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   358篇
  免费   31篇
  国内免费   1篇
  390篇
  2023年   2篇
  2022年   3篇
  2021年   7篇
  2020年   5篇
  2019年   3篇
  2018年   13篇
  2017年   12篇
  2016年   8篇
  2015年   15篇
  2014年   16篇
  2013年   25篇
  2012年   22篇
  2011年   25篇
  2010年   21篇
  2009年   14篇
  2008年   16篇
  2007年   25篇
  2006年   17篇
  2005年   27篇
  2004年   19篇
  2003年   11篇
  2002年   19篇
  2001年   6篇
  2000年   8篇
  1999年   8篇
  1998年   1篇
  1997年   2篇
  1993年   1篇
  1992年   1篇
  1991年   5篇
  1990年   1篇
  1987年   2篇
  1985年   4篇
  1984年   4篇
  1983年   2篇
  1982年   3篇
  1980年   2篇
  1979年   2篇
  1974年   1篇
  1973年   1篇
  1972年   1篇
  1971年   1篇
  1969年   1篇
  1968年   2篇
  1966年   4篇
  1965年   1篇
  1954年   1篇
排序方式: 共有390条查询结果,搜索用时 0 毫秒
1.
In 17 hospitalized patients affected by acute myocardial infarction (AMI) PGE2 urinary excretion, renal function and, furthermore, cortisol urinary excretion were tested during a 21 days trial. In 12 patients all the parameters under consideration underwent a similar trend: PGE2 urinary excretion exactly like glomerular filtration rate, Na+ excretion and diuresis tended to be reduced during the first 5 days and they rapidly recovered the normality after this period. Cortisol urinary excretion displayed a characteristic pattern: i.e. the highest values were observed in the first days, followed by a progressive decrease towards physiological levels since the 4th day. Different findings were obtained in 5 cases treated with an antiinflammatory drug (Indoprophen i.m. 200 mg x2 die). In fact the low levels of urinary PGE2 on the first days did not display any increasing and GFR, urinary flow, and Na+ tubular balance underwent irregular and not significant variations. These data suggest that an impaired Prostaglandin synthesis may be related to a compromised renal function often occurring in AMI.  相似文献   
2.
3.
We aim to unravel the biogeographic structuring of western Palaearctic longhorn beetles with focus on the location of different refugia, barriers to dispersal and postglacial range expansions with their particular filters. The interaction of different ecological features with these structures is analysed. The western Palaearctic was divided into 95 geographic entities. We produced presence-only matrices for all 955 Cerambycoidea species autochthonous to this area and derived species richness distributions and extracted faunal regions and faunal elements by cluster analyses and principal component analyses. Similar analyses were performed for sub-families and ecological groups. Longhorn beetles show a strong biogeographic structuring in the western Palaearctic. Species numbers strongly decrease to the north and west. Less mobile species and root feeders mostly contribute to the fauna of the Mediterranean region, whilst mobile species are more widespread. Feeders on broad-leaved trees dominate in western Europe, whilst feeders on coniferous trees are most important in northern Europe. Our results support multiple refugia in the Mediterranean region and underline the importance of Provence, Crimea and Crete as such refugia. Crete even might be an area of old endemism. The Atlanto- and the Ponto-Mediterranean regions are more strongly structured than assumed in classical biogeography. Mediterranean assemblages are mostly composed of non-flying species, root feeders and species with small distributions not found outside their glacial refugia. Tree feeders left their glacial retreats with their host plants. These range dynamics result in biogeographic structures with several dispersal barriers and filters composed of mountains, sea straits and climatic conditions.  相似文献   
4.

Background

Influenza causes annual epidemics and often results in extensive outbreaks in closed communities. To minimize transmission, a range of interventions have been suggested. For these to be effective, an accurate and timely diagnosis of influenza is required. This is confirmed by a positive laboratory test result in an individual whose symptoms are consistent with a predefined clinical case definition. However, the utility of these clinical case definitions and laboratory testing in mass gathering outbreaks remains unknown.

Methods and Results

An influenza outbreak was identified during World Youth Day 2008 in Sydney. From the data collected on pilgrims presenting to a single clinic, a Markov model was developed and validated against the actual epidemic curve. Simulations were performed to examine the utility of different clinical case definitions and laboratory testing strategies for containment of influenza outbreaks. Clinical case definitions were found to have the greatest impact on averting further cases with no added benefit when combined with any laboratory test. Although nucleic acid testing (NAT) demonstrated higher utility than indirect immunofluorescence antigen or on-site point-of-care testing, this effect was lost when laboratory NAT turnaround times was included. The main benefit of laboratory confirmation was limited to identification of true influenza cases amenable to interventions such as antiviral therapy.

Conclusions

Continuous re-evaluation of case definitions and laboratory testing strategies are essential for effective management of influenza outbreaks during mass gatherings.  相似文献   
5.
6.
Human salivary cystatins, five major (S, S1, S2, SA, SN) and two minor (C and D), are multifunctional proteins playing a different role in the oral environment. Salivary cystatin SN is able to effectively inhibit lysosomal cathepsins B, C, H and L and cystatin SA inhibits cathepsins C and L in vitro. These activities suggest, particularly for cystatin SN, an important role in the control of proteolytic events in vivo. Differently, cystatins S are involved, together with statherin, in the mineral balance of the tooth. Due to their distinct role, a reliable method for identification and quantification of the different cystatins, as well as of possible truncated and derived forms, could be helpful for the assessment of the status of the oral cavity. To this purpose high-performance liquid chromatography electrospray ionization mass spectrometry (HPLC-ESI MS) was applied to the analysis of human saliva obtained from healthy subjects. All known salivary cystatins, with the exception of cystatin C, were detected. Strong evidence was also obtained for the presence in saliva of post-translational modified isoforms of cystatins, which may be related to donor habits. Cystatin SN and cystatins S, S1 and S2 were well separated by HPLC-ESI MS coupling from other components and thus this approach can be successfully applied to their quantification.  相似文献   
7.
Optical properties of tissues are required for theoretical modeling of Laser Ablation in tumor therapy. The light scattering characteristic of tissues is described by the anisotropy coefficient, g. The relationship between the angular distribution of scattered light and g is given by the Henyey‐Greenstein (HG) phase function. This work describes the estimation of anisotropy coefficients of ex vivo swine pancreas, liver and muscle at 1064 nm. The intensities of scattered light at fixed angles were measured under repeatability conditions. Experimental data were fitted with a two‐term HG, estimating the anisotropy coefficients for the forward (e.g., 0.956 for pancreas, 0.964 for liver and 0.968 for muscle) and the backward (e.g., –0.481 for pancreas, –0.414 for liver and –0.372 for muscle) scattering.

Experimental set up employed to estimate the anisotropy coefficient of biological tissues. The image on the left depicts the holder used to house tissue, laser fiber and photodetector; on the left an example of scattered light beam is shown, as well as the effect due to Snell's law.  相似文献   

8.
Ion channels provide a means for sensitive pH measurement at membrane interfaces. Detailed knowledge of the structure and function of gramicidin channels permits the engineering of pH-sensitive derivatives. Two derivatives, gramicidin-ethylenediamine and gramicidin-histamine, are shown to exhibit pH-dependent single-channel behaviour over the pH ranges 9-11 and 6.5-8.5, respectively. Thermal isomerization of a carbamate group at the entrance of the channels leads to a pattern of steps in single-channel recordings. The size of the steps depends on the time-averaged degree of protonation of the appended group (ethylenediamine or histamine). Measurement of the size of the steps thus permits single-molecule pH sensing under symmetrical pH conditions or in the presence of a pH gradient.  相似文献   
9.
The results of 2-aminohistamine (compound I) and 2-amino-5-methylhistamine (compound II) on cat acid secretion and on guinea pig gall-bladder motility are described and compared with those of Histamine or Dimaprit. The compound (I) showed a greater H2- than H1-receptor stimulating activity, while compound (II), inactive on H1, was effective on H2-receptors, being endowed with a less "potency" and "efficacy" than compound (I). The pharmacological activities of both compounds, related to their chemical structure, are discussed.  相似文献   
10.
The chemical composition of the essential oils obtained from the seeds of bush onion (Afrostyrax lepidophyllus) and tropical garlic tree (Scorodophloeus zenkeri), plants used as spices in the traditional African cuisine, was determined by GC‐FID and GC/MS analyses. Moreover, in vitro biological properties of the oils, namely, the cytotoxic, antioxidant, and antimicrobial activities, were investigated by the MTT, the DPPH. and ABTS.+ scavenging, and the agar disc‐diffusion methods, respectively. Both oils were composed mainly by S‐containing compounds, accounting for 91.0–96.1% of the total oil compositions, which provided them the typical garlic‐ and onion‐like odors of spices. The predominant compound in both oils, 2,4,5,7‐tetrathiaoctane ( 1 ; 51.5–52.9%), was isolated by preparative TLC and structurally elucidated by 1H‐ and 13C‐NMR data. The oils exhibited a strong inhibitory effect on the growth of human cancer cells, namely, T98G (human glioblastoma multiforme cell line), MDA‐MB 231 (human breast adenocarcinoma cell line), A375 (human malignant melanoma cell line), and HCT116 (human colon carcinoma cell line) cells, and a good DPPH.‐ and ABTS.+‐scavenging activity, while the antimicrobial effects were negligible. The volatile compositions of A. lepidophyllus and S. zenkeri oils supported their use as odorous spices. The significant inhibition activities detected make these oils worthy of further investigation as promising chemopreventive agents to be exploited in the African pharmaceutical market.  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