全文获取类型
收费全文 | 5359篇 |
免费 | 264篇 |
国内免费 | 3篇 |
出版年
2022年 | 20篇 |
2021年 | 39篇 |
2019年 | 33篇 |
2018年 | 45篇 |
2017年 | 39篇 |
2016年 | 63篇 |
2015年 | 93篇 |
2014年 | 118篇 |
2013年 | 352篇 |
2012年 | 250篇 |
2011年 | 249篇 |
2010年 | 175篇 |
2009年 | 153篇 |
2008年 | 269篇 |
2007年 | 288篇 |
2006年 | 274篇 |
2005年 | 297篇 |
2004年 | 300篇 |
2003年 | 323篇 |
2002年 | 304篇 |
2001年 | 129篇 |
2000年 | 115篇 |
1999年 | 124篇 |
1998年 | 80篇 |
1997年 | 78篇 |
1996年 | 61篇 |
1995年 | 59篇 |
1994年 | 61篇 |
1993年 | 46篇 |
1992年 | 108篇 |
1991年 | 72篇 |
1990年 | 78篇 |
1989年 | 72篇 |
1988年 | 68篇 |
1987年 | 57篇 |
1986年 | 55篇 |
1985年 | 71篇 |
1984年 | 63篇 |
1983年 | 56篇 |
1982年 | 55篇 |
1981年 | 52篇 |
1980年 | 32篇 |
1979年 | 36篇 |
1978年 | 41篇 |
1977年 | 35篇 |
1976年 | 27篇 |
1975年 | 35篇 |
1974年 | 23篇 |
1973年 | 25篇 |
1970年 | 19篇 |
排序方式: 共有5626条查询结果,搜索用时 31 毫秒
61.
From 1964 to 1967, 6,646 monkeys, representing 10 primate species, were examined for Shigella and Salmonella infections upon arrival at the National Center for Primate Biology. Of these animals, 12% were infected with Shigella, and 75% of the Shigella isolates were S. flexneri 4. The incidence of Salmonella infections decreased from 12 to 3% during the period of study. Epidemiological studies of animals in the colony for 90 days or more indicated no seasonal variation in the occurrence of Shigella and Salmonella. Many of the isolates from incoming monkeys as well as from laboratory-conditioned animals were resistant to chloramphenicol, dihydrostreptomycin, and tetracycline. The possible operation of drug-resistance factors in these infections is discussed. 相似文献
62.
63.
64.
65.
66.
67.
68.
The febrile responses of male Sprague-Dawley rats to a semi-purified endogenous pyrogen (EP) derived from human monocytes are markedly enhanced 3 days after the animals are intravenously injected with a variety of immunoadjuvants. The present study was designed to investigate the site within the body at which these substances act to produce this febrile-enhancing phenomenon. Stainless steel microinjection cannula guide tubes were implanted within the region of the organum vasculosum lamina terminalis (OVLT) of the rats and control febrile dose-response curves to EP were established. Minute quantities of the immunoadjuvants zymosan, lipopolysaccharide endotoxin, and the synthetic adjuvant peptide, muramyl dipeptide, were microinjected into the OVLT region and 3 days later, the febrile responses of the animals were retested. In each case the febrile response elicited by a standard dose of EP was more than doubled, the slope of the fever dose-response curve was tripled, and the dose threshold was lowered by a factor of four to five. These responses are identical with those produced when much larger amounts of these immunoadjuvants are injected intravenously, and, thus, we conclude that the site of action of these substances in enhancing fever in response to EP resides in or near the OVLT region. It is proposed that EP stimulates a type of reticuloendothelial cell residing within the OVLT to release prostaglandin E, which in turn crosses the blood-brain barrier to effect the changes in the thermoregulatory neurons of the preoptic anterior hypothalamic area that result in fever. 相似文献
69.
70.
Kazutake Shimada Yoshihiro Komine Kuniko Mitamura 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1991,565(1-2)
The high-performance liquid chromatographic separation of bile acid pyrenacyl esters with cyclodextrin-containing mobile phase is presented. Compared with conventional methods, inclusion chromatography gives much more satisfactory separation of derivatized bile acids in a short time. The application of this method to the separation of glycine-conjugated bile acids in human bile is also described. 相似文献