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   315篇
  免费   14篇
  2023年   2篇
  2022年   4篇
  2021年   3篇
  2020年   7篇
  2019年   14篇
  2018年   5篇
  2017年   8篇
  2016年   12篇
  2015年   6篇
  2014年   18篇
  2013年   29篇
  2012年   25篇
  2011年   26篇
  2010年   19篇
  2009年   15篇
  2008年   15篇
  2007年   20篇
  2006年   26篇
  2005年   13篇
  2004年   22篇
  2003年   19篇
  2002年   6篇
  2001年   5篇
  2000年   1篇
  1999年   3篇
  1998年   1篇
  1994年   2篇
  1993年   1篇
  1985年   1篇
  1982年   1篇
排序方式: 共有329条查询结果,搜索用时 46 毫秒
81.
Using laboratory challenge experiments, we examined whether Campylobacter-specific maternal antibody (MAB) plays a protective role in young chickens, which are usually free of Campylobacter under natural production conditions. Kinetics of C. jejuni colonization were compared by infecting 3-day-old broiler chicks, which were naturally positive for Campylobacter-specific MAB, and 21-day-old broilers, which were negative for Campylobacter-specific MAB. The onset of colonization occurred much sooner in birds challenged at the age of 21 days than it did in the birds inoculated at 3 days of age, which suggested a possible involvement of specific MAB in the delay of colonization. To further examine this possibility, specific-pathogen-free layer chickens were raised under laboratory conditions with or without Campylobacter infection, and their 3-day-old progenies with (MAB(+)) or without (MAB(-)) Campylobacter-specific MAB were orally challenged with C. jejuni. Significant decreases in the percentage of colonized chickens were observed in the MAB(+) group during the first week compared with the MAB(-) group. These results indicate that Campylobacter-specific MAB plays a partial role in protecting young chickens against colonization by C. jejuni. Presence of MAB in young chickens did not seem to affect the development of systemic immune response following infection with C. jejuni. However, active immune responses to Campylobacter occurred earlier and more strongly in birds infected at 21 days of age than those infected at 3 days of age. Clearance of Campylobacter infection was also observed in chickens infected at 21 days of age. Taken together, these findings (i) indicate that anti-Campylobacter MAB contributes to the lack of Campylobacter infection in young broiler chickens in natural environments and (ii) provide further evidence supporting the feasibility of development of immunization-based approaches for control of Campylobacter infection in poultry.  相似文献   
82.
We searched for serum concentrations of trace elements and correlated them to malondialdehyde (MDA), which is an indirect marker of oxidative stress, in order to clarify if routine evaluation is necessary in chronic obstructive pulmonary disease (COPD) outpatients. Serum concentrations of copper (Cu), zinc (Zn), and magnesium (Mg) were determined by atomic absorption spectrophotometry and iron (Fe) by a ILLab 1800 autoanalyzer with ILLab test kits. Serum MDA concentrations were detected in terms of TBARS (thiobarbituric acid reactive substances) spectrophotometrically. Serum Cu, Zn, Mg, Fe, and MDA concentrations in patient and control groups were all in the normal reference range. The results respectively were as follows: Cu:123±29.2 and 122.2±23.4 μg/dL; Zn: 87.8±17.8 and 96.9 ± 12.9 μg/dL; Mg: 2.3±0,5 and 2.04±0.28 mg/dL; Fe: 73.8±35.5 and 80.7±51.2 μg/dL; MDA: 1.09±0.11 and 0.95±0.06 nmol/L. MDA was not correlated to Cu, Zn, Mg, or Fe (p>0.05 for all). The serum Zn concentration of COPD group was lower than the control group (p=0.042), whereas the Mg concentration was higher (p=0.021). There was no statistical difference in other study parameters. Oxidative stress was not increased in clinically stable, regularly treated COPD patients. Although there was no deficiency in trace elements (Cu, Fe, Mg, and Zn), serum Zn was close to the lower limit of the reference value. There is no need for routine evaluation of trace elements in clinically stable, regularly treated COPD outpatients.  相似文献   
83.
Background. N‐acetyl cystein, a mucolytic agent, might make Helicobacter pylori antigens shed more easily to stool, and might therefore contribute to the diagnostic accuracy of the Helicobacter pylori stool antigen test. The aim of this study is to investigate if N‐acetyl cystein contributes to the diagnostic accuracy of the Helicobacter pylori stool antigen test by increasing the sensitivity and specificity of the test. Materials and Methods. 107 patients were separated into treatment and placebo groups. The AC group (n = 53) was given 5 ml of acetyl cystein (4%) t.i.d. and the Placebo group (n = 54) was given placebo, for 3 days. Helicobacter pylori status was determined by both histology and CLOtest. Stool samples were assayed using a specific ELISA kit for Helicobacter pylori stool antigen. Results. The sensitivity, specificity, positive predictive value, negative predictive value and diagnostic accuracy of Helicobacter pylori stool antigen test were 76%, 79%, 90%, 55%, and 77%, respectively, in AC group; and 85%, 89%, 93%, 76% and 86%, respectively, in placebo group. Conclusions. N‐acetyl cystein did not increase, and actually decreased, the sensitivity and specificity of the Helicobacter pylori stool antigen test according to our results. We believe that this finding can be taken into consideration when setting up the exclusion criteria for future studies, which will use Helicobacter pylori stool antigen tests.  相似文献   
84.
85.
We determined activities of adenosine deaminase (ADA), 5′ nucleotidase (5NT), xanthine oxidase (XO), superoxide dismutase (Cu---Zn SOD), and catalase (CAT) enzymes in 15 human laryngeal tissues with-differentiated squamous cell carcinomas, in 15 corresponding tumor-free adjacent tissues and in 7 normal laryngeal tissues. We found lower ADA and 5NT and higher XO, Cu---Zn SOD, and CAT activities in cancerous tissues than those in corresponding noncancerous ones. In the correlation analysis, we established one positive intercorrelation, which was between ADA activities of tumor tissues and noncancerous adjacent tissues. We also found some significant intracorrelations between enzyme activities of the tissues, all of which were positive in cancerous ones.  相似文献   
86.
In this study, magnesium concentrations were measured in lymphocytes from patients with acute myeloblastic leukemia (AML), chronic megalositer leukemia (KML) and acute lymphoblastic leukemia (ALL) before and after chemotherapy management, and results were compared with those of control subjects. Magnesium concentrations were higher in the patient groups compared with control values. However, no meaningful differences were found among magnesium concentrations of the patient groups themselves. Similarly, no statistically meaningful differences were found between lymphocyte magnesium concentrations before and after chemotherapy management in the patient groups. In the inter-correlation analysis, we observed no correlations between pre- and post-magnesium concentrations in patients' lymphocytes. It has been suggested that magnesium concentrations of leukemic lymphocytes might increase due to the high ATP requirement of the leukemic cells since magnesium is known to play an important part as a cofactor in most of the energy-producing reactions.  相似文献   
87.
Although considerable evidence implicates involvement of nitric oxide (NO) in circadian regulation, little is known about possible 24h variations in basal NO metabolism. In this study, daily variations in serum nitrite levels were studied in locally bred mice and rats during the months of September and October. The serum was separated from blood samples obtained at six different times of the day and night (lh, 5h, 9h, 13h, 17h, and 21h after lights off [HALO] from male albino mice and rats). As an index of in vivo NO generation, serum nitrite levels (determined by the diazotization method) in rats exhibited significant temporal fluctuation (unpaired Student t test), with the concentration highest at 5 HALO and 21 HALO and lowest at 9 HALO. No such temporal variation was detected in mice in these studies conducted on locally bred animals in the autumn. (Chwnobiology International, 16(4), 527-532, 1999)  相似文献   
88.
Arterial distribution of the upper lip was investigated in this study. The location, course, length, and diameter of the superior labial artery and its alar and septal branches were determined on 14 preserved cadaver heads. Another cadaver head was used to show the arterial tree by the colored silicone injection technique. The superior labial artery was the main artery of the upper lip and always originated from the facial artery. The superior labial artery was 45.4 mm in length, with a range from 29 to 85 mm. The mean distance of the origin of the superior labial artery from the labial commissura was 12.1 mm. The superior labial artery was 1.3 mm in external diameter at its origin. The mean distance of origin of the superior labial artery from the lower border of the mandible was 46.4 mm. The alar division of the superior labial artery was mostly found as a single branch (82 percent). Its mean length was 14.8 mm and the mean diameter at the origin was 0.5 mm. The distance between the origins of the superior labial artery and the septal branch was 33.3 mm. The septal branch was single in most of the cases (90 percent). The mean length of the septal branch was 18.0 mm and the diameter at its origin was 0.9 mm. After all dissections, it was concluded that the arterial distribution of the upper lip was not constant. The superior labial artery can occur in different locations unilaterally and bilaterally, with the branches showing variability.  相似文献   
89.
The submental artery island flap is a versatile option in head and neck reconstruction. This flap may be used for the coverage of perioral, intraoral, and other facial defects, leaving a relatively acceptable donor-site scar. In this study, the submental region of 13 formalin-fixed cadavers was dissected bilaterally. Comprehensive anatomical information regarding the pedicle of the flap and its relationship with the important adjacent structures is provided. The mean values of the measurements of the facial and submental arteries were as follows: the facial artery was 2.7 mm in diameter at the origin, and it crossed the mandibular border 26.6 mm from the mandibular angle. The origin of the submental artery was 27.5 mm from the origin of the facial artery, 5.0 mm from the mandibular border, and 23.8 mm from the mandibular angle. The diameter of the submental artery was 1.7 mm at the origin. The artery was found mostly to course superficial to the submandibular gland. In one case, the artery passed through the gland. The total length of the submental artery was 58.9 mm. The artery anastomosed with the contralateral artery in 92 percent of the cadavers. The submental artery was deep to the anterior belly of the digastric muscle in 81 percent of the cases. This study presents detailed anatomical data about the location, dimension, and relationship of the facial artery, the submental artery, and the submental vein that may be useful during dissection of the submental artery island flap.  相似文献   
90.
Cigarette smoking leads to uptake of a multitude of reactive chemicals including many electrophiles and may also give rise to oxidative stress. Human red blood cells are important targets for electrophilic and oxidant foreign compounds. We investigated the oxidative stress in erythrocytes upon cigarette smoking, and the response of antioxidant defense system against it. With this aim, simultaneous determination of erythrocyte superoxide dismutase (SOD), selenium dependent glutathione peroxidase (Se-GPx), catalase (CAT), glutathione S-transferase (GST) activities and plasma levels of thiobarbituric acid reactive substances (TBARS), and the degree of erythrocyte membrane lipid peroxidation (EMLP) were carried out in blood samples of smokers and their controls. Plasma TBARS levels and EMLP in smokers were significantly higher than the control levels (p < 0.01 and p < 0.005, respectively). SOD activity was diminished in smokers compared to nonsmoker controls (p < 0.005). Erythrocyte Se-GPx activity was also found significantly diminished in smokers (p < 0.005), while plasma Se-GPx activity was not changed. We observed that erythrocyte CAT activity was not different in smokers compared to nonsmoker controls. We found that the erythrocyte GST activity is significantly lower in young adult smokers (3.03 +/- 0.18 U/mg protein; mean +/- SEM; n = 46) than in nonsmoking contemporaries (3.98 +/- 0.26 U/mg protein; mean +/- SEM; n = 41). Together with previously reported data, it can be concluded that the decrease in GST activity leads to extra GST synthesis during erythrocyte proliferation. The same data were also analyzed for the sex differences. The statistically significant differences remained the same between nonsmoker and smoker females. Only EMLP degree and SOD activity were significantly different between nonsmoker and smoker males; however, when compared the parameters between male and female nonsmokers, GST activity was found to be significantly higher in females than that of males.  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