
  国内免费   1905篇
电工技术   6250篇
综合类   310篇
化学工业   44762篇
金属工艺   13941篇
机械仪表   10040篇
建筑科学   7705篇
矿业工程   1028篇
能源动力   9587篇
轻工业   25793篇
水利工程   2735篇
石油天然气   3819篇
武器工业   30篇
无线电   45470篇
一般工业技术   66738篇
冶金工业   65877篇
原子能技术   6068篇
自动化技术   25903篇
  2022年   1836篇
  2021年   2772篇
  2020年   2018篇
  2019年   2518篇
  2018年   4205篇
  2017年   4218篇
  2016年   4375篇
  2015年   3015篇
  2014年   5167篇
  2013年   15341篇
  2012年   8266篇
  2011年   11678篇
  2010年   9403篇
  2009年   10845篇
  2008年   11390篇
  2007年   11438篇
  2006年   10116篇
  2005年   9065篇
  2004年   8753篇
  2003年   8767篇
  2002年   8043篇
  2001年   8660篇
  2000年   8029篇
  1999年   8613篇
  1998年   22647篇
  1997年   15564篇
  1996年   12202篇
  1995年   8812篇
  1994年   7856篇
  1993年   7762篇
  1992年   5325篇
  1991年   5221篇
  1990年   5009篇
  1989年   4666篇
  1988年   4454篇
  1987年   3670篇
  1986年   3627篇
  1985年   3922篇
  1984年   3536篇
  1983年   3369篇
  1982年   3202篇
  1981年   3050篇
  1980年   2905篇
  1979年   2680篇
  1978年   2453篇
  1977年   3002篇
  1976年   4315篇
  1975年   2017篇
  1974年   1963篇
  1973年   1887篇
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
51.
52.
The Frizzled genes encode receptors for WNTs, secreted glycoproteins implicated in development as well as in carcinogenesis. In this paper, we report molecular cloning of Hfz6, the human homologue of Mfz6. Nucleotide sequence analysis showed that the Hfz6 gene encodes the 706 amino-acid protein with seven transmembrane domains, a cystein-rich domain in the N-terminal extracellular region, two N-linked glycosylation sites, and two cystein residues in the second and third extracellular loops. Hfz6 mRNA 4.4-kb in size was detected in various normal adult and fetal tissues, and a larger amount of Hfz6 mRNA was detected in both fetal lung and fetal kidney. The Hfz6 gene has been mapped to human chromosome 8q22.3-q23.1. In conclusion, we have cloned Hfz6, which encodes a seven-transmembrane receptor with the cystein-rich domain in the N-terminal extracellular region, but without the Ser/Thr-X-Val motif in the C-terminus.  相似文献   
53.
Bone marrow examination revealed a lipid-laden histiocytosis in seven patients undergoing long-term total parenteral nutrition necessitated by extensive short-bowel surgical resection. Clinical abnormalities occurred during this treatment which required bone marrow examination. These included hepatosplenomegaly and peripheral blood cytopenia; the median time to the detection of these abnormalities was 64 months. The most striking change within the bone marrow was the presence of many pigment-laden histiocytes which had the typical morphology of sea-blue histiocytes seen in the so-called idiopathic sea-blue histiocyte syndrome. The occurrence of sea-blue histiocytosis in the bone marrow in association with long-term parenteral nutrition for short-bowel syndrome has not, to our knowledge, been reported previously and should now be considered in the differential diagnosis of bone marrow sea-blue histiocytosis.  相似文献   
54.
One month following the Great Hanshin Earthquake of January 17, 1995, we conducted a survey of 173 hospitals in Aichi Prefecture to pinpoint problems related to their actual disaster-readiness and the medical backup systems in place to deal with such disasters. This study revealed that staff at 50% of the surveyed hospitals could reach the hospital within an hour, but that communication is almost entirely dependent on phone lines, suggesting that cordless/portable/mobile phones, radio systems, Internet, communications satellites and the like should be studied in the days to come for possible use as effective communication alternatives in times of disaster. Whereas 92% of the surveyed hospitals had manuals dealing with fire outbreaks, other areas were less well represented. For example, only 36.9% of surveyed hospitals had manuals for earthquakes, 31.7% had manuals for power outages and 14.2% had manuals to deal with flooding and water disasters. New manuals must be developed incorporating the key points garnered from experience (especially Hanshin) and be ready for use immediately. It is the time for each hospital to seriously rethink the measures it should take to deal with disasters.  相似文献   
55.
56.
A low threshold current density of ~100 A/cm2 has been obtained at 1.55 μm using a graded-index separate-confinement-heterostructure strained InGaAsP single-quantum-well laser. The design of the laser structure is based on results calculated from the viewpoint of effective carrier injection into the well  相似文献   
57.
The biotransformation of oxazepam by Bifidobacterium bifidum was studied. The major metabolite was purified by chromatographic methods and found to be desmethyldiazepam using NMR, IR and other physicochemical data.  相似文献   
58.
59.
60.
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