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   463篇
  免费   17篇
  480篇
  2022年   16篇
  2021年   16篇
  2020年   5篇
  2019年   10篇
  2018年   15篇
  2017年   6篇
  2016年   19篇
  2015年   30篇
  2014年   21篇
  2013年   38篇
  2012年   25篇
  2011年   40篇
  2010年   23篇
  2009年   11篇
  2008年   16篇
  2007年   27篇
  2006年   25篇
  2005年   20篇
  2004年   9篇
  2003年   10篇
  2002年   11篇
  2001年   5篇
  2000年   9篇
  1998年   3篇
  1997年   5篇
  1996年   3篇
  1994年   3篇
  1993年   3篇
  1992年   3篇
  1989年   3篇
  1987年   3篇
  1985年   2篇
  1984年   5篇
  1983年   3篇
  1982年   2篇
  1981年   5篇
  1980年   4篇
  1978年   1篇
  1976年   2篇
  1975年   1篇
  1974年   1篇
  1973年   6篇
  1971年   1篇
  1970年   1篇
  1969年   2篇
  1968年   2篇
  1967年   1篇
  1960年   1篇
  1955年   1篇
  1954年   1篇
排序方式: 共有480条查询结果,搜索用时 15 毫秒
1.
The production of micronuclei in mouse bone marrow by the pyrethroid insecticide, cypermethrin and the botanical insecticide, rotenone was examined. Three routes of administration were used for the insecticides: intraperitoneal, oral and dermal. The different routes of treatment with cypermethrin and rotenone caused toxicity of marrow as indicated by a significant increase in the percentage of polychromatic erythrocytes (PEs) over that of the control. Cypermethrin showed mutagenic potential as evidenced by a positive response in the micronucleus assay. Oral administration of the insecticide at a dietary level of 900 ppm for 7 and 14 consecutive days as well as double and multiple (total 4) dermal treatments (360 mg/kg body wt.) induced a statistically significant increase in the frequency of PEs with micronuclei. The conducted intraperitoneal (i.p.) treatments with cypermethrin: single injection at 60 and 180 mg/kg body wt., double and multiple injections (total 3) at 60 mg/kg body wt. did not affect the percentage of PEs with micronuclei. The different treatments with rotenone: single, double and multiple (i.p.) injections (total 3) at 2 and 3 mg/kg body wt., oral administration for 14 consecutive days at dietary level of 225 ppm and multiple dermal treatments (total 4) with 135 mg/kg body wt. showed no effect on the frequency of micronuclei in PEs.  相似文献   
2.
The lepidopteran mitochondrial control region: structure and evolution   总被引:8,自引:3,他引:5  
For several species of lepidoptera, most of the approximately 350-bp mitochondrial control-region sequences were determined. Six of these species are in one genus, Jalmenus; are closely related; and are believed to have undergone recent rapid speciation. Recent speciation was supported by the observation of low interspecific sequence divergence. Thus, no useful phylogeny could be constructed for the genus. Despite a surprising conservation of control-region length, there was little conservation of primary sequences either among the three lepidopteran genera or between lepidoptera and Drosophila. Analysis of secondary structure indicated only one possible feature in common--inferred stem loops with higher-than-random folding energies-- although the positions of the structures in different species were unrelated to regions of primary sequence similarity. We suggest that the conserved, short length of control regions is related to the observed lack of heteroplasmy in lepidopteran mitochondrial genomes. In addition, determination of flanking sequences for one Jalmenus species indicated (i) only weak support for the available model of insect 12S rRNA structure and (ii) that tRNA translocation is a frequent event in the evolution of insect mitochondrial genomes.   相似文献   
3.
4.
Bio-fertilization is a sustainable agricultural practice that includes using bio-fertilizers to increase soil nutrient content resulting in higher productivity. Soil micro-flora has been exposed to improve soil fertility and increase biomass productivity and identified as a correct environmentally friendly bio-based fertilizer for pollution-free agricultural applies. The majority of cyanobacteria can fix nitrogen from the atmosphere and several species including Anabaena sp., Nostoc sp., and Oscillatoria angustissima is known to be effective cyanobacterial based bio fertilizers. Acutodesmus dimorphus, Spirulina platensis Chlorella vulgaris, Scenedesmus dimorphus, Anabaena azolla, and Nostoc sp. are some of the green microalgae and cyanobacteria species that have been successfully used as bio fertilizers to boost crop growth. Also, Chlorella vulgaris is one of the most commonly used microalgae in bio fertilizer studies. The addition of seaweed species that are Sargassum sp. and Gracilaria verrucosa leads to chemical changes as a soil fertility indicator on clay and sandy soils, and the addition of seaweed conditioner to soil can improve its organic content, return pH to normal, and reduce C/N ratio in both sandy and clay soil. This review provides an effective approach to increase soil fertility via environmentally friendly bio-based fertilizer using micro and macro algae. Instead of the usage of inorganic and organic fertilizers that have polluted impacts to soil as aggregation of heavy metals, in addition to there their human carcinogenic effects.  相似文献   
5.
Macrophages activate autophagy as an immediate response to Legionella pneumophila infection, but what marks the pathogen phagosome as a target for the autophagy machinery is not known. Because a variety of bacteria, parasites, viruses, and toxins that associate with the endoplasmic reticulum enter host cells by a cholesterol-dependent route, we tested the hypothesis that autophagy is triggered when microbes engage components of lipid raft domains. As the intracellular respiratory pathogen L. pneumophila or the extracellular uropathogen FimH(+) Escherichia coli entered macrophages by a cholesterol-sensitive mechanism, they immediatezly resided in vacuoles rich in glycosylphosphatidylinositol moieties and the autophagy enzyme Atg7. As expected for autophagosomes, the vacuoles sequentially acquired the endoplasmic reticulum protein BiP, the autophagy markers Atg8 and monodansyl-cadaverine, and the lysosomal protein LAMP-1. A robust macrophage response to the pathogens was cholesterol-dependent, since fewer Atg7-rich vacuoles were observed when macrophages were pretreated with methyl-beta-cyclodextrin or filipin. A model in which macrophages exploit autophagy to capture pathogens within the lipid raft pathway for antigen presentation prior to disposal in lysosomes is discussed.  相似文献   
6.
We aimed to shed new light on the roles of microRNAs (miRNAs) in liver cancer using an integrative in silico bioinformatics analysis. A new protocol for target prediction and functional analysis is presented and applied to the 26 highly differentially deregulated miRNAs in hepatocellular carcinoma. This framework comprises: (1) the overlap of prediction results by four out of five target prediction tools, including TargetScan, PicTar, miRanda, DIANA-microT and miRDB (combining machine-learning, alignment, interaction energy and statistical tests in order to minimize false positives), (2) evidence from previous microarray analysis on the expression of these targets, (3) gene ontology (GO) and pathway enrichment analysis of the miRNA targets and their pathways and (4) linking these results to oncogenesis and cancer hallmarks. This yielded new insights into the roles of miRNAs in cancer hallmarks. Here we presented several key targets and hundreds of new targets that are significantly enriched in many new cancer-related hallmarks. In addition, we also revealed some known and new oncogenic pathways for liver cancer. These included the famous MAPK, TGFβ and cell cycle pathways. New insights were also provided into Wnt signaling, prostate cancer, axon guidance and oocyte meiosis pathways. These signaling and developmental pathways crosstalk to regulate stem cell transformation and implicate a role of miRNAs in hepatic stem cell deregulation and cancer development. By analyzing their complete interactome, we proposed new categorization for some of these miRNAs as either tumor-suppressors or oncomiRs with dual roles. Therefore some of these miRNAs may be addressed as therapeutic targets or used as therapeutic agents. Such dual roles thus expand the view of miRNAs as active maintainers of cellular homeostasis.  相似文献   
7.
We investigated leptin effects on lymphocyte interactions with hepatic-stellate-cells (HSCs). Leptin showed pro-fibrotic effects on HSCs with oxidative status imbalance.In co-cultures, leptin activates HSCs and consequently adhered HCV-lymphocytes more than healthy ones. Leptin also increased healthy and HCV lymphocyte proliferations; increased their reactive-oxygen-species; decreased antioxidants (reduced-glutathione) levels while inhibited apoptosis only of HCV-lymphocytes. The leptin-treated HCV-lymphocytes activated HSCs, increase interleukin-4 while decreased their apoptosis.Leptin-receptor-deficient (dbdb)-HSCs did not adhere lymphocytes. db/db-lymphocytes however showed fewer adherences to HSCs when compared to WT-counterparts.This study presents immune and oxidative modulatory effects of leptin on lymphocytes and their consequent interaction with HSCs.  相似文献   
8.
This article examines recent developments in the South China Sea; in particular, the China-Vietnam relationship. The developments are presented in the broader context of the Sino-Vietnamese approach to managing border disputes since full normalization of relations in late 1991. The challenges for China and Vietnam in managing their disputes and related tension in the South China Sea are also discussed.  相似文献   
9.

Purpose

Storage of cultured human oral keratinocytes (HOK) allows for transportation of cultured transplants to eye clinics worldwide. In a previous study, one-week storage of cultured HOK was found to be superior with regard to viability and morphology at 12°C compared to 4°C and 37°C. To understand more of how storage temperature affects cell phenotype, gene expression of HOK before and after storage at 4°C, 12°C, and 37°C was assessed.

Materials and Methods

Cultured HOK were stored in HEPES- and sodium bicarbonate-buffered Minimum Essential Medium at 4°C, 12°C, and 37°C for one week. Total RNA was isolated and the gene expression profile was determined using DNA microarrays and analyzed with Partek Genomics Suite software and Ingenuity Pathway Analysis. Differentially expressed genes (fold change > 1.5 and P < 0.05) were identified by one-way ANOVA. Key genes were validated using qPCR.

Results

Gene expression of cultures stored at 4°C and 12°C clustered close to the unstored control cultures. Cultures stored at 37°C displayed substantial change in gene expression compared to the other groups. In comparison with 12°C, 2,981 genes were differentially expressed at 37°C. In contrast, only 67 genes were differentially expressed between the unstored control and the cells stored at 12°C. The 12°C and 37°C culture groups differed most significantly with regard to the expression of differentiation markers. The Hedgehog signaling pathway was significantly downregulated at 37°C compared to 12°C.

Conclusion

HOK cultures stored at 37°C showed considerably larger changes in gene expression compared to unstored cells than cultured HOK stored at 4°C and 12°C. The changes observed at 37°C consisted of differentiation of the cells towards a squamous epithelium-specific phenotype. Storing cultured ocular surface transplants at 37°C is therefore not recommended. This is particularly interesting as 37°C is the standard incubation temperature used for cell culture.  相似文献   
10.

Background

Tick-borne rickettsioses are caused by obligate intracellular bacteria belonging to the spotted fever group (SFG) rickettsiae. Although Spotted Fever is prevalent in the Middle East, no reports for the presence of tick-borne pathogens are available or any studies on the epidemiology of this disease in the West Bank. We aimed to identify the circulating hard tick vectors and genetically characterize SFG Rickettsia species in ixodid ticks from the West Bank-Palestinian territories.

Methodology/Principal Findings

A total of 1,123 ixodid ticks belonging to eight species (Haemaphysalis parva, Haemaphysalis adleri, Rhipicephalus turanicus, Rhipicephalus sanguineus, Rhipicephalus bursa, Hyalomma dromedarii, Hyalomma aegyptium and Hyalomma impeltatum) were collected from goats, sheep, camels, dogs, a wolf, a horse and a tortoise in different localities throughout the West Bank during the period of January-April, 2014. A total of 867 ticks were screened for the presence of rickettsiae by PCR targeting a partial sequence of the ompA gene followed by sequence analysis. Two additional genes, 17 kDa and 16SrRNA were also targeted for further characterization of the detected Rickettsia species. Rickettsial DNA was detected in 148 out of the 867 (17%) tested ticks. The infection rates in Rh. turanicus, Rh. sanguineus, H. adleri, H. parva, H. dromedarii, and H. impeltatum ticks were 41.7, 11.6, 16.7, 16.2, 11.8 and 20%, respectively. None of the ticks, belonging to the species Rh. bursa and H. aegyptium, were infected. Four SFG rickettsiae were identified: Rickettsia massiliae, Rickettsia africae, Candidatus Rickettsia barbariae and Candidatus Rickettsia goldwasserii.

Significance

The results of this study demonstrate the geographic distribution of SFG rickettsiae and clearly indicate the presence of at least four of them in collected ticks. Palestinian clinicians should be aware of emerging tick-borne diseases in the West Bank, particularly infections due to R. massiliae and R. africae.  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