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   2211篇
  免费   3篇
化学工业   14篇
金属工艺   2篇
机械仪表   3篇
建筑科学   18篇
能源动力   1篇
轻工业   24篇
水利工程   1篇
石油天然气   1篇
无线电   19篇
一般工业技术   15篇
冶金工业   2090篇
原子能技术   5篇
自动化技术   21篇
  2021年   2篇
  2017年   1篇
  2016年   2篇
  2015年   2篇
  2014年   1篇
  2013年   15篇
  2012年   2篇
  2011年   2篇
  2010年   5篇
  2009年   4篇
  2008年   8篇
  2007年   13篇
  2006年   7篇
  2005年   5篇
  2004年   7篇
  2003年   3篇
  2002年   6篇
  2001年   1篇
  2000年   1篇
  1999年   84篇
  1998年   675篇
  1997年   363篇
  1996年   236篇
  1995年   148篇
  1994年   116篇
  1993年   115篇
  1992年   19篇
  1991年   14篇
  1990年   15篇
  1989年   24篇
  1988年   25篇
  1987年   24篇
  1986年   20篇
  1985年   20篇
  1984年   6篇
  1983年   7篇
  1982年   7篇
  1981年   15篇
  1980年   14篇
  1979年   2篇
  1978年   6篇
  1977年   63篇
  1976年   95篇
  1975年   4篇
  1971年   3篇
  1970年   1篇
  1969年   1篇
  1966年   1篇
  1965年   1篇
  1964年   1篇
排序方式: 共有2214条查询结果,搜索用时 15 毫秒
81.
BACKGROUND: A major reduction in the energy demand of the myocardium results from the electromechanical arrest, and cooling contributes to a lesser degree to this reduction. It is from this assumption that strategies of myocardial protection, utilizing warm blood cardioplegic induction, followed by cold cardioplegia with terminal warm reperfusion before removal of the aortic cross clamp, became established as optimal myocardial protection. Continuous normothermic perfusion 'closed the loop' by avoiding myocardial ischemia and linking warm induction and terminal reperfusion. A series of laboratory and clinical data confirmed the benefits of warm heart surgery on myocardial function and metabolism. The disadvantages of continuous warm blood cardioplegia including disturbance of the operative field, led surgeons to administer warm hyperkalaemic blood intermittently as a new cardioplegic strategy. METHODS: This review examines the laboratory and clinical data with reference to the intermittent warm blood cardioplegia, to establish its experimental basis and place in clinical practice. CONCLUSIONS: Experimental observation and clinical application have established intermittent warm blood cardioplegia as a practical, effective and cheap myocardial protection technique, particularly with reference to coronary artery surgery.  相似文献   
82.
A total of 732 individuals affiliated with six Amazonian Indian populations were variously studied in relation to 26 protein genetic systems. Eleven of them were found to be monomorphic in these groups, in accordance with previous investigations. Similarities and dissimilarities (the latter involving the Rh, Duffy, haptoglobin and transferrin systems) were observed in relation to earlier investigations in four of these populations (Galibi, Palikour, Mundurucu and Tenharim). A dimeric, cathodal variant of albumin was found among two Galibi subjects, and the fairly common occurrence of CP* ACAY among some South American Indian populations was confirmed. The results in the six populations were compared with those from 29 others. When relationships are searched for among tribes of the same linguistic group, the factor that seems to be most influential is geographical localization, an exception being the pattern observed among the Cayapo subgroups. The latter shows genetic differences of the same level of magnitude as those observed among Ge-speaking tribes.  相似文献   
83.
84.
85.
86.
PURPOSE: To describe adolescents' and young adults' knowledge about their health insurance, and to identify factors associated with correct knowledge of health insurance in this population. METHODS: Data were analyzed from a confidential questionnaire administered to 830 patients at a hospital-based adolescent medicine clinic. The questionnaire contained items pertaining to insurance type, demographics, health status, and health-risk behaviors. Actual health insurance data and information regarding utilization of health services were obtained from the hospital billing data-base. Predictors of health insurance knowledge were determined through bivariate analyses followed by stepwise logistic regression. RESULTS: A total of 50.7% of respondents correctly identified their type of health insurance. Those who correctly identified their insurance had a higher mean age. Only 48.5% of participants who were 11-18 years old could identify their insurance type, versus 53.1% of 19-21-year-olds and 64.7% of 22-24-year-olds (p = 0.02). Sixty-five percent of Medicaid patients and 76.3% of hospital free care patients knew how their medical bills were paid, versus 17.9% of self-pay patients and 47.3% of patients with private insurance (p < 0.01). Greater utilization of health services was associated with increased rates of insurance knowledge among 19-24-year-olds on bivariate analysis; however, this factor was not significant when controlling for other factors. Regression analysis revealed that older age and insurance type other than self-payment were independent predictors of health insurance knowledge in adolescents (11-18 years old), while female gender and insurance type other than self-payment were independent predictors of insurance knowledge in young adults (19-24 years old). CONCLUSIONS: Approximately half of adolescents and young adults do not know how their medical bills are paid. Validation of self-reported insurance data is, therefore, critical both in clinical practice and health services research.  相似文献   
87.
Non-invasive evaluation of gastric emptying is generally performed by scintigraphy which is, however, not always applicable and is not suitable for children and child-bearing women. Recently, a new method based on stable isotope breath testing has been introduced in clinical practice i.e., the 13C-octanoic acid breath test. An overview is made here of the current knowledge on this technique with special emphasis on the principle of the test, the mathematics used to analyse the results, and the physiological, pathological, and pharmacological aspects of gastric emptying studied with this new method. Possible pitfalls of the test are also reported.  相似文献   
88.
89.
Giant-cell interstitial Pneumonia (GIP) is a very uncommon respiratory disease. The majority of cases of GIP are caused by exposure to cobalt, tungsten and other hard metals. In this report, we describe GIP in a patient who worked in gas station and dealt in propane gas vessels. He presented with clinical features of chronic interstitial lung disease and underwent an open lung biopsy that showed DIP-like reaction with large numbers of intra-alveolar macrophages and numerous large, multinucleated histiocytes which were admixed with the macrophages. Analysis of lung tissue for hard metals was done. Cobalt was the main component of detected hard metals. Corticosteroid therapy was started and he recovered fully.  相似文献   
90.
To assess the involvement of cellular inhibition and the appearance of apoptosis in regression of the hyperplastic thyroid gland towards normality, an experimental design was used to elicit non-toxic goiter by inducing hyperplastic goiter in rats by treatment with methimazole. We performed a morphological and PCNA immunocytochemical study together with in situ end labelling with bromodeoxyuridine in thyroid glands of rats receiving methimazole in their drinking water over 21 days after which they were allowed a recovery period of 0, 12, 24, 36, 48 and 72 h and 7, 14, 21 and 44 days. Serum T3 and T4 levels were found to be very low in the methimazole-treated animals although they increased after the goitrogenic compound had been withdrawn. Inhibition of cell proliferation and the burst of apoptosis play important roles in the regression of hyperplastic goiter in rats. Cell proliferation, which was strongly stimulated during goiter, fell significantly at 24 h, thereafter decreasing gradually as the recovery period progressed. Isolated cases of thyrocyte necrosis were observed ultrastructurally. Light and transmission electron microscopy revealed the existence of thyroid apoptosis with respect to the development of the study over time. Most apoptotic thyrocytes became detached from the follicular epithelium and later underwent cellular degeneration in the follicular lumen. The remaining apoptotic cells retracted their cytoplasm, lost contact with the follicular lumen and became located at the base of the follicles. The percentage of apoptosis showed that during the first week of thyroid involution apoptosis was already present but with low percentages while maximum values were attained at 21 days of survival. Our results suggest that, in the rat, during the return of thyroid follicular cells to normality after methimazole-induced hyperplastic goiter a balance arises between proliferation and cell death and that this balance is due to the inhibition of cellular proliferation and, secondarily, to the appearance of apoptosis, which becomes particularly evident towards the end of the first week after withdrawing the goitrogenic agent.  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