全文获取类型
收费全文 | 422672篇 |
免费 | 44002篇 |
国内免费 | 194篇 |
出版年
2016年 | 4598篇 |
2015年 | 6104篇 |
2014年 | 7196篇 |
2013年 | 10798篇 |
2012年 | 11725篇 |
2011年 | 12217篇 |
2010年 | 8288篇 |
2009年 | 7604篇 |
2008年 | 10851篇 |
2007年 | 11515篇 |
2006年 | 10855篇 |
2005年 | 10338篇 |
2004年 | 10424篇 |
2003年 | 10204篇 |
2002年 | 9962篇 |
2001年 | 17479篇 |
2000年 | 17490篇 |
1999年 | 14061篇 |
1998年 | 4878篇 |
1997年 | 5207篇 |
1996年 | 4909篇 |
1995年 | 4786篇 |
1994年 | 4682篇 |
1993年 | 4692篇 |
1992年 | 12343篇 |
1991年 | 12152篇 |
1990年 | 12128篇 |
1989年 | 11909篇 |
1988年 | 11227篇 |
1987年 | 10548篇 |
1986年 | 9855篇 |
1985年 | 10283篇 |
1984年 | 8471篇 |
1983年 | 7319篇 |
1982年 | 5657篇 |
1981年 | 5058篇 |
1980年 | 4713篇 |
1979年 | 8113篇 |
1978年 | 6337篇 |
1977年 | 5960篇 |
1976年 | 5695篇 |
1975年 | 6153篇 |
1974年 | 6727篇 |
1973年 | 6592篇 |
1972年 | 6149篇 |
1971年 | 5557篇 |
1970年 | 4789篇 |
1969年 | 4796篇 |
1968年 | 4463篇 |
1967年 | 3820篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
Sexual selection influences the evolution of morphological traits that increase the likelihood of monopolizing scarce resources. When such traits are used during contests, they are termed weapons. Given that resources are typically linked to monopolizing mating partners, theory expects only males to bear weapons. In some species, however, females also bear weapons, although typically smaller than male weapons. Understanding why females bear smaller weapons can thus help us understand the selective pressures behind weapon evolution. However, most of our knowledge comes from studies on weapon size, while the biomechanics of weapons, such as the size of the muscles, efficiency, and shape are seldom studied. Our goal was to test if the theoretical expectations for weapon size sexual dimorphism also occur for weapon biomechanics using two aeglid crab species. Males of both species had larger claws which were also stronger than female claws. Male claws were also more efficient than females' claws (although we used only one species in this analysis). For weapon shape, though, only one species differed in the mean claw shape. Regarding scaling differences, in both species, male claws had higher size scaling than females, while only one species had a higher shape scaling. However, male weapons did not have higher scaling regarding strength and efficiency than females. Thus, males apparently allocate more resources in weapons than females, but once allocated, muscle and efficiency follow a similar developmental pathway in both sexes. Taken together, our results show that sexual dimorphism in weapons involves more than differences in size. Shape differences are especially intriguing because we cannot fully understand its causes. Yet, we highlight that such subtle differences can only be detected by measuring and analysing weapon shape and biomechanical components. Only then we might better understand how weapons are forged. 相似文献
82.
83.
84.
Robert R Edwards Ajay D Wasan Clifton O Bingham III Joan Bathon Jennifer A Haythornthwaite Michael T Smith Gayle G Page 《Arthritis research & therapy》2009,11(3):R61-9
Introduction
Maladaptive physiological responses to stress appear to play a role in chronic inflammatory diseases such as rheumatoid arthritis (RA). However, relatively little stress research in RA patients has involved the study of pain, the most commonly reported and most impairing stressor in RA. In the present study, we compared psychophysical and physiological responses to standardized noxious stimulation in 19 RA patients and 21 healthy controls. 相似文献85.
86.
87.
88.
Daw-Yang Hwang Stefan Kohl Xueping Fan Asaf Vivante Stefanie Chan Gabriel C. Dworschak Julian Schulz Albertien M. van Eerde Alina C. Hilger Heon Yung Gee Tracie Pennimpede Bernhard G. Herrmann Glenn van de Hoek Kirsten Y. Renkema Christoph Schell Tobias B. Huber Heiko M. Reutter Neveen A. Soliman Natasa Stajic Radovan Bogdanovic Elijah O. Kehinde Richard P. Lifton Velibor Tasic Weining Lu Friedhelm Hildebrandt 《Human genetics》2015,134(8):905-916
89.
90.