全文获取类型
收费全文 | 1159篇 |
免费 | 88篇 |
国内免费 | 1篇 |
出版年
2022年 | 4篇 |
2021年 | 17篇 |
2020年 | 20篇 |
2019年 | 9篇 |
2018年 | 20篇 |
2017年 | 25篇 |
2016年 | 22篇 |
2015年 | 59篇 |
2014年 | 62篇 |
2013年 | 73篇 |
2012年 | 70篇 |
2011年 | 65篇 |
2010年 | 64篇 |
2009年 | 40篇 |
2008年 | 51篇 |
2007年 | 61篇 |
2006年 | 46篇 |
2005年 | 38篇 |
2004年 | 41篇 |
2003年 | 44篇 |
2002年 | 36篇 |
2001年 | 35篇 |
2000年 | 26篇 |
1999年 | 25篇 |
1998年 | 17篇 |
1997年 | 9篇 |
1996年 | 14篇 |
1995年 | 12篇 |
1994年 | 13篇 |
1993年 | 14篇 |
1992年 | 27篇 |
1991年 | 11篇 |
1990年 | 14篇 |
1989年 | 15篇 |
1988年 | 11篇 |
1987年 | 16篇 |
1986年 | 10篇 |
1985年 | 13篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1979年 | 4篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 10篇 |
1972年 | 7篇 |
1971年 | 7篇 |
1970年 | 4篇 |
1969年 | 8篇 |
1968年 | 7篇 |
1966年 | 4篇 |
排序方式: 共有1248条查询结果,搜索用时 15 毫秒
1.
Hanna ten Brink Renske E. Onstein André M. de Roos 《Evolution; international journal of organic evolution》2020,74(8):1826-1850
Although metamorphosis is widespread in the animal kingdom, several species have evolved life-cycle modifications to avoid complete metamorphosis. Some species, for example, many salamanders and newts, have deleted the adult stage via a process called paedomorphosis. Others, for example, some frog species and marine invertebrates, no longer have a distinct larval stage and reach maturation via direct development. Here we study which ecological conditions can lead to the loss of metamorphosis via the evolution of direct development. To do so, we use size-structured consumer-resource models in conjunction with the adaptive-dynamics approach. In case the larval habitat deteriorates, individuals will produce larger offspring and in concert accelerate metamorphosis. Although this leads to the evolutionary transition from metamorphosis to direct development when the adult habitat is highly favorable, the population will go extinct in case the adult habitat does not provide sufficient food to escape metamorphosis. With a phylogenetic approach we furthermore show that among amphibians the transition of metamorphosis to direct development is indeed, in line with model predictions, conditional on and preceded by the evolution of larger egg sizes. 相似文献
2.
3.
Bioturbation by cyprinid fish affecting the food availability for predatory water mites 总被引:1,自引:0,他引:1
Summary Field observations suggested that benthivorous fish, causing bioturbation, are able to effect the food availability for predacious water mites feeding on bottom dwelling chironomid larvae. This hypothesis was tested in the laboratory. In an undisturbed situation the predation rate exercised by the water mites on the tube dwelling chironomid Cladotanytarsus mancus was very low. However, when the sediment was disturbed, the predation rate increased substantially. The relevance of this for the field situation is discussed. 相似文献
4.
Evolutionary relationships of the scrub-birds Atrichornis were investigated using complete sequences of the recombination-activating gene RAG-1 and the proto-oncogene c-mos for two individuals of the noisy scrub-bird Atrichornis clamosus. Phylogenetic analysis revealed that Atrichornis was sister to the genus Menura (the lyrebirds) and that these two genera (the Menurae) were sister to the rest of the oscine passerines. A sister relationship
between Atrichornis and Menura supports the traditional view, based on morphology and DNA hybridization, that these taxa are closely related. Similarly,
a sister relationship with the remaining oscine passerines agrees with the morphological distinctiveness of Atrichornis and Menura, although this result contradicts conclusions based on DNA hybridization studies. Although Atrichornis is very well known morphologically, previous conclusions regarding its relationships were hampered by a lack of comparative
knowledge of other passerines, making concurrence of the sequence data of particular significance. 相似文献
5.
On mitosis in the multicellular alga Ulva mutabilis F?yn 总被引:3,自引:0,他引:3
6.
Wei Zhang Nick Bansback Annelies Boonen Adam Young Amitabh Singh Aslam H Anis 《Arthritis research & therapy》2010,12(5):R177
Introduction
The Work Productivity and Activity Impairment (WPAI) questionnaire is a well validated instrument to measure impairments in work and activities. However, its validation among patients with rheumatoid arthritis (RA) has not been well established. The present study's purpose is to evaluate the construct validity of the WPAI-general health version among RA patients and its ability to differentiate between RA patients with varying health status. 相似文献7.
8.
9.
A patent foramen ovale is a common intracardiac finding that is located between the left and right atrium. It can cause right-to-left shunting and has a high prevalence in patients who suffer a cryptogenic stroke. Earlier trials did not show superiority of percutaneous patent foramen ovale closure with standard medical therapy over standard medical therapy alone in the treatment of cryptogenic stroke. Interestingly, several meta-analyses show positive results regarding closure, suggesting underpowering of the individual trials. Recently, two large prospective trials and one long-term follow-up study showed benefit of percutaneous closure over standard medical therapy in treatment of cryptogenic stroke. A larger right-to-left shunt or the presence of an atrial septal aneurysm were predictors for a recurrent event. Therefore, percutaneous patent foramen ovale closure after cryptogenic stroke should be recommended over antiplatelet therapy alone in patients younger than 55 years of age with a high-risk patent foramen ovale. 相似文献
10.