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   650篇
  免费   55篇
  2024年   2篇
  2023年   6篇
  2022年   11篇
  2021年   18篇
  2020年   21篇
  2019年   21篇
  2018年   26篇
  2017年   27篇
  2016年   31篇
  2015年   34篇
  2014年   47篇
  2013年   53篇
  2012年   53篇
  2011年   42篇
  2010年   30篇
  2009年   29篇
  2008年   28篇
  2007年   32篇
  2006年   25篇
  2005年   22篇
  2004年   19篇
  2003年   14篇
  2002年   21篇
  2001年   11篇
  2000年   13篇
  1999年   7篇
  1998年   4篇
  1997年   2篇
  1996年   4篇
  1995年   2篇
  1993年   2篇
  1992年   5篇
  1991年   2篇
  1989年   2篇
  1988年   3篇
  1985年   5篇
  1984年   2篇
  1983年   2篇
  1982年   2篇
  1981年   1篇
  1980年   1篇
  1979年   1篇
  1978年   4篇
  1977年   3篇
  1976年   5篇
  1975年   2篇
  1974年   1篇
  1973年   3篇
  1972年   1篇
  1971年   1篇
排序方式: 共有705条查询结果,搜索用时 15 毫秒
181.
TT virus (TTV) is a newly described nonenveloped human virus, with a circular, negative-stranded DNA genome, that was first identified in the blood of a patient with posttransfusion hepatitis of unknown etiology. PCR primers and conditions used for TTV DNA amplification may greatly influence the level of TTV detection in serum. Three PCR assays, with different regions of the genome as targets, were used to test TTV DNA in 130 sera from children and adults visiting a hospital in the south of Brazil, most of them for routine procedure. Forty-four percent of adult sera and 73% of sera from children aged 0-10 years were TTV positive with at least one PCR assay. However, the three assays were able to detect only 33%, 35%, and 70% of the total positive samples. Our results showed a high prevalence of TTV infection in the south of Brazil, particularly among young children, and confirmed the necessity of performing several PCR assays to assess the true TTV prevalence in a determined population.  相似文献   
182.
On-line monitoring biomass concentration in mycelial fed-batch cultivations of Streptomyces clavuligerus grown with soluble and partially insoluble complex media, was investigated with an in-situ capacitance probe fitted to an industrial pilot-plant tank. Standard off-line and on-line biomass determinations, including cell dry weight, packed mycelial volume, viscosity, DNA concentration and total CO(2) evolution in the exhaust gases, were performed throughout the experiments and compared to on-line capacitance measurements. Linear relations between capacitance and all other measurements were developed for both media that hold only in defined process phases, depending on the biomass state and the amount of insoluble matter present. For the industrial complex culture media good linear relations were obtained in the fast growth phase between capacitance and DNA concentration and total CO(2) evolution, while in the subsequent transition and stationary phases only with apparent viscosity was a reasonable correlation found. The capacitance probe was shown to be a valuable tool for real-time monitoring biomass concentration in industrial-like cultivation of mycelial streptomycetes.  相似文献   
183.
Positive and negative effects of dilution of raw effluents from swine breeding are discussed, as to the treatability of those waste waters. Its effects on oxygen consumption and on the variation of inhibitory actions possibly observed, are studied and quantified. Using BRADENDER and VANDEPUTTE techniques based on peptone degradation, and determining PHELPS'S equation parameters for different consumption curves observed, the advantages of dilution versus treatment of raw effluents is studied.  相似文献   
184.
Evaluation of Chagas' disease transmission through breast-feeding   总被引:2,自引:0,他引:2  
One hundred milk or colostrum samples from 78 mothers with chronic Chagas' disease were parasitologically studied for Trypanosoma cruzi infection by means of direct examination and inoculation of mice. The mice were submitted to direct blood examination three times a week. At the end of 45 days, xenodiagnosis and indirect immunofluorescent test (IFAT) for T. cruzi antibodies were carried out in the animals. No parasitized sample was observed even though five mothers had parasitemia at milk collection. In addition, 97 breast-fed children of chronic chagasic mothers, born free of infection, were tested for IgG antibodies to T. cruzi using IFAT. No case of T. cruzi infection was detected. The authors conclude that breast-feeding should not be avoided for children of chronic chagasic women. However, as these mothers had intermittent parasitemia, they should avoid nursing when there is nipple bleeding.  相似文献   
185.
186.
Some aspects of the kinetics of bioremoval of pollutants during biodegradation of swine-breeding waste waters are studied and a biphasic model is proposed. The concentration of nitrogen and phosphorus compounds during the process is followed. Following a previous contribution on the same subject, the aspects of dilution of those effluents are discussed, and it is proposed to treat raw effluents, in spite of the reduction of possible biostatic actions. Dilution will be acceptable only if strong inhibitory effects are observed.  相似文献   
187.
188.

Objective

To evaluate the effect of total breastfeeding, breastfeeding duration and type of breastfeeding at 3 months of age on bone mass at 18 and 30 years.

Study Design

A prospective, longitudinal study was conducted with two birth cohorts (1982 and 1993) in Pelotas, Southern Brazil. Measurements of bone mineral content (BMC) and bone mineral density (BMD) at 18 and 30 years of age were obtained by dual-energy X-ray absorptiometry (DXA). Information on breastfeeding was collected during the first 4 years of life. Analyses were performed by linear regression and stratified by sex.

Results

A total of 1109 and 3226 participants provided complete information on breastfeeding in early life and bone mass at 18 and 30 years, respectively. No association between breastfeeding and bone mass was observed in women at both ages nor among men at age 30. Among men at the age of 18, BMC and BMD were higher among those breastfed regardless of duration (p=0.032 and p=0.043, respectively).

Conclusions

Despite a very weak positive effect of breastfeeding (yes/no) on BMC and BMD at age 18 in men, most findings pointed to a lack of association between breastfeeding and bone mass until young adulthood.  相似文献   
189.

Introduction

Plasmodium vivax is the most prevalent malaria species in the American region. Brazil accounts for the higher number of the malaria cases reported in pregnant women in the Americas. This study aims to describe the characteristics of pregnant women with malaria in an endemic area of the Brazilian Amazon and the risk factors associated with prematurity and low birth weight (LBW).

Methods/Principal Findings

Between December 2005 and March 2008, 503 pregnant women with malaria that attended a tertiary health centre were enrolled and followed up until delivery and reported a total of 1016 malaria episodes. More than half of study women (54%) were between 20–29 years old, and almost a third were adolescents. The prevalence of anaemia at enrolment was 59%. Most women (286/503) reported more than one malaria episode and most malaria episodes (84.5%, 846/1001) were due to P. vivax infection. Among women with only P. vivax malaria, the risk of preterm birth and low birth weight decreased in multigravidae (OR, 0.36 [95% CI, 0.16–0.82]; p = 0.015 and OR 0.24 [95% CI, 0.10–0.58]; p = 0.001, respectively). The risk of preterm birth decreased with higher maternal age (OR 0.43 [95% CI, 0.19–0.95]; p = 0.037) and among those women who reported higher antenatal care (ANC) attendance (OR, 0.32 [95% CI, 0.15–0.70]; p = 0.005).

Conclusion

This study shows that P. vivax is the prevailing species among pregnant women with malaria in the region and shows that vivax clinical malaria may represent harmful consequences for the health of the mother and their offsprings particularly on specific groups such as adolescents, primigravidae and those women with lower ANC attendance.  相似文献   
190.
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