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   2806篇
  免费   1篇
电工技术   1篇
化学工业   13篇
机械仪表   1篇
建筑科学   1篇
轻工业   9篇
石油天然气   2篇
无线电   4篇
一般工业技术   11篇
冶金工业   2757篇
原子能技术   1篇
自动化技术   7篇
  2018年   1篇
  2015年   1篇
  2013年   1篇
  2012年   2篇
  2011年   2篇
  2010年   3篇
  2008年   5篇
  2007年   2篇
  2006年   2篇
  2004年   1篇
  2003年   3篇
  2002年   1篇
  2000年   2篇
  1999年   80篇
  1998年   808篇
  1997年   437篇
  1996年   308篇
  1995年   170篇
  1994年   151篇
  1993年   170篇
  1992年   17篇
  1991年   34篇
  1990年   34篇
  1989年   37篇
  1988年   43篇
  1987年   39篇
  1986年   27篇
  1985年   32篇
  1984年   1篇
  1983年   3篇
  1982年   15篇
  1981年   14篇
  1980年   31篇
  1978年   8篇
  1977年   94篇
  1976年   213篇
  1975年   5篇
  1973年   1篇
  1971年   1篇
  1969年   2篇
  1967年   2篇
  1955年   4篇
排序方式: 共有2807条查询结果,搜索用时 0 毫秒
61.
BACKGROUND: Surgical defects of the central upper lip (philtrum) are a particularly difficult area to achieve satisfactory cosmetic and functional repair. Reconstruction of the central upper lip has been accomplished primarily through the use of side-to-side closure, bilateral advancement or rotation flap, and full-thickness graft. Repair may be complicated by distortion of the vermilion border, obliteration of the normal contour of the philtrum, eclabium, and trapdooring of the flap. OBJECTIVE: We review the options for reconstruction of this area and describe our experience using an island pedicle flap to complete reconstruction. METHODS: Four patients presented with basal cell carcinomas of the mid upper lip (philtrum). Tumors were cleared by Mohs micrographic surgery. Reconstruction was achieved by island pedicle flaps utilizing donor tissue from the superior philtrum. RESULTS: The patients had excellent cosmetic results with minimal distortion of the vermilion border or obliteration of the philtrum or philtral ridges. Scars healed in a nearly imperceptible fashion, keeping within one cosmetic unit (the philtrum) without extending along the vermilion border as seen in bilateral advancement or rotation flaps. CONCLUSIONS: Island pedicle flaps may be an effective cosmetic and functional repair of selected surgical defects of the central upper lip involving the philtrum.  相似文献   
62.
63.
The effects of denervation of central noradrenergic system on the interpartner relationships of adult cats were examined in a predatory test in the competitive situation for paired animals. Direct administration of the noradrenaline neurotoxin, N-2-chloroethyl-N-ethyl-2-bromobenzylamine (DSP-4 12 microg) into the medial forebrain bundle (MFB) of submissive cats changed previously established dominant-submissive relationship. Biochemical analysis demonstrated a significant reduction of noradrenaline (NA) concentration in the hypothalamus (AH), amygdala (AM), hippocampus (HC), and frontal cortex (CTX), and elevation of NA content in the midbrain central gray matter (CG) in MFB-lesioned cats. Simultaneously, DSP-4-induced lesions exerted significant decrease of 3-methoxy-4-hydroxyphenylethylene glycol (MHPG) content in AH, CG, HC and CTX, and increased GABA level in AH, CG, AM, and HC. These results suggest that a coincident decrease of NA metabolism and increase of GABA metabolism led to fear drive reduction.  相似文献   
64.
Human hair was collected from the occipital crown region of the head from several subjects; these hair samples were presumptively positive for amphetamines by a previously evaluated immunoassay. Hair was washed briefly with methanol to remove external contamination, then extracted with hot methanol for 2 h to recover the drugs. The extracts were evaporated to dryness, reconstituted in buffer, and analyzed using a new enzyme-linked immunosorbent assay (ELISA) technique adapted for the detection of amphetamines in hair. Gas chromatography-mass spectrometry was used as the reference technique. Cross-reactivity of several related compounds was evaluated by equating the inverse of the ligand concentration at 50% antibody binding to the affinity constant for each compound. The ratio of a compound's affinity constant to that for d-methamphetamine was used to derive percent crossreactivity. These experiments yielded values of 30.8% for d-amphetamine, 7.4% for I-methamphetamine, 4.3% for phentermine, 2.9% for I-amphetamine, and <1% for ephedrine, methylenedioxyamphetamine, and methylenedioxymethamphetamine. Cross-reactivity of unrelated compounds was found to be non-existent. The optimum cutoff concentration was determined by receiver operating characteristic curve analysis to be 300 pg/mg and the observed limit of detection was 60 pg/mg. Intra-assay precision at 300 pg/mg was 3.3% (coefficient of variation, CV), and the interassay CV was 10.5%. The sensitivity and specificity of the method were 83% and 92%, respectively.  相似文献   
65.
66.
67.
68.
69.
70.
There continues to be considerable effort towards the construction of compound libraries targeted for the inhibition of protease enzymes. New tag-encoding methods for library deconvolution have been applied to this problem and there has been particular interest in novel solid-phase linkers for the introduction of key pharmacophore groups required for protease inhibition. Recent reports have tended to focus on nonpeptidic libraries, and, notably, structure-based design methods are now being applied to direct library design.  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