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   677篇
  免费   36篇
  国内免费   3篇
  2024年   2篇
  2023年   18篇
  2022年   36篇
  2021年   58篇
  2020年   27篇
  2019年   40篇
  2018年   41篇
  2017年   22篇
  2016年   37篇
  2015年   35篇
  2014年   54篇
  2013年   63篇
  2012年   55篇
  2011年   40篇
  2010年   30篇
  2009年   6篇
  2008年   19篇
  2007年   18篇
  2006年   10篇
  2005年   17篇
  2004年   18篇
  2003年   8篇
  2002年   12篇
  2001年   8篇
  2000年   5篇
  1999年   6篇
  1998年   4篇
  1997年   7篇
  1996年   3篇
  1995年   1篇
  1994年   4篇
  1993年   3篇
  1992年   3篇
  1991年   1篇
  1988年   1篇
  1984年   2篇
  1973年   1篇
  1872年   1篇
排序方式: 共有716条查询结果,搜索用时 93 毫秒
191.

Background

Insecticide treated nets (ITN) and indoor residual spraying (IRS) are the two pillars of malaria vector control in Africa, but both interventions are beset by quality and coverage concerns. Data from three control programs were used to investigate the impact of: 1) the physical deterioration of ITNs, and 2) inadequate IRS spray coverage, on their respective protective effectiveness.

Methods

Malaria indicator surveys were carried out in 2009 and 2010 in Bioko Island, mainland Equatorial Guinea and Malawi to monitor infection with P.falciparum in children, mosquito net use, net condition and spray status of houses. Nets were classified by their condition. The association between infection and quality and coverage of interventions was investigated.

Results

There was reduced odds of infection with P.falciparum in children sleeping under ITNs that were intact (Odds ratio (OR): 0.65, 95% CI: 0.55–0.77 and OR: 0.81, 95% CI: 0.56–1.18 in Equatorial Guinea and in Malawi respectively), but the protective effect became less with increasingly worse condition of the net. There was evidence for a linear trend in infection per category increase in deterioration of nets. In Equatorial Guinea IRS offered protection to those in sprayed and unsprayed houses alike when neighbourhood spray coverage was high (≥80%) compared to those living in areas of low IRS coverage (<20%), regardless of whether the house they lived in was sprayed or not (adjusted OR = 0.54, 95% CI 0.33–0.89). ITNs provided only personal protection, offering no protection to non users. Although similar effects were seen in Malawi, the evidence was much weaker than in Equatorial Guinea.

Conclusions

Universal coverage strategies should consider policies for repair and replacement of holed nets and promote the care of nets by their owners. IRS programs should ensure high spray coverage since inadequate coverage gives little or no protection at all.  相似文献   
192.
Three wheat and two barley populations were studied in order to find loci responsible for dormancy and pre-harvest sprouting. A classical quantitative trait loci analysis was combined with an association mapping approach. Many quantitative trait loci and marker trait associations could be detected on all seven chromosome groups of wheat and on the chromosomes 2H, 3H, 5H, 6H, and 7H of barley. Especially, the known regions on chromosomes 3A and 4A for wheat and 5H for barley were confirmed. Putative functions could be found via a candidate homologues search and via expressed sequence tag annotation. On chromosome 3A, the viviparous1 gene is located which is associated to preharvest sprouting and dormancy. On chromosome 4A, a protein is detected which belongs to the aquaporin family. In barley, an association with the aleurain gene on chromosome 5H was found. The expression of aleurain is regulated by abscisic acid and gibberelic acid. An influence of both hormones on dormancy and pre-harvest sprouting is known. It can be concluded that dormancy and pre-harvest sprouting are very complex traits regulated by multigenes and/or quantitative trait loci.  相似文献   
193.
This study was conducted to evaluate the influence of boron (B) application through seed coating on leaf elongation, tillering, water relations, panicle sterility, kernel yield, and grain biofortification of fine grain aromatic rice. Boron was applied as seed coating at 1.0, 1.5, 2.0, 2.5, and 3.0 g B kg?1 seed in two rice cultivars Super Basmati and Shaheen Basmati. Boron seed coating significantly affected the leaf elongation, water relations, panicle fertility, kernel yield and grain biofortification in both rice cultivars. However, seed coating with 1.0–2.0 g B kg?1 seed was effective in improving the leaf emergence and elongation, and tillering. Whereas water relations (water and osmotic potential) were improved by all B seed coating treatments, but pressure potential was only improved from seed coating with 2.0–3.0 g B kg?1 seed. Kernel yield was improved by all B seed coating treatments; however seed coating with 2 g B kg?1 seed was the most effective treatment in this regard. Increase in kernel yield, by B seed coating, was attributed to decrease in panicle sterility. Leaf and kernel B contents were increased with increase in B concentration in seed coating.  相似文献   
194.
Phloem-sucking mustard aphid (Lipaphis erysimi) is a major pest of mustard (Brassica juncea). Pot experiment with randomised block design was conducted with five replicates of each of five cultivars (Alankar, Pusa Jai Kisan, Rohini, Sakha and Varuna) of the mustard for their degree of inherited resistance and/or susceptibility to the mustard aphid infestation. Forty-five days old (from date of sowing) pot-grown plants of all selected cultivars of mustard were exposed to 40 adult mustard aphids. The aphid-infested plants were kept in specially designed net houses of fine mesh to protect from predators and/or migration of aphids from one to other host. The aphid population and some growth attributes of the selected cultivars of mustard were recorded 15 and 30 days later (i.e. at 60 and 75 days after sowing). The aphid population multiplied more rapidly on Rohini than other four cultivars. Cultivar Alankar resisted most and supported to least number of aphid’s off-springs. Statistically analysed growth attributes (fresh plant mass, dry plant mass, protein, chlorophyll and carotenoid contents), resistance attribute (proline) and population demography of aphids revealed that some inherited characteristics of avoidance, antibiosis and repellence to herbivores helped cultivar Alankar to excel despite equal degree of aphid attacks as on other cultivars. Cultivar Rohini for the want of such resisting factors remained vulnerable to aphid herbivory. These two cultivars (Alankar and Rohini) form good research material for comparative studies on plant defences to herbivory and a tri- trophic resistance through volatile chemical signalling.  相似文献   
195.
196.
The activity of Rho-specific guanine nucleotide dissociation inhibitor α (RhoGDIα) is regulated by its own phosphorylation at different amino acid sites. These phosphorylation sites may have a crucial role in local Rho GTPases activation during cell migration. This paper is designed to explore the influence of phosphorylation on shear stress-induced spatial RhoGDIα activation. Based on the fluorescence resonance energy transfer biosensor sl-RhoGDIα, which was constructed to test the RhoGDIα activity in living cells, new RhoGDIα phosphomimetic mutation (sl-S101E/S174E, sl-Y156E, sl-S101E, sl-S174E) and phosphorylation-deficient mutation (sl-S101A/S174A, sl-Y156A, sl-S101A, sl-S174A) biosensors were designed to test their effects on RhoGDIα activation upon shear stress application in human umbilical vein endothelial cells (HUVECs). The results showed lower RhoGDIα activity at the downstream of HUVECs (the region from the edge of the nucleus to the edge of the cell along with the flow). The overall decrease in RhoGDIα activity was inhibited by Y156A-mutant, whereas the polarized RhoGDIα and Rac1 activity were blocked by S101A/S174A mutant. It is concluded that the Tyr156 phosphorylation mainly mediates shear stress-induced overall RhoGDIα activity, while Ser101/Ser174 phosphorylation mediates its polarization. This study demonstrates that differential phosphorylation of RhoGDIα regulates shear stress-induced spatial RhoGDIα activation, which could be a potential target to control cell migration.  相似文献   
197.
Abstract

Potentially toxic elements and particulate matter (PM) in the ecosystem are regarded as extremely hazardous because of their persistence, toxicity and bioaccumulative characteristics. Therefore, present study was conducted to estimate the ecological and human health risks of potentially toxic elements (Cu, Mn, Pb, Cd and Ni) and particle pollution (TSP, PM10 and PM2.5) at 2 and 60 m roadside distance from 15 different sites at dust polluted megacity of Pakistan. The AQI assessments suggested that the majority of sites were found unhealthy for sensitive at 2 and 60 m roadside distance, which reveals that that quality of road pavement and streets are far below than the required standards resulting huge quantity of dust particles suspended in air by natural and anthropogenic activities. The maximum geo-accumulation index (I geo) values (1.47 and 0.52) and pollution index (PI) values (4.18 and 2.15) were observed for Ni at 2 and 60 m distance away from the muddy edge of the roads. Similarly, maximum contamination factor (CF) values (24.5 and 94.5) and ecological risk index (ERI) values (4.11 and 3.15) were found for Cd at 2 and 60 m. The I geo and PI indicated that the road dust at a distance of 2 m was relatively more contaminated as compared to 60 m roadside distance. Highest cancer risk (CR) values (2.33 adult and 10.9 for children) were observed for Pb at 2 m, while highest CR values (1.21 for adult and 5.67 for children) at 60 m distance. No probable health risk was observed as the total hazard index (HIexp) of all potentially toxic elements was <1. However, children were appeared to be more susceptible to potentially toxic elements. Based on the results, we believe that the exponential increase in traffic load and industries have aggravated the pollution level and it is expected to be increased in the future.  相似文献   
198.

Background

Plants have widely been used and documented for their therapeutic potential in many parts of the world. There are, however, few reports on the use of plants for the treatment of diseases of equines. To this end, participatory epidemiology and rapid rural appraisal techniques were used to document the plants having pharmacotherapeutic significance against different ailments of equines in selected population of Punjab, Pakistan.

Methods

A survey was conducted to interview a total of 450 respondents (150 from each of the districts of Faisalabad, Lahore and Sargodha of Pakistan) to collect information about disease recognition of the equines and their treatment on a well ? structured questionnaire. A total of 60 plants belonging to 40 families were documented. An inventory was developed depicting detailed information of plants used in treatment of different conditions of equines.

Results

The top ten species of plants used were: Allium cepa, Zingiber officinale, Vernonia anthelmintica, Capsicum annum, Brassica campestris, Trachyspermum ammi, Anethum graveolens, Picrorhiza kurroa, Azadirachta indica, and Citrullus colocynthis. Seeds were the most frequently used (n?=?16/60) parts, followed by leaves (n?=?12/60) and fruits (n?=?11/60) of plants. Based on the combination of different parts of plants used in different ratios and variation in their dose or mode of preparation led to a large number of recipes/remedies against wounds, lameness, bronchitis, colic, anorexia, dermatitis, weakness, parasitism (internal & external), fever, heat stress, urine retention, swelling, toxemia, and indigestion.

Conclusions

This study generated lot of data on phytomedicinal approach for the treatment of ailments in the equines in some selected areas. It would, therefore, be imperative to expand similar studies in other parts of Pakistan and elsewhere. Moreover, use of the documented plants may be validated employing standard scientific procedures, which may have their application in the drug discovery/development by the pharmaceutical industry.
  相似文献   
199.
Alginate is an important polysaccharide used widely in the food, textile, printing and pharmaceutical industries for its viscosifying, and gelling properties. All commercially produced alginates are isolated from farmed brown seaweeds. These algal alginates suffer from heterogeneity in composition and material properties. Here, we will discuss alginates produced by bacteria; the molecular mechanisms involved in their biosynthesis; and the potential to utilize these bacterially produced or modified alginates for high-value applications where defined material properties are required.  相似文献   
200.
The worldwide dissemination of CTX-M type β-lactamases is a threat to human health. Previously, we have reported the spread of bla CTX-M-15 gene in different clinical strains of Enterobacteriaceae from the hospital settings of Aligarh in north India. In view of the varying resistance pattern against cephalosporins and other β-lactam antibiotics, we intended to understand the correlation between MICs and catalytic activity of CTX-M-15. In this study, steady-state kinetic parameters and MICs were determined on E. coli DH5α transformed with bla CTX-M-15 gene that was cloned from Enterobacter cloacae (EC-15) strain of clinical background. The effect of conventional β-lactamase inhibitors (clavulanic acid, sulbactam and tazobactam) on CTX-M-15 was also studied. We have found that tazobactam is the best among these inhibitors against CTX-M-15. The inhibition characteristic of tazobactam is defined by its very low IC50 value (6 nM), high affinity (K i = 0.017 µM) and better acylation efficiency (k +2/K′ = 0.44 µM−1s−1). It forms an acyl-enzyme covalent complex, which is quite stable (k +3 = 0.0057 s−1). Since increasing resistance has been reported against conventional β-lactam antibiotic-inhibitor combinations, we aspire to design a non-β-lactam core containing β-lactamase inhibitor. For this, we screened ZINC database and performed molecular docking to identify a potential non-β-lactam based inhibitor (ZINC03787097). The MICs of cephalosporin antibiotics in combination with this inhibitor gave promising results. Steady-state kinetics and molecular docking studies showed that ZINC03787097 is a reversible inhibitor which binds non-covalently to the active site of the enzyme through hydrogen bonds and hydrophobic interactions. Though, it’s IC50 (180 nM) is much higher than tazobactam, it has good affinity for CTX-M-15 (K i = 0.388 µM). This study concludes that ZINC03787097 compound can be used as seed molecule to design more efficient non-β-lactam containing β-lactamase inhibitor that could evade pre-existing bacterial resistance mechanisms.  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