全文获取类型
收费全文 | 302篇 |
免费 | 12篇 |
国内免费 | 1篇 |
专业分类
315篇 |
出版年
2022年 | 4篇 |
2021年 | 6篇 |
2020年 | 2篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 9篇 |
2015年 | 8篇 |
2014年 | 10篇 |
2012年 | 2篇 |
2011年 | 6篇 |
2010年 | 8篇 |
2009年 | 8篇 |
2008年 | 7篇 |
2007年 | 11篇 |
2006年 | 10篇 |
2005年 | 7篇 |
2004年 | 11篇 |
2003年 | 4篇 |
2002年 | 6篇 |
2001年 | 13篇 |
2000年 | 8篇 |
1999年 | 11篇 |
1998年 | 13篇 |
1997年 | 11篇 |
1996年 | 9篇 |
1995年 | 6篇 |
1994年 | 9篇 |
1993年 | 11篇 |
1992年 | 5篇 |
1991年 | 8篇 |
1990年 | 4篇 |
1989年 | 11篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1974年 | 4篇 |
1968年 | 3篇 |
1967年 | 2篇 |
1939年 | 2篇 |
1930年 | 4篇 |
1929年 | 2篇 |
1928年 | 6篇 |
1927年 | 2篇 |
1919年 | 2篇 |
排序方式: 共有315条查询结果,搜索用时 37 毫秒
81.
82.
83.
84.
Andrew RJ Mitchell Philip Roberts Jonas Eichhöfer Jonathan Timperley Oliver JM Ormerod 《Cardiovascular ultrasound》2004,2(1):1-4
Percutaneous coronary intervention can be associated with distal embolization of thrombotic material causing myocardial necrosis and infarction. We discuss the role of intravascular imaging to guide the use of a distal protection device by describing the outcome of a young woman presenting with non-ST elevation myocardial infarction. Coronary angiography demonstrated an isolated minor stenosis in the proximal left anterior descending coronary artery with slight haziness beyond the lesion. Intravascular ultrasound confirmed an extensive thrombus overlying a bulky atherosclerotic plaque. A distal filter wire was therefore successfully used to reduce the risk of distal embolization. The use of intravascular ultrasound in patients presenting with acute coronary syndrome may reveal large thrombi that are difficult to image using conventional angiographic techniques. Intravascular ultrasound can therefore be used as a tool to select lesions requiring distal protection. 相似文献
85.
A pregnant female rhesus macaque died spontaneously during stage two labor. Gross and histopathologic findings included severe pulmonary edema, with low numbers of blood vessels containing pale basophilic mucinous material (Alcian Blue positive and PTAH negative), consistent with intravascular amniotic fluid-derived mucin resulting in pulmonary amniotic fluid embolism. 相似文献
86.
Integrating animal temperament within ecology and evolution 总被引:9,自引:0,他引:9
Réale D Reader SM Sol D McDougall PT Dingemanse NJ 《Biological reviews of the Cambridge Philosophical Society》2007,82(2):291-318
Temperament describes the idea that individual behavioural differences are repeatable over time and across situations. This common phenomenon covers numerous traits, such as aggressiveness, avoidance of novelty, willingness to take risks, exploration, and sociality. The study of temperament is central to animal psychology, behavioural genetics, pharmacology, and animal husbandry, but relatively few studies have examined the ecology and evolution of temperament traits. This situation is surprising, given that temperament is likely to exert an important influence on many aspects of animal ecology and evolution, and that individual variation in temperament appears to be pervasive amongst animal species. Possible explanations for this neglect of temperament include a perceived irrelevance, an insufficient understanding of the link between temperament traits and fitness, and a lack of coherence in terminology with similar traits often given different names, or different traits given the same name. We propose that temperament can and should be studied within an evolutionary ecology framework and provide a terminology that could be used as a working tool for ecological studies of temperament. Our terminology includes five major temperament trait categories: shyness-boldness, exploration-avoidance, activity, sociability and aggressiveness. This terminology does not make inferences regarding underlying dispositions or psychological processes, which may have restrained ecologists and evolutionary biologists from working on these traits. We present extensive literature reviews that demonstrate that temperament traits are heritable, and linked to fitness and to several other traits of importance to ecology and evolution. Furthermore, we describe ecologically relevant measurement methods and point to several ecological and evolutionary topics that would benefit from considering temperament, such as phenotypic plasticity, conservation biology, population sampling, and invasion biology. 相似文献
87.
Collin M. McCabe Simon M. Reader Charles L. Nunn 《Proceedings. Biological sciences / The Royal Society》2015,282(1799)
Culturally transmitted traits are observed in a wide array of animal species, yet we understand little about the costs of the behavioural patterns that underlie culture, such as innovation and social learning. We propose that infectious diseases are a significant cost associated with cultural transmission. We investigated two hypotheses that may explain such a connection: that social learning and exploratory behaviours (specifically, innovation and extractive foraging) either compensate for existing infection or increase exposure to infectious agents. We used Bayesian comparative methods, controlling for sampling effort, body mass, group size, geographical range size, terrestriality, latitude and phylogenetic uncertainty. Across 127 primate species, we found a positive association between pathogen richness and rates of innovation, extractive foraging and social learning. This relationship was driven by two independent phenomena: socially contagious diseases were positively associated with rates of social learning, and environmentally transmitted diseases were positively associated with rates of exploration. Because higher pathogen burdens can contribute to morbidity and mortality, we propose that parasitism is a significant cost associated with the behavioural patterns that underpin culture, and that increased pathogen exposure is likely to have played an important role in the evolution of culture in both non-human primates and humans. 相似文献
88.
Reader JS Metzgar D Schimmel P de Crécy-Lagard V 《The Journal of biological chemistry》2004,279(8):6280-6285
Queuosine (Q) is a hypermodified 7-deazaguanosine nucleoside located in the anticodon wobble position of four amino acid-specific tRNAs. In bacteria, Q is produced de novo from GTP via the 7-deazaguanosine precursor preQ1 (7-aminoethyl 7-deazaguanine) by an uncharacterized pathway. PreQ1 is subsequently transferred to its specific tRNA by a tRNA-guanine transglycosylase (TGT) and then further modified in situ to produce Q. Here we use comparative genomics to implicate four gene families (best exemplified by the B. subtilis operon ykvJKLM) as candidates in the preQ1 biosynthetic pathway. Deletions were constructed in genes for each of the four orthologs in Acinetobacter. High pressure liquid chromatography analysis showed the Q nucleoside was absent from the tRNAs of each of four deletion strains. Electrospray ionization mass spectrometry confirmed the absence of Q in each mutant strain. Finally, introduction of the Bacillus subtilis ykvJKLM operon in trans complemented the Q deficiency of the two deletion mutants that were tested. Thus, the products of these four genes (named queC, -D, -E, and -F) are essential for the Q biosynthetic pathway. 相似文献
89.
M. D. J. Sayer J. P. Reader R. Morris 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1991,161(5):537-542
Summary Calcium fluxes were measured simultaneously in brown trout fry maintained in an artificial soft water medium of [Ca] 20 mol·l-1 and pH 5.6, and exposed to each of six trace metals (Al, Cu, Fe, Ni, Pb, and Zn). The trace metal concentrations represented typical and maximum levels found in acid waters experiencing declining fishery status. In the absence of trace metals, evidence is presented which suggests that ca. 91% of Ca taken up from the external medium was by extraintestinal active transport. Calcium efflux was stimulated by both concentrations of Al, Cu, Fe, and Pb. Efflux was also stimulated by [Ni] 170 nmol·l-1 and [Zn] 3000 nmol·l-1. In some cases, response to increased efflux was stimulation of influx. Lack of stimulation of influx resulted in negative net Ca fluxes. Net Ca losses were recorded at both concentrations of Al, Pb, and Ni, lower concentrations only of Fe, and higher concentrations only of Cu and Zn.Abbreviations
J
in
influx
-
J
net
net flux
-
J
out
efflux
Henceforward in this paper, chemical elements are referred to by their chemical symbols rather than by full names 相似文献
90.