全文获取类型
收费全文 | 171篇 |
免费 | 16篇 |
出版年
2020年 | 3篇 |
2019年 | 5篇 |
2018年 | 1篇 |
2017年 | 7篇 |
2016年 | 4篇 |
2015年 | 4篇 |
2014年 | 4篇 |
2013年 | 11篇 |
2012年 | 10篇 |
2011年 | 13篇 |
2010年 | 9篇 |
2009年 | 8篇 |
2008年 | 11篇 |
2007年 | 19篇 |
2006年 | 10篇 |
2005年 | 12篇 |
2004年 | 8篇 |
2003年 | 9篇 |
2002年 | 11篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1995年 | 1篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 1篇 |
排序方式: 共有187条查询结果,搜索用时 109 毫秒
181.
Fridtjof Jerve Petter Fylling Steinar Stenby 《Prostaglandins & other lipid mediators》1979,17(1):121-123
Rupture of the uterine body was found after induction of therapeutic abortion with vaginal suppositories containing 16,16-dimethyl prostaglandin E 2 in a 20-year-old primigravida. A short discussion is given on the cervical complications that can occur after prostaglandin induction of abortion, stating that rupture of the uterine body also can be seen. So far, no prostaglandin compound seems to avoid such complications. 相似文献
182.
Yngvild Vindenes Aline Magdalena Lee Steinar Engen Bernt‐Erik Sæther 《Evolution; international journal of organic evolution》2010,64(4):1063-1075
Recent studies of rates of evolution have revealed large systematic differences among organisms with different life histories, both within and among taxa. Here, we consider how life history may affect the rate of evolution via its influence on the fixation probability of slightly beneficial mutations. Our approach is based on diffusion modeling for a finite, stage‐structured population with stochastic population dynamics. The results, which are verified by computer simulations, demonstrate that even with complex population structure just two demographic parameters are sufficient to give an accurate approximation of the fixation probability of a slightly beneficial mutation. These are the reproductive value of the stage in which the mutation first occurs and the demographic variance of the population. The demographic variance also determines what influence population size has on the fixation probability. This model represents a substantial generalization of earlier models, covering a large range of life histories. 相似文献
183.
Bernt‐Erik Sæther Steinar Engen Vidar Grøtan Thomas Bregnballe Christiaan Both Piotr Tryjanowski Agu Leivits Jonathan Wright Anders Pape Møller Marcel E. Visser Wolfgang Winkel 《Oikos》2008,117(8):1197-1208
The theta-logistic model of density regulation is an especially flexible class of density regulation models where different forms of non-linear density regulation can be expressed by only one parameter, θ. Estimating the parameters of the theta-logistic model is, however, challenging. This is mainly due to the need for information concerning population growth at low densities as well as data on fluctuations around the carrying capacity K in order to estimate the strength of density regulation. Here we estimate parameters of the theta-logistic model for 28 populations of three species of birds that have grown from very small population sizes followed by a period of fluctuations around K. We then use these parameters to estimate the quasi-stationary distribution of population size. There were often large uncertainties in these parameters specifying the form of density regulation that were generally independent of the duration of the study period. In contrast, precision in the estimates of environmental variance increased with the length of the time series. In most of the populations, a large proportion of the probability density of the (quasi-) stationary distribution of population sizes was located at intermediate population sizes relative to K. Thus, we suggest that the (quasi-) stationary distribution of population sizes represents a useful summary statistic that in many cases provides a more robust characterisation of basic population dynamics (e.g. range of variation in population fluctuations or proportion of time spent close to K) than can be obtained from analyses of single model parameters. 相似文献
184.
185.
186.
Steinar Økland 《Zoomorphology》1980,96(1-2):1-19
Summary The ultrastructure of the auricles, the ostia, and the ventricle of L. asellus and T. marmorea is described. The heart wall consists of an epicardium, a basement membrane, and an inner loose myocardium. The epicardial cells of the auricle are podocytes. The exposed cell body and the branched processes show pedicles. Ventricular epicardium is flat and simple. The slender, unbranched, mononucleated muscle fibres have a peripheral nucleus located midway along the fibre. Mitochondria are peripherally located, leaving the center to longitudinally running thick and thin myofilaments. Dense bodies and attachment plaques make up the Z-material. Sarcomeres and myofibrils are absent, as are transverse tubules and intercalated disks. The sarcoplasmic reticulum consists of peripheral tubules and subsarcolemmal cisternae, some of which radiate, branch, and run between myofilaments. Couplings are lacking. Ventricular fibres in T. marmorea show nexuses and desmosomes; in L. asellus only nexuses. The muscular ostia are tubular, and muscle fibres resemble those of the ventricle; nexuses are detected in T. marmorea and desmosomes in L. asellus. The only nervous elements observed are some nerve processes, structurally similar to those of other molluscs.Supported by grants from the Norwegian Research Council for Science and Humanities 相似文献
187.
Tormod Mørk Steinar Waage Tore Tollersrud Bjørg Kvitle Ståle Sviland 《Acta veterinaria Scandinavica》2007,49(1):23