全文获取类型
收费全文 | 4476篇 |
免费 | 285篇 |
国内免费 | 1篇 |
出版年
2023年 | 31篇 |
2022年 | 63篇 |
2021年 | 90篇 |
2020年 | 62篇 |
2019年 | 60篇 |
2018年 | 92篇 |
2017年 | 91篇 |
2016年 | 121篇 |
2015年 | 174篇 |
2014年 | 184篇 |
2013年 | 252篇 |
2012年 | 281篇 |
2011年 | 289篇 |
2010年 | 211篇 |
2009年 | 148篇 |
2008年 | 199篇 |
2007年 | 232篇 |
2006年 | 196篇 |
2005年 | 177篇 |
2004年 | 157篇 |
2003年 | 128篇 |
2002年 | 115篇 |
2001年 | 80篇 |
2000年 | 71篇 |
1999年 | 65篇 |
1998年 | 32篇 |
1997年 | 30篇 |
1996年 | 33篇 |
1995年 | 37篇 |
1994年 | 32篇 |
1993年 | 37篇 |
1992年 | 47篇 |
1991年 | 40篇 |
1990年 | 38篇 |
1989年 | 48篇 |
1988年 | 43篇 |
1987年 | 51篇 |
1986年 | 56篇 |
1985年 | 43篇 |
1984年 | 54篇 |
1983年 | 43篇 |
1982年 | 33篇 |
1981年 | 36篇 |
1980年 | 40篇 |
1979年 | 47篇 |
1977年 | 53篇 |
1976年 | 31篇 |
1975年 | 32篇 |
1974年 | 34篇 |
1972年 | 28篇 |
排序方式: 共有4762条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
Detailed flow patterns in the nasal cavity. 总被引:9,自引:0,他引:9
The human nasal cavity filters and conditions inspired air while providing olfactory function. Detailed experimental study of nasal airflow patterns has been limited because of the complex geometry of the nasal cavity. In this work, particle image velocimetry was used to determine two-dimensional instantaneous velocity vector fields in parallel planes throughout a model of the nasal cavity that was subjected to a nonoscillatory flow rate of 125 ml/s. The model, which was fabricated from 26 computed tomography scans by using rapid prototyping techniques, is a scaled replica of a human right nasal cavity. The resulting vector plots show that the flow is laminar and regions of highest velocity are in the nasal valve and in the inferior airway. The relatively low flow in the olfactory region appears to protect the olfactory bulb from particulate pollutants. Low flows were also observed in the nasal meatuses, whose primary function has been the subject of debate. Comparison of sequentially recorded data suggests a steady flow. 相似文献
5.
Divergence time estimates of mammals from molecular clocks and fossils: Relevance of new fossil finds from India 总被引:1,自引:0,他引:1
G. V. R. Prasad 《Journal of biosciences》2009,34(5):649-659
This paper presents a brief review of recent advances in the classification of mammals at higher levels using fossils and
molecular clocks. It also discusses latest fossil discoveries from the Cretaceous — Eocene (66–55 m.y.) rocks of India and
their relevance to our current understanding of placental mammal origins and diversifications. 相似文献
6.
7.
8.
9.
Gisela Drews Kai Graszynski 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1987,157(3):345-353
Summary Euryhaline Crustacea living in dilute media, counterbalance the salt loss by active absorption of NaCl across the gill epithelium. To investigate the mechanisms involved in salt absorption, transeptithelial potential difference (PDte) was measured in isolated, perfused gills of the fiddler crab,Uca tangeri. The influence of some specific inhibitors of epithelial ion transport on the PDte was tested.With symmetrical conditions on both sides of the epithelium, the posterior gills ofUca tangeri showed a spontaneous PDte of +5 to +10 mV, that is an active transport potential which was positive on the bath side as referred to the hemolymph side. This potential decreased considerably after application of KCN or 2,4-dinitrophenol (DNP) to the perfusion saline.Omission of K+ from the perfusion saline or addition of ouabain led to a reversible drop of the PDte, suggesting that the absorption of Na+ and also of Cl– is driven by the (Na++K+)ATPase located in the basolateral membrane of the epithelial cells.Perfusion of the hemolymph space with saline containing diphenylamine-2-carboxylate (DPC) or the loop diuretic furosemide resulted in a decrease of the PDte.After application of amiloride to the bath saline the PDte increased. Half-maximum response to amiloride was reached at a concentration of about 10–5 mol·l–1. This suggests that one of the Na+ pathways across the apical membrane may consist of Na+ channels.Abbreviations
PD
te
transepithelial potential difference
-
DPC
diphenylamine-2-carboxylate
-
R
ps
resistance of perfusate shunt
-
R
te
transepithelial resistance
-
R
in
input resistance
-
DNP
2,4-dinitrophenol
Parts of this study have been reported at the 1st Congress of Comparative Physiology and Biochemistry, Liège 1984, and at the Vth European Colloquium on Renal Physiology, Frankfurt, 1985 相似文献
10.
The Role of Gravity in Apical Dominance : Effects of Clinostating on Shoot Inversion-Induced Ethylene Production, Shoot Elongation, and Lateral Bud Growth 下载免费PDF全文
Shoot inversion-induced release of apical dominance in Pharbitis nil is inhibited by rotating the plant at 0.42 revolutions per minute in a vertical plane perpendicular to the axis of rotation of a horizontal clinostat. Clinostating prevented lateral bud outgrowth, apparently by negating the restriction of the shoot elongation via reduction of ethylene production in the inverted shoot. Radial stem expansion was also decreased. Data from experiments with intact tissue and isolated segments indicated that shoot-inversion stimulates ethylene production by increasing the activity of 1-aminocyclopropane-1-carboxylic acid synthase. The results support the hypothesis that shoot inversion-induced release of apical dominance in Pharbitis nil is due to gravity stress and is mediated by ethylene-induced retardation of the elongation of the inverted shoot. 相似文献