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   137篇
  免费   5篇
  2023年   1篇
  2021年   5篇
  2020年   2篇
  2019年   2篇
  2018年   3篇
  2017年   2篇
  2016年   4篇
  2015年   7篇
  2014年   12篇
  2013年   6篇
  2012年   12篇
  2011年   6篇
  2010年   9篇
  2008年   5篇
  2007年   11篇
  2006年   3篇
  2005年   3篇
  2004年   4篇
  2003年   11篇
  2002年   4篇
  2001年   6篇
  2000年   4篇
  1999年   8篇
  1998年   1篇
  1997年   1篇
  1995年   1篇
  1992年   2篇
  1988年   2篇
  1986年   2篇
  1981年   1篇
  1980年   1篇
  1971年   1篇
排序方式: 共有142条查询结果,搜索用时 31 毫秒
71.
We sought to determine whether carotid baroreflex (CBR) control of muscle sympathetic nerve activity (MSNA) was altered during dynamic exercise. In five men and three women, 23.8 +/- 0.7 (SE) yr of age, CBR function was evaluated at rest and during 20 min of arm cycling at 50% peak O(2) uptake using 5-s periods of neck pressure and neck suction. From rest to steady-state arm cycling, mean arterial pressure (MAP) was significantly increased from 90.0 +/- 2.7 to 118.7 +/- 3.6 mmHg and MSNA burst frequency (microneurography at the peroneal nerve) was elevated by 51 +/- 14% (P < 0.01). However, despite the marked increases in MAP and MSNA during exercise, CBR-Delta%MSNA responses elicited by the application of various levels of neck pressure and neck suction ranging from +45 to -80 Torr were not significantly different from those at rest. Furthermore, estimated baroreflex sensitivity for the control of MSNA at rest was the same as during exercise (P = 0.74) across the range of neck chamber pressures. Thus CBR control of sympathetic nerve activity appears to be preserved during moderate-intensity dynamic exercise.  相似文献   
72.
73.
Muscle sympathetic nerve activity (MSNA) and arterial pressure increase concomitantly during apnea, suggesting a possible overriding of arterial baroreflex inhibitory input to sympathoregulatory centers by apnea-induced excitatory mechanisms. Apnea termination is accompanied by strong sympathoinhibition while arterial pressure remains elevated. Therefore, we hypothesized that the sensitivity of carotid baroreflex control of MSNA would decrease during apnea and return upon apnea termination. MSNA and heart rate responses to -60-Torr neck suction (NS) were evaluated during baseline and throughout apnea. Responses to +30-Torr neck pressure (NP) were evaluated during baseline and throughout 1 min postapnea. Apnea did not affect the sympathoinhibitory or bradycardic response to NS (P > 0.05); however, whereas the cardiac response to NP was maintained postapnea, the sympathoexcitatory response was reduced for 50 s (P < 0.05). These data demonstrate that the sensitivity of carotid baroreflex control of MSNA is not attenuated during apnea. We propose a transient rightward and upward resetting of the carotid baroreflex-MSNA function curve during apnea and that return of the function curve to, or more likely beyond, baseline (i.e., a downward and leftward shift) upon apnea termination may importantly contribute to the reduced sympathoexcitatory response to NP.  相似文献   
74.
We tested the hypothesis that the cardiac-related rhythm in muscle sympathetic nerve activity (MSNA) of humans reflects entrainment of a central oscillator by pulse-synchronous baroreceptor nerve activity. Partial autospectral analysis was used to mathematically remove the portion of cardiac-related power in MSNA autospectra that was attributable to its linear relationship to the ECG. In 54 of 98 cases, > or =15% of cardiac-related power remained after partialization with the ECG; peak residual cardiac-related power was often at a frequency different than heart rate. When assessed on a cardiac-related burst-by-burst basis, there was a progressive and cyclic change in the ECG-MSNA interval (delay from R wave to peak of cardiac-related burst) on the time scale of respiration in four subjects. In these subjects, as well as in some in which the interval appeared to change randomly, there was an inverse relationship between the ECG-MSNA interval and cardiac-related burst amplitude. However, in 45% of the cases, these parameters were not related. These results support the view that the cardiac-related rhythm in MSNA reflects forcing of a nonlinear oscillator rather than periodic inhibition of unstructured, random activity.  相似文献   
75.
Bananal is an important focus of Schistosoma mansoni in the State of S?o Paulo. Accordingly, programmed active search for human cases, annual coproscopic surveys and treatment of infected cases were started in 1998, aiming at producing a sharp prevalence rate drop by the year 2000. S. mansoni eggs were searched for in two Kato-Katz slides per patient. Cases were followed up according to the routine of the local Family Health Program. In 1998, 130 samples out of 3,860 showed S. mansoni eggs; in 1999, 105 out of 3,550, and in 2000, 64 out of 3,528. Prevalence rates were 3.4%, 2.9%, and 1.8%, and average egg-counts 59, 64, and 79 eggs per gram of feces respectively. Prevalence rates decreased steadily after treatment, but persistently positive cases showed no significant decrease in parasite burdens. Egg count variation depended on sex and age bracket. Persistent residual cases admittedly preclude the eradication of this infection by only searching for and treating carriers. In addition, resistance to therapy and low sensitivity of fecal examinations, can not be ignored. Moderate to heavy worm burdens, frequently associated with hepatomegaly elsewhere, produced no serious cases in Bananal.  相似文献   
76.
Caramelization of maltose solution in presence of alanine   总被引:1,自引:0,他引:1  
Fadel HH  Farouk A 《Amino acids》2002,22(2):199-213
Summary. Two solutions of maltose in water were used to prepare caramels. Alanine as a catalyst was added to one of these solutions. The caramelization was conducted at 130°C for total time period 90 minutes. Convenient samples were taken of each caramel solution every 30 min and subjected to sensory analysis and isolation of volatile components. The odour and colour sensory tests were evaluated according to the international standard methods (ISO). The results showed that, the presence of alanine gave rise to a high significant (P < 0.01) decrease in acid attributes and remarkable increase in the sweet and caramel attributes, which are the most important caramel notes. On the other hand the increase in heating time in presence of alanine as a catalyst resulted in a high significant (P < 0.01) increase in the browning rate of caramel solution. The new technique Solid Phase Micro Extraction (SPME) was used for trapping the volatile components in the headspace of each caramel samples followed by thermal desorption and GC and GC – MS analysis. The 5-hydroxymethyl-2-furfural (HMF), the main characteristic caramel product, showed its highest value in sample containing alanine after heating for 60 minutes. The best sensory results of the sample contains alanine were confirmed by the presence of high concentrations of the most potent odorants of caramel besides to the formation of some volatile compounds have caramel like flavours such as 2-acetyl pyrrole, 2-furanones and 1-(2-furanyl)1,2-propandione. Received April 26, 2000 Accepted February 8, 2001  相似文献   
77.
A common measure of the relative toxicity is the ratio of median lethal doses for responses estimated in two bioassays. Robertson and Preisler previously proposed a method for constructing a confidence interval for the ratio. The applicability of this technique in common experimental situations, especially those involving small samples, may be questionable because the sampling distribution of this ratio estimator may be highly skewed. To examine this possibility, we did a computer simulation experiment to evaluate the coverage properties of the Robertson and Preisler method. The simulation showed that the method provided confidence intervals that performed at the nominal confidence level for the range of responses often observed in pesticide bioassays. Results of this study provide empirical support for the continued use this technique.  相似文献   
78.
Although a large part of the global domestic dog population is free-ranging and free-breeding, knowledge of genetic diversity in these free-breeding dogs (FBDs) and their ancestry relations to pure-breed dogs is limited, and the indigenous status of FBDs in Asia is still uncertain. We analyse genome-wide SNP variability of FBDs across Eurasia, and show that they display weak genetic structure and are genetically distinct from pure-breed dogs rather than constituting an admixture of breeds. Our results suggest that modern European breeds originated locally from European FBDs. East Asian and Arctic breeds show closest affinity to East Asian FBDs, and they both represent the earliest branching lineages in the phylogeny of extant Eurasian dogs. Our biogeographic reconstruction of ancestral distributions indicates a gradual westward expansion of East Asian indigenous dogs to the Middle East and Europe through Central and West Asia, providing evidence for a major expansion that shaped the patterns of genetic differentiation in modern dogs. This expansion was probably secondary and could have led to the replacement of earlier resident populations in Western Eurasia. This could explain why earlier studies based on modern DNA suggest East Asia as the region of dog origin, while ancient DNA and archaeological data point to Western Eurasia.  相似文献   
79.
The resumption of tuberculosis led to an increased need to understand the molecular mechanisms of drug action and drug resistance, which should provide significant insight into the development of newer compounds. Isoniazid (INH), the most prescribed drug to treat TB, inhibits an NADH-dependent enoyl-acyl carrier protein reductase (InhA) that provides precursors of mycolic acids, which are components of the mycobacterial cell wall. InhA is the major target of the mode of action of isoniazid. INH is a pro-drug that needs activation to form the inhibitory INH-NAD adduct. Missense mutations in the inhA structural gene have been identified in clinical isolates of Mycobacterium tuberculosis resistant to INH. To understand the mechanism of resistance to INH, we have solved the structure of two InhA mutants (I21V and S94A), identified in INH-resistant clinical isolates, and compare them to INH-sensitive WT InhA structure in complex with the INH-NAD adduct. We also solved the structure of unliganded INH-resistant S94A protein, which is the first report on apo form of InhA. The salient features of these structures are discussed and should provide structural information to improve our understanding of the mechanism of action of, and resistance to, INH in M. tuberculosis. The unliganded structure of InhA allows identification of conformational changes upon ligand binding and should help structure-based drug design of more potent antimycobacterial agents.  相似文献   
80.
Bloodstream infection caused by Clostridium symbiosum was previously reported in only one case, from a highly immunocompromised patient with metastic colon cancer. We describe the second case of clinical bacteraemic sepsis caused by C. symbiosum from a previously healthy man, which underlines the pathogenicity of this species.  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