全文获取类型
收费全文 | 4355篇 |
免费 | 254篇 |
国内免费 | 1篇 |
专业分类
4610篇 |
出版年
2023年 | 35篇 |
2022年 | 81篇 |
2021年 | 109篇 |
2020年 | 77篇 |
2019年 | 77篇 |
2018年 | 113篇 |
2017年 | 98篇 |
2016年 | 131篇 |
2015年 | 173篇 |
2014年 | 204篇 |
2013年 | 276篇 |
2012年 | 289篇 |
2011年 | 284篇 |
2010年 | 210篇 |
2009年 | 138篇 |
2008年 | 194篇 |
2007年 | 223篇 |
2006年 | 177篇 |
2005年 | 157篇 |
2004年 | 142篇 |
2003年 | 105篇 |
2002年 | 95篇 |
2001年 | 82篇 |
2000年 | 72篇 |
1999年 | 64篇 |
1998年 | 28篇 |
1995年 | 33篇 |
1994年 | 29篇 |
1993年 | 30篇 |
1992年 | 46篇 |
1991年 | 41篇 |
1990年 | 33篇 |
1989年 | 41篇 |
1988年 | 46篇 |
1987年 | 45篇 |
1986年 | 52篇 |
1985年 | 38篇 |
1984年 | 50篇 |
1983年 | 32篇 |
1982年 | 30篇 |
1981年 | 32篇 |
1980年 | 33篇 |
1979年 | 45篇 |
1978年 | 20篇 |
1977年 | 47篇 |
1976年 | 24篇 |
1975年 | 28篇 |
1974年 | 31篇 |
1973年 | 24篇 |
1972年 | 22篇 |
排序方式: 共有4610条查询结果,搜索用时 0 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.
The mechanism of mass collaboration in risk management was studied during the Sichuan earthquake under a Web-based “PeopleFinder” project, where information is contributed and shared among mass contributors. The case study is provided by a great earthquake that happened in Wenchuan County, Sichuan Province, of southwestern China at 2:28 p.m. on May 12, 2008. We witnessed and experienced the rescue and relief efforts for the great earthquake. In this article, two fundamental frameworks are developed to study the mechanism of mass collaboration. Mass collaboration is proven to be effective in a big public crisis such as the Sichuan earthquake. 相似文献
7.
8.
9.
10.