全文获取类型
收费全文 | 1735篇 |
免费 | 2篇 |
专业分类
电工技术 | 1篇 |
化学工业 | 11篇 |
金属工艺 | 1篇 |
机械仪表 | 1篇 |
轻工业 | 1篇 |
无线电 | 2篇 |
一般工业技术 | 2篇 |
冶金工业 | 1716篇 |
自动化技术 | 2篇 |
出版年
2021年 | 2篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2016年 | 2篇 |
2007年 | 1篇 |
2005年 | 2篇 |
2004年 | 1篇 |
2003年 | 2篇 |
1999年 | 55篇 |
1998年 | 572篇 |
1997年 | 295篇 |
1996年 | 198篇 |
1995年 | 83篇 |
1994年 | 81篇 |
1993年 | 95篇 |
1992年 | 11篇 |
1991年 | 30篇 |
1990年 | 21篇 |
1989年 | 22篇 |
1988年 | 18篇 |
1987年 | 23篇 |
1986年 | 21篇 |
1985年 | 26篇 |
1984年 | 1篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 8篇 |
1980年 | 18篇 |
1979年 | 1篇 |
1978年 | 5篇 |
1977年 | 38篇 |
1976年 | 87篇 |
1975年 | 4篇 |
1962年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有1737条查询结果,搜索用时 15 毫秒
61.
62.
Fc receptor (FcR) and complement receptor (CR) expression on HIV-infected monocyte-derived macrophages may be an important determinant of immune function. We studied the effects of HIV-1 infection of macrophages in vitro on FcR and CR expression. Macrophages were infected with HIV-1DV 7 days following isolation, and the expression of Fc gamma RI-III and CR3 were measured at intervals thereafter by flow cytometry. We found a reduction in receptor expression with the percentage of cells expressing FcRI 14 days post infection declining from 77% to 13%, FcRII fell from 96% to 85%, FcRIII from 45% to 9%, and CR3 from 91% to 67% 14 days following infection. As these receptors are important for macrophage function, their down-modulation may contribute to the pathogenesis of HIV-related disease. 相似文献
63.
64.
65.
66.
Nutritional pharmacology and malignant disease: a therapeutic modality in patients with cancer 总被引:1,自引:0,他引:1
It is now established that certain nutrients have a significant effect on cellular metabolism and growth, tissue repair and regeneration, and modulation of host defences. So far, however, potential clinical benefits have been difficult to demonstrate. Nevertheless, the use of nutrients in combinations seems to have promise and may be associated with a reduction in infectious complications and length of hospital stay. Nutritional pharmacology in the future may be able to improve tumour response to chemotherapy and may minimize the metabolic effect of cachexia. 相似文献
67.
The study investigated the psychological health level and related psychosocial factors of nurses. Through cluster sampling, 650 clinical nurses, who come from 5 city hospitals in Changsha, were interviewed with the Symptom Check List-90 (SCL-90), The Life Event Scale, Type A Behavior Questionnaire, and The Social Support Rating Scale. The results indicated that subjects' average symptom score and most factor scores of SCL-90 were significantly higher than that of the chinese norm. Somatization, depression, and obsession are common psychological problems of the clinical nurses, and the psychological health level of middle age group was significantly lower than that of other groups. Regression analysis (both single factor and multiple factors) suggested that TH and CH scores on Type A Questionnaire as well as life event score on the life event score were negatively related to psychological health level while social support score was positively related to it. The influences of psychosocial factors on psychological health level of clinical nurses were discussed. 相似文献
68.
Human chorionic gonadotropin (hCG) is a glycoprotein composed of two subunits, alpha and beta, linked together by a covalent bond. Ectopic production of hCG has been described in various histological types of cancer. Actually, these malignant tumors predominantly secrete the free beta subunit (hCG beta) and not hCG. Production of free hCG beta is especially found in patients with bladder, pancreas, uterine and lung tumors. In patients with neuroendocrine tumors, serum levels of free hCG beta are higher in gastrointestinal-pancreatic and lung tumors. The significance of ectopic production of hCG beta--epiphenomena or intrinsic biological role--remains unknown. Several reports on the similar structure of hCG beta and certain growth factors suggest that free hCG beta could have an effect on cell proliferation. Increased serum levels of the free alpha subunit are found mainly in patients with neuroendocrine tumors localized in the gut or lung. Serum levels may also be raised in patients with a pituitary tumor, but such production is often associated with a rise in other pituitary hormones. The free alpha subunit plays a role in embryon development and would stimulate production of prolactin by decidual cells. The free alpha subunit may also play a role in tumor growth. 相似文献
69.
OBJECTIVE: The purpose of this study was to determine if P300 latency is prolonged in geriatric depression and if longer P300 latency and deficits in initiation and errors of perseveration in depressed elderly patients are related to risk factors for vascular disease. METHOD: Geriatric patients with unipolar depression (N = 43) and elderly comparison subjects (N = 24) were assessed for depressive symptoms, cognitive functions, risk factors for vascular disease, and P300 latency. RESULTS: Depressed elderly patients had longer P300 latency than normal elderly subjects. In the depressed patients, P300 latency was related to deficits in initiation and errors in perseveration. Risk factors for vascular disease were associated not only with P300 latency but also with deficits in initiation and errors in perseveration. CONCLUSIONS: Functional impairment of the cortico-striato-pallido-thalamo-cortical pathways from vascular disease, implicated in late-life depressive disorders, may explain not only deficits in initiation and errors in perseveration but also longer P300 latency in depressed elderly patients. These results are preliminary and need further examination with brain imaging and more sensitive neuropsychological measures. 相似文献
70.
SD Bouffler 《Canadian Metallurgical Quarterly》1998,404(1-2):199-204
The genomes of higher eukaryotes are not homogeneous in terms of structure or function. Many examples of chromosomal regions particularly prone to involvement in aberrations have been reported. The molecular structures of some of these regions have now been determined, most notably the folate-sensitive fragile sites and FRA16B-a distamycin A-sensitive fragile site. In addition, a number of cytological studies suggest that telomeric sequences can in some circumstances be involved in chromosomal aberrations more frequently than expected. Here, the roles of telomeric DNA sequences, both terminal and interstitial, and telomerase in chromosomal aberration formation are reviewed. 相似文献