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   140篇
  免费   7篇
  147篇
  2022年   4篇
  2021年   6篇
  2020年   7篇
  2019年   11篇
  2018年   5篇
  2017年   5篇
  2016年   6篇
  2015年   12篇
  2014年   6篇
  2013年   10篇
  2012年   5篇
  2011年   7篇
  2010年   5篇
  2009年   10篇
  2008年   11篇
  2007年   7篇
  2006年   4篇
  2005年   1篇
  2004年   5篇
  2003年   1篇
  2002年   5篇
  2001年   4篇
  2000年   2篇
  1999年   1篇
  1995年   1篇
  1991年   1篇
  1990年   1篇
  1987年   1篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
排序方式: 共有147条查询结果,搜索用时 15 毫秒
111.
A plant that showed morphological closeness to Aspilia africana (Pers) C. D. Adams (Asteraceae) was spotted and collected in 2015 along Afe Babalola University road, Ado‐Ekiti, Ekiti State, Nigeria with coordinates 7°36′59.99″N, 5°12′60.00″E. However, upon closer observation some distinct and peculiar characteristics that clearly distinguished it from Aspilia africana were revealed, e.g. sterility of the disc florets and production of achenes by ray florets only. Another striking character of the plant was total emptying of the capitulum after achene maturation, leaving an empty capitulum cup on the plant. Literature and herbarium searches revealed that the plant had neither been reported from West Tropical Africa nor collected in any herbarium in Nigeria before. The plant was eventually identified as Melampodium divaricatum (L.) which is an annual erect herb, distributed in tropical and subtropical regions but mostly restricted to Mexico, North America and Central America. Morphological, reproductive and cytological studies carried out on the plant revealed it to possess a highly branched erect pigmented stem, simple opposite sub sessile leaves with acute apex and distantly serrated margins, capitula with yellow unisexual disc and ray florets, sterile disc florets, fertile ray florets, relatively high pollen fertility (92.85%), a somatic chromosome number of 2n = 24 and regular formation of 12 bivalents, indicating the plant to be a diploid species. Further studies on Melampodium in Nigeria and a general revision of the flora of West Tropical Africa is suggested as well as the need to monitor M. divaricatum in the region since it appears to have the capacity to become invasive.  相似文献   
112.
Background Increasing morbidity and mortality associated with HIV/AIDS may be attributable to the lifestyle of individuals. Appropriate sexual behaviour and lifestyle modification may be helpful strategies for prevention and control of HIV/AIDS in many countries.Aim The study was designed to assess the impact of attitudes and sexual behaviour on control of HIV/AIDS among unmarried people living with HIV/AIDS in Uyo, a community in the Niger Delta region of Nigeria.Method A total of 365 unmarried individuals living with HIV/AIDS were assessed at the HIV clinic of the University of Uyo Teaching Hospital. Attitudes and sexual behaviour were evaluated using the Attitude and Sexual Behaviour Questionnaire adapted from previous studies.Results Of the 365 individuals living with HIV/AIDS, 142 (38.9%) were male and 223 (61.1%) were female. The majority of the subjects were below 50 years of age. The mean ages (± SD) of men and women were 36.8 ± 3.9 and 29.2 ± 1.7 years, respectively. Sexual attitudes and behaviours were variable. There was no change in the partner''s reaction to sex for 28.9% of men and 27.8% of women, abstinence in 7.7% of men and 8.1% of women, and breakdown of the relationship with the partner for 4.9% of men and 7.2% of women. More women than men agreed to undergo testing after their partners had tested positive for HIV. Sexual activity was higher in women than men, with 4.9% of men and 10.3% of women reporting daily sexual intercourse, 16.2% of men and 15.7% of women reporting weekly intercourse, and occasional sexual intercourse being reported by 44.4% of both men and women. After testing positive, 58.4% of male partners and 56.9% of female partners were persuaded to use condoms during sexual intercourse.Conclusion This study has demonstrated unhealthy attitudes and sexual behaviour among individuals living with HIV/AIDS in the Niger Delta region of Nigeria. This can potentially limit efforts and investment in controlling HIV/AIDS in this region. Therefore there is a need to initiate concrete policies and programmes that would encourage people living with HIV/AIDS in the Niger Delta region to adopt a healthy lifestyle.  相似文献   
113.
Obesity is an inflammatory condition that is also associated with increased extracellular matrix (ECM) gene expression. However, a direct link between adipose tissue inflammation and ECM gene expression has not been established. Therefore, we determined the effect of chronic inflammation induced by obesity and acute inflammation by lipopolysaccharide (LPS) challenge on ECM genes including biglycan (BGN), collagen 1A1 (COL1A1) and COL6A1, major ECM genes in adipose tissue. Male C57BL/6J mice fed either a control diet (10% fat calories) or a high-fat diet (HFD) (60% fat calories) for 6 weeks were treated with LPS or saline 24 h before sacrifice. Expression of ECM genes in the epididymal (EWAT) and subcutaneous adipose tissue (SWAT) was determined by RT-PCR and protein abundance by Western blotting. Human SWAT from lean and obese subjects was also analyzed. Increased messenger RNA (mRNA) expression of ECM genes BGN and COL1A1 was observed in the mouse EWAT after HFD (P<.05). However, reduced amount of COL1A1 protein was observed in EWAT of mice on HFD and in SWAT from obese human subjects. Acute inflammation induced BGN mRNA in EWAT, enhanced the gene expression of matrix metalloproteases (MMPs) 3 and 9. Acute inflammation also resulted in higher MMP9 gelatinolytic activity; however, this showed no association with COL1A1 protein abundance. Higher MMP2 expression in mice on HFD suggests its involvement in the reduction of COL1A1 protein abundance with HFD. Elevated MMP9 gelatinolytic activity in SWAT from obese humans indicates a prominent role for MMP9 in SWAT COL1A1 protein turnover in humans.  相似文献   
114.
115.

Introduction

Mortality data provide essential evidence on the health status of populations in crisis-affected and resource-poor settings and to guide and assess relief operations. Retrospective surveys are commonly used to collect mortality data in such populations, but require substantial resources and have important methodological limitations. We evaluated the feasibility of an alternative method for rapidly quantifying mortality (the informant method). The study objective was to assess the economic feasibility of the informant method.

Methods

The informant method captures deaths through an exhaustive search for all deaths occurring in a population over a defined and recent recall period, using key community informants and next-of-kin of decedents. Between July and October 2008, we implemented and evaluated the informant method in: Kabul, Afghanistan; Mae La camp for Karen refugees, Thai-Burma border; Chiradzulu District, Malawi; and Lugufu and Mtabila refugee camps, Tanzania. We documented the time and cost inputs for the informant method in each site, and compared these with projections for hypothetical retrospective mortality surveys implemented in the same site with a 6 month recall period and with a 30 day recall period.

Findings

The informant method was estimated to require an average of 29% less time inputs and 33% less monetary inputs across all four study sites when compared with retrospective surveys with a 6 month recall period, and 88% less time inputs and 86% less monetary inputs when compared with retrospective surveys with a 1 month recall period. Verbal autopsy questionnaires were feasible and efficient, constituting only 4% of total person-time for the informant method''s implementation in Chiradzulu District.

Conclusions

The informant method requires fewer resources and incurs less respondent burden. The method''s generally impressive feasibility and the near real-time mortality data it provides warrant further work to develop the method given the importance of mortality measurement in such settings.  相似文献   
116.
117.
Spoladea recurvalis (Fbr.) (Lepidoptera: Crambidae) larvae can cause up to 100% foliage loss on amaranths during severe outbreaks. The Bacillus thuringiensis Subsp. kurstaki product Halt® is a biologically safe biopesticide recommended for the management of Spodoptera exigua (Hübner) and Plutella xylostella (Linnaeus). Spoladea recurvalis larvae are less susceptible to the product. Thirteen chemical additives to improve the efficacy of a Bt spray for control of S. recurvalis were evaluated in laboratory bioassays against second-instar larvae. All the additives except calcium chloride caused an increase in mortality when applied in mixtures with Bt. Among the seven inorganic salts, boric acid was the only inorganic acid that caused more than 50% larval mortality. Boric acid at a concentration of 0.05% increased the activity of B. thuringiensis by 2.9-fold. Boric acid had the shortest LT50 values of 5.3 days compared with all other combinations. Two nitrogenous compounds, peptone and sodium nitrate, caused 54 and 51% larval mortalities; however, this increase in efficacy was not significantly different from the mortalities caused by Bt applied without any additive. Urea increased larval mortality from 40% to 51%, although the increase was not significant from a Bt spray application only. Citric acid had no significant effect on the efficacy of Bt spray against S. recurvalis larvae. Overall, among the additives evaluated, the efficacy of Bt spray was most enhanced by boric acid and could be further evaluated under field conditions for validation, and integration into an Integrated Pest Management (IPM) strategy for S. recurvalis management.  相似文献   
118.
Tomato, Solanum lycopersicum, is a widely consumed and economically important vegetable in the tropics. However, its production and productivity have been recently hampered by the invasive Tuta absoluta (Meyrick), a key pest of tomato causing extensive economic damage in Africa. Currently, the commonly used management strategy is synthetic insecticides with hazardous effects on humans and environment. The application of entomopathogenic fungal and viral-based biopesticides is promising alternatives. To identify potent strains, pathogenicity of dry conidia of 12 Metarhizium anisopliae isolates was evaluated against adult T. absoluta. Further effects of the most potent isolates on pupation through the late 4th instar larval infection, adult emergence and horizontal transmission of inoculum were assessed. Metarhizium anisopliae ICIPE 18, ICIPE 20 and ICIPE 665 outperformed the other isolates causing adult mortality of 95.0%, 87.5% and 86.25%, respectively. The three potent isolates differed significantly for LT50 values of 5.13, 3.17 and 2.38 days for ICIPE 18, ICIPE 20 and ICIPE 665, respectively. Pupation and adult emergence were significantly reduced by these potent isolates, which were also compatible with Tuta pheromone (TUA-Optima®) with ≥90% conidial germination 24 hr post-exposure. These potent isolates could be developed as effective biopesticides and used in combination with TUA-Optima® for mass trapping and autodissemination for T. absoluta management in solanaceous crop production systems.  相似文献   
119.
The biodegradation of polychlorinated biphenyls (PCBs) by diverse bacteria including those utilized in this study is often incomplete, a concomitant accumulation of chlorobenzoic acids (CBAs) are released as dead-end products. The build-up of these metabolites in the growth medium may result in feed-back inhibition and impede PCB biotransformation. In this investigation using GC-ECD and HPLC analyses, we confirmed that CBAs inhibit growth and PCB biodegradation potentials of five tropical bacteria namely, Pseudomonas aeruginosa SA-1, Enterobacter sp. SA-2, Ralstonia sp. SA-3, Ralstonia sp. SA-5 and Pseudomonas sp. SA-6. Among the four CBAs (2-CBA, 3-CBA, 4-CBA acids and 2,3-diCBA), 3-CBA was the strongest inhibitor followed by 4-CBA. Furthermore, we found that 3-CBA heavily inhibited growth of SA-3 and SA-6 on monochlorobiphenyls by 82–90% while elimination rate was inhibited by 71–88%. In the case of 2,3-diCBA, inhibition was generally less than 60%. However, effects of both acids were stronger in SA-3 than SA-6. We also found that 3-CBA and 2,3-diCBA completely inhibited carbon-chloride cleavage of 2-CB and 3-CB since cultivation in the absence of the acids resulted in recovery of 23–50% chloride in the culture fluids of organisms. These findings may therefore, have practical and ecological significance and are useful for improving the efficiency and the stability of some biological treatment processes.  相似文献   
120.
We surveyed the macrofungi of an area dominated by northern Guinea savanna habitats in north‐east Nigeria. A total of 93 different species of mushrooms were found in the study area. These species belong to 29 different families, most species belonging to the family Agaricaceae, Lyophyllaceae, Bolbitiaceae, Pluteaceae and Polyporaceae. A total of 48 species belonged to the Agaricaceae, followed by Lyophyllaceae represented by 6 species. The micro‐habitats of mushrooms in the study area include wood, soil around dead tree stump, waste dump, cow dung, fallow, arable land, and 22 different living trees species. The most important habitats in term of mushroom species diversity were Parkia biglobosa, Tamarindus indica and dead wood. The Parkia biglobosa tree had the highest species richness (45) and species diversity (Shannon diversity index, SDI: 3.6). Tamarindus indica was the second, having 28 species richness and 2.7 SDI. These were followed by dead wood where 22 different mushroom species were recorded and has of 2.1 SDI. Also, these three habitats (Parkia biglobosa, dead wood and Tamarindus indica) had the highest number of mushroom species (14, 8 and 6 respectively) that were confined to them. Most of the other mushroom species were confined to only one microhabitat. There was no statistically significant difference in mushroom abundance between arable land and fallow. Collectively, the indigenous trees were associated by more mushroom species (63) than the exotic trees (20) and the indigenous trees also had significantly higher mushroom abundance than the exotic trees. However, the non‐indegenous trees had more species forming mycorrhiza than the indegenous trees, presumaby because the former were able to form symbioses with both native fungi and introduced species from their origina habitats. Inter‐annual variation of mushroom species diversity was also observed. Human activities contribute positively to mushroom diversity in the study area by creating some unique micro‐habitats that support the growth of certain unique mushroom species. Therefore, for maximum conservation of mushroom diversity, conservation measures excuding all human activities should be avoided.  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