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   281篇
  免费   30篇
  311篇
  2024年   1篇
  2023年   5篇
  2022年   7篇
  2021年   15篇
  2020年   10篇
  2019年   13篇
  2018年   7篇
  2017年   9篇
  2016年   12篇
  2015年   10篇
  2014年   12篇
  2013年   12篇
  2012年   18篇
  2011年   18篇
  2010年   12篇
  2009年   11篇
  2008年   11篇
  2007年   16篇
  2006年   7篇
  2005年   18篇
  2004年   7篇
  2003年   7篇
  2002年   4篇
  2001年   6篇
  2000年   5篇
  1999年   2篇
  1998年   3篇
  1997年   7篇
  1995年   1篇
  1994年   2篇
  1992年   6篇
  1991年   3篇
  1990年   5篇
  1989年   2篇
  1988年   5篇
  1986年   4篇
  1985年   3篇
  1984年   2篇
  1983年   2篇
  1982年   1篇
  1981年   1篇
  1980年   4篇
  1975年   3篇
  1972年   1篇
  1960年   1篇
排序方式: 共有311条查询结果,搜索用时 0 毫秒
51.
Natural sources,i.e. fungal strains and species producing ergot alkaloids (EA), are surveyed together with the chemical structures of EA and a list of new natural EA discovered in the last three decades. Other topics include new efficient chromatographic methods (HPLC) for the separation and isolation of new natural EA and also immunological methods of EA detection.  相似文献   
52.
53.
The estimate of food consumption by the bluegill sunfish ( Lepomis macrochirus ) population of Wyland Lake, Indiana, was examined with reference to recent research on the length of the growing season and the effect of body weight, ration and activity on growth efficiency. Growth efficiency was measured in the laboratory in terms of protein, comparing nitrogen assimilated with nitrogen accumulated over a period of about 30 days.
The revised consumption of protein was 134.9kg (or 1407kg live weight of aquatic organisms, 444 kg/ha) during a growing season of 111 days compared with the original estimate of 127.3 kg calculated for an assumed growing season of 150 days, a difference of only 6%. The correspondence between the two estimates was coincidental. The original estimate was made at a time when the growing season had not been measured and the effect of ration and body size on growth efficiency was not precisely known. Corrections for these factors plus that for activity compensated for one another, closely approaching, by chance, the original value.  相似文献   
54.
The aim of this study was to investigate the processes involved in developing close peer mentoring relationships among African American and Latino male adolescents in a school-based, group peer mentoring program. Qualitative one-on-one in-depth interviews were conducted with six school staff members, who administer the program, and 26 program participants about their experiences in the mentoring program. Data analysis revealed five program processes that led to close mentoring relationships: (a) rapport-building activities, (b) safe space, (c) mutual support, (d) group identity, and (e) trust. These processes ultimately led to bonding and friendship among program members, which further solidified the previous processes. Implications and future directions are discussed.  相似文献   
55.
Mutations in the gene encoding human copper-zinc superoxide dismutase (SOD1) cause a dominant form of the progressive neurodegenerative disease amyotrophic lateral sclerosis. Transgenic mice expressing the human G85R SOD1 variant develop paralytic symptoms concomitant with the appearance of SOD1-enriched proteinaceous inclusions in their neural tissues. The process(es) through which misfolding or aggregation of G85R SOD1 induces motor neuron toxicity is not understood. Here we present structures of the human G85R SOD1 variant determined by single crystal x-ray diffraction. Alterations in structure of the metal-binding loop elements relative to the wild type enzyme suggest a molecular basis for the metal ion deficiency of the G85R SOD1 protein observed in the central nervous system of transgenic mice and in purified recombinant G85R SOD1. These findings support the notion that metal-deficient and/or disulfide-reduced mutant SOD1 species contribute to toxicity in SOD1-linked amyotrophic lateral sclerosis.  相似文献   
56.
We report here the effects of a range of ascorbic acid concentrations (0.07, 0.3, 3.0, and 30.0 g l?1) in artificial diets on growth rates, adult weights, fecundity, and survival over two generations of the predatory stink bug, Podisus maculiventris (Say) (Heteroptera: Pentatomidae). Overall, a dietary level of 3.0 g l?1 gave the shortest developmental times over two generations. The likelihood of egg hatch at one ascorbic acid concentration compared to another concentration suggested that egg hatch increased as the concentration of ascorbic acid increased from 0.07 to 3.0 g l?1 and then declined from 3.0 to 30.0 g l?1. The combination of the maximum egg oviposition at 0.3 and 3.0 g l?1, egg hatch at 3.0 g l?1, and survival at 0.07 and 0.3 g l?1 suggests an overall superior performance at a concentration between 0.3 and 3.0 g l?1. Depletion of ascorbic acid below 3.0 g l?1 or addition of ascorbic acid above 3.0 g l?1 lowered the likelihood of egg hatch, which became more pronounced in the second generation. This is consistent with previously published information for phytophagous insects.  相似文献   
57.
58.
59.
The discovery of vitamins and clarification of their role in preventing frank essential nutrient deficiencies occurred in the early 1900s. Much vitamin research has understandably focused on public health and the effects of single nutrients to alleviate acute conditions. The physiological processes for maintaining health, however, are complex systems that depend upon interactions between multiple nutrients, environmental factors, and genetic makeup. To analyze the relationship between these factors and nutritional health, data were obtained from an observational, community-based participatory research program of children and teens (age 6–14) enrolled in a summer day camp in the Delta region of Arkansas. Assessments of erythrocyte S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH), plasma homocysteine (Hcy) and 6 organic micronutrients (retinol, 25-hydroxy vitamin D3, pyridoxal, thiamin, riboflavin, and vitamin E), and 1,129 plasma proteins were performed at 3 time points in each of 2 years. Genetic makeup was analyzed with 1 M SNP genotyping arrays, and nutrient status was assessed with 24-h dietary intake questionnaires. A pattern of metabolites (met_PC1) that included the ratio of erythrocyte SAM/SAH, Hcy, and 5 vitamins were identified by principal component analysis. Met_PC1 levels were significantly associated with (1) single-nucleotide polymorphisms, (2) levels of plasma proteins, and (3) multilocus genotypes coding for gastrointestinal and immune functions, as identified in a global network of metabolic/protein–protein interactions. Subsequent mining of data from curated pathway, network, and genome-wide association studies identified genetic and functional relationships that may be explained by gene–nutrient interactions. The systems nutrition strategy described here has thus associated a multivariate metabolite pattern in blood with genes involved in immune and gastrointestinal functions.

Electronic supplementary material

The online version of this article (doi:10.1007/s12263-014-0408-4) contains supplementary material, which is available to authorized users.  相似文献   
60.
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