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   522篇
  免费   20篇
  2023年   3篇
  2022年   6篇
  2021年   13篇
  2020年   10篇
  2019年   15篇
  2018年   17篇
  2017年   16篇
  2016年   18篇
  2015年   18篇
  2014年   22篇
  2013年   24篇
  2012年   51篇
  2011年   31篇
  2010年   30篇
  2009年   14篇
  2008年   22篇
  2007年   32篇
  2006年   21篇
  2005年   15篇
  2004年   15篇
  2003年   16篇
  2002年   18篇
  2001年   8篇
  2000年   9篇
  1999年   8篇
  1998年   3篇
  1997年   5篇
  1996年   5篇
  1995年   3篇
  1994年   2篇
  1993年   2篇
  1992年   2篇
  1991年   4篇
  1990年   5篇
  1989年   2篇
  1988年   3篇
  1986年   3篇
  1985年   9篇
  1984年   5篇
  1982年   3篇
  1981年   2篇
  1980年   4篇
  1977年   2篇
  1973年   3篇
  1972年   2篇
  1970年   6篇
  1968年   3篇
  1966年   2篇
  1961年   2篇
  1939年   1篇
排序方式: 共有542条查询结果,搜索用时 316 毫秒
111.
Human skin is body’s vital organ constantly exposed to abiotic oxidative stress. This can have deleterious effects on skin such as darkening, skin damage, and aging. Plant-derived products having skin-protective effects are well-known traditionally. Triphala, a formulation of three fruit products, is one of the most important rasayana drugs used in Ayurveda. Several skin care products based on Triphala are available that claim its protective effects on facial skin. However, the skin protective effects of Triphala extract (TE) and its mechanistic action on skin cells have not been elucidated in vitro. Gallic acid, ellagic acid, and chebulinic acid were deduced by LC-MS as the major constituents of TE. The identified key compounds were docked with skin-related proteins to predict their binding affinity. The IC50 values for TE on human dermal fibroblasts (HDF) and human keratinocytes (HaCaT) were 204.90 ± 7.6 and 239.13 ± 4.3 μg/mL respectively. The antioxidant capacity of TE was 481.33 ± 1.5 mM Trolox equivalents in HaCaT cells. Triphala extract inhibited hydrogen peroxide (H2O2) induced RBC haemolysis (IC50 64.95 μg/mL), nitric oxide production by 48.62 ± 2.2%, and showed high reducing power activity. TE also rescued HDF from H2O2-induced damage; inhibited H2O2 induced cellular senescence and protected HDF from DNA damage. TE increased collagen-I, involucrin and filaggrin synthesis by 70.72 ± 2.3%, 67.61 ± 2.1% and 51.91 ± 3.5% in HDF or HaCaT cells respectively. TE also exhibited anti-tyrosinase and melanin inhibition properties in a dose-dependent manner. TE increased the mRNA expression of collagen-I, elastin, superoxide dismutase (SOD-2), aquaporin-3 (AQP-3), filaggrin, involucrin, transglutaminase in HDF or HaCaT cells, and decreased the mRNA levels of tyrosinase in B16F10 cells. Thus, Triphala exhibits protective benefits on skin cells in vitro and can be used as a potential ingredient in skin care formulations.  相似文献   
112.
Summary Protoplast fusion was carried out between two strains ofAspergillus niger 8-2, a fast growing culture and poor producer of glucoamylase enzyme andA.niger 8-7, a slow growing culture and good producer of the enzyme. The nonconidiating fused mass in presence of benomyl, produced fast growing segregants showing various combinations of the two parental gene markers. Some of the segregants produced up to 68% more glucoamylase than the better yielding parent 8-7.  相似文献   
113.
Two strains of Trichoderma reesei, wild type QM6a and mutant Rut-C30, were grown in meida containing an inducer, insoluble crystalline cellulose (Avicel PH101), as carbon source for 11 days. The cell growth, expressed as myceliar protein content, of Rut-C30 was 4–5 times higher than QM6a. The lack of ultrastructural disorganization, and absence of intracellular enzyme release into the growth medium, indicated that none of these two strains had undergone any significant autolysis during the entire growth phase. Cellulase activities, mainly endoglucanase, cellobiase and filter paper degrading activity (disc) were enhanced in Rut-C30 cells. A major change was observed in the endoglucanase activity which was 30 times higher in Rut-C30 than QM6a, whereas, both -glucosidase and disc activities were 3 times enhanced in Rut-C30 compared to QM6a. In addition to synthesis, cellulase secretion was also enhanced in Rut-C30. Both the organisms contained same amounts of intracellular marker enzyme activities (e.g., inosine diphosphatase, thiamine pyrophosphatase, alkaline phosphatase). Finally, the enahncement of secretory activity of Rut-C30 was correlated with the proliferation of rough endoplasmic reticulum (RER) and increased phospholipid content. It appears that Rut-C30 is not only a hypercellulolytic but also a hypersecretor mutant.  相似文献   
114.
Motivated by our previous study on Sm3+ ions as thermoluminescence (TL) sensitizers to the BaO–ZnO–LiF–B2O3–Yb2O3 glass system, in the current study we examined the effect of Er3+ ion co-doping on the TL characteristics of this glass system. The 4f4f electronic transitions of the Er3+ and Yb3+ ions were confirmed via the optical absorption spectrum. Notably, the use of Yb3+–Er3+ ions failed to improve the TL intensity, sensitivity, and trap density. However, they enabled the glass system to function as an activator–quencher system. The linearity range and effective atomic number remained unaffected after co-doping. In addition, the problem of anomalous fading caused a remnant signal of just 58% after a week of storage of the Yb3+ monodoped glass. This was resolved by the optimum co-doping of Er3+ ions to achieve an 89% signal. The co-doping of Er3+ ions to the BaO–ZnO–LiF–B2O3–Yb2O3 glass system regulated its thermal stability and therefore supplemented its potential for radiation monitoring in food processing and retrospective dosimetry.  相似文献   
115.
Copper is an essential element that becomes highly cytotoxic when concentrations exceed the capacity of cells to sequester the ion. Here, we identify a new copper-specific repressor (CsoR) of a copper-sensitive operon (cso) in Mycobacterium tuberculosis (Mtb) that is representative of a large, previously uncharacterized family of proteins (DUF156). Electronic and X-ray absorption spectroscopies reveal that CsoR binds a single-monomer mole equivalent of Cu(I) to form a trigonally coordinated (S(2)N) Cu(I) complex. The 2.6-A crystal structure of copper-loaded CsoR shows a homodimeric antiparallel four-helix bundle architecture that represents a novel DNA-binding fold. The Cu(I) is coordinated by Cys36, Cys65' and His61' in a subunit bridging site. Cu(I) binding negatively regulates the binding of CsoR to a DNA fragment encompassing the operator-promoter region of the Mtb cso operon; this results in derepression of the operon in Mtb and the heterologous host Mycobacterium smegmatis. Substitution of Cys36 or His61 with alanine abolishes Cu(I)- and CsoR-dependent regulation in vivo and in vitro. Potential roles of CsoR in Mtb pathogenesis are discussed.  相似文献   
116.
Foxp3(+) CD4(+) regulatory T cells (Tregs) represent a highly suppressive T cell subset with well-characterized immunosuppressive effects during immune homeostasis and chronic infections, although the role of these cells in acute viral infections is poorly understood. The present study sought to examine the induction of Foxp3(+) CD4(+) Tregs in a nonlethal murine model of pulmonary viral infection by the use of the prototypical respiratory virus influenza A. We establish that influenza A virus infection results in a robust Foxp3(+) CD4(+) T cell response and that regulatory T cell induction at the site of inflammation precedes the effector T cell response. Induced Foxp3(+) CD4(+) T cells are highly suppressive ex vivo, demonstrating that influenza virus-induced Foxp3(+) CD4(+) T cells are phenotypically regulatory. Influenza A virus-induced regulatory T cells proliferate vigorously in response to influenza virus antigen, are disseminated throughout the site of infection and primary and secondary lymphoid organs, and retain Foxp3 expression in vitro, suggesting that acute viral infection is capable of inducing a foreign-antigen-specific Treg response. The ability of influenza virus-induced regulatory T cells to suppress antigen-specific CD4(+) and CD8(+) T cell proliferation and cytokine production correlates closely to their ability to respond to influenza virus antigens, suggesting that virus-induced Tregs are capable of attenuating effector responses in an antigen-dependent manner. Collectively, these data demonstrate that primary acute viral infection is capable of inducing a robust, antigen-responsive, and suppressive regulatory T cell response.  相似文献   
117.
We report the 4.94-Mb genome sequence of Xanthomonas axonopodis pv. punicae strain LMG 859, the causal agent of bacterial leaf blight disease in pomegranate. The draft genome will aid in comparative genomics, epidemiological studies, and quarantine of this devastating phytopathogen.  相似文献   
118.
It is well recognized that label-free biosensors are the only class of sensors that can rapidly detect antigens in real-time and provide remote environmental monitoring and point-of-care diagnosis that is low-cost, specific, and sensitive. Electrical impedance spectroscopy (EIS) based label-free biosensors have been used to detect a wide variety of antigens including bacteria, viruses, DNA, and proteins due to the simplicity of their detection technique. However, their commercial development has been hindered due to difficulty in interpreting the change in impedance upon antigen binding and poor signal reproducibility as a result of surface fouling and non-specific binding. In this study, we develop a circuit model to adequately describe the physical changes at bio functionalized surface and provide an understanding of the detection mechanism based on electron exchange between electrolyte and surface through pores surrounding antibody-antigen. The model was successfully applied to extract quantitative information about the bio surface at different stages of surface functionalization. Further, we demonstrate boron-doped ultrananocrystalline diamond (UNCD) microelectrode array (3 × 3 format, 200 μm diameter) improves signal reproducibility significantly and increases sensitivity by four orders of magnitude. This study marks the first demonstration of UNCD array based biosensor that can reliably detect a model Escherichia coli K12 bacterium using EIS, positioning this technology for rapid adoption in point-of-use applications.  相似文献   
119.
Twenty-five commercially grown Indian rice hybrids developed by both the public and private sectors, were analysed for molecular diversity and identification of simple sequence repeat (SSR) marker(s) that can distinguish them from each other. For diversity analysis, a total of fifty eight SSR markers providing genome wide coverage, were used. Forty out of fifty eight SSR markers were polymorphic amplifying a total of 121 alleles with molecular weight ranging from 70 bp ?C 280 bp. Further, characterisation of these markers was carried out generating parameters of heterozygosity (0.42), polymorphism information content (0.31), probability of identity (4.2?×?10?8) and probability of exclusion (99.99%). Cluster analysis based on a set of fourty highly polymorphic SSR markers generated three groups with dissimilarity index values ranging from 0.0 to 0.8. The hybrids based on common female parent IR58025A grouped together indicating a narrow genetic base of hybrid breeding programme. By combining the rapid and simple method of utilising these unique SSR markers alone or in combination, as molecular tags, identification of all the hybrids was possible even without having their parental lines. Twenty SSR loci produced hybrid specific unique alleles, which will be useful in establishing hybrid??s identity. The results have wide prospective in diversifying the genetic base of hybrid breeding programme, identification of rice hybrids, authentication of genetic purity of hybrid seed and protection of IPR.  相似文献   
120.
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