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   838篇
  免费   34篇
  872篇
  2023年   10篇
  2022年   13篇
  2021年   33篇
  2020年   22篇
  2019年   23篇
  2018年   21篇
  2017年   23篇
  2016年   25篇
  2015年   29篇
  2014年   38篇
  2013年   52篇
  2012年   54篇
  2011年   87篇
  2010年   42篇
  2009年   34篇
  2008年   62篇
  2007年   59篇
  2006年   51篇
  2005年   44篇
  2004年   46篇
  2003年   30篇
  2002年   25篇
  2001年   18篇
  2000年   8篇
  1999年   8篇
  1998年   1篇
  1997年   4篇
  1996年   3篇
  1990年   1篇
  1988年   1篇
  1972年   1篇
  1968年   1篇
  1967年   1篇
  1964年   1篇
  1962年   1篇
排序方式: 共有872条查询结果,搜索用时 15 毫秒
1.
In a previous study, our laboratory showed that young dogs born at sea level (SL) and raised from 2.5 mo of age to beyond somatic maturity at a high altitude (HA) of 3,100 m show enhanced resting lung function (Johnson RL Jr, Cassidy SS, Grover RF, Schutte JE, and Epstein RH. J Appl Physiol 59: 1773-1782, 1985). To examine whether HA-induced adaptation improves pulmonary gas exchange during exercise and whether adaptation is reversible when animals return to SL before somatic maturity, we raised 2.5-mo-old foxhounds at HA (3,800 m) for 5 mo (to age 7.5 mo) before returning them to SL. Lung function was measured under anesthesia 1 mo and 2 yr after return to SL and during exercise approximately 1 yr after return. In animals exposed to HA relative to simultaneous litter-matched SL controls, resting circulating blood and erythrocyte volumes, lung volumes, septal volume estimated by a rebreathing technique, and lung tissue volume estimated by high-resolution computed tomography scan were persistently higher. Lung diffusing capacity, membrane diffusing capacity, and pulmonary capillary blood volume estimated at a given cardiac output were significantly higher in animals exposed to HA, whereas maximal oxygen uptake and hematocrit were similar between groups. We conclude that relatively short exposure to HA during somatic maturation improves long-term lung function into adulthood.  相似文献   
2.
Apoptosis is a complex process involving a variety of mechanisms and it has been shown to be a response of cells to various chemical agents including chemotherapeutic ones. We aimed to induce DNA breaks and apoptosis in cultured endometrial stromal cells by mitomycin C (MMC), a chemotherapeutic agent, and also we aimed to observe the effects of beta-carotene and folic acid on MMC-induced apoptosis. Cultured endometrial stromal cells were exposed to MMC for 48 and 72 hours and in order to reverse MMC effects, we added beta-carotene and folic acid to the cultures. DNA fragmentation was observed in all cells. Apoptotic cell ratios and caspase-3 activity were observed to be dependent on exposure time. Ultrastructural examinations revealed positive effects of beta-carotene and folic acid, however they were not sufficient enough to prevent apoptosis in all cells. Beta-carotene profoundy reduced caspase-3 activity whereas folic acid did not seem to have a similar effect. As apoptosis involves several mechanisms, in a cell in which all these mechanisms are triggered, we think that antioxidants and DNA repair agents alone are not enough to reverse all of them.  相似文献   
3.
We investigated the effect of PON 55 and PON 192 polymorphisms on serum PON1 activity and lipid profiles in 213 non-insulin dependent diabetes mellitus (NIDDM) individuals and 116 non-diabetic controls among Turkish subjects. The distribution of PON 55/192 gene polymorphism was determined by polymerase chain reaction-based restriction fragment length polymorphism. Serum lipid levels were measured enzymically. PON activity was measured by spectrophotometric assay of p-nitrophenol production following addition of paraoxon. We found that PON 55 and 192 genotype distribution was similar in patients and controls and paraoxonase activity was generally lower in diabetics than in control subjects. We showed that PON 55 and 192 genotypes have a major effect on serum PON activity. PON 192 BB homozygotes had significantly higher PON activity than AA and AB genotypes among the control and NIDDM populations (p<0.001). PON 55 MM homozygotes had significantly lower PON activity than did LL and LM genotypes in control and NIDDM populations (p<0.05). The PON1 55 and 192 polymorphisms did not consistently influence the serum lipid profiles in either population. In conclusion, our results suggest that the paraoxonase activities are affected by PON1 genetic variability in Turkish NIDDM patients and controls.  相似文献   
4.
Early detection of bladder cancer is particularly important since it dramatically affects the survival rates. However, neither urinary cytology nor tumor markers that are currently used are sensitive enough for the early detection of bladder cancer or recurrent disease. The ras genes are frequently mutated in cancer. In this study, we investigated the diagnostic potential of ras mutation analysis in urinary sediments of patients with bladder cancer using a single-strand conformation polymorphism analysis and polymerase chain reaction. Mutation in codon 12 of the H-ras gene was observed in 39% of the patients. Our results indicate that this approach may significantly improve diagnostic sensitivity in detecting bladder tumors.  相似文献   
5.
BackgroundPhlebotomy is one of the most important steps in the preanalytical phase of a clinical laboratory process. In order to decrease phlebotomy errors, this specific procedure should be taught in detail by laboratory organizations. Our study aims to practice the training program on venous blood sampling and observe the close follow-up results.MethodsIn this observational study, 127 students who started their summer internship in Antalya Education and Research Hospital were given a one-day theoretical phlebotomy training in accordance with the Venous Blood Sampling Guidelines. After the theoretical training, phlebotomy applications of 10 students who were working in the field of out-patient blood sampling were observed both with and without their knowledge. A comprehensive checklist related to phlebotomy was created by the trainers in Antalya Education and Research Hospital and the observers answered each question as yes or no. For the statistical analysis, IBM SPSS Statistics 21.0 was used.ResultsAfter the theoretical education, the trainees were observed but no significant difference was found between the first and the second informed observations (p = 0.125). The students were observed three times more in the following week without their knowledge. There was a statistically significant difference between the first and the third unannounced observations (p=0.001).ConclusionsIn order to perform phlebotomy correctly, apart from theoretical education, a close follow-up is necessary too.  相似文献   
6.
7.
Yazici  R.  Yilmaz  M.  Yazicioğlu  O. 《Journal of Ichthyology》2021,61(3):452-459
Journal of Ichthyology - In this study, vertebrae, otoliths (asteriscus and lapillus), sectioned lapillus and pectoral fin rays were evaluated for age determination of Silurus glanis L., 1758...  相似文献   
8.
9.
Nanocarriers for encapsulation and sustained release of agrochemicals such as auxins have emerged as an attractive strategy to provide enhanced bioavailability and efficacy for improved crop yields and nutrition quality. Here, a comparative study was conducted on the effectiveness of chitosan-as a biopolymeric nanocarrier- and silver-as a metallic nanocarrier- on in vitro adventitious rooting potential of microcuttings in apple rootstocks, for the first time. Auxins indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) loaded silver (nAg) or chitosan nanoparticles (nChi) were synthesized. Scanning electron microscopy and transmission electron microscopy studies showed the spherical shape of the nanoparticles. The average particle size of IAA-nChi was 167.5 ± 0.1 nm while that of IBA-nChi was 123.2 ± 2.6 nm. The hydrodynamic diameter of the nAg-IAA and nAg-IBA particles were measured as 93.66 ± 5 nm and 71.41 ± 3 nm, respectively. Fourier transform infrared spectroscopy analyses confirmed the encapsulation of IAA or IBA in the chitosan nanoparticles. Meanwhile, the characteristic peaks of IAA or IBA were detected on silver nanoparticles. In-vitro adventitious rooting of microcuttings of Malling Merton 106 (MM 106) was significantly higher both in chitosan and silver nanoparticles loaded with IAA or IBA (91.7%–62.5%) compared to free IAA or IBA applications (50.0%–33.3%), except for 2.0 mg L–1 IBA (66.7%). However, the application of 2 mg L–1 IBA and IBA-nChi at all concentrations caused an undesirable large callus development.  相似文献   
10.
Yilmaz  Şehnaz  Yoldas  Oguz  Dumani  Aysin  Guler  Gizem  Ilgaz  Seda  Akbal  Eylül  Oksuz  Hale  Celik  Ayla  Yilmaz  Bertan 《Molecular biology reports》2020,47(7):5377-5383
Molecular Biology Reports - Antimicrobial irrigation solutions are widely used under clinical settings. Their effect on dental tissue is a subject of recent research, which aims for a safer...  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