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   2037篇
  免费   4篇
化学工业   27篇
金属工艺   1篇
机械仪表   1篇
建筑科学   2篇
轻工业   13篇
水利工程   1篇
无线电   4篇
一般工业技术   22篇
冶金工业   1962篇
原子能技术   1篇
自动化技术   7篇
  2020年   2篇
  2017年   2篇
  2015年   2篇
  2014年   6篇
  2013年   4篇
  2012年   2篇
  2011年   2篇
  2010年   2篇
  2007年   3篇
  2005年   2篇
  2004年   1篇
  2003年   5篇
  2002年   3篇
  2001年   1篇
  2000年   2篇
  1999年   66篇
  1998年   574篇
  1997年   359篇
  1996年   245篇
  1995年   123篇
  1994年   100篇
  1993年   123篇
  1992年   13篇
  1991年   29篇
  1990年   14篇
  1989年   22篇
  1988年   22篇
  1987年   17篇
  1986年   18篇
  1985年   14篇
  1984年   2篇
  1983年   5篇
  1982年   9篇
  1981年   10篇
  1980年   12篇
  1979年   3篇
  1978年   5篇
  1977年   64篇
  1976年   127篇
  1975年   8篇
  1972年   1篇
  1971年   1篇
  1970年   1篇
  1968年   1篇
  1967年   1篇
  1965年   1篇
  1963年   1篇
  1955年   2篇
  1954年   1篇
  1910年   2篇
排序方式: 共有2041条查询结果,搜索用时 15 毫秒
161.
Lymphoblastoid cell lines from patients with xeroderma pigmentosum (2 forms) and progeria (unusual form) were established using transformation of peripheral blood lymphocytes by Epstein--Barr virus. The influence of different UV doses on cell vitality, proliferation and cell cycle progression was studied by means of flow cytometry. The cell vitality was determined after incubation of cells with etidium bromide and FDA. We used cytograms with two logarithmic signals (log green/log red) to discriminate the cell cycle status. Cell cultures were used with density of 500,000 cells per 1 ml, previously synchronized at G-phase by the incubation in a medium with low serum content. The effect of UV irradiation was followed during 72 h. Among four analysed cell lines only line XP2SP demonstrated enhanced UV sensitivity, expressed by decreasing of the amount of living cells after the UV dose of 2.5 J/m2 and higher. The cell cycle studies showed that cells were blocked in S-phase and simultaneously the amount of apoptotic cells with both reduced DNA content and ability to bind FDA was seen increased. Similar events were observed in the control line only after the dose of 20 J/m2 and higher.  相似文献   
162.
OBJECTIVE: The aim of this study was to assess the frequency and severity of depressive symptoms, to determine the rate of depressive disorder, to explore possible reasons for the development of depressive symptoms and to examine the effects of depression in a group of human immunodeficiency virus (HIV)-positive patients. METHOD: HIV-positive patients attending an outpatient treatment facility were assessed by the research psychologist and completed a number of questionnaires: the Beck Depression Inventory (BDI); the Life Event Inventory (LEI); the Core Bereavement Item (CBI-17) questionnaire; and the Psychosocial Adjustment to illness Scale (PAIS). Patients scoring > or = 14 on the BDI were seen by the psychiatrist for further assessment, and where appropriate, diagnoses were made according to DSM-III-R criteria. RESULTS: One hundred and ninety-two patients participated in the study; 95 scored > or = 14 on the BDI and one-third of these were found to have a depressive disorder. Factors significantly predictive of a BDI score > or = 14 were: an LEI score > 77; a diagnosis of acquired immunodeficiency syndrome (AIDS); being on sickness benefits or a pension; no current relationship; and a past history of depression. Few differences were demonstrated between those with a depressive disorder and those with a BDI score > or = 14 but no diagnosis of depressive disorder. Both groups had high mean PAIS scores indicating significant illness effects in multiple areas of function. CONCLUSIONS: Depressive symptoms are common among patients with HIV infection. Few factors differentiate between patients with a depressive disorder and those whose depressive symptoms do not meet diagnostic criteria. Substantial disability is present in both groups.  相似文献   
163.
164.
High-affinity nicotine, alpha-bungarotoxin (alpha BT) and muscarinic receptor binding was measured in the human hippocampal formation in a series of 57 cases aged between 24 weeks gestation and 100 years. Changes in nicotine receptor binding during development and aging were more striking than differences in alpha BT and muscarinic binding. Nicotine binding was higher at the late foetal stage than at any other subsequent time in all areas investigated. In the hippocampus a fall in binding then occurred within the first six months of life, with little or no subsequent fall during aging, whereas in the entorhinal cortex and the presubiculum the major loss of nicotine binding occurred after the fourth decade. alpha BT binding was significantly elevated in the CA 1 region, but in no other region of the hippocampus, in the late foetus, and there was also a fall in alpha BT binding in the entorhinal cortex during aging from the second decade. The modest changes in total muscarinic binding, which appeared to reflect those in M1 and M3 + 4 rather than M2 binding, were a rise in the entorhinal cortex between the foetal stage and childhood and a tendency for receptors to fall with age in the hippocampus and subicular complex. These findings implicate mechanisms controlling the expression of nicotinic receptors to a greater extent than muscarinic receptors in postnatal development and aging in the human hippocampus.  相似文献   
165.
166.
167.
The relationship between selected foods and nutrients and breast cancer risk was investigated in strata of age and menopausal status using data from a case-control study on breast cancer conducted between June 1991 and April 1994 in six Italian areas. Cases were 2,569 women with histologically confirmed incident breast cancer admitted to the major teaching and general hospitals of the study areas; controls were 2,588 women with no history of cancer admitted to hospitals in the same catchment area as cases for acute, nonneoplastic, nongynecological conditions unrelated to hormonal or digestive tract diseases or to long-term modifications of diet. Dietary habits were investigated using a validated food frequency questionnaire, including 78 foods or food groups. Among food groups, bread was directly and significantly related to breast cancer risk in older women and, consequently, in postmenopause, whereas the protection conferred by fish consumption was stronger in postmenopause and that exerted by raw vegetables was stronger in premenopause. Among nutrients, unsaturated fatty acids were inversely related to breast cancer risk, the association being stronger in postmenopausal and elderly women. The pattern was similar for total fats. For starch, available carbohydrates, and total proteins, no heterogeneity emerged across strata of age and menopausal status. Among micronutrients, protection diminished with increasing age for beta-carotene and calcium, whereas no heterogeneity emerged for vitamin E. Thus this age-specific analysis of the largest investigation to date on diet and breast cancer did not show any consistent pattern of breast cancer risk in relation to selected dietary factors across strata of age and menopausal status.  相似文献   
168.
169.
Lymphatic mapping and sentinel node biopsy in breast cancer   总被引:1,自引:0,他引:1  
  相似文献   
170.
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