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   248篇
  免费   1篇
化学工业   23篇
建筑科学   1篇
矿业工程   1篇
能源动力   2篇
轻工业   5篇
水利工程   1篇
无线电   15篇
一般工业技术   8篇
冶金工业   189篇
自动化技术   4篇
  2022年   5篇
  2020年   2篇
  2019年   2篇
  2018年   3篇
  2016年   2篇
  2013年   6篇
  2012年   4篇
  2011年   2篇
  2009年   3篇
  2008年   1篇
  2006年   2篇
  2005年   1篇
  2004年   2篇
  2003年   2篇
  2000年   1篇
  1999年   4篇
  1998年   53篇
  1997年   30篇
  1996年   26篇
  1995年   13篇
  1994年   7篇
  1993年   12篇
  1992年   2篇
  1991年   3篇
  1990年   3篇
  1989年   2篇
  1986年   1篇
  1985年   3篇
  1983年   1篇
  1982年   2篇
  1981年   3篇
  1980年   1篇
  1979年   4篇
  1978年   1篇
  1977年   8篇
  1976年   8篇
  1975年   1篇
  1973年   1篇
  1972年   1篇
  1970年   2篇
  1968年   2篇
  1967年   1篇
  1964年   3篇
  1963年   1篇
  1962年   1篇
  1959年   2篇
  1957年   1篇
  1955年   1篇
  1944年   1篇
  1932年   2篇
排序方式: 共有249条查询结果,搜索用时 78 毫秒
51.
The author reviews the literature on factors which influence the health of African Americans. The concept of poverty as a health problem is discussed as well as the feminization of poverty. The author implores health care workers, to begin to implement the concepts of ethnicity and culture when giving care to clients of color.  相似文献   
52.
Ischaemic injury was produced in the dog heart by occluding the left anterior descending coronary artery just below the second diagonal branch for the duration of 3 h. A prostacyclin analogue, ZK 36374 (Iloprost) was administered (10 micrograms/kg) just before the coronary artery occlusion. During 3 h occlusion ATP levels in the ischaemic area declined from 65.4 +/- 7.1 mM/g protein in sham-operated group to 31.5 +/- 5.2 microM/g protein in no-drug group and to 44.1 +/- 5.0 microM/g protein in Iloprost group. Creatine phosphate decreased from 112 +/- 14 microM/g protein, to 81 +/- 10 microM/g protein in no-drug group and to 95 +/- 12 microM/g protein in Iloprost group. The energy charge (ATP + 0.5 ADP/ATP + ADP + AMP) decreased slightly but not significantly in no-drug and Iloprost group. Three hours of LAD occlusion produced a significant fall in SOD activity in the ischaemic heart in comparison to the non-ischaemic and Iloprost-treated hearts.  相似文献   
53.
The first annual Flaviviridae Symposium, sponsored by ICN Pharmaceuticals Inc., was held in Lyon, France, on 9 October, 1997, to communicate current understanding on the Flaviviridae. This multidisciplinary symposium attracted over 300 international delegates and presentations covered virology, viral pathogenesis, potential therapies and strategies for vaccine development. The symposium reviewed the research area that may lead to the discovery and design of human and veterinary medicines against members of this virus family.  相似文献   
54.
BACKGROUND: Myocardial revascularization without cardiopulmonary bypass has been proposed as a potential therapeutic alternative in high-risk patients undergoing coronary artery bypass grafting. To evaluate this possibility we compared 15 high-risk (HR) patients in whom minimally invasive direct coronary artery bypass grafting was used as the method of revascularization with 41 consecutive patients who underwent conventional coronary artery bypass grafting during 1 month. METHODS: Patients undergoing myocardial revascularization without cardiopulmonary bypass were significantly older than their low-risk (LR) counterparts (72.2 +/- 11.6 versus 63.3 +/- 9.7 years, p = 0.006). The demographic profile for HR versus LR patients was as follows: female patients, 60.0% versus 26.8%, p = 0.02; diabetes, 20.0% versus 24.4%, p = 0.7; prior stroke, 33.3% versus 7.4%, p = 0.03; chronic obstructive pulmonary disease, 60.0% versus 9.8%, p < 0.0001; peripheral vascular disease, 33.3% versus 12.2%, p = 0.03, congestive heart failure, 26.6% versus 9.8%, p = 0.09; impaired left ventricular (ejection fraction < 0.40), 40.0% versus 17.0%, p = 0.07; urgent operation, 86.6% versus 46.3%, p < 0.0001; and redo operation, 20.0% versus 0%, p = 0.003. RESULTS: There were no deaths in the HR group and one death in the LR group. The average intensive care unit stay was 1.1 +/- 0.5 days in HR patients versus 1.6 +/- 1.6 days in LR individuals (p = 0.2), and the average hospital stay was 6.1 +/- 1.8 versus 7.3 +/- 4.4 days, respectively (p = 0.3). We used an acuity risk score index developed by the Adult Cardiac Care Network of Ontario to predict outcome in the HR group. The expected intensive care unit stay in HR patients was 4.1 +/- 1.2 days (versus the observed stay of 1.1 +/- 0.5 days, p < 0.0001), and the expected hospital stay was 12.5 +/- 1.5 days (versus the observed stay of 6.1 +/- 1.8 days, p < 0.0001). The expected mortality in the HR group was 6.1% versus 0%, p = 0.3. A cost regression model was used to examine predicted versus actual cost (in Canadian dollars) for the HR patient cohort (based on Ontario Ministry of Health funding). The expected cost for the HR cohort would have been $11,997 per patient. In contrast, the average cost for these 15 patients was $5,997 per patient, an estimated cost saving of 50%. CONCLUSIONS: Myocardial revascularization without cardiopulmonary bypass appears to be a safe and cost-effective therapeutic modality for HR patients requiring myocardial revascularization.  相似文献   
55.
OBJECTIVE: To examine the functional integrity of the hypothalamic-pituitary-adrenal (HPA) and thyroid axes in Sj?gren's syndrome (SS) via the assessment of basal and stimulated adrenocorticotropin (ACTH), cortisol, thyroid stimulating hormone (TSH), and prolactin levels. METHODS: Pituitary function of the HPA axis was assessed by determining the basal plasma levels of ACTH in the late afternoon, as well as the ACTH released to ovine corticotropin releasing hormone (oCRH) stimulation; adrenal function was assessed by measuring plasma cortisol levels in the late afternoon at baseline and after release of the endogenous ACTH during oCRH stimulation. Basal and thyrotropin releasing hormone (TRH) stimulated levels of TSH and prolactin were also assessed. Healthy volunteers were used as controls. RESULTS: Patients with SS, compared to controls, were characterized by significantly lower ACTH levels (pg/ml), (5.1 +/- 0.5 vs 11.4 +/- 1.5, respectively; p < 0.05) and cortisol levels (microg/ml), (2.4 +/- 0.6 vs 5.9 +/- 1.2, respectively; p < 0.05). Furthermore, a blunted pituitary and adrenal response to oCRH compared to controls was observed: peak plasma ACTH and cortisol levels for patients with SS were 46.2 +/- 5.4 pg/ml and 15.7 +/- 1.6 microg/ml, respectively, and for controls 61.5 +/- 3.8 and 19.6 +/- 0.7, respectively (p < 0.05). Basal TSH levels were significantly elevated in patients (1.3 +/- 0.3 microIU/ml vs 0.9 +/- 0.05 microIU/ml; p < 0.05). CONCLUSION: The above findings indicate hypoactivity of the HPA axis in patients with SS. Further studies are needed to definitively identify the locus of the defects and assess the significance of the pattern of the perturbations to the pathogenesis and expression of SS.  相似文献   
56.
Unreliability of numerical data causes difficulties in computer systems for decision-making, risk assessment, and similar activities. Much human judgment is non-numerical and able to make useful evaluations of alternatives under uncertainty. The Logic of Argumentation (LA) offers a basis for computerized support of decision-making in the absence of numerical data, and it is being used in a project on carcinogenic risk assessment, StAR. There are potential applications of LA in other artificial intelligence systems in chemistry, such as for synthesis planning.  相似文献   
57.
58.
59.
A highly integrated transmit integrated circuit intended for dual-band (CELL/PCS) and triple-mode (CDMA/TDMA/AMPS) cellular mobile stations is presented. It features a linear-in-dB gain-control range of 90 dB and provides a high output power of 9 dBm (PCS band) while meeting linearity requirements (-53-dBc ACPR) and achieving the receive-band noise floor of -133 dBm/Hz. It consumes only 130-mA current (3-V supply) in the PCS band. A dynamic-biasing feature results in additional power savings at lower signal levels. The circuit is fabricated in a 30-GHz f/sub T/ BiCMOS technology.  相似文献   
60.
Laser Doppler anemometer (LDA) experiments were performed to gain quantitative information on the differences between the large-scale flow phenomena in a non-stenosed and a stenosed model of the carotid artery bifurcation. The influence of the presence of the stenosis was compared to the effect of flow pulse variation to evaluate the feasibility of early detection of stenosis in clinical practice. Three-dimensional Plexiglass models of a non-stenosed and a 25% stenosed carotid artery bifurcation were perfused with a Newtonian fluid. The flow conditions approximated physiological flow. The results of the velocity measurements in the non-stenosed model agreed with the results from previous hydrogen-bubble visualization. A shear layer separated the low-velocity area near the non-divider wall from the high-velocity area near the divider wall. In this shear layer, vortex formation occurred during the deceleration phase of the flow pulse. The instability of this shear layer dictated the flow disturbances. The influences of the mild stenosis, located at the non-divider wall, was mainly limited to the stability of the shear layer. No disturbances were found downstream of the stenosis near the non-divider wall. Using a pulse wave with an increased systolic deceleration time, the velocity distribution showed an extended region with reversed flow, a more pronounced shear layer and increased vortex strength. From these measurements it is obvious that the influence of the presence of a mild stenosis, mainly limited to the stability of the shear layer, can hardly be distinguished from the effects of a variation of the flow pulse. From this it can be concluded that methods for detection of mild stenosis, using solely the large-scale flow phenomena, as can be measured by ultrasound or MRI techniques, will hardly have any clinical relevance.  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