全文获取类型
收费全文 | 19494篇 |
免费 | 2527篇 |
国内免费 | 4篇 |
出版年
2021年 | 247篇 |
2020年 | 202篇 |
2019年 | 199篇 |
2018年 | 229篇 |
2017年 | 221篇 |
2016年 | 380篇 |
2015年 | 620篇 |
2014年 | 633篇 |
2013年 | 783篇 |
2012年 | 995篇 |
2011年 | 948篇 |
2010年 | 586篇 |
2009年 | 589篇 |
2008年 | 818篇 |
2007年 | 906篇 |
2006年 | 830篇 |
2005年 | 784篇 |
2004年 | 746篇 |
2003年 | 713篇 |
2002年 | 624篇 |
2001年 | 490篇 |
2000年 | 500篇 |
1999年 | 502篇 |
1998年 | 262篇 |
1997年 | 215篇 |
1996年 | 232篇 |
1995年 | 222篇 |
1994年 | 223篇 |
1993年 | 246篇 |
1992年 | 388篇 |
1991年 | 361篇 |
1990年 | 341篇 |
1989年 | 312篇 |
1988年 | 329篇 |
1987年 | 294篇 |
1986年 | 292篇 |
1985年 | 334篇 |
1984年 | 284篇 |
1983年 | 224篇 |
1982年 | 214篇 |
1981年 | 173篇 |
1979年 | 235篇 |
1978年 | 212篇 |
1977年 | 180篇 |
1976年 | 213篇 |
1975年 | 201篇 |
1974年 | 169篇 |
1973年 | 206篇 |
1972年 | 193篇 |
1970年 | 169篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
J. L. Breslow H. R. Sloan V. J. Ferrans J. L. Anderson R. I. Levy 《Experimental cell research》1973,78(2):441-453
The previously reported mouse liver cell line FL83B has been characterized more completely with respect to its light and electron microscopic appearance, chromosomal composition, and ability to secrete various serum proteins. These cells bear many striking morphological similarities to parenchymal liver cells. Chromosomal analysis showed that the cells were transformed. The ability of these cells to grow in a completely chemically defined medium permitted the unequivocal demonstration of the synthesis of at least 12 mouse serum proteins including albumin and high density lipoprotein. 相似文献
993.
Astrocytes mediate either constriction or dilation of local brain arterioles in response to synaptic activity. Recent work
indicates that the directionality of this response may be dictated by ambient oxygen levels. 相似文献
994.
995.
996.
Salmonellae and Edwardsiella tarda in Gull Feces: a Source of Contamination in Fish Processing Plants 总被引:4,自引:3,他引:1
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The incidence of Salmonella and Edwardsiella tarda in gull feces on the Oregon coast was studied to determine the role these birds may have in the contamination of fish products with these organisms. Approximately 2.1 and 0.4% of 521 fecal specimens examined were found to contain Salmonella or E. tarda, respectively. 相似文献
997.
Hollis J. Hawkins Alan G.E. Wilson Marshall W. Anderson Thomas E. Eling 《Prostaglandins & other lipid mediators》1977,14(2):251-259
We have investigated the uptake and subsequent metabolism of the prostaglandins (PGs) PGE1, PGA1, and PGB1 by rat, guinea pig and rabbit isolated perfused lungs (IPL). Significant species differences were not observed in the uptake or metabolism of any PG on passage through the IPL. However, differences in the uptake of PGA1 and PGB1 and in the metabolism of PGA1 were observed with a given species when the composition of the perfusion medium was varied. The IPL removed minimal amounts (<20% of the supply rate) of PGA1 and PGB1 from the circulation when the perfusate contained 4.5% bovine serum albumin (BSA). In the absence of BSA, however, both PGA1 and PGB1 were substantially removed from circulation (~53% of the supply rate) and PGA1 was also metabolized. The composition of the perfusate had no effect on the uptake and metabolism of PGE1 which was always taken up and metabolized to a greater extent than was PGA1 and PGB1. Thus, the apparent species differences previously reported for the pulmonary biotransformation of PGA can result from differences in the perfusion medium used. Our data suggest that both plasma protein binding and a transport system play important roles in determining the selectivity of the uptake of PGs by the lung. 相似文献
998.
999.
Respondents to a respiratory survey of Berlin, New Hampshire, residents in 1961 have been studied to assess the relationship between co-operation and respiratory disease prevalence. Two hundred and forty-three unco-operative subjects, interviewed at home, had significantly more morning phlegm and a lower vital capacity than carefully matched subjects who attended the central clinic. Fifty-one volunteers had the same prevalence of respiratory disease symptoms and physiological abnormalities as carefully matched subjects drawn from a probability sample of the city.It is concluded that respiratory disease prevalence will be underestimated if calculated from studies of co-operative subjects who attend a clinic. Case-finding by respiratory disease screening clinics will also miss many persons who suffer from chronic bronchitis. 相似文献
1000.
The heights of some stranded shores in Gippsland, Australia, greatly exceed the level to which the ocean would rise if all present-day ice were to melt, and uplift is thus implied. Differences in level shown by comparison of these interglacial shorelines with others in South Carolina may therefore be the result of movement of one area relative to the other. Contemporary shorelines in the two localities can nevertheless be recognized from certain physiographic similarities and from the meagre measured age data presently available. We believe, furthermore, that there is sufficient information to permit estimation of the average rate of relative movement, and we attempt to analyse the field observations by applying a simple model that relates shoreline elevation to implied rate of uplift. This model is based on the supposition that the earth movements actually experienced were continuous, or can be reasonably represented as small fluctuations about a regular long-term trend. use of the model permits estimation of absolute ages (calculated from differences in altitude of correlated levels) for each high sea level stage that is recognized. Although the calculated or “altimetric” ages derived in this way are quite speculative, they agree with radiometric ages of Alaskan transgressions, interglacial littoral faunas, and warm intervals identified in deep-sea cores, and seem therefore to be verified by these comparisons. Particular correlations between high sea levels and warm core stages are implied: if these pairings are accepted, the altimetric ages can be re-estimated using the ages of the core stages. Predictions which use the calculated ages also provide tests of their value. 相似文献