全文获取类型
收费全文 | 2404篇 |
免费 | 220篇 |
出版年
2023年 | 7篇 |
2022年 | 16篇 |
2021年 | 44篇 |
2020年 | 29篇 |
2019年 | 37篇 |
2018年 | 31篇 |
2017年 | 57篇 |
2016年 | 75篇 |
2015年 | 143篇 |
2014年 | 168篇 |
2013年 | 181篇 |
2012年 | 226篇 |
2011年 | 235篇 |
2010年 | 159篇 |
2009年 | 108篇 |
2008年 | 176篇 |
2007年 | 174篇 |
2006年 | 155篇 |
2005年 | 165篇 |
2004年 | 106篇 |
2003年 | 108篇 |
2002年 | 85篇 |
2001年 | 23篇 |
2000年 | 12篇 |
1999年 | 17篇 |
1998年 | 16篇 |
1997年 | 9篇 |
1996年 | 11篇 |
1995年 | 11篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 7篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1981年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有2624条查询结果,搜索用时 15 毫秒
991.
Spatial genetic structure (SGS) of plants results from the nonrandom distribution of related individuals. SGS provides information on gene flow and spatial patterns of genetic diversity within populations. Seed dispersal creates the spatial template for plant distribution. Thus, in zoochorous plants, dispersal mode and disperser behaviour might have a strong impact on SGS. However, many studies only report the taxonomic group of seed dispersers, without further details. The recent increase in studies on SGS provides the opportunity to review findings and test for the influence of dispersal mode, taxonomic affiliation of dispersers and their behaviour. We compared the proportions of studies with SGS among groups and tested for differences in strength of SGS using Sp statistics. The presence of SGS differed among taxonomic groups, with reduced presence in plants dispersed by birds. Strength of SGS was instead significantly influenced by the behaviour of seed dispersal vectors, with higher SGS in plant species dispersed by animals with behavioural traits that result in short seed dispersal distances. We observed high variance in the strength of SGS in plants dispersed by animals that actively or passively accumulate seeds. Additionally, we found SGS was also affected by pollination and marker type used. Our study highlights the importance of vector behaviour on SGS even in the presence of variance created by other factors. Thus, more detailed information on the behaviour of seed dispersers would contribute to better understand which factors shape the spatial scale of gene flow in animal‐dispersed plant species. 相似文献
992.
Stephan Macher-Goeppinger Martina Keith Gencay Hatiboglu Markus Hohenfellner Peter Schirmacher Wilfried Roth Katrin E. Tagscherer 《Translational oncology》2017,10(6):869-875
BNIP3 (Bcl-2/adenovirus E1B 19-kDa interacting protein 3) is a BH3-only protein that regulates apoptosis and autophagy. BNIP3 plays also an important role in hypoxia-induced cell response and is regulated by HIF1. Here, we studied a possible association of BNIP3 expression and the prognosis of patients with renal cell carcinomas (RCCs) and examined the functional relevance of BNIP3 in the regulation of cell survival and apoptosis of renal carcinoma cells. BNIP3 expression was determined by immunohistochemistry in RCC tumor tissue samples of 569 patients using a tissue microarray. Functional characterization of BNIP3 in renal carcinoma cells indicates prosurvival effects. In human RCC tumor samples, high cytoplasmic BNIP3 expression was associated with high-grade RCCs and regional lymph node metastasis. BNIP3 expression correlated negatively with disease-specific survival. Multivariate Cox regression analysis retained BNIP3 expression as an independent prognostic factor in patients without distant metastasis. Together, our studies imply that BNIP3 regulates cell survival in RCCs and its expression is an independent prognostic marker in patients with localized RCCs. 相似文献
993.
994.
Fixation of CO2 using the ethylmalonyl‐CoA pathway in the photoheterotrophic marine bacterium Dinoroseobacter shibae 下载免费PDF全文
995.
A review of the ecosystem functions in oil palm plantations,using forests as a reference system 下载免费PDF全文
Alexander C. Keyel Jan Salecker Yael Kisel Katrin M. Meyer Mark Auliya Andrew D. Barnes Marife D. Corre Kevin Darras Heiko Faust Bastian Hess Stephan Klasen Alexander Knohl Holger Kreft Ana Meijide Fuad Nurdiansyah Fenna Otten Guy Pe'er Stefanie Steinebach Suria Tarigan Merja H. Tölle Teja Tscharntke Kerstin Wiegand 《Biological reviews of the Cambridge Philosophical Society》2017,92(3):1539-1569
Oil palm plantations have expanded rapidly in recent decades. This large‐scale land‐use change has had great ecological, economic, and social impacts on both the areas converted to oil palm and their surroundings. However, research on the impacts of oil palm cultivation is scattered and patchy, and no clear overview exists. We address this gap through a systematic and comprehensive literature review of all ecosystem functions in oil palm plantations, including several (genetic, medicinal and ornamental resources, information functions) not included in previous systematic reviews. We compare ecosystem functions in oil palm plantations to those in forests, as the conversion of forest to oil palm is prevalent in the tropics. We find that oil palm plantations generally have reduced ecosystem functioning compared to forests: 11 out of 14 ecosystem functions show a net decrease in level of function. Some functions show decreases with potentially irreversible global impacts (e.g. reductions in gas and climate regulation, habitat and nursery functions, genetic resources, medicinal resources, and information functions). The most serious impacts occur when forest is cleared to establish new plantations, and immediately afterwards, especially on peat soils. To variable degrees, specific plantation management measures can prevent or reduce losses of some ecosystem functions (e.g. avoid illegal land clearing via fire, avoid draining of peat, use of integrated pest management, use of cover crops, mulch, and compost) and we highlight synergistic mitigation measures that can improve multiple ecosystem functions simultaneously. The only ecosystem function which increases in oil palm plantations is, unsurprisingly, the production of marketable goods. Our review highlights numerous research gaps. In particular, there are significant gaps with respect to socio‐cultural information functions. Further, there is a need for more empirical data on the importance of spatial and temporal scales, such as differences among plantations in different environments, of different sizes, and of different ages, as our review has identified examples where ecosystem functions vary spatially and temporally. Finally, more research is needed on developing management practices that can offset the losses of ecosystem functions. Our findings should stimulate research to address the identified gaps, and provide a foundation for more systematic research and discussion on ways to minimize the negative impacts and maximize the positive impacts of oil palm cultivation. 相似文献
996.
997.
José Alberto Rodríguez‐Castillo Jennifer Quantius Susanne Herold Elie El Agha Saverio Bellusci Isabelle Salwig Thomas Braun Robert Voswinckel Werner Seeger Rory E. Morty Katrin Ahlbrecht 《Genesis (New York, N.Y. : 2000)》2017,55(12)
Pulmonary diseases such as chronic obstructive pulmonary disease, lung fibrosis, and bronchopulmonary dysplasia are characterized by the destruction or malformation of the alveolar regions of the lung. The underlying pathomechanisms at play are an area of intense interest since these mechanisms may reveal pathways suitable for interventions to drive reparative processes. Lipid‐laden fibroblasts (lipofibroblasts) express the Perilipin 2 (Plin2) gene‐product, PLIN2, commonly called adipose‐differentiation related protein (ADRP). These cells are also thought to play a role in alveolarization and repair after injury to the alveolus. Progress in defining the functional contribution of lipofibroblasts to alveolar generation and repair is hampered by a lack of in vivo tools. The present study reports the generation of an inducible mouse Cre‐driver line to target cells of the ADRP lineage. Robust Cre‐mediated recombination in this mouse line was detected in mesenchymal cells of the postnatal lung, and in additional organs including the heart, liver, and spleen. The generation and validation of this valuable new tool to genetically target, manipulate, and trace cells of the ADRP lineage is critical for assessing the functional contribution of lipofibroblasts to lung development and repair. 相似文献
998.
Population history and life history influence the migration rate of female Glanville fritillary butterflies 总被引:4,自引:0,他引:4
Ilkka Hanski Casper J. Breuker Katrin Schps Rosemary Setchfield Marko Nieminen 《Oikos》2002,98(1):87-97
This study examines the causes of emigration from small fragments of suitable habitat in a species that has a distinct metapopulation structure, frequent turnover of local populations, and substantial migration among local populations and currently unoccupied habitat fragments. We conducted a field experiment in which 727 individuals of the Glanville fritillary butterfly ( Melitaea cinxia ) originating from four regions were marked and released simultaneously in a natural environment. In three of the four source regions, larvae for the experiment were collected from dozens of small local populations, some of which had been established in the previous summer (new populations), whereas the remaining populations were older. In two of the source regions, female butterflies prefer a host plant ( Veronica spicata ) that is not present in the release area, where there is only Plantago lanceolata , the preferred host plant of females from the other two source regions. We found that migration rate of males was unrelated to any of the factors studied in this experiment. In contrast, two factors influenced the migration rate of females. First, Veronica -preferring females had higher emigration rate than Plantago- preferring females from the Plantago -containing release patches, demonstrating that the individual perception of habitat quality significantly influences the migration rate of females. Second, females from newly-established populations were more dispersive than females from older populations, supporting the notion that metapopulation processes (recurrent colonizations) select for increased migration. The observed migration rate was not correlated with any body size measurements, and thus the observed differences in migration rate were apparently caused by differences in the behaviour of female butterflies rather than in their flight capacity. 相似文献
999.
1000.
The previously unclear taxonomic status of the high-Antarctic bivalve Limatula ovalis Thiele, 1912 and the sub-Antarctic L. pygmaea (Philippi, 1845) was investigated using molecular techniques (18S rDNA, 16S rDNA, ITS-1). L. ovalis and L. pygmaea were recovered as sister taxa, and L. hodgsoni (Smith, 1907) as their sister, supporting the subgenus Antarctolima Habe, 1977. Various different molecular clock calculations placed the timing of the L. ovalis/pygmaea divergence (1.36-8.03 MYA with 16S rDNA, 6.81-19.12 MYA with 18S rDNA, 0.24-2.87 MYA with ITS-1) well after the formation of the Antarctic Polar Front (23.5 MYA, APF), indicating a more recent speciation process. The vicariance hypothesis that the APF is a barrier for geneflow favouring speciation processes in the Southern Ocean has to be questioned. 相似文献