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   284篇
  免费   35篇
  2021年   8篇
  2019年   5篇
  2018年   4篇
  2017年   6篇
  2016年   9篇
  2015年   12篇
  2014年   9篇
  2013年   17篇
  2012年   13篇
  2011年   11篇
  2010年   15篇
  2009年   10篇
  2008年   12篇
  2007年   15篇
  2006年   10篇
  2005年   12篇
  2004年   13篇
  2003年   11篇
  2002年   8篇
  2001年   9篇
  2000年   12篇
  1999年   4篇
  1998年   4篇
  1997年   2篇
  1996年   4篇
  1993年   4篇
  1992年   2篇
  1991年   4篇
  1989年   3篇
  1988年   3篇
  1986年   3篇
  1985年   3篇
  1984年   3篇
  1983年   6篇
  1982年   10篇
  1981年   4篇
  1979年   3篇
  1977年   2篇
  1975年   3篇
  1974年   2篇
  1973年   4篇
  1972年   5篇
  1970年   2篇
  1967年   3篇
  1966年   2篇
  1957年   1篇
  1940年   1篇
  1938年   2篇
  1936年   1篇
  1932年   1篇
排序方式: 共有319条查询结果,搜索用时 15 毫秒
1.
OBJECTIVE--To determine the incidence of haemorrhagic disease of the newborn in the British Isles, study risk factors, and examine the effect of vitamin K prophylaxis. DESIGN--Prospective survey of all possible cases of haemorrhagic disease of the newborn as reported by consultant paediatricians using the monthly notification cards of the British Paediatric Surveillance Unit and a follow up questionnaire for each case to validate the diagnosis and accrue further data. SETTING--Britain (England, Scotland, and Wales) and Ireland (Northern Ireland and the Irish Republic) during December 1987 to March 1990. PATIENTS--27 infants classified as having confirmed (n = 25) or probable (n = 2) haemorrhagic disease of the newborn. RESULTS--24 of the 27 infants were solely breast fed. 10 suffered intracranial haemorrhage; two of these died and there was clinical concern about the remainder. 20 infants had received no vitamin K prophylaxis, and seven had received oral prophylaxis. Relative risk ratios for these groups compared with babies who had received intramuscular vitamin K were 81:1 and 13:1 respectively. Six infants had hepatitis (alpha 1 antitrypsin deficiency in four), unsuspected until presentation with haemorrhagic disease of the newborn, of whom four had received oral prophylaxis. One other baby had prolonged jaundice. One mother had taken phenytoin during pregnancy. CONCLUSIONS--All newborn infants should receive vitamin K prophylaxis. Intramuscular vitamin K is more effective than oral prophylactic regimens currently used in the British Isles.  相似文献   
2.
The tetrasaccharides GalNAcß1-4[NeuAc2-3]Galß1-4Glc and GalNAcß1-4[NeuAc2-3]Galß1-4GlcNAc were synthesised by enzymic transfer of GalNAc from UDP-GalNAc to 3-sialyllactose (NeuAc2-3Galß1-4Glc) and 3-sialyl-N-acetyllactosamine (NeuAc2-3Galß1-4GlcNAc). The structures of the products were established by methylation and1H-500 MHz NMR spectroscopy. In Sda serological tests the product formed with 3-sialyl-N-acetyllactosamine was highly active whereas that formed with 3-sialyllactose had only weak activity.  相似文献   
3.
The effect of long-term application of heavy metal-laden sewage sludge on the total heterotrophic aerobic and the cadmium-resistant soil bacterial communities was studied. Gram-positive bacteria were completely absent from resistant communities. These findings suggest that this group is highly susceptible to Cd. Shannon's diversity indices estimated for total communities did not reveal negative effects on the communities that developed in the presence of sludge. However, Cd-resistant communities isolated from long-term sludge-amended soils were more diverse than the resistant communities from a control sample, suggesting that adaptation to Cd as a stressor had occurred in the presence of sludge constituents. This higher diversity was attributed to Cd resistance in pseudomonads and gram-negative fermenters. Resistance did not develop by dissemination of Cd resistance plasmids, because these were rarely detected in the genomes of resistant strains.  相似文献   
4.
5.
Carnitine is an essential cofactor for the beta-oxidation of fats. Both hypertrophic and congestive cardiomyopathies have been reported in primary and secondary carnitine deficiency. Conversely in avian cardiomyopathy models abnormally elevated plasma and tissue carnitine concentrations have been described. We measured plasma carnitine concentrations in 25 cardiomyopathy patients. In 14 patients with either hypertrophic or congestive cardiomyopathy plasma carnitine concentrations were abnormally elevated. Patients with secondary cardiomyopathies tended to have normal carnitine values. One patient with systemic carnitine deficiency was diagnosed. Her cardiac function normalized with L-carnitine replacement. Six of 14 patients with high plasma carnitine concentrations died. None of the 10 with low or normal plasma carnitine have died. Plasma carnitine determination may be a useful adjunct in the diagnostic evaluation of idiopathic cardiomyopathy.  相似文献   
6.
7.
8.
Bull shark (Carcharhinus leucas) is a near-threatened elasmobranch species capable of moving between the fresh and salty waters of tropical and subtropical coastal areas, for which we still lack important ecological information. During their first years of life, bull sharks use estuarine systems as nursery areas, making them highly susceptible to environmental and anthropogenic pressures. We studied the trophic ecology of juveniles found in the Coyote estuary, a potential nursery area in Costa Rica, to understand the potential impact of further bull shark declines and gain knowledge that could aid in their conservation. We analysed the trophic ecology of juvenile bull sharks [81–103 cm total length (TL)] in the Coyote estuary, Costa Rica, using stable isotopes of δ15N and δ13C. Since one problem using this technique in juveniles is the confounding effect of the maternal signature, we sampled different tissues (muscle and plasma), verified the status of the shark's umbilical scar and identified the size at which the isotope signature is a result of the animal's current diet. The isotopic values of the muscle tissue reflected the maternal isotopic signature. In contrast, plasma values reflected the diet of juvenile bull sharks >95 cm TL and with a closed umbilical scar. Juvenile bull sharks fed primarily on teleost fishes of the order Anguilliformes and Siluriformes, and have a high trophic position (≥4.0) in the Coyote estuary. Our findings suggest that this estuary is an important feeding site for juvenile bull sharks of the Pacific of Costa Rica. Thus, the protection of essential habitats such as the Coyote estuary will benefit not only bull shark conservation, but also the conservation of an array of fish species that also use this habitat as a rookery, many of which are of commercial interest.  相似文献   
9.
Cereals are the world's major source of food for human nutrition. Among these, rice (Oryza sativa) is the most prominent and represents the staple diet for more than two-fifths (2.4 billion) of the world's population, making it the most important food crop of the developing world (Anon., 2000a). Rice production in vast stretches of coastal areas is hampered due to high soil salinity. This is because rice is a glycophyte and it does not grow well under saline conditions. In order to increase rice production in these areas there is a need to develop rice varieties suited to saline environments. Research has shown that Porteresia coarctata, a highly salt tolerant wild relative of rice growing in estuarine soils, is an important material for transferring salt tolerant characteristics to rice. It is quite possible that Porteresia may be used as a parent for evolving better and truly salt resistant varieties. The inadequate results and the difficulties associated with conventional breeding techniques necessitate the use of the tools of crop biotechnology in unravelling some of the characteristics of Porteresia that have been highlighted in this report. In view of the limited resources available for increasing salinity tolerance to the breeders to wild rice germplasm, Porteresia is undoubtedly one of the key source species for elevating salinity tolerance in cultivated rice.  相似文献   
10.
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