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   826篇
  免费   48篇
  国内免费   2篇
  876篇
  2024年   3篇
  2023年   9篇
  2022年   8篇
  2021年   25篇
  2020年   21篇
  2019年   17篇
  2018年   17篇
  2017年   26篇
  2016年   32篇
  2015年   43篇
  2014年   36篇
  2013年   62篇
  2012年   68篇
  2011年   56篇
  2010年   38篇
  2009年   23篇
  2008年   43篇
  2007年   28篇
  2006年   37篇
  2005年   32篇
  2004年   30篇
  2003年   27篇
  2002年   25篇
  2001年   12篇
  2000年   7篇
  1999年   11篇
  1998年   7篇
  1997年   3篇
  1995年   5篇
  1994年   5篇
  1993年   5篇
  1992年   11篇
  1991年   7篇
  1990年   8篇
  1989年   11篇
  1988年   4篇
  1987年   6篇
  1986年   5篇
  1985年   7篇
  1984年   3篇
  1982年   3篇
  1980年   4篇
  1979年   5篇
  1978年   6篇
  1977年   3篇
  1975年   4篇
  1973年   3篇
  1972年   3篇
  1965年   2篇
  1936年   2篇
排序方式: 共有876条查询结果,搜索用时 15 毫秒
21.
Human MECP2 gene located at q28 arm of X chromosome was identified as target for thermal co-amplification with HIV-1 proviral DNA of infected individuals. The selected MECP2 gene-specific primers functioned at a wide range of annealing temperature, extension time and exhibited no significant interaction with pathogen specific primers. A 466 bp PCR amplicon originating from human MECP2 gene was found to be diagnostic for inhibition-free PCR reaction when co-amplified with the HIV-1 target gene in a multiplexed, nested PCR reaction. The 5' end of the MECP2 primers were engineered to position an EcoRI restriction endonuclease site to facilitate rapid cloning in various DNA vector molecules at the corresponding EcoRI sites. Cell mass of Escherichia coli (XL1Blue) harboring the recombinant plasmid when added to pleural fluid of HIV-1 infected individuals co-infected with Mycobacterium tuberculosis, generated the diagnostic 466 bp MECP2 PCR amplicon as well as the 194 bp PCR amplicon of target gene from M. tuberculosis. The experiment underlined potential of the region spanning nucleotide position 4118099 to 4118552 of human MECP2 gene (NCBI accession number NT_011726.13) as a reliable target for multiplex PCR to accommodate a wide range of thermal cycling and multiplex reaction conditions. In both cases of this study, electrophoresis-based separation of the 466 bp MECP2 fragment and the 232 bp and 194 bp HIV-1 and M. tuberculosis fragments respectively was distinct and unambiguous. The potential of this human MECP2 gene available from human genome or recombinant plasmid as a potent target to monitor PCR inhibition for a range of different PCR reactions is discussed.  相似文献   
22.
23.
Vanadium has been reported to have broad pharmacological activity both in vitro and in vivo. Vanadium compound, sodium orthovanadate, Na3VO4, is well known for its hypoglycaemic effects. However, Na3VO4 exerts these effects at relatively high doses (0.6 mg/ml) and exhibit several toxic effects. In the present study lower doses of Na3VO4 (0.2 mg/ml) are combined with Trigonella foenum graecum seed powder (TSP), another hypoglycaemic agent, to reduce its toxicity without compromising its antidiabetic potential. The efficacy of the lower doses of Na3VO4 has been investigated in restoring the altered glucose metabolism and histological structure in the sciatic nerves in 21 and 60 days alloxan diabetic rats. A portion of the glucose was found to be channelled from the normal glycolytic route to polyol pathway, evident by the reduced hexokinase activity and increased polyol pathway enzymes aldose reductase and sorbitol dehydrogenase activity causing accumulation of sorbitol and fructose in diabetic conditions. Ultrastructural observation of the sciatic nerve showed extensive demylination and axonal loss after eight weeks of diabetes induction. Blood glucose levels increased in diabetic rats were normalized with the lower dose of vanadium and Trigonella treatment. The treatment of the diabetic rats with vanadium and Trigonella prevented the activation of the polyol pathway and sugar accumulations. The sciatic nerves were also protected against the structural abnormalities found in diabetes with Trigonella foenum graecum as well as Na3VO4. Results suggest that lower doses of Na3VO4 may be used in combination with TSP as an efficient antidiabetic agent to effectively control the long-term complications of diabetes in tissues like peripheral nerve.  相似文献   
24.
25.
A K Giri  S K Das  G Talukder  A Sharma 《Cytobios》1990,62(249):111-117
Sister chromatid exchanges (SCEs) and chromosomal aberrations induced by curcumin (a natural dye) and tartrazine (a synthetic dye) were studied on bone marrow cells of mice and rats following acute and chronic exposure via the diet. Except for two low concentrations in the curcumin and one low concentration in the tartrazine treated series a significant increase in SCEs was observed in all the concentrations of the two dyes tested. Except for two high concentrations during the 9 months treatment no significant increase in chromosomal aberrations was observed in the curcumin treated series, whereas tartrazine showed a significant increase in chromosomal aberrations in some of the higher concentrations in all the series tested. The results indicate that tartrazine is more clastogenic than curcumin.  相似文献   
26.
In this study, batch removal of hexavalent chromium from aqueous solutions by powdered Colocasia esculenta leaves was investigated. Batch experiments were conducted to study the effects of adsorption of Cr(VI) at different pH values, initial concentrations, agitation speeds, temperatures, and contact times. The biosorbent was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier transform infrared spectrometer analysis. The biosorptive capacity of the adsorbent was dependent on the pH of the chromium solution in which maximum removal was observed at pH 2. The adsorption equilibrium data were evaluated for various adsorption isotherm models, kinetic models, and thermodynamics. The equilibrium data fitted well with Freundlich and Halsey models. The adsorption capacity calculated was 47.62 mg/g at pH 2. The adsorption kinetic data were best described by pseudo-second-order kinetic model. Thus, Colocasia esculenta leaves can be considered as one of the efficient and cheap biosorbents for hexavalent chromium removal from aqueous solutions.  相似文献   
27.
The effects of dietary Pseudomonas aeruginosa VSG-2 supplementation on innate immunity and protection against Aeromonas hydrophila infection were evaluated in Labeo rohita. Fish were fed for 60 days with control diet or 3 experimental diets containing P. aeruginosa VSG-2 at 10(5), 10(7), and 10(9) cfu g(-l), respectively. Various innate immune parameters were examined at 30 and 60 days post-feeding. Fish were challenged with A. hydrophila 60 days post-feeding and mortalities were recorded over 10 days post-infection. Dietary supplementation of P. aeruginosa VSG-2 significantly increased serum lysozyme and alternative complement pathway (ACP) activities, phagocytosis, and respiratory burst activity in head kidney macrophages of L. rohita throughout the experimental period. Superoxide dismutase (SOD) activity significantly increased after 60 days in the groups fed diets containing 10(7) and 10(9) cfu g(-1) P aeruginosa. Serum IgM levels were significantly higher in the treatment groups than in the control group after 30 days of feeding; however, the opposite result was observed at 60 days. Moreover, fish fed diets containing 10(7) and 10(9) cfu g(-1)P. aeruginosa had significantly higher post-challenge survival rates against A. hydrophila infection. Further, P. aeruginosa VSG-2 was found to be safe for mammals. These results indicate that dietary P. aeruginosa VSG-2 supplementation at 10(7) cfu g(-1) can effectively improve innate immunity and disease resistance in L. rohita.  相似文献   
28.
29.
Potato chips industry wastewater was collected and analyzed for biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS) and total carbohydrates. Two Aspergillus species, A. foetidus and A. niger, were evaluated for their ability to grow and produce biomass and reduce the organic load of the wastewater. A. foetidus MTCC 508 and A. niger ITCC 2012 were able to reduce COD by about 60% and produce biomass 2.4 and 2.85 gl(-1), respectively. Co-inoculation of both Aspergillus strains resulted in increased fungal biomass production and higher COD reduction than in individual culture at different culture pH. pH 6 was optimum for biomass production and COD reduction. Amendment of the wastewater with different N and P sources, increased the biomass production and COD reduction substantially. Under standardized conditions of pH 6 and amendment of wastewater with 0.1% KH2PO4 and 0.1% (NH4)2 SO4, a mixed culture gave 90% reduction in COD within 60 h of incubation.  相似文献   
30.
South America has been influenced by different geoclimatic events ever since its separation from Africa. The inland water fauna has evolved in response to the changing landscape. Currently, there are indications of variations in populations, occurring to different degrees that would indicate a clinal pattern in morphology. Among South America's fauna, the freshwater anomuran, Aegla, is an enigmatic group as a result of its endemicity and is composed of only one genus. Of all the species in this family, Aegla uruguayana has the broadest distribution. Its native habitats have been influenced by several marine transgressions during the Miocene–Quaternary Periods; thus, it is likely that their current distribution has been more recent. Its habitat spreads across a number of isolated basins and sub‐basins that display distinct degrees of isolation/connection, making clinal variation patterns in the morphology of this species possible. The present study aimed to evaluate the pattern of carapace shape variation in A. uruguayana and how it relates to the isolation and/or connection of populations from different basins and sub‐basins, allowing the determination of any extant clinal patterns. The specimens studied belong to 25 separate populations, representing all areas in which the species currently exists. A total of 523 crabs were analyzed. We identified 13 landmarks and four semi‐landmarks in the carapace. The aeglids were divided into seven size intervals to avoid an allometry effect. In each size category, shape relationships analyzed by principal component analysis suggest a geographical pattern corresponding to the distribution of the populations studied. An evaluation of covariation between body shape and geographical coordinates reveals a strong pattern and shows that population distribution had a significant effect on species morphology. Additionally, according to covariance analysis, the variation in shape was not associated with the environmental variables studied. We observed a clinal pattern throughout the species distribution, which could be attributed to genetic drift. It is possible that this process is being amplified by the geographical isolation of the basins, differences in environmental characteristics, and low dispersal ability. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 914–930.  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