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   1939篇
  免费   1篇
  国内免费   2篇
综合类   2篇
化学工业   7篇
金属工艺   1篇
机械仪表   3篇
建筑科学   3篇
轻工业   5篇
石油天然气   4篇
无线电   1篇
一般工业技术   2篇
冶金工业   1907篇
自动化技术   7篇
  2023年   1篇
  2022年   1篇
  2021年   2篇
  2014年   2篇
  2011年   2篇
  2010年   2篇
  2009年   2篇
  2008年   2篇
  2007年   4篇
  2006年   1篇
  2005年   1篇
  2004年   1篇
  2003年   5篇
  2001年   1篇
  2000年   3篇
  1999年   56篇
  1998年   600篇
  1997年   341篇
  1996年   209篇
  1995年   123篇
  1994年   93篇
  1993年   102篇
  1992年   26篇
  1991年   26篇
  1990年   24篇
  1989年   15篇
  1988年   21篇
  1987年   23篇
  1986年   25篇
  1985年   17篇
  1983年   3篇
  1982年   9篇
  1981年   15篇
  1980年   14篇
  1979年   2篇
  1978年   5篇
  1977年   52篇
  1976年   106篇
  1955年   1篇
  1924年   1篇
  1923年   1篇
  1921年   2篇
排序方式: 共有1942条查询结果,搜索用时 15 毫秒
131.
The triflates and pivalates of 3 alpha-hydroxymethyl-6-substituted-2,2-dimethylpenam sulfones 3, 5; methyl and benzyl 6-substituted penicillanates 6-9 and 3-exo-methylene-6-substituted-2,2-dimethylpenam sulfone 4 were synthesized. These novel compounds were evaluated as elastase inhibitors using porcine pancreatic elastase. The effects that structural modifications of substituents on C-3 and C-6 in the penam nucleus have on elastase activity were examined and several similarities and distinctions were identified when compared to the reported penicillin esters and amides elastase inhibitors.  相似文献   
132.
133.
An arginine to glutamine missense mutation at position 403 of the beta-cardiac myosin heavy chain causes familial hypertrophic cardiomyopathy. Here we study mice which have this same missense mutation (alphaMHC403/+) using an isolated, isovolumic heart preparation where cardiac performance is measured simultaneously with cardiac energetics using 31P nuclear magnetic resonance spectroscopy. We observed three major alterations in the physiology and bioenergetics of the alphaMHC403/+ mouse hearts. First, while there was no evidence of systolic dysfunction, diastolic function was impaired during inotropic stimulation. Diastolic dysfunction was manifest as both a decreased rate of left ventricular relaxation and an increase in end-diastolic pressure. Second, under baseline conditions alphaMHC403/+ hearts had lower phosphocreatine and increased inorganic phosphate contents resulting in a decrease in the calculated value for the free energy released from ATP hydrolysis. Third, hearts from alphaMHC403/+ hearts that were studied unpaced responded to increased perfusate calcium by decreasing heart rate approximately twice as much as wild types. We conclude that hearts from alphaMHC403/+ mice demonstrate work load-dependent diastolic dysfunction resembling the human form of familial hypertrophic cardiomyopathy. Changes in high-energy phosphate content suggest that an energy-requiring process may contribute to the observed diastolic dysfunction.  相似文献   
134.
135.
Hypoxia lowers the basic thermoregulatory responses of animals and humans. In cold-exposed animals, hypoxia increases core temperature (Tco) cooling rate and suppresses shivering thermogenesis. In humans, the experimental effects of hypoxia on thermoregulation are equivocal. Also, the effect of hypoxia has not been separated from that of hypocapnia consequent to hypoxic hyperventilation. To determine the isolated effects of hypoxia on warm and cold thermoregulatory responses and core cooling during mild cold stress, we examined the Tco thresholds for sweating, vasoconstriction, and shivering as well as the core cooling rates of eight subjects immersed in 28 degrees C water under eucapnic conditions. On 2 separate days, subjects exercised on an underwater cycle ergometer to elevate Tco above the sweating threshold. They then rested and cooled until they shivered vigorously. Subjects inspired humidified room air during the control trial. For the eucapnic hypoxia trial, they inspired 12% O2-balance N2 with CO2 added to maintain eucapnia. Eucapnic hypoxia lowered the Tco thresholds for vasoconstriction and shivering by 0.14 and 0.19 degrees C, respectively, and increased core cooling rate by 33% (1.83 vs. 1.38 degrees C/h). These results demonstrate that eucapnic hypoxia enhances the core cooling rate in humans during mild cold stress. This may be attributed in part to a delay in the onset of vasoconstriction and shivering as well as increased respiratory heat loss during hypoxic hyperventilation.  相似文献   
136.
OBJECTIVES: To ascertain the effects of dietary omega-3 (n-3) fatty acids on biochemical and histopathologic components of the inflammatory stage of wound healing. ANIMALS: 30 purpose-bred Beagles. PROCEDURE: Dogs were allotted to 5 groups of 6. Each group was fed a unique dietary fatty acid ratio of omega-6 to n-3--diet A, 5.3:1; diet B, 10.4:1; diet C, 24.1:1; diet D, 51.6:1; and diet E, 95.8:1. Dogs were fed once daily for 12 weeks, then biopsy specimens were taken from 4-day-old wounds of each dog and analyzed by gas chromatography-mass spectrometry for: prostaglandin E2 (PGE2) metabolites, and ratios of omega-6 to n-3 fatty acids, arachidonic acid (AA) to eicosapentaenoic acid (EPA), adrenic acid to docosahexaenoic acid, and PGE2 to prostaglandin E3 (PGE3) metabolites. RESULTS: Qualitative analysis was carried out on AA, EPA, adrenic acid, docosahexaenoic acid, and the major metabolite from the PGE2 and PGE3 pathway. These molecules were further quantified with respect to diet to determine significant differences. By analysis of the AA-to-EPA ratio, diet A was different from diets D and E and diets B and C were different from diet E (P < 0.05). By analysis of the PGE2-to-PGE3 metabolite ratio, diet A was different from diet E (P < 0.05). Though biochemical analysis indicated dietary dependence, histopathologic data indicated no significant difference with respect to diet groups. CONCLUSION: The biochemical component of the inflammatory stage of wound healing can be manipulated by diet. CLINICAL RELEVANCE: Omega-3 fatty acid-enriched diets can be used to control inflammation associated with dermatologic conditions.  相似文献   
137.
138.
The fungus Cunninghamella elegans was used to biotransform 6-nitrochrysene, a mutagen that is a widespread environmental contaminant. After 6 days, 74% of the 3H-labeled 6-nitrochrysene added had been metabolized to two isomeric sulfate conjugates. These conjugates were separated by high-performance liquid chromatography and identified by UV-visible, 1H nuclear magnetic resonance, and mass spectral techniques as 6-nitrochrysene 1-sulfate and 6-nitrochrysene 2-sulfate.  相似文献   
139.
A 35-year-old woman underwent reconstruction of her right pulmonary artery for treatment of acquired right pulmonary artery stenosis. The stenosis was secondary to tuberculosis causing both an extrinsic and an intrinsic obstructive component. After her reconstruction, the patient made an uneventful recovery, and perfusion to the right lung was subsequently restored.  相似文献   
140.
Under in vitro conditions N-alpha-tosyl L-arginine methyl ester (TAME) induced a concentration dependent contractile response on ileal strips with EC50 of 4.3 x 10(-5) M as compared to acetylcholine which induced sustainable contractions with EC50 of 3.2 x 10(-6) M. The present study is the first to demonstrate that TAME is a potent constrictor of non-airway smooth muscle.  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