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   3554篇
  免费   231篇
  国内免费   1篇
  3786篇
  2023年   19篇
  2022年   56篇
  2021年   113篇
  2020年   95篇
  2019年   96篇
  2018年   116篇
  2017年   115篇
  2016年   149篇
  2015年   210篇
  2014年   204篇
  2013年   256篇
  2012年   287篇
  2011年   250篇
  2010年   154篇
  2009年   147篇
  2008年   192篇
  2007年   140篇
  2006年   148篇
  2005年   124篇
  2004年   117篇
  2003年   108篇
  2002年   107篇
  2001年   85篇
  2000年   63篇
  1999年   53篇
  1998年   27篇
  1997年   32篇
  1996年   22篇
  1995年   26篇
  1994年   29篇
  1993年   15篇
  1992年   23篇
  1991年   27篇
  1990年   21篇
  1989年   18篇
  1988年   8篇
  1987年   7篇
  1986年   8篇
  1985年   11篇
  1984年   11篇
  1983年   10篇
  1982年   12篇
  1979年   7篇
  1977年   5篇
  1976年   6篇
  1975年   6篇
  1974年   10篇
  1973年   5篇
  1972年   8篇
  1967年   4篇
排序方式: 共有3786条查询结果,搜索用时 0 毫秒
51.
The population interest in health products is increasing day-by-day. Thus, the demand for natural products to be added in food and pharmaceutical commodity is also rising. Among these additives, colorants, which provides color to products, can be produced by microorganism through bioprocess. Looking for new source of natural colorants, fungi have been employed to this purpose producing novel and safer natural colorants. So, the main goal of this study was to describe a Talaromyces species able to produce natural colorants and investigate nutritional parameters of colorants production using statistical tool. The taxonomy classified the microorganism as Talaromyces amestolkiae. The statistical design evaluated pH and glucose, meat extract and meat peptone concentration as independent variables, and red colorants production as main response. Under the best condition (g/L: glucose 30, meat extract 1, meat peptone 10, and initial pH of 7.0) an increase of 229% in the red colorant production was achieved as compared with the initial media used. The dried fermented broth containing red colorants showed low cytotoxicity against fibroblasts cells (IC50 > 187.5 g/L) and effective antimicrobial activity against S. aureus (MIC of 2.5 g/L). Thus, T. amestolkiae colorants can be attractive to food and pharmaceutical applications as it does not produce toxic compounds and can promote protection against microorganism contaminants. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2684, 2019  相似文献   
52.
53.
Stem cell therapy holds great promises in medical treatment by, e.g., replacing lost cells, re-constitute healthy cell populations and also in the use of stem cells as vehicles for factor and gene delivery. Embryonic stem cells have rightfully attracted a large interest due to their proven capacity of differentiating into any cell type in the embryo in vivo. Tissue-specific stem ceils are however already in use in medical practice, and recently the first systematic medical trials involving human neural stem cell (NSC) therapy have been launched. There are yet many obstacles to overcome and procedures to improve. To ensure progress in the medical use of stem cells increased basic knowledge of the molecular mechanisms that govern stem cell characteristics is necessary. Here we provide a review of the literature on NSCs in various aspects of cell therapy, with the main focus on the potential of using biomaterials to control NSC characteristics, differentiation, and delivery. We summarize results from studies on the characteristics of endogenous and transplanted NSCs in rodent models of neurological and cancer diseases, and highlight recent advancements in polymer compatibility and applicability in regulating NSC state and fate. We suggest that the development of specially designed polymers, such as hydrogels, is a crucial issue to improve the outcome of stem cell therapy in the central nervous system.  相似文献   
54.
55.
56.
The alkaloid camptothecin uncouples the growth and adivision of chick embryo cells. At a moderate dose (0.5 microgram/ml) it inhibits the incorporation of thymidine but not of uridine and leucine and the cell protein content increases and reaches twice that of control after 4 days of treatment. Twelve hours after addition of the drug, the activities per cell of the mitochondrial enzymes poly A hydrolase (EC 3.1. 4.21), cytochrome c oxidase (EC 1.9.3.1), and succinate dehydrogenase (EC 1.3.99.1) are greater than that of the control and keep increasing for at least 96 H. The increase in the activities of the mitochondrial enzymes precede that of NADPH-cytochrome c reductase (EC 1.6.2.4) and cytidine triphosphatase (EC 3.6.1.15), which are microsomal and plasma membranes enzymes respectively. Actinomycin D (0.01 microgram/ml) also inhibits the multiplication of the chick cells and the synthesis of DNA. The protein content of the actinomycin D treated cells decreases to 70% of the control by day 2. Nevertheless, the activities of the mitochondrial enzymes increase over that of the control but to a smaller extent that with camptothecin. The activities of the enzymes of the other organelles are not stimulated. Camptothecin at a higher dose (5.0 microgram/ml) induces effects similar to those of actinomycin D.  相似文献   
57.
  • Enantiostyly is a floral polymorphism in which two floral forms in the same species differ in deflection of the stigma to right or left position. In monomorphic enantiostylous plants, flowers of the two morphs occur within the same individual, usually in the same proportion. In self‐compatible species the function of monomorphic enantiostyly is proposed to increase outcrossing rates and offer a reproductive advantage under pollination limitation. Enantiostylous species are usually self‐compatible and show heteranthery, with poricide anthers and pollen as pollinator reward; however, there are families, such as Vochysiaceae, that have different characteristics.
  • We analysed the reproductive system and pollination biology of Qualea parviflora and Q. multiflora, two enantiostylous species from the Brazilian Cerrado that have specific morphological and physiological traits. For this, we characterized flower traits, performed hand pollinations and studied floral visitors.
  • We found no differences between morphs in the proportion of flowers, nectar produced or its concentration, pollen quantity and fruit set. Both species were self‐incompatible and quite generalist regarding floral visitors.
  • Enantiostyly in self‐incompatible plants seems to confer a reproductive advantage by reducing self‐interference resulting from stigma clogging. This novel result helps to expand our knowledge on this complex floral polymorphism and opens new avenues for future research on this topic.
  相似文献   
58.
59.
Coral reef fisheries support the livelihoods of millions of people in tropical countries, despite large‐scale depletion of fish biomass. While human adaptability can help to explain the resistance of fisheries to biomass depletion, compensatory ecological mechanisms may also be involved. If this is the case, high productivity should coexist with low biomass under relatively high exploitation. Here we integrate large spatial scale empirical data analysis and a theory‐driven modelling approach to unveil the effects of human exploitation on reef fish productivity–biomass relationships. We show that differences in how productivity and biomass respond to overexploitation can decouple their relationship. As size‐selective exploitation depletes fish biomass, it triggers increased production per unit biomass, averting immediate productivity collapse in both the modelling and the empirical systems. This ‘buffering productivity’ exposes the danger of assuming resource production–biomass equivalence, but may help to explain why some biomass‐depleted fish assemblages still provide ecosystem goods under continued global fishing exploitation.  相似文献   
60.
Probiotics and Antimicrobial Proteins - The use of natural products together with standard antimicrobial drugs has recently received more attention as a strategy to combat infectious diseases...  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