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排序方式: 共有130条查询结果,搜索用时 15 毫秒
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Matthew G. Betts Lenore Fahrig Adam S. Hadley Katherine E. Halstead Jeff Bowman W. Douglas Robinson John A. Wiens David B. Lindenmayer 《Ecography》2014,37(6):517-527
Theoretical models predict strong influences of habitat loss and fragmentation on species distributions and demography, but empirical studies have shown relatively inconsistent support across species and systems. We argue that species’ responses to landscape‐scale habitat loss and fragmentation are likely to appear less idiosyncratic if it is recognized that species perceive the same landscapes in different ways. We present a new quantitative approach that uses species distribution models (SDMs) to measure landscapes (e.g. patch size, isolation, matrix amount) from the perspective of individual species. First, we briefly summarize the few efforts to date demonstrating that once differences in habitat distributions are controlled, consistencies in species’ responses to landscape structure emerge. Second, we present a detailed example providing step‐by‐step methods for application of a species‐centered approach using freely available land‐cover data and recent statistical modeling approaches. Third, we discuss pitfalls in current applications of the approach and recommend avenues for future developments. We conclude that the species‐centered approach offers considerable promise as a means to test whether sensitivity to habitat loss and fragmentation is mediated by phylogenetic, ecological, and life‐history traits. Cross‐species generalities in responses to habitat loss and fragmentation will be challenging to uncover unless landscape mosaics are defined using models that reflect differing species‐specific distributions, functional connectivity, and domains of scale. The emergence of such generalities would not only enhance scientific understanding of biotic processes driving fragmentation effects, but would allow managers to estimate species sensitivities in new regions. 相似文献
76.
In the absence of recombination, a mutator allele can spread through a population by hitchhiking with beneficial mutations that appear in its genetic background. Theoretical studies over the past decade have shown that the survival and fixation probability of beneficial mutations can be severely reduced by population size bottlenecks. Here, we use computational modelling and evolution experiments with the yeast S. cerevisiae to examine whether population bottlenecks can affect mutator dynamics in adapting asexual populations. In simulation, we show that population bottlenecks can inhibit mutator hitchhiking with beneficial mutations and are most effective at lower beneficial mutation supply rates. We then subjected experimental populations of yeast propagated at the same effective population size to three different bottleneck regimes and observed that the speed of mutator hitchhiking was significantly slower at smaller bottlenecks, consistent with our theoretical expectations. Our results, thus, suggest that bottlenecks can be an important factor in mutation rate evolution and can in certain circumstances act to stabilize or, at least, delay the progressive elevation of mutation rates in asexual populations. Additionally, our findings provide the first experimental support for the theoretically postulated effect of population bottlenecks on beneficial mutations and demonstrate the usefulness of studying mutator frequency dynamics for understanding the underlying dynamics of fitness‐affecting mutations. 相似文献
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Conserved and divergent patterns of expression of DAZL,VASA and OCT4 in the germ cells of the human fetal ovary and testis 总被引:1,自引:0,他引:1
Richard A Anderson Norma Fulton Gillian Cowan Shona Coutts Philippa TK Saunders 《BMC developmental biology》2007,7(1):136
Background
Germ cells arise from a small group of cells that express markers of pluripotency including OCT4. In humans formation of gonadal compartments (cords in testis, nests in ovary) takes place during the 1st trimester (6–8 weeks gestation). In the 2nd trimester germ cells can enter meiotic prophase in females whereas in males this does not occur until puberty. We have used qRTPCR, Westerns and immunohistochemical profiling to determine which of the germ cell subtypes in the human fetal gonads express OCT4, DAZL and VASA, as these have been shown to play an essential role in germ cell maturation in mice. 相似文献78.
Adriaan D Bins Jacco van Rheenen Kees Jalink Jonathan R Halstead Nullin Divecha David M Spencer John BAG Haanen Ton NM Schumacher 《BMC biotechnology》2007,7(1):2
Background
Advances in fluorescence microscopy and mouse transgenesis have made it possible to image molecular events in living animals. However, the generation of transgenic mice is a lengthy process and intravital imaging requires specialized knowledge and equipment. Here, we report a rapid and undemanding intravital imaging method using generally available equipment. 相似文献79.
Eduardo A. Undurraga Miguel Betancourt-Cravioto José Ramos-Casta?eda Ruth Martínez-Vega Jorge Méndez-Galván Duane J. Gubler María G. Guzmán Scott B. Halstead Eva Harris Pablo Kuri-Morales Roberto Tapia-Conyer Donald S. Shepard 《PLoS neglected tropical diseases》2015,9(3)
BackgroundDengue imposes a substantial economic and disease burden in most tropical and subtropical countries. Dengue incidence and severity have dramatically increased in Mexico during the past decades. Having objective and comparable estimates of the economic burden of dengue is essential to inform health policy, increase disease awareness, and assess the impact of dengue prevention and control technologies.ConclusionWith this study, Mexico joins Panama, Puerto Rico, Nicaragua, and Thailand as the only countries or areas worldwide with comprehensive (illness and preventive) empirical estimates of dengue burden. Burden varies annually; during an outbreak, dengue burden may be significantly higher than that of the pre-vaccine level of rotavirus diarrhea. In sum, Mexico’s potential economic benefits from dengue control would be substantial. 相似文献
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Fenella D. Halstead Maryam Rauf Naiem S. Moiemen Amy Bamford Christopher M. Wearn Adam P. Fraise Peter A. Lund Beryl A. Oppenheim Mark A. Webber 《PloS one》2015,10(9)