全文获取类型
收费全文 | 4529篇 |
免费 | 453篇 |
国内免费 | 17篇 |
出版年
2022年 | 39篇 |
2021年 | 81篇 |
2020年 | 25篇 |
2019年 | 45篇 |
2018年 | 75篇 |
2017年 | 51篇 |
2016年 | 96篇 |
2015年 | 230篇 |
2014年 | 257篇 |
2013年 | 274篇 |
2012年 | 347篇 |
2011年 | 346篇 |
2010年 | 220篇 |
2009年 | 162篇 |
2008年 | 224篇 |
2007年 | 209篇 |
2006年 | 221篇 |
2005年 | 189篇 |
2004年 | 182篇 |
2003年 | 136篇 |
2002年 | 119篇 |
2001年 | 131篇 |
2000年 | 101篇 |
1999年 | 57篇 |
1998年 | 42篇 |
1997年 | 36篇 |
1996年 | 42篇 |
1995年 | 25篇 |
1994年 | 40篇 |
1993年 | 31篇 |
1992年 | 67篇 |
1991年 | 50篇 |
1990年 | 57篇 |
1989年 | 62篇 |
1988年 | 38篇 |
1987年 | 50篇 |
1986年 | 32篇 |
1985年 | 45篇 |
1984年 | 38篇 |
1983年 | 33篇 |
1982年 | 49篇 |
1980年 | 20篇 |
1979年 | 42篇 |
1978年 | 25篇 |
1977年 | 33篇 |
1976年 | 33篇 |
1975年 | 40篇 |
1974年 | 36篇 |
1973年 | 40篇 |
1971年 | 24篇 |
排序方式: 共有4999条查询结果,搜索用时 15 毫秒
51.
52.
Four fungal species were selected as the test systems for the Microbial Ecology Evaluation Device (MEED) of Apollo 16. Fungal cells were exposed to various quantitative and qualitative spaceflight parameters then returned for postflight analyses. Survival rates and phenotype numbers varied according to exposure parameters. Additional studies underway will further identify the spaceflight changes. 相似文献
53.
54.
The regularly occurring secondary constrictions on metaphase chromosomes of mammalian cells prove to be nucleolus organizers as expected. The expression of nucleolus organizers as secondary constrictions, however, varies from cell to cell and from tissue to tissue, including cultivation in vitro. Electron micrographs of the organizer region show that the nucleolus organizer at metaphase is not a constriction. The width of the organizer area is the same as the condensed chromosomal arms; but the filaments, which are the major components of this region, show a diameter of 50–70 Å. The condensed chromosome arms consist of filaments 150–200 Å in diameter. In some mammalian species, structures similar to the nucleolus organizer are located at the end of chromosomes. These may be terminal nucleolus organizers.Supported in part by Research Grants DRG-269 from Damon Runyon Memorial Fund for Cancer Research, E-286 from American Cancer Society, and HD-2590 from National Institutes of Health. 相似文献
55.
56.
57.
Crossing over frequency was determined for five marked regions covering most of a chromosome arm. The results of a 12th backcross were compared with previously published results from the noninbred f1. Exchange frequency increased significantly following inbreeding. Chiasma interference remained positieve, but was somewhat less intense in b12.Supported in part by Public Health Service Research Grants AI 01462 and GM 1882-01, by a National Science Foundation Faculty Fellowship to H. R. C., and by Public Health Service Research Career Award K6-GM-4899 to D. D. P.Technical Paper No. 2054, Oregon Agricultural Experiment Station, Corvallis. 相似文献
58.
59.
Effects of carbon–dioxide-bicarbonate mixtures on oxidative phosphorylation by cauliflower mitochondria 下载免费PDF全文
1. Carbon dioxide-bicarbonate mixtures markedly inhibited oxidation and phosphorylation rates of mitochondria prepared from cauliflower. Inhibition occurred with succinate, malate, citrate, isocitrate and NADH as substrates. 2. Indophenol-reductase systems with malate, succinate, isocitrate and NADH as substrates were inhibited by 5% and 15% carbon dioxide. Cytochrome c oxidase was not inhibited by 15% carbon dioxide. 相似文献
60.