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   1048篇
  免费   16篇
电工技术   2篇
化学工业   62篇
金属工艺   14篇
机械仪表   3篇
建筑科学   7篇
能源动力   4篇
轻工业   31篇
水利工程   3篇
石油天然气   2篇
无线电   14篇
一般工业技术   23篇
冶金工业   875篇
自动化技术   24篇
  2024年   1篇
  2022年   13篇
  2021年   9篇
  2020年   3篇
  2019年   9篇
  2018年   6篇
  2017年   6篇
  2016年   11篇
  2015年   5篇
  2014年   7篇
  2013年   17篇
  2012年   19篇
  2011年   13篇
  2010年   14篇
  2009年   7篇
  2008年   8篇
  2007年   5篇
  2006年   9篇
  2005年   7篇
  2004年   5篇
  2003年   4篇
  2002年   2篇
  1999年   22篇
  1998年   226篇
  1997年   150篇
  1996年   98篇
  1995年   63篇
  1994年   44篇
  1993年   48篇
  1992年   10篇
  1991年   14篇
  1990年   18篇
  1989年   18篇
  1988年   31篇
  1987年   13篇
  1986年   10篇
  1985年   14篇
  1982年   5篇
  1981年   8篇
  1980年   6篇
  1977年   24篇
  1976年   57篇
  1975年   2篇
  1955年   3篇
排序方式: 共有1064条查询结果,搜索用时 0 毫秒
111.
We investigated song sharing and dispersion of song types in the wild in a colour-marked population of the non-migratory Nuttall's white-crowned sparrow, Zonotrichia leucophrys nuttalli. The songs of fathers, their male progeny (sons), and the neighbours of the sons at recruitment sites were analysed spectrographically and compared qualitatively and quantitatively. To determine whether a son's song more closely matched that of his father or a neighbour at the site settled, we subjected frequency and temporal characteristics of songs within each father-son-neighbour triad to multivariate cluster analysis. The songs of 14 of 16 sons clustered with their neighbours' rather than their fathers' songs, confirming that song matching of neighbours is an integral component of territory settlement by juveniles. Principal components analysis of frequency and temporal measurements of song within a dialectal area show that songs group into neighbourhoods and are non-randomly distributed. Multivariate analysis suggests that sons may entrain on frequency and temporal characteristics of a neighbour's song without matching phrases or complex syllables. Implications for models of instructive versus selective learning are discussed. The timing of closure of the sensitive phase, the length of the silent interval between the sensory phase and plastic song stage, and the time to song crystallization remain open questions in song ontogeny. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.  相似文献   
112.
IFN-gamma is a potent pro-inflammatory cytokine involved in the immunologic rejection of transplanted organs. Having previously demonstrated differential suppressive effects of methylprednisolone (MP), prednisolone (P) and cyclosporine (CsA) on dialysis patients' lymphocyte proliferative responses to phytohaemagglutinin (PHA), we studied the effects of these drugs on dialysis patients' lymphocyte IFN-gamma production during mitogenic and allogeneic (MLR) stimulation. The mean +/- SEM 50% inhibitory concentration (ng/ml) on cell proliferation was significantly lower for MP than P in PHA-stimulated haemodialysis (HD) patients' (35 +/- 7 vs 152 +/- 25, P < 0.001) and peritoneal dialysis (PD) patients' (35 +/- 11 vs 134 +/- 33, P = 0.001) cultures and in HD patients' MLR cultures (15 +/- 3 vs 48 +/- 9, P < 0.001). The mean +/- SEM fractional responses (PHA or MLR + drug/PHA or MLR) in culture supernatant IFN-gamma concentrations were significantly lower with 10(-7) M concentrations of MP than P in HD (0.19 +/- 0.05 vs 0.31 +/- 0.06, P = 0.01) and PD (0.30 +/- 0.11 vs 0.46 +/- 0.11, P < 0.05) PHA cultures and in HD MLR cultures (0.15 +/- 0.04 vs 0.28 +/- 0.07, P = 0.01). CsA (400 ng/ml) alone not only caused less than 50% inhibition of IFN-gamma production in 15/27 HD PHA, 6/14 PD PHA and 4/13 HD MLR cultures, but actually stimulated it in 9 HD and 5 PD PHA cultures. The results suggest that: (1) MP has greater immunosuppressive potential than P for renal transplant recipients; (2) the stimulation of IFN-gamma by CsA in some patients could be harmful in patients with initial allograft dysfunction; and (3) pre-transplant in-vitro assessment of recipients' PBMC responsiveness to glucocorticoids and CsA may help individualize the post-transplant immunosuppressive regimen.  相似文献   
113.
114.
OBJECTIVE: To review the relationship between quality of life (QOL) and dementia. Development. QOL is a factor which takes into account all the different aspects of life which make a person feel that life is worth living, such as: 1. Physical health. 2. Functional status. 3. Psychological and cognitive sphere, and 4. Social health. There are two types of instruments for evaluating these aspects: firstly general ones which measure the QOL independently of illness, and secondly those which are specific to the illness concerned. In dementia, QOL covers the same traditional areas: cognitive competence, capacity to carry out everyday activities, social conduct and the balance between positive and negative emotions. However, evaluation of QOL in dementia has its own specific difficulties, since it is often impossible to determine such a fundamental factor as the subjective well-being of the patient, in which case the opinion of the person looking after the patient is essential. According to Lawton's approximation, as well as the subjective aspect of perceived psychic welfare and quality of life, the QOL in dementia is composed of external social and objective dimensions such as behaviorally competence and the quality of the patient's environment. In a review done in 1995 it was found that most of the instruments designed to measure the QOL have not been sufficiently validated for Alzheimer's disease. CONCLUSIONS: QOL in dementia has specific features including external aspects such as the opinion of the carer and the quality of the patient's environment in addition to the subjective aspects. It is necessary to develop and validate specific instruments for QOL in dementia.  相似文献   
115.
This study assessed the impact of diabetes mellitus on atherosclerotic lesion formation. Seventy insulin-treated diabetics, 150 non-insulin-treated diabetics, and 607 nondiabetics with chronic anginal syndromes and de novo native coronary stenoses were studied using (1) angiography, and (2) intravascular ultrasound (reference and lesion arterial, lumen, and plaque areas; area stenosis [reference-lesion/reference lumen area]; remodeling index [reference-lesion lumen area/lesion-reference plaque area]; and slope of the regression line relating lumen area to plaque burden [plaque/arterial area]). Despite being diabetic for longer and having similar lumen compromise, insulin-treated patients had (1) less reference plaque (8.3 +/- 3.4 vs 10.5 +/- 4.5 mm2, p = 0.0015), (2) less stenosis plaque (13.0 +/- 4.9 vs 16.9 mm2, p <0.0001), (3) smaller reference arterial areas (17.1 +/- 5.4 vs 19.7 +/- 6.2 mm2, p = 0.0063), and (4) smaller stenosis arterial areas (15.3 +/- 4.9 vs 19.5 +/- 6.5 mm2, p <0.0001) than non-insulin-treated diabetics. With use of multivariate linear regression analysis, insulin use was an independent (and negative) predictor of reference plaque and arterial areas (p = 0.0308 and p = 0.0179) and stenosis plaque and arterial areas (p = 0.0117 and p = 0.0066). This was also true when normalized for body surface area. The remodeling index showed that insulin treatment resulted in an exaggerated impact of plaque accumulation on lumen compromise. This was confirmed by the slope of the regression line relating lumen area to plaque burden. Patients with a longer duration of diabetes who were treated with insulin for > or = 1 year had (paradoxically) less reference segment and stenosis plaque accumulation. Possible explanations include impaired adaptive remodeling and/or arterial (and plaque) shrinkage.  相似文献   
116.
This paper reports two cases of orbital apex syndrome. The most salient clinical signs, ophthalmoplegia and eyelid ptosis, arose from perineural spread of facial squamous cell carcinomas that were previously excised with tumour-free surgical margins and exhibited no signs of local or other regional recurrence. The interest of these two cases lies in the fairly rare occurrence of this type of tumour spread and the highly aggressive nature of the tumour, unequivocal diagnosis of which usually arrives too late for a surgical solution. Awareness of the possibility of such perineural spread may allow the clinician to establish an early diagnosis and thus undertake radical surgery, thereby increasing the likelihood of success in combination with postoperative radiotherapy.  相似文献   
117.
118.
119.
The inhibitory activity of five bacteriocin (Bac)-producer strains of Staphylococcus aureus was tested against bacteria pathogenic for cattle. Sixty-five epidemiologically unrelated strains of Staph. aureus involved in bovine mastitis were used as indicators in an agar diffusion test. Bacteriocins produced by four strains could inhibit only a limited number of test organisms. However, all 65 indicator strains proved to be susceptible to the combined action of both bacteriocins encoded by pRJ9, a Bac plasmid found in strain A53. Therefore, the bacteriocins produced by this strain may represent new antimicrobial peptides with potential applications in the prevention and treatment of bovine mastitis.  相似文献   
120.
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