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   339篇
  免费   24篇
  2024年   2篇
  2023年   14篇
  2022年   7篇
  2021年   14篇
  2020年   18篇
  2019年   11篇
  2018年   14篇
  2017年   10篇
  2016年   19篇
  2015年   19篇
  2014年   26篇
  2013年   19篇
  2012年   20篇
  2011年   25篇
  2010年   17篇
  2009年   6篇
  2008年   22篇
  2007年   23篇
  2006年   15篇
  2005年   13篇
  2004年   5篇
  2003年   5篇
  2002年   2篇
  2001年   4篇
  1995年   1篇
  1994年   1篇
  1992年   1篇
  1991年   3篇
  1990年   1篇
  1989年   3篇
  1988年   3篇
  1986年   2篇
  1984年   1篇
  1982年   2篇
  1981年   1篇
  1978年   1篇
  1977年   2篇
  1976年   2篇
  1973年   1篇
  1972年   1篇
  1971年   2篇
  1970年   1篇
  1969年   1篇
  1965年   1篇
  1962年   1篇
  1959年   1篇
排序方式: 共有363条查询结果,搜索用时 15 毫秒
151.
The present work details the decrease-increase profiles of Cu, Cr, and Pb by the aquatic plant Lemna minor. A mixture of these metals were utilized at different concentrations. Removal profiles of each metal was determined with water samples taken every 24 h for a 144 h period after the 48 h mark and was examined with correlation analysis. Removal profiles of Cr and Pb by L. minor  from the mixture were observed to be highly similar with each other (r = 0.943). High proportion of Cr and Pb were removed compared to Cu and removal equations were defined with the aid of regression analysis.  相似文献   
152.
The crowned coumarin complexes are well known compounds for their ion recognition abilities. They undergo photophysical changes upon cation binding. On the basis of density functional theory calculations, we examined the sodium cation (Na+) binding energies of coumarin-crown ethers based on 15-Crown-5 (15 C5) and 18-Crown-6 (18 C6) as well as the optical absorptions of coumarin-crown ethers based on 12-Crown-4 (12 C4), 15 C5 and 18 C6. We explored why the attachment of crown ether ring to coumarin affects the Na+ binding energies of coumarin-crown ethers and also why the optical absorption of coumarin is modified by the crown ethers. Our study reveals that the Na+ ion binding energies of coumarin-crown ethers depend strongly on the size of the crown ether ring and also on the attachment position of the ether ring on coumarin. These factors affect the intramolecular charge transfer and overall stability of the complexes. The absorptions of the coumarin and ether ring parts of coumarin-crown ether are red shifted from those of isolated coumarin and crown ether, respectively. The red-shift of the coumarin ester group absorption is much stronger depending on the attachment position of the ether ring to coumarin. The absorption intensity of the coumarin part in coumarin-crown ethers is reduced for the benzene group absorption, but is enhanced for the ester group absorption.
Figure
In this study, the several Na+ - coumarin-crown ether coordination complexes based on 12-Crown-4, 15-Crown-5 and 18-Crown-6 were examined by the density functional theory method. The structural effects on the Na+ binding energies and optical properties were studied.  相似文献   
153.
154.

Background

Recently, increased cardiac norepinephrine levels were observed in patients who were exposed to irregular stimulation during electrophysiological testing. The molecular mechanisms remain unclear. Intrinsic cardiac adrenergic (ICA) cells are present in mammalian hearts and contain catecholamine-synthesizing enzymes sufficient to produce biologically active norepinephrine levels. Thus, we aimed to investigate the expression of catecholamine-synthesizing enzymes by ICA cells exposed to irregular pacing.

Methods

Co-cultures of cardiomyocytes and ICA cells were exposed to irregular pacing for 48 h (standard deviation (SD) = 5%, 25% and 50% of mean cycle length) at a constant rate of 5 Hz. The expression of catecholamine-synthesizing enzymes including tyrosine hydroxylase (TH) and dopamine beta hydroxylase (DBH) were analyzed on mRNA and protein levels.

Results

First, immunolabeling identified ICA cells presenting TH and DBH staining around the cell nucleus. Irregular pacing with 25% SD at a constant rate of 5 Hz significantly increased the expression of TH and DBH enzyme synthesis. Pharmacological approaches have shown that both metoprolol and losartan reversed the irregular pacing induced DBH increase, whereas the expression of TH was only blocked by metoprolol in a significant manner. Blockade of the endothelin-A receptor by BQ123 or the calcineurin–NFAT pathway by cyclosporine-A, 11R-VIVIT or FK506 revealed a potential role of both cascades in irregular pacing induced catecholamine-synthesizing enzyme expression.

Conclusions

ICA cells respond to irregular electrical activation with an increase in catecholamine-synthesizing enzymes. Drugs commonly used in clinical routine significantly influence the expression of TH and DBH by ICA cells via different signaling routes.  相似文献   
155.
Verbascum L. (Scrophulariaceae) species are used for desiccating wounds and as a fish poison in Anatolia as well as for diarrhea and dysentery of animals in several countries. To further evaluate their activity, methanolic extracts obtained from 13 Verbascum species growing in Turkey, including V. chionophyllum Hub.-Mor., V. cilicicum Boiss., V. dudleyanum (Hub.-Mor.) Hub.-Mor., V. lasianthum Boiss., V. latisepalum Hub.-Mor., V. mucronatum Lam., V. olympicum Boiss., V. pterocalycinum var. mutense Hub.-Mor., V. pycnostachyum Boiss. & Heldr., V. salviifolium Boiss., V. splendidum Boiss., V. stachydifolium Boiss. & Heldr. and V. uschackense (Murb.) Hub.-Mor. were evaluated for their in vivo anthelmintic activity. The extracts from V. lasianthum, V. latisepalum, V. mucronatum and V. salviifolum showed the highest inhibitory rates against Aspiculuris tetraptera at 100 mg/kg in mice. Additionally, extracts from V. dudleyanum and V. pterocalycinum var. mutense were found generally highly effective. The remaining species did not show any activity. Results of the present study support the utilization of these plant species employed in Turkish folk medicine.  相似文献   
156.
One consequence of chronic kidney disease (CKD) is an elevated risk for cancer. There is sufficient evidence to conclude that there is an increased incidence of at least some cancers in kidney-dialysis patients. Cancer risk after kidney transplantation has mainly been attributed to immunosuppressive therapy. There are no data evaluating DNA damage in children with CKD, in dialysis patients, or following kidney transplantation. In this study, the comet assay and the enzyme-modified comet assay - with the use of endonuclease III (Endo III) and formamidopyrimidine glycosylase (FPG) enzymes - were conducted to investigate the basal damage and the oxidative DNA damage as a result of treatment in peripheral blood lymphocytes of children. Children at various stages of treatment for kidney disease, including pre-dialysis patients (PreD) (n=17), regular hemodialysis patients (HD) (n=15), and those that received kidney transplants (Tx) (n=17), comprised the study group. They were compared with age- and gender-matched healthy children (n=20) as a control group. Our results show that the %DNA intensity, a measure of basal damage, was significantly increased in children with CKD (mean ± SD) (5.22 ± 1.57) and also in each of the PreD, HD, and Tx groups [(4.92 ± 1.23), (4.91 ± 1.35), and (5.79 ± 1.94), respectively, vs the healthy children (2.74 ± 2.91) (p<0.001). Significant increases in oxidative DNA damage were only found in the FPG-sensitive sites for the PreD and Tx groups, compared with control and HD groups (p<0.05), suggesting that basal DNA damage was more evident for the PreD, HD, and Tx groups. The findings of the present study indicate a critical need for further research on genomic damage with different endpoints and also for preventive measures and improvements in treatment of pediatric patients, in order to improve their life expectancy.  相似文献   
157.
Usage of magnetic resonance imaging (MRI) is continuously increasing due to its excellent soft-tissue contrast and improving diagnostic values. MRI also has the advantage that it operates without ionizing radiation. The main safety concerns are torque, acceleration by the static field, nerve stimulation by the gradient fields, and tissue heating by the radio-frequency (RF) fields. This paper investigates if children and fetuses are at higher risks than adults when the current RF regulations are applied. We analyzed and compared local absorption hotspots, i.e., the peak spatial specific absorption rate averaged over any 10 g (psSAR10g) for five adults, three children of ages 5, 11 and 14 years, and 1 pregnant female (36 weeks’ gestation) in 10 different Z-positions (head to calves). In the First Level Operating Mode (4 W/kg whole-body averaged exposure), the psSAR10g values found for adults were as large as 60 W/kg in the trunk and 104 W/kg in the extremities. The corresponding values for children were 43 and 58 W/kg, respectively, and 14 W/kg for the unborn child. Modeling of worst case anatomical RF loops can substantially increase the psSAR10g values, i.e., by factor >>2.The results suggest that local exposure for children and fetuses is smaller than for adults (15–75%), i.e., no special considerations for children and the unborn child are needed regarding psSAR10g due to RF. However, the local thermal load of the unborn may be significantly increased due to the high exposure average (up to 4 W/kg) of the non-perfused amniotic fluid.  相似文献   
158.
A high-frequency in vitro regeneration of Digitalis davisiana Heywood (Alanya foxglove) and cardiotonic glycoside production from both in vitro produced materials (regenerated plantlets or germinated seedlings) and leaves of natural populations were obtained. Cardiac glycosides regulate heart rhythm and are effective in cancer chemotherapy, in particular for prostate and breast cancer treatments. Testing six different types of culture media revealed that Linsmaier and Skoog (LS) was the most effective for shoot production. Shoot regeneration efficiency was higher when flamingo-bill or hypocotyl explants were cultured on LS medium containing 0.5 mg/l thidiazuron (TDZ) and 0.25 mg/l indoleacetic acid (IAA). Rooting of all shoots that regenerated was readily achieved, even in the absence of plant growth regulators (PGRs). Production of cardenolides (lanatoside C and digoxin) in the materials grown in vitro seemed to correlate with several parameters, such as nutritional and hormonal compositions of the culture medium as well as the duration of culture on the initial regeneration and/or final growth medium. Higher amounts of digoxin accumulation were obtained when shoots were regenerated on LS or Gamborg’s B5 medium containing 0.5 mg/l TDZ and 0.25 mg/l IAA, producing 12.59 and 11.93 mg/kg dry weight (dw) digoxin, respectively. For natural populations, seasonal variations seemed to affect the production of digoxin in the leaves. The highest amount of digoxin (246.58 mg/kg dw) was in leaf samples collected in July, which coincides with the flowering stage of the plant in the region of collection.  相似文献   
159.
The presenting study was investigated the associations between individual susceptibility and cigarette smoke on maternal chromosomal damage and neonatal birth growth in smoking mothers since little known about genetic susceptibility to cigarette smoke in relation to adverse pregnancy outcome such as birth growth. Sixty-one pregnant women who completed a questionnaire at Ankara Education and Research Hospital, Department of Obstetrics and Gynecology have enrolled in this study. GSTM1 and OGG1 ser326Cys gene polymorphisms were analysed by RFLP-PCR (Restriction Fragment Length Polymorphism-Polymerase Chain Reaction) as possible genetic factors affecting susceptibility to such health effects of smoking and chromosomal damage was performed by chromosomal aberration assay (CAA) in maternal blood lymphocytes. Maternal self-reported history of pregnancy smoking was informed by questionnaire declaration. Our results showed that maternal smoking had significant effect on chromosomal damage, birth weight, and length. The frequencies of CA in smokers was significantly higher than that of the nonsmokers (3.46 ± 2.06 and 2.00 ± 1.3, P = 0.001). Birth weight and length in smokers were significantly higher that of nonsmokers (3,355 g and 49.57 cm, P = 0.001; 3,639 g and 50.79 cm, P = 0.002). On the other hand, there was a slightly increased in the frequencies of CA and reduction birth weight and length in GSTM1 null and length in OGG1 variant genotypes, those differences were not statistically significant (P > 0.05); likely due to small sample size. Larger sample size needs to reach significance.  相似文献   
160.
Currently, some Toxoplasma gondii genotypes are being associated with serious clinical presentations. A recent report showing the Africa 1 genotype in two local congenital toxoplasmosis cases acquired in Turkey formed the basis of this study because atypical Africa 1 genotype is most frequently detected in animals and patients from sub-Saharan Africa. Since stray cats are considered as the linkage between wild life and urban life in T. gondii transmission, the present study aimed to isolate and characterize T. gondii strains circulating in stray cats of İzmir (Western Turkey). A secondary objective was to determine toxoplasmosis seroprevalence in this cat population. Tissues obtained from 100 deceased stray cats were bioassayed and isolated strains were genotyped using 15 microsatellite markers. In addition, toxoplasmosis seroprevalence was analyzed in 1121 cat sera collected from several large veterinary clinics in İzmir. Among the 22 isolates, 19 were Type II (86.3%), two were Type III (9%) and one was Africa 1 genotype (4.5%). The overall seropositivity rates in cats were 42–48% and 33.4–34.4% according to IFA and ELISA, respectively. Seroprevalence in deceased cats was significantly higher than in healthy cats (P = 0.0033). Finding both the major clonal Type II lineage together with the Type III lineage also found in Middle East, and an atypical genotype, Africa 1 appears consistent with the specific geographic location of Turkey between three continents and raises the possibility of transportation of these strains between continents through trade routes or long distance migratory birds. In addition, the first large study of toxoplasma seroprevalence in a stray cat population was also reported. The relatively high seropositivity rates and the variety of T. gondii genotypes confirm the local stray cat population as a risk factor for human toxoplasmosis in İzmir.  相似文献   
[首页] « 上一页 [11] [12] [13] [14] [15] 16 [17] [18] [19] [20] [21] 下一页 » 末  页»
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