全文获取类型
收费全文 | 179篇 |
免费 | 26篇 |
专业分类
205篇 |
出版年
2021年 | 2篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 2篇 |
2015年 | 10篇 |
2014年 | 9篇 |
2013年 | 11篇 |
2012年 | 9篇 |
2011年 | 9篇 |
2010年 | 6篇 |
2009年 | 7篇 |
2008年 | 9篇 |
2007年 | 8篇 |
2006年 | 14篇 |
2005年 | 5篇 |
2004年 | 8篇 |
2003年 | 5篇 |
2002年 | 16篇 |
2001年 | 5篇 |
2000年 | 5篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1990年 | 1篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1965年 | 1篇 |
1929年 | 1篇 |
1928年 | 1篇 |
1921年 | 1篇 |
1913年 | 1篇 |
排序方式: 共有205条查询结果,搜索用时 0 毫秒
31.
Xia Z Webster A Du F Piatkov K Ghislain M Varshavsky A 《The Journal of biological chemistry》2008,283(35):24011-24028
32.
Silvia M O Titan Sheila Bingham Ailsa Welch Robert Luben Suzy Oakes Nicholas Day Kay-Tee Khaw 《BMJ (Clinical research ed.)》2001,323(7324):1286
ObjectivesTo examine the relation between self reported eating frequency and serum lipid concentrations in a free living population.Design Cross sectional population based study.Setting Norfolk, England.Participants 14 666 men and women aged 45-75 years from the Norfolk cohort of the European prospective investigation into cancer (EPIC-Norfolk).Results Mean concentrations of total cholesterol and low density lipoprotein cholesterol decreased in a continuous relation with increasing daily frequency of eating in men and women. No consistent relation was observed for high density lipoprotein cholesterol, body mass index, waist to hip ratio, or blood pressure. Mean cholesterol concentrations differed by about 0.25 mmol/l between people eating more than six times a day and those eating once or twice daily; this difference was reduced to 0.15 mmol/l after adjustment for possible confounding variables, including age, obesity, cigarette smoking, physical activity, and intake of energy and nutrients (alcohol, fat, fatty acids, protein, and carbohydrate).Conclusions Concentrations of total cholesterol and low density lipoprotein cholesterol are negatively and consistently associated with frequency of eating in a general population. The effects of eating frequency on lipid concentrations induced in short term trials in animals and human volunteers under controlled laboratory conditions can be observed in a free living general population. We need to consider not just what we eat but how often we eat.
What is already known on this topic
Studies in animals and small human trials indicate that eating frequency is inversely related to serum lipid concentrationsFew studies have examined this in a free living population under no dietary restrictionsWhat this study adds
In a free living population increased eating frequency was negatively and significantly associated with concentrations of total cholesterol and low density lipoprotein cholesterolThis association was still present after adjustment for body mass index, physical activity, cigarette smoking, and dietary intakeMean age adjusted cholesterol concentrations differed by 0.25 mmol/l between people eating more than six times a day and those eating less than twice daily 相似文献33.
The three-dimensional structure of supercoiled deoxyribonucleic acid in solution. Evidence obtained from the angular distribution of scattered light 总被引:6,自引:6,他引:0 下载免费PDF全文
1. The size and shape of superhelical double-stranded circular DNA from bacteriophage ØX174 were investigated by light-scattering. The molecular weight of the DNA is 3.17×106 and the root-mean-square radius is 103.5nm. 2. The light-scattering envelopes of various theoretical three-dimensional models for such DNA molecules were calculated by repetitive computational techniques, and the results were compared with the experimental findings. 3. It is concluded that the structure of supercoiled DNA containing −12 superhelical turns in buffer of I0.2 corresponds best to one of the more compact models for superhelix structure such as the branched model, and the commonly employed straight interwound superhelix model is incompatible with the experimental results, at the superhelix density found. 相似文献
34.
35.
Jason J. Head Gregg F. Gunnell Patricia A. Holroyd J. Howard Hutchison Russell L. Ciochon 《Proceedings. Biological sciences / The Royal Society》2013,280(1763)
Mammals dominate modern terrestrial herbivore ecosystems, whereas extant herbivorous reptiles are limited in diversity and body size. The evolution of reptile herbivory and its relationship to mammalian diversification is poorly understood with respect to climate and the roles of predation pressure and competition for food resources. Here, we describe a giant fossil acrodontan lizard recovered with a diverse mammal assemblage from the late middle Eocene Pondaung Formation of Myanmar, which provides a historical test of factors controlling body size in herbivorous squamates. We infer a predominately herbivorous feeding ecology for the new acrodontan based on dental anatomy, phylogenetic relationships and body size. Ranking body masses for Pondaung Formation vertebrates indicates that the lizard occupied a size niche among the larger herbivores and was larger than most carnivorous mammals. Paleotemperature estimates of Pondaung Formation environments based on the body size of the new lizard are approximately 2–5°C higher than modern. These results indicate that competitive exclusion and predation by mammals did not restrict body size evolution in these herbivorous squamates, and elevated temperatures relative to modern climates during the Paleogene greenhouse may have resulted in the evolution of gigantism through elevated poikilothermic metabolic rates and in response to increases in floral productivity. 相似文献
36.
37.
V Shingler F C Franklin M Tsuda D Holroyd M Bagdasarian 《Journal of general microbiology》1989,135(5):1083-1092
Pseudomonas strain CF600 is able to utilize phenol and 3,4-dimethylphenol as sole carbon and energy source. We demonstrate that growth on these substrates is by virtue of plasmid-encoded phenol hydroxylase and a meta-cleavage pathway. Screening of a genomic bank, with DNA from the previously cloned catechol 2,3-dioxygenase gene of the TOL plasmid pWW0, was used in the identification of a clone which could complement a phenol-hydroxylase-deficient transposon insertion mutant. Deletion mapping and polypeptide production analysis identified a 1.2 kb region of DNA encoding a 39.5 kDa polypeptide which mediated this complementation. Enzyme activities and growth properties of Pseudomonas strains harbouring this fragment on a broad-host-range expression vector indicate that phenol hydroxylase is a multicomponent enzyme containing the 39.5 kDa polypeptide as one component. 相似文献
38.
Background
There is overwhelming evidence that behavioural factors influence health, but their combined impact on the general population is less well documented. We aimed to quantify the potential combined impact of four health behaviours on mortality in men and women living in the general community.Methods and Findings
We examined the prospective relationship between lifestyle and mortality in a prospective population study of 20,244 men and women aged 45–79 y with no known cardiovascular disease or cancer at baseline survey in 1993–1997, living in the general community in the United Kingdom, and followed up to 2006. Participants scored one point for each health behaviour: current non-smoking, not physically inactive, moderate alcohol intake (1–14 units a week) and plasma vitamin C >50 mmol/l indicating fruit and vegetable intake of at least five servings a day, for a total score ranging from zero to four. After an average 11 y follow-up, the age-, sex-, body mass–, and social class–adjusted relative risks (95% confidence intervals) for all-cause mortality(1,987 deaths) for men and women who had three, two, one, and zero compared to four health behaviours were respectively, 1.39 (1.21–1.60), 1.95 (1.70–-2.25), 2.52 (2.13–3.00), and 4.04 (2.95–5.54) p < 0.001 trend. The relationships were consistent in subgroups stratified by sex, age, body mass index, and social class, and after excluding deaths within 2 y. The trends were strongest for cardiovascular causes. The mortality risk for those with four compared to zero health behaviours was equivalent to being 14 y younger in chronological age.Conclusions
Four health behaviours combined predict a 4-fold difference in total mortality in men and women, with an estimated impact equivalent to 14 y in chronological age. 相似文献39.
40.
Geoffry Fordyce Michael R. McGowan Allan Lisle Tracy Muller Jack Allen Christian Duff Richard G. Holroyd Nicholas J. Corbet Brian M. Burns 《Theriogenology》2014
Normal range for scrotal circumference in Australian beef bulls was established using more than 300,000 measurements of breed, management group, age, liveweight, and scrotal circumference. The data used were derived from Australian bull breeders and two large research projects in northern Australia. Most bulls were within 250 to 750 kg liveweight and 300 to 750 days of age. The differences between breeds and variances within breeds were higher when scrotal circumference was predicted from age rather than liveweight, because of variance in growth rates. The average standard deviation for predicted scrotal circumference from liveweight and age was 25 and 30 mm, respectively. Scrotal circumference by liveweight relationships have a similar pattern across all breeds, except in Waygu, with a 50 to 70 mm range in average scrotal circumference at liveweights between 250 and 750 kg. Temperate breed bulls tended to have higher scrotal circumference at the same liveweight than tropically adapted breeds. Five groupings of common beef breeds in Australian were identified, within which there were similar predictions of scrotal circumference from liveweight. It was concluded that liveweight and breed are required to identify whether scrotal circumference is within normal range for Australian beef bulls that experience a wide range of nutritional conditions. 相似文献