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   1499篇
  免费   71篇
  国内免费   268篇
  1838篇
  2023年   29篇
  2022年   35篇
  2021年   45篇
  2020年   56篇
  2019年   54篇
  2018年   43篇
  2017年   51篇
  2016年   49篇
  2015年   54篇
  2014年   66篇
  2013年   90篇
  2012年   46篇
  2011年   74篇
  2010年   50篇
  2009年   53篇
  2008年   82篇
  2007年   87篇
  2006年   68篇
  2005年   56篇
  2004年   60篇
  2003年   57篇
  2002年   50篇
  2001年   47篇
  2000年   48篇
  1999年   42篇
  1998年   44篇
  1997年   37篇
  1996年   25篇
  1995年   44篇
  1994年   39篇
  1993年   37篇
  1992年   23篇
  1991年   15篇
  1990年   20篇
  1989年   16篇
  1988年   6篇
  1987年   8篇
  1986年   5篇
  1985年   19篇
  1984年   18篇
  1983年   10篇
  1982年   9篇
  1981年   7篇
  1980年   10篇
  1979年   12篇
  1978年   8篇
  1977年   7篇
  1976年   8篇
  1975年   4篇
  1974年   8篇
排序方式: 共有1838条查询结果,搜索用时 15 毫秒
941.
Zhi-Gang  Wang 《Mycopathologia》1998,144(3):165-167
Fusarium moniliforme and its fumonisins have been shown to be carcinogenic in lab animals and have been linked to high incidences of human esophageal cancer. In this study we report the dimorphic fungus characteristic of fumonisin-producing strains of F. moniliforme from foodstuffs in Zhejiang, China. All of the twenty strains of F. moniliforme shown produce fumonisin B1 475.9–6322.2 μg/g in corn medium. These strains of F. moniliforme form yeast-like colonies in Sabouraud's agar plates contained 9% NaCl at 37 °C incubator and shows mostly budding reproduction. In blood agar plates these strains of F. moniliforme appear grass-green haemolytic reactions. This is the first report that yeast-like growth, dimorphic pathogenic fungus feature is found in F. moniliforme. These results suggest that it is also important to program epidemiological surveys of F. moniliforme as a primary pathogenic fungus, while proceeding to produce mycotoxins of F. moniliforme in food hygiene. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
942.
Abstract The effect of added l-amino acids and NH4+ on manganese peroxidase activity in ligninolytic cultures of Phanerochaete chrysosporium were investigated. Among 11 amino acids (0.2 mM) tested, including phenylalanine, glutamate, glutamine, histidine, alanine, iso-leucine, ornithine, glycine, aspartate, proline, and arginine, phenylalanine was the most effective in suppression of manganese peroxidase synthesis. However, all the amino acids tested except proline completely suppressed the enzyme synthesis at 2 mM concentration.  相似文献   
943.
Two nitrogen-deregulated mutants of Phanerochaete chrysosporium, der8-2 and der8-5, were isolated by subjecting wild type conidia to gamma irradiation, plating on Poly-R medium containing high levels of nitrogen, and identifying colonies that are able to decolorize Poly-R. The mutants showed high levels of ligninolytic activity (14C-synthetic lignin 14CO2), and lignin peroxidase, manganese peroxidase and glucose oxidase activities in both low nitrogen (2.4 mM) and high nitrogen (24 mM) media. The wild type on the otherhand displayed these activities in low nitrogen medium but showed little or no activities in high nitrogen medium. Fast protein liquid chromatographic analyses showed that the wild type as well as the der mutants produce three major lignin peroxidase peaks (designated L1, L2 and L3) with lignin peroxidase activity in low nitrogen medium. Furthermore, in low nitrogen medium, mutant der8-5 produced up to fourfold greater lignin peroxidase activity than that produced by the wild type. In high nitrogen medium, the wild type produced no detectable lignin peroxidase peaks whereas the mutants produced peaks L1 and L2, but not L3, and a new lignin peroxidase protein peak designated LN. Mutants der8-2 and der8-5 also produced high levels of glucose oxidase, an enzyme known to be associated with secondary metabolism and an important source of H2O2 in ligninolytic cultures, both in low and high nitrogen media. In contrast, the wild type produced high levels of glucose oxidase in low nitrogen medium and only trace amounts of this enzyme in high nitrogen medium. The results of this study indicate that the der mutants are nitrogen-deregulated for the production of a set of secondary metabolic activities associated with lignin degradation such as lignin peroxidases, manganese peroxidases and glucose oxidase.  相似文献   
944.
目的探讨延安市某医院2006—2010年皮肤科门诊患者真菌感染的菌群分布、特点及变迁情况,为临床防治真菌感染提供研究依据。方法采用回顾性调查方法,收集5年来该院皮肤科门诊患者的所有真菌检查的病例资料,对标本来源、菌群分布及菌种变迁进行调查和分析。结果5年中真菌感染阳性率为9.98%-44.05%,男性感染率高于女性,浅部真菌感染率高于深部真菌,差异均有统计学意义(P〈0.005);60岁以上患者占38.18%,感染以白假丝酵母菌为主但所占比例5年间下降了16.86%(P〈0.05),而其他假丝酵母菌所占比例则呈上升趋势。结论5年来该院真菌感染菌群分布发生了变迁;真菌感染以老年男性为主,儿童真菌感染亦不容忽视,临床应加强对这些真菌感染的预防和监测,防止真菌感染。  相似文献   
945.
In July and August 2005, the occurrence, distribution, and ecology of lichen species were studied in northeastern Sørkapp Land region (Spitsbergen) in areas undergoing the process of rapid glacier recession over the past century. A total of 48 lichen species were observed and two species (Acarospora heppii and Pycnothelia papillaria) are newly reported for the Svalbard archipelago.  相似文献   
946.
栎金钱菌活性提取物抗衰老研究   总被引:1,自引:0,他引:1  
用栎金钱菌活性提取物灌胃衰老模型小鼠,观察其对小鼠血清SOD活性、肝组织MDA和脂褐素的含量、脾指数、胸腺指数和肾指数的影响。结果表明,栎金钱菌活性提取物能使雄性小鼠血清SOD活性提高40.16%,肝MDA含量减少47.12%,肝脂褐素含量减少89.48%,脾指数增加35.13%,胸腺指数增加48.92%,肾指数增加11.26%,表明栎金钱菌活性提取物具有良好的抗衰老作用。栎金钱菌活性提取物800mg/kg·d的剂量具有最好的抗衰老效果,且具有性别的差异,对雄性小鼠的抗衰老作用略优于对雌性小鼠的。  相似文献   
947.
The entomopathogenic fungus Metarhizium anisopliae (Metsch.) Sorokin (Hypocreales: Clavicipitaceae) was applied in maize fields to control the Western Corn Rootworm Diabrotica virgifera virgifera Le Conte (Coleoptera: Chrysomelidae). Establishment and persistence of two strains of M. anisopliae were investigated after application as ‘fungal colonized barley kernels’ (FCBK) into the soil and as a spore suspension on maize leaves and on the soil surface in 2006 and 2007 at two locations in Hungary. The applied fungal strains were able to establish at both locations and a long‐term persistence of at least 15 months could be recorded in the soil. A positive correlation between density of colony forming units (CFU) in the soil and the soil inhabiting stages of the host insect D. v. virgifera could be found. M. anisopliae spores applied on maize leaves were able to survive for no longer than 3 days after application, whereas on the soil surface a noticeably increase of fungus densities were found after treatments. Molecular markers were used to identify the applied M. anisopliae strains before and after application of FCBK into the soil of the maize field.  相似文献   
948.
目的了解实验所用常见致病真菌能否在常用医用原材料上生存及生存时间。方法选择8种常见致病真菌,活化后将它们分别接种在5种常用的医用原材料上,接种后及以后的每24h将接种有真菌的医用材料放入巯基乙酸盐液体培养基中并观察能否生存,记录存活时间。结果红色毛癣菌和须癣毛癣菌在棉布、纸板、铁皮、玻璃表面存活25~28d,在地板胶表面存活14~15d;新生隐球菌在棉布、纸板、铁皮表面存活24~27d,在玻璃和地板胶表面存活14~18d;茄病镰刀菌在上述5种材料上存活22~27d;石膏样小孢子菌在棉布、纸板、铁皮和玻璃表面存活20~27d,在地板胶表面存活8d;申克孢子丝菌在棉布、纸板、玻璃和地板胶表面存活17~24d,在铁皮表面存活10d;白念珠菌在棉布、纸板、铁皮和地板胶表面存活15~20d,在玻璃表面存活4d;犬小孢子菌在棉布、纸板、铁皮、玻璃和地板胶上存活时间分别为10d、9d、3d、2d和1d。结论实验所用各种真菌在医用原材料上都能存活,其时间长短不仅与菌种有关,还与所存在的材料有关。真菌在吸水性强、表面粗糙的材料(棉布、纸板)上的平均存活时间长于在吸水性差、表面光滑的材料(玻璃、铁皮和地板胶)。  相似文献   
949.
Fungal endophytes have been isolated from almost every plant, infecting their hosts without causing visible disease symptoms, and yet have still proved to be involved in plant secondary metabolites acc...  相似文献   
950.
Nondestructive techniques to obtain DNA from organisms can further genetic analyses such as estimating genetic diversity, dispersal and lifetime fitness, without permanently removing individuals from the population or removing body parts. Possible DNA sources for insects include frass, exuviae, and wing and leg clippings. However, these are not feasible approaches for organisms that cannot be removed from their natural environment for long periods or when adverse effects of tissue removal must be avoided. This study evaluated the impacts and efficacy of extracting haemolymph from a defensive secretion to obtain DNA for amplification of microsatellites using a nondestructive technique. A secretion containing haemolymph was obtained from Bolitotherus cornutus (the forked fungus beetle) by perturbation of the defensive gland with a capillary tube. A laboratory experiment demonstrated that the sampling methodology had no impact on mortality, reproductive success or gland expression. To evaluate the quality of DNA obtained in natural samples, haemolymph was collected from 187 individuals in the field and successfully genotyped at nine microsatellite loci for 95.7% of samples. These results indicate that haemolymph-rich defensive secretions contain DNA and can be sampled without negative impacts on the health or fitness of individual insects.  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