全文获取类型
收费全文 | 5617篇 |
免费 | 462篇 |
国内免费 | 11篇 |
出版年
2022年 | 37篇 |
2021年 | 95篇 |
2020年 | 60篇 |
2019年 | 82篇 |
2018年 | 143篇 |
2017年 | 103篇 |
2016年 | 126篇 |
2015年 | 234篇 |
2014年 | 284篇 |
2013年 | 367篇 |
2012年 | 431篇 |
2011年 | 363篇 |
2010年 | 257篇 |
2009年 | 221篇 |
2008年 | 315篇 |
2007年 | 259篇 |
2006年 | 259篇 |
2005年 | 251篇 |
2004年 | 256篇 |
2003年 | 195篇 |
2002年 | 188篇 |
2001年 | 126篇 |
2000年 | 128篇 |
1999年 | 106篇 |
1998年 | 66篇 |
1997年 | 46篇 |
1996年 | 34篇 |
1995年 | 38篇 |
1994年 | 45篇 |
1993年 | 35篇 |
1992年 | 61篇 |
1991年 | 59篇 |
1990年 | 58篇 |
1989年 | 48篇 |
1988年 | 49篇 |
1987年 | 36篇 |
1986年 | 50篇 |
1985年 | 37篇 |
1984年 | 42篇 |
1983年 | 30篇 |
1979年 | 28篇 |
1978年 | 23篇 |
1977年 | 27篇 |
1976年 | 21篇 |
1972年 | 26篇 |
1970年 | 29篇 |
1969年 | 31篇 |
1968年 | 28篇 |
1967年 | 22篇 |
1965年 | 22篇 |
排序方式: 共有6090条查询结果,搜索用时 46 毫秒
61.
Two abnormalities, one in lateral elements of synaptonemal complexes the other involving whole complexes, have been studied with the electron microscope in pollen mother cells of the lily hybrid, Lilium aureliensis × L. henryi, which with the light microscope showed almost complete bivalent formation at metaphase. Brief water treatment of pollen mother cells prior to fixation, revealed that the aberrant configurations in lateral elements arose by breakage and subsequent folding of severed fragments up to about 0.8 m long. The abnormality ocurred at recognisable heterologous regions, apparently immediately after pairing. The folded fragments were eliminated from the chromosomes at some time during pachytene. Pseudo pairing was observed after synapsis between either more than one pair of homologues or one pair bent back on themselves, so as to produce polycomplexes. Seemingly, central elements could develop between lateral elements on their outer face under these conditions. 相似文献
62.
63.
64.
65.
66.
67.
68.
69.
The variations in nasal and pharyngeal resistance induced by changes in the central inspiratory drive were studied in 10 normal men. To calculate resistances we measured upper airway pressures with two low-bias flow catheters; one was placed at the tip of the epiglottis and the other in the posterior nasopharynx, and we measured flow with a Fleisch no. 3 pneumotachograph connected to a tightly fitting mask. Both resistances were obtained continuously during CO2 rebreathing (Read's method) and during the 2 min after a 1-min voluntary maximal hyperventilation. The inspiratory drive was estimated by measurements of inspiratory pressure generated at 0.1 s after the onset of inspiration (P0.1) and by the mean inspiratory flow (VT/TI). In each subject both resistances decreased during CO2 rebreathing; these decreases were correlated with the increase in P0.1. During the posthyperventilation period, ventilation fell below base line in seven subjects; this was accompanied by an increase in both nasal and pharyngeal resistances. These resistances increased exponentially as VT/TI decreased. Parallel changes in nasal and pharyngeal resistances were seen during CO2 stimulus and during the period after the hyperventilation. We conclude that 1) the indexes quantifying the inspiratory drive reflect the activation of nasopharyngeal dilator muscles (as assessed by the changes in upper airway resistance) and 2) both nasal and pharyngeal resistances are similarly influenced by changes in the respiratory drive. 相似文献
70.