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   247篇
  免费   14篇
  国内免费   1篇
  2023年   2篇
  2022年   3篇
  2021年   3篇
  2020年   3篇
  2019年   3篇
  2018年   7篇
  2017年   3篇
  2016年   12篇
  2015年   13篇
  2014年   13篇
  2013年   8篇
  2012年   19篇
  2011年   7篇
  2010年   8篇
  2009年   4篇
  2008年   9篇
  2007年   7篇
  2006年   10篇
  2005年   10篇
  2004年   6篇
  2003年   4篇
  2001年   4篇
  2000年   3篇
  1999年   6篇
  1997年   5篇
  1995年   2篇
  1994年   6篇
  1992年   2篇
  1991年   3篇
  1990年   2篇
  1989年   5篇
  1988年   4篇
  1987年   3篇
  1985年   2篇
  1984年   5篇
  1983年   5篇
  1982年   6篇
  1980年   4篇
  1979年   3篇
  1978年   2篇
  1977年   2篇
  1976年   3篇
  1975年   4篇
  1974年   3篇
  1973年   6篇
  1971年   3篇
  1970年   3篇
  1969年   2篇
  1968年   2篇
  1967年   3篇
排序方式: 共有262条查询结果,搜索用时 78 毫秒
71.

Background

Preeclampsia is one of the leading causes of maternal and neonatal morbidity and mortality in the world, but its appearance is still unpredictable and its pathophysiology has not been entirely elucidated. Genetic studies have associated single nucleotide polymorphisms in genes encoding nitric oxide synthase and matrix metalloproteases with preeclampsia, but the results are largely inconclusive across different populations.

Objectives

To investigate the association of single nucleotide polymorphisms (SNPs) in NOS3 (G894T, T-786C, and a variable number of tandem repetitions VNTR in intron 4), MMP2 (C-1306T), and MMP9 (C-1562T) genes with preeclampsia in patients from Southeastern Brazil.

Methods

This prospective case-control study enrolled 77 women with preeclampsia and 266 control pregnant women. Clinical data were collected to assess risk factors and the presence of severe complications, such as eclampsia and HELLP (hemolysis, elevated liver enzymes, and low platelets) syndrome.

Results

We found a significant association between the single nucleotide polymorphism NOS3 T-786C and preeclampsia, independently from age, height, weight, or the other SNPs studied, and no association was found with the other polymorphisms. Age and history of preeclampsia were also identified as risk factors. The presence of at least one polymorphic allele for NOS3 T-786C was also associated with the occurrence of eclampsia or HELLP syndrome among preeclamptic women.

Conclusions

Our data support that the NOS3 T-786C SNP is associated with preeclampsia and the severity of its complications.  相似文献   
72.
Herbivores are attracted to young shoots and leaves because of their tender tissues. However, in extrafloral nectaried plants, young leaves also attract patrolling ants, which may chase or prey on herbivores. We examined this scenario in extrafloral nectaried shrubs of Banisteriopsis malifolia resprouting after fire, which promoted both the aseasonal production of leaves and the activity of extrafloral nectaries (EFNs). Results were compared between resprouting (burned) and unburned control plants. The aggressive ant species Camponotus crassus and the herbivorous thrips Pseudophilothrips obscuricornis were respectively rapidly attracted to resprouting plants because of the active EFNs and their less sclerophyllous leaves. The abundance of these insects was almost negligible in the control (unburned) shrubs. Ants failed to protect B. malifolia, as no thrips were preyed upon or injured by ants in resprouting plants. Consequently, on average, 37 % of leaves from resprouting shrubs had necrosis marks. Upon contact with ants, thrips released small liquid droplets from their abdomen, which rapidly displaced ants from the surroundings. This study shows that P. obscuricornis disrupted the facultative mutualism between C. crassus and B. malifolia, since ants received extrafloral nectar from plants, but were unable to deter herbivore thrips.  相似文献   
73.
In the Brazilian savanna many plant species bear regular associations with patrolling ants that are aggressive towards insect herbivores. However, not only ants but also several species of predatory wasps are attracted to plants due to the extrafloral nectaries (EFNs). Such wasps feed on both herbivores and plant exudates. In this study we describe the foraging behavior of the social Polistinae wasp Brachygastra lecheguana in the extrafloral nectaried shrub Banisteriopsis malifolia, and investigated the influence of patrolling ants Camponotus blandus on the activity of the wasp. Brachygastra lecheguana fed on the endophytic larvae of Anthonomus (Curculionidae) beetles that developed inside flower buds. The wasp lacerated the bud layers to reach the beetle larvae located at the bud core. The wasp visits to Ba. malifolia were statistically related to the abundance of flower buds and beetles. Ant exclusion experiments revealed that the hunting behavior of B. lecheguana on beetles was not related to the absence of C. blandus. However we found that wasps spent more time consuming extrafloral nectar on branches where ants were excluded. This is the first study reporting extrafloral nectar consumption by B. lecheguana, as well as the predation on herbivores in natural areas. In cerrado vegetation, ants benefit the plant by reducing insect herbivores, and our study provides evidence that the B. lecheguana – Ba. malifolia system represents a potential interaction where the wasp may also benefit the host plant. The value of this wasp species as a plant‐guard is discussed.  相似文献   
74.
Current evidence suggests that in Hetaerina damselflies males exhibit lek mating system. In this study, in order to answer if the same occurs in Hetaerina rosea Selys, we manipulated vegetation substrates used as territories and quantified the number of visiting females, males defending territories and fight intensity. We also examined whether body size and wing pigmentation are selectable traits in male-male competition, and if age affects male territorial behavior. Our results showed that males with larger pigmented areas won more contests, independently of body size. Old males changed from territoriality to sneaking strategy. Contrary to other Hetaerina species, males of H. rosea do not display lek behavior, but defend resources according to the resource defense polygyny strategy.  相似文献   
75.

Background

In 2006, Brazil began routine immunization of infants <15 wk of age with a single-strain rotavirus vaccine. We evaluated whether the rotavirus vaccination program was associated with declines in childhood diarrhea deaths and hospital admissions by monitoring disease trends before and after vaccine introduction in all five regions of Brazil with varying disease burden and distinct socioeconomic and health indicators.

Methods and Findings

National data were analyzed with an interrupted time-series analysis that used diarrhea-related mortality or hospitalization rates as the main outcomes. Monthly mortality and admission rates estimated for the years after rotavirus vaccination (2007–2009) were compared with expected rates calculated from pre-vaccine years (2002–2005), adjusting for secular and seasonal trends. During the three years following rotavirus vaccination in Brazil, rates for diarrhea-related mortality and admissions among children <5 y of age were 22% (95% confidence interval 6%–44%) and 17% (95% confidence interval 5%–27%) lower than expected, respectively. A cumulative total of ∼1,500 fewer diarrhea deaths and 130,000 fewer admissions were observed among children <5 y during the three years after rotavirus vaccination. The largest reductions in deaths (22%–28%) and admissions (21%–25%) were among children younger than 2 y, who had the highest rates of vaccination. In contrast, lower reductions in deaths (4%) and admissions (7%) were noted among children two years of age and older, who were not age-eligible for vaccination during the study period.

Conclusions

After the introduction of rotavirus vaccination for infants, significant declines for three full years were observed in under-5-y diarrhea-related mortality and hospital admissions for diarrhea in Brazil. The largest reductions in diarrhea-related mortality and hospital admissions for diarrhea were among children younger than 2 y, who were eligible for vaccination as infants, which suggests that the reduced diarrhea burden in this age group was associated with introduction of the rotavirus vaccine. These real-world data are consistent with evidence obtained from clinical trials and strengthen the evidence base for the introduction of rotavirus vaccination as an effective measure for controlling severe and fatal childhood diarrhea. Please see later in the article for the Editors'' Summary  相似文献   
76.
In male odonates, both size and fat content are related to territory defence and mating success. Males that are larger and have higher energy reserves win relatively more disputes for territory and attract more females. Wing colour has also been regarded as a mechanism that influences agonistic behaviour between males, as wing pigmentation might be regarded as a sign of male quality. In this study, we analysed whether a set of male physical (body size and wing colour), physiological (body fat content) and behavioural (disputes between males) characteristics were involved in the territory defence and mating behaviour of the neotropical dragonfly Zenithoptera lanei Santos, 1941 (Anisoptera: Libellulidae). Males were characterised as territorial whenever they warded‐off other males and remained in the same place within the pond for two consecutive days. In general, these territorial males were larger and had more abdominal and thoracic fat, engaged in pursuits more frequently, spent more time on sexual behaviour and female guarding, and mated more in comparison to subordinate males. By evaluating whether the percentage of wing area covered by black ink influenced male behaviour, we found that territorial males tended to act aggressively towards other males whose wings were partially painted, and sexually towards females irrespective of wing area painted. In Z. lanei, both body size and fat content play a role in defining territoriality. By subduing competitors and dominating preferred locations within high‐quality sites, these males are likely to be visited by females and engage in mating.  相似文献   
77.
78.
RP1 (synonym: MAPRE2, EB2) is a member of the microtubule binding EB1 protein family, which interacts with APC, a key regulatory molecule in the Wnt signalling pathway. While the other EB1 proteins are well characterized the cellular function and regulation of RP1 remain speculative to date. However, recently RP1 has been implicated in pancreatic cancerogenesis. CK2 is a pleiotropic kinase involved in adhesion, proliferation and anti-apoptosis. Overexpression of protein kinase CK2 is a hallmark of many cancers and supports the malignant phenotype of tumor cells. In this study we investigate the interaction of protein kinase CK2 with RP1 and demonstrate that CK2 phosphorylates RP1 at Ser236 in vitro. Stable RP1 expression in cell lines leads to a significant cleavage and down-regulation of N-cadherin and impaired adhesion. Cells expressing a Phospho-mimicking point mutant RP1-ASP236 show a marked decrease of adhesion to endothelial cells under shear stress. Inversely, we found that the cells under shear stress downregulate endogenous RP1, most likely to improve cellular adhesion. Accordingly, when RP1 expression is suppressed by shRNA, cells lacking RP1 display significantly increased cell adherence to surfaces. In summary, RP1 phosphorylation at Ser236 by CK2 seems to play a significant role in cell adhesion and might initiate new insights in the CK2 and EB1 family protein association.  相似文献   
79.
Biochars produced at different heat treatment temperatures (HTT) are molecularly distinct and thus expected to show variable sorbent characteristics. We investigated the difference in sorption behavior of norflurazon (NORO) and fluridone (FLUN) to biochars from wood and grass feedstocks produced at different HTT. Amorphous biochars (HTT = 400 °C) exhibited the highest sorption parameter (KOC) for the two herbicides, emphasizing the importance of amorphous structural arrangement of aromatic moieties in these chars. Negative correlation between biochar aromaticity and isotherm nonlinearity (n) suggests that the n values were related mainly to total aromatic C content, not to that in the individual phases. Sorption of FLUN and NORO to low-temperature biochars (HTT = 400 °C) was about 1100 times and 6400 times greater, respectively, than a sediment sample, confirming that applications of low-temperature biochars to arable soils may reduce the mobility of FLUN and NORO, thus preventing unwanted herbicide leaching and subsequent contamination of sensitive water bodies.  相似文献   
80.
This study aimed to evaluate whether maternal obesity leads to the onset of diabetes in adult Wistar rats offspring. MSG solution neonatally administration induced obesity in rats (F(1)MSG group, n=30); and saline solution was also administrated to control rats (F(1)CON group, n=13). In 3rd month of age, both control and MSG groups were mated for offspring (generation F(2)), named as F(2)CON, n=28 and F(2)MSG groups, n=15; and so both generations were studied until 7th month of life. Lee Index was measured for experimental obesity validation from 5th to 7th month. Glycemia was weekly determined during pregnancy and monthly from 3rd to 7th month. In the end of experimental period all rats were submitted to oral glucose tolerance test (OGTT), with estimation of total area under the curve (AUC); and insulin tolerance test (ITT). Rats were then anesthetized and killed. Data were statistically analyzed with significance level of p<0.05. Lee Index has confirmed obesity in all MSG rats. Glycemic levels comparisons between generations showed significant maternal interference in control and MSG groups. OGTT analysis showed higher glycemia in obese rats (F(1)MSG) and their offspring (F(2)MSG) as compared to their respective controls; and MSG groups increased AUC from OGTT. As regards ITT, F(2)MSG showed higher glycemia at 30 and 120 min, suggesting a delay of insulin action decreasing. Although glucose intolerance and insulin resistance clinical conditions represent as a factors for type 2 Diabetes mellitus development, this experimental model proposal was not efficient to induce type 2 Diabetes mellitus, but for obesity developing, glucose intolerance and insulin resistance in successive generations of rats.  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