全文获取类型
收费全文 | 1557篇 |
免费 | 2篇 |
专业分类
化学工业 | 8篇 |
金属工艺 | 2篇 |
机械仪表 | 1篇 |
能源动力 | 4篇 |
轻工业 | 3篇 |
无线电 | 14篇 |
一般工业技术 | 4篇 |
冶金工业 | 1513篇 |
原子能技术 | 1篇 |
自动化技术 | 9篇 |
出版年
2021年 | 1篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2017年 | 1篇 |
2015年 | 3篇 |
2014年 | 1篇 |
2012年 | 1篇 |
2011年 | 1篇 |
2009年 | 1篇 |
2008年 | 3篇 |
2007年 | 2篇 |
2006年 | 4篇 |
2005年 | 2篇 |
2003年 | 3篇 |
2002年 | 1篇 |
2001年 | 1篇 |
1999年 | 49篇 |
1998年 | 526篇 |
1997年 | 265篇 |
1996年 | 175篇 |
1995年 | 92篇 |
1994年 | 78篇 |
1993年 | 110篇 |
1992年 | 14篇 |
1991年 | 20篇 |
1990年 | 14篇 |
1989年 | 15篇 |
1988年 | 16篇 |
1987年 | 10篇 |
1986年 | 13篇 |
1985年 | 11篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1977年 | 36篇 |
1976年 | 52篇 |
1975年 | 3篇 |
1956年 | 1篇 |
排序方式: 共有1559条查询结果,搜索用时 21 毫秒
81.
Selenium is a trace element which plays a vital role in many metabolic functions and in particular is an integral part of the antioxidant enzyme glutathione peroxidase. It may be involved in the prevention of a number of diseases including cardiovascular diseases and cancer, which are the main causes of death in Singapore with ethnic differences. The National University of Singapore Heart Study measured cardiovascular risk factors, including serum selenium, in a random of the general population aged 30 to 69 years from 1993 to 1995. Mean serum selenium was higher in Chinese (males 126 and females 119 micrograms/L) and Malays (males 122 and females 122 micrograms/L) than Indians (males 117 and females 115 micrograms/L). These levels (with an estimated mean of 122 micrograms/L in Singapore) are lower than those in the USA but higher than those in Western Europe. The proportions with serum selenium < 80 micrograms/L (classified as low values) were low, though highest in Indians (males 1.2% and females 1.2%), then Chinese (males 0.6% and females 1.3%) and then Malays (males 0.0% and females 0.0%), but the differences were not statistically significant. The overall estimate for the prevalence of low selenium in Singapore was 0.8%. It is concluded that levels of serum selenium in Singapore are satisfactory and no action with regard to dietary supplementation is needed. Serum selenium levels are slightly lower in Indians than in Chinese and Malays (probably due to a more vegetarian diet) and this may make a small contribution to Indians' higher rates of coronary heart disease compared to Chinese and Malays. 相似文献
82.
P Garside E Ingulli RR Merica JG Johnson RJ Noelle MK Jenkins 《Canadian Metallurgical Quarterly》1998,281(5373):96-99
Early events in the humoral immune response were visualized in lymph nodes by simultaneous tracking of antigen-specific CD4 T and B cells after immunization. The T cells were initially activated in the T cell areas when the B cells were still randomly dispersed in the B cell-rich follicles. Both populations then migrated to the edges of the follicles and interacted there, resulting in CD154-dependent B cell proliferation and germinal center formation. These results provide visual documentation of cognate T-B cell interactions and localize them to the follicular border. 相似文献
83.
The pool of thrombin and fibrinogen in circulation, in organs, and on cardiopulmonary bypass devices was quantified during and after cardiopulmonary bypass in four groups of 24 Yorkshire pigs (weight, 30-35 kg); two groups of 10 unoperated pigs were used as controls. Thrombin-alpha and fibrinogen were iodinated with 125iodide using an iodogen transfer technique; 250-300 microCi of these tracers were injected intravenously 1 hr before cardiopulmonary bypass. All pigs were systematically heparinized (activated clotting time > 400 sec); cardiopulmonary bypass was performed at 2.5-3.5 L/min at 28 degrees C using a centrifugal pump, oxygenator (Bentley Univox 1.8 m2; Bentley Inc., Irvine, CA), arterial filter (0.25 m2), and cardiotomy reservoir (BMR 3500) for 90 min, followed by a 90 min reperfusion and 180 min of cardiopulmonary bypass. Iodinated thrombin-alpha and fibrinogen in intact organs and samples of blood, organs, tissues, and oxygenator-arterial filter-cardiotomy reservoir were quantified with an ion chamber and a gamma counter, respectively. The percent of injected iodinated thrombin-alpha and fibrinogen dose (mean +/- SD) in organs and cardiopulmonary bypass devices of all groups of cardiopulmonary bypass pigs was calculated. Thrombin generated at the small area of surgical wounds (0.016-0.038 m2), and fibrin deposited on surfaces of cardiopulmonary bypass devices (2.59 m2), initiate and propagate thrombus formation and embolization. The protein level reached saturation values on all cardiopulmonary bypass devices at 180 min. High levels of thrombin and fibrinogen-fibrin circulate in blood and organs, and are adsorbed on cardiopulmonary bypass devices; this large blood pool of pro-coagulants in the cardiac cradle, tissues, and perfused organs may account for thrombi and emboli during and after cardiopulmonary bypass. 相似文献
84.
85.
ML van Oppenraay CM van der Beek JE de Boer M Danz MK Schutte JP Verduijn 《Canadian Metallurgical Quarterly》1998,142(12):633-636
The Central Medical Pharmaceutical Committee of the Health Insurance Council informs the medical profession annually about the effects of drugs through the Pharmacotherapeutical Compass. The 1998 edition now contains a chapter on pharmacokinetics as well. Compared with previous editions the main alterations of the contents concern an introduction and advice on the antidepressants, two protocols with respect to the medical treatment of patients suffering from epilepsy, advice with respect to oral drugs for the treatment of inflammatory bowel disease, an introduction and advice regarding the treatment of allergic rhinitis, the treatment of patients suffering from AIDS with antiretroviral drugs, the treatment of genital herpes, the taking of insulin lispro by patients with diabetes and the taking of bisphosphonates to prevent or to treat osteoporosis. Two corrections to the 1998 edition are given. 相似文献
86.
87.
MF Hovell S Russos MK Beckhelm JA Jones SM Burkham-Kreitner DJ Slymen CR Hofstetter B Rubin 《Canadian Metallurgical Quarterly》1995,11(5):288-293
A sample of private orthodontic practices (n = 40) from a controlled trial for clinician-initiated tobacco-use prevention was used to test the effectiveness of preventive medicine representative (PMR) visits in creating and maintaining an anti-tobacco office environment. Clinical staff of 20 offices, randomly assigned to the experimental group, were trained by a PMR on the use of anti-tobacco materials (no-smoking signs, posters, and print materials). Twenty control-group offices did not receive any training or special treatment. Subsequently, experimental-group offices were visited by a PMR once every three months and were telephoned six weeks after each visit over a 12-month period. During visits and phone calls, PMRs prompted offices to order anti-tobacco materials. Visits served to introduce offices to new materials and to encourage their continued use. Data from direct observations and self-report measures showed significant differences between experimental and control offices for display of anti-tobacco materials at 1.5 months and 12 months (P < .001). Results suggest that PMR visits may serve as an effective method of introducing and maintaining preventive medicine procedures in clinical environments. 相似文献
88.
The chaperonins GroEL and GroES of Escherichia coli facilitate protein folding in an adenosine triphosphate (ATP)-dependent reaction cycle. The kinetic parameters for the formation and dissociation of GroEL-GroES complexes were analyzed by surface plasmon resonance. Association of GroES and subsequent ATP hydrolysis in the interacting GroEL toroid resulted in the formation of a stable GroEL:ADP:GroES complex. The complex dissociated as a result of ATP hydrolysis in the opposite GroEL toroid, without formation of a symmetrical GroEL:(GroES)2 intermediate. Dissociation was accelerated by the addition of unfolded polypeptide. Thus, the functional chaperonin unit is an asymmetrical GroEL:GroES complex, and substrate protein plays an active role in modulating the chaperonin reaction cycle. 相似文献
89.
To determine the minimal contrast dosage required for diagnostic contrast-enhanced three-dimensional (3D) magnetic resonance angiography (MRA) image quality of the pulmonary (PAs) or renal arteries (RAs). In 12 volunteers (10 females, 2 males; mean age 24 years) imaging was performed with 4 different dosages: 0.05, 0.1, 0.2 and 0.3 mmol/kg of body weight (BW) 0.5 M gadolinium (Gd) contrast agent. The PAs and RAs were evaluated separately each in groups of six volunteers. Qualitative and quantitative signal-to-noise ratio (SNR) image analysis was performed. For the PAs, the increases in signal-to-noise ratio were paralleled by increases in image quality ratings. For the PAs, with the use of 0.05 mmol/kg, only 50.3% of all segments were rated diagnostic, whereas with higher dosages the percentage rose to 89.2% for 0.1 mmol/kg, 98.2% for 0.2 mmol/kg. and 99.1% for 0.3 mmol/kg. For the RAs, 0.3 mmol/kg provided no significant increase in singal-to-noise ratio compared to 0.2 mmol/kg (p = 0.4). Only by a dosage of 0.2 and 0.3 mmol/kg, all evaluated segments were diagnostic evaluable. A dose of 0.2 mmol/kg is required for proper assessment of the RAs or PAs. 相似文献
90.
MK Hong SW Park CW Lee DH Kang JK Song JJ Kim SJ Park MK Hong GS Mintz MB Leon 《Canadian Metallurgical Quarterly》1998,82(5):670-3, A8
We evaluated the role of intravascular ultrasound (IVUS) in 16 patients with unprotected left main coronary artery (LMCA) stenting compared with 80 patients with other (non-LMCA) native coronary artery stenting and found that (1) additional high-pressure or larger size balloon dilations were more frequently performed in LMCA stenting than in non-LMCA stenting (p <0.05) and (2) after IVUS-guided stent implantation, minimum lumen area was > or = 9 mm2 in 88% of patients who underwent LMCA stenting and in 19% of those who underwent non-LMCA stenting (p <0.001). IVUS guidance may be a more important adjunctive imaging modality in the stenting of unprotected LMCA stenoses than in stenting of non-LMCA stenoses. 相似文献