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   368篇
  免费   21篇
  国内免费   1篇
  2023年   14篇
  2022年   9篇
  2021年   8篇
  2020年   9篇
  2019年   9篇
  2018年   12篇
  2017年   15篇
  2016年   13篇
  2015年   22篇
  2014年   17篇
  2013年   40篇
  2012年   34篇
  2011年   40篇
  2010年   22篇
  2009年   11篇
  2008年   14篇
  2007年   15篇
  2006年   11篇
  2005年   6篇
  2004年   12篇
  2003年   9篇
  2002年   8篇
  2001年   2篇
  2000年   1篇
  1999年   1篇
  1998年   1篇
  1997年   1篇
  1995年   5篇
  1994年   2篇
  1992年   1篇
  1991年   2篇
  1990年   1篇
  1989年   2篇
  1988年   2篇
  1987年   1篇
  1986年   1篇
  1985年   1篇
  1984年   3篇
  1983年   2篇
  1982年   1篇
  1980年   1篇
  1978年   1篇
  1977年   1篇
  1976年   1篇
  1973年   1篇
  1972年   2篇
  1968年   1篇
  1967年   1篇
  1966年   1篇
排序方式: 共有390条查询结果,搜索用时 187 毫秒
121.
By bioactive-guided fractionation of methanol extract of the Ficus microcarpa leaves, one new C-glucosylflavone, ficuflavoside (1), one new megastigmane glycoside, ficumegasoside (8), and twelve known compounds including flavonoids (2-6), phenylpropanoids (7), megastigmanes (9-11) and sterol derivatives (12-14) were isolated. Their chemical structures were elucidated by mass, 1D, and 2D NMR spectroscopies. The antioxidant activities of these compounds were measured using the oxygen radical absorbance capacity methods. Compounds 1-6 exhibited potent antioxidant activities of 6.6-9.5 μM Trolox equivalents at the concentration of 2.0 μM. The results indicated 2, 3, and 5 having meaningful reducing capacity of copper (I) ions concentration of 6.1-8.4 μM.  相似文献   
122.
Journal of Plant Biochemistry and Biotechnology - Silver nanoparticles (AgNPs) were biosynthesized at room temperature under sunlight irradiation, using the extract of Jasminum subtriplinerve Blume...  相似文献   
123.
In Vitro Cellular & Developmental Biology - Plant - Aconitum carmichaelii Debx. is a medicinal plant that contains a variety of valuable medicinal substances, including flavonoids, alkaloids,...  相似文献   
124.
Bioprocess and Biosystems Engineering - Unfortunately, the author name was wrongly published as Pailin Sukwang.instead of Pailin Sukwong.  相似文献   
125.
A sensitive determination of a synthetic fluoroquinolone antibacterial agent, moxifloxacin (MOX), by an enhanced chemiluminescence (CL) method using a microfluidic chip is described. The microfluidic chip was fabricated by a soft‐lithographic procedure using polydimethyl siloxane (PDMS). The fabricated PDMS microfluidic chip had three‐inlet microchannels for introducing the sample, chemiluminescent reagent and oxidant, and a 500 µm wide, 250 µm deep and 82 mm long microchannel. An enhanced CL system, luminol–ferricyanide, was adopted to analyze the MOX concentration in a sample solution. CL light was emitted continuously after mixing luminol and ferricyanide in the presence of MOX on the PDMS microfluidic chip. The amount of MOX in the luminol–ferricyanide system influenced the intensity of the CL light. The linear range of MOX concentration was 0.14–55.0 ng/mL with a correlation coefficient of 0.9992. The limit of detection (LOD) and limit of quantification (LOQ) were 0.06 and 0.2 ng/mL respectively. The presented method afforded good reproducibility, with a relative standard deviation (RSD) of 1.05% for 10 ng/mL of MOX, and has been successfully applied for the determination of MOX in pharmaceutical and biological samples. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   
126.
The area of degraded forests in Vietnam is substantial, currently about 3.1 million ha of which about 1.7 million ha (55 %) were granted to individual farms for reforestation. However, the result of farmers’ reforestation efforts is limited. We aimed to examine the financial return, technical efficiency, and factors determining reforestation with a native tree species (Canarium album) by farms. Our results showed that reforestation with C. album is less financially profitable than that with an exotic tree species (Acacia mangium) as the alternative land use option. The subsidy from the government is found insufficient to compensate for the income losses of farmers participating in reforestation with the native tree species. Reforestation with C. album could be more successful if participating farmers were equipped to be more technically efficient. Finally, our findings clearly showed that the security of forest land property rights and the provision of forest extension services are among the determinants of participation in, and the subsequent success of reforestation with C. album.  相似文献   
127.
Southeast Asia harbours abundant biodiversity, hypothesized to have been generated by Pliocene and Pleistocene climatic and environmental change. Vicariance between the island of Borneo, the remaining Indonesian archipelago and mainland Southeast Asia caused by elevated sea levels during interglacial periods has been proposed to lead to diversification in the littoral zone mosquito Anopheles (Cellia) sundaicus (Rodenwaldt) sensu lato. To test this biogeographical hypothesis, we inferred the population history and assessed gene flow of A. sundaicus s.l. sampled from 18 populations across its pan‐Asian species range, using sequences from mitochondrial cytochrome c oxidase subunit 1 (CO1), the internal transcribed spacer 2 (ITS2) and the mannose phosphate isomerase (Mpi) gene. A hypothesis of ecological speciation for A. sundaicus involving divergent adaptation to brackish and freshwater larval habitats was also previously proposed, based on a deficiency of heterozygotes for Mpi allozyme alleles in sympatry. This hypothesis was not supported by Mpi sequence data, which exhibited no fixed differences between brackish and freshwater larval habitats. Mpi and CO1 supported the presence of up to eight genetically distinct population groupings. Counter to the hypothesis of three allopatric species, divergence was often no greater between Borneo, Sumatra/Java and the Southeast Asian mainland than it was between genetic groupings within these landmasses. An isolation‐with‐migration (IM) model indicates recurrent gene flow between the current major landmasses. Such gene flow would have been possible during glacial periods when the current landmasses merged, presenting opportunities for dispersal along expanding and contracting coastlines. Consequently, Pleistocene climatic variation has proved a homogenizing, rather than diversifying, force for A. sundaicus diversity.  相似文献   
128.
Multiple myeloma is a bone marrow plasma cell tumor which is supported by the external growth factors APRIL and IL-6, among others. Recently, we identified eosinophils and megakaryocytes to be functional components of the micro-environmental niches of benign bone marrow plasma cells and to be important local sources of these cytokines. Here, we investigated whether eosinophils and megakaryocytes also support the growth of tumor plasma cells in the MOPC315.BM model for multiple myeloma. As it was shown for benign plasma cells and multiple myeloma cells, IL-6 and APRIL also supported MOPC315.BM cell growth in vitro, IL-5 had no effect. Depletion of eosinophils in vivo by IL-5 blockade led to a reduction of the early myeloma load. Consistent with this, myeloma growth in early stages was retarded in eosinophil-deficient ΔdblGATA-1 mice. Late myeloma stages were unaffected, possibly due to megakaryocytes compensating for the loss of eosinophils, since megakaryocytes were found to be in contact with myeloma cells in vivo and supported myeloma growth in vitro. We conclude that eosinophils and megakaryocytes in the niches for benign bone marrow plasma cells support the growth of malignant plasma cells. Further investigations are required to test whether perturbation of these niches represents a potential strategy for the treatment of multiple myeloma.  相似文献   
129.
Vu Nguyen T  Le Van P  Le Huy C  Weintraub A 《Anaerobe》2005,11(1-2):109-114
Enterotoxigenic Bacteroides fragilis (ETBF) are considered as an emerging enteropathogen causing diarrhea in children. Eight hundred and thirty-six (836) children less than 5 years of age including 587 children with diarrhea and 249 age-matched controls were involved in the study. Within the group of children with diarrhea, 7.3% (43/587) ETBF was detected by immunoseparation in combination with polymerase chain reaction. The corresponding figure for the controls was 2.4% (6/249) (P<0.01). Within the diarrhea group, the prevalence was significantly higher in children older than 1 year of age. Three subtypes of ETBF isolates have been identified with the prevalence of 67.4%, 18.6%, and 16% for bft-1, bft-2, and a new bft, respectively. In the controls, two of the subtypes were identified, 5 bft-1 and 1 bft-2. More than half (55.8%) of the samples harboring ETBF also had other identified pathogens. The clinical symptoms of the single ETBF infection were not different from those of co-infections. This is the first study of the role of ETBF in children's diarrhea in Vietnam and it is concluded that this pathogen is an important causative agent of diarrhea in children in Hanoi, Vietnam.  相似文献   
130.
Wet markets are common in many parts of the world and may promote the emergence, spread and maintenance of livestock pathogens, including zoonoses. A survey was conducted in order to assess the potential of Vietnamese and Cambodian live bird markets (LBMs) to sustain circulation of highly pathogenic avian influenza virus subtype H5N1 (HPAIV H5N1). Thirty Vietnamese and 8 Cambodian LBMs were visited, and structured interviews were conducted with the market managers and 561 Vietnamese and 84 Cambodian traders. Multivariate and cluster analysis were used to construct a typology of traders based on their poultry management practices. As a result of those practices and large poultry surplus (unsold poultry reoffered for sale the following day), some poultry traders were shown to promote conditions favorable for perpetuating HPAIV H5N1 in LBMs. More than 80% of these traders operated in LBMs located in the most densely populated areas, Ha Noi and Phnom Penh. The profiles of sellers operating at a given LBM could be reliably predicted using basic information about the location and type of market. Consequently, LBMs with the largest combination of risk factors for becoming virus reservoirs could be easily identified, potentially allowing control strategies to be appropriately targeted. These findings are of particular relevance to resource-scarce settings with extensively developed LBM systems, commonly found in South-East Asia.  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