全文获取类型
收费全文 | 57375篇 |
免费 | 4831篇 |
国内免费 | 49篇 |
专业分类
62255篇 |
出版年
2023年 | 202篇 |
2022年 | 596篇 |
2021年 | 1026篇 |
2020年 | 570篇 |
2019年 | 754篇 |
2018年 | 1161篇 |
2017年 | 918篇 |
2016年 | 1597篇 |
2015年 | 2659篇 |
2014年 | 2955篇 |
2013年 | 3458篇 |
2012年 | 4446篇 |
2011年 | 4251篇 |
2010年 | 2697篇 |
2009年 | 2374篇 |
2008年 | 3398篇 |
2007年 | 3162篇 |
2006年 | 2896篇 |
2005年 | 2614篇 |
2004年 | 2555篇 |
2003年 | 2269篇 |
2002年 | 1955篇 |
2001年 | 1668篇 |
2000年 | 1546篇 |
1999年 | 1233篇 |
1998年 | 545篇 |
1997年 | 477篇 |
1996年 | 413篇 |
1995年 | 399篇 |
1994年 | 311篇 |
1993年 | 301篇 |
1992年 | 646篇 |
1991年 | 518篇 |
1990年 | 478篇 |
1989年 | 480篇 |
1988年 | 409篇 |
1987年 | 393篇 |
1986年 | 319篇 |
1985年 | 330篇 |
1984年 | 274篇 |
1983年 | 224篇 |
1982年 | 191篇 |
1981年 | 163篇 |
1980年 | 163篇 |
1979年 | 220篇 |
1978年 | 199篇 |
1977年 | 182篇 |
1976年 | 170篇 |
1974年 | 197篇 |
1972年 | 155篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
182.
183.
184.
Ting-Yang Lee Irwin A. Schafer 《Biochimica et Biophysica Acta (BBA)/General Subjects》1974,354(2):264-274
The glycosaminoglycan composition of human amniotic fluid between 12–21 weeks gestation has been studied by Dowex column chromatography coupled with enzymatic analyses of the specific glycosaminoglycan in each column fraction. The total uronic acid recovered from the columns consisted of “glycopeptides” (7%), hyaluronic acid (34%), nonsulfated chondroitin (14%), chondroitin-4-sulfate (13%), chondroitin-6-sulfate (20%), dermatan sulfate (5%), and heparan sulfate (6%). Based on these studies a simple screening procedure was devised to detect increased quantities of heparan sulfate and dermatan sulfate in 5–10-ml samples of amniotic fluid and tested in the antenatal diagnosis of Hurler and Hunter's syndrome. A false negative result was recorded in a Hunter fluid obtained early gestation and a false positive result recorded in a normal fluid obtained at
weeks. These data suggest that the time in gestation when amniotic fluid is sampled for chemical analysis is an important variable affecting glycosaminoglycan composition in both normal and pathological pregnancies. 相似文献
185.
Summary The effects of BrdU (3×10–4 M) on morphogenesis of the chick embryo explanted at the definitive streak stage and cultured for 24 hours were studied. Compared to controls treated embryos often showed (1) an open neural tube and (2) less numerous somites. Heart development was not significantly affected by BrdU. The damage caused by BrdU was not permanent, i.e., the embryos retained the ability to undergo fairly normal morphogenesis when, after 4–5 hours of BrdU treatment, they were subcultured on a medium with excess thymidine.This study was supported by a grant from the Rutgers University Research Council No. 07-2189. 相似文献
186.
187.
188.
189.
190.
Chemically synthesized ricinine-3,5-14C was used to study the metabolism of this alkaloid in the plant which produces it, Ricinus communis L. In a time course study, ricinine-3,5-14C was administered to a series of castor plants (Ricinus communis L.) and the radioactivity recovered in the ricinine samples showed a decrease with increase in time. It was also observed that the alkaloid was translocated to the seed. The in vivo conversion of ricinine-3,5-14C to respiratory 14CO2 occurred in both light and dark and indicated that the α-pyridone ring of ricinine could be degraded. 相似文献