全文获取类型
收费全文 | 611篇 |
免费 | 75篇 |
出版年
2023年 | 5篇 |
2021年 | 10篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 5篇 |
2017年 | 17篇 |
2016年 | 16篇 |
2015年 | 25篇 |
2014年 | 31篇 |
2013年 | 19篇 |
2012年 | 40篇 |
2011年 | 29篇 |
2010年 | 22篇 |
2009年 | 19篇 |
2008年 | 23篇 |
2007年 | 16篇 |
2006年 | 17篇 |
2005年 | 28篇 |
2004年 | 17篇 |
2003年 | 23篇 |
2002年 | 32篇 |
2001年 | 20篇 |
2000年 | 20篇 |
1999年 | 14篇 |
1998年 | 12篇 |
1997年 | 12篇 |
1996年 | 12篇 |
1995年 | 4篇 |
1994年 | 10篇 |
1993年 | 6篇 |
1992年 | 10篇 |
1991年 | 10篇 |
1990年 | 10篇 |
1989年 | 14篇 |
1988年 | 5篇 |
1987年 | 8篇 |
1985年 | 4篇 |
1984年 | 15篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1974年 | 6篇 |
1970年 | 3篇 |
1969年 | 5篇 |
1968年 | 3篇 |
1967年 | 3篇 |
排序方式: 共有686条查询结果,搜索用时 31 毫秒
51.
Conditional mutation of Rb causes cell cycle defects without apoptosis in the central nervous system 总被引:12,自引:0,他引:12
下载免费PDF全文
![点击此处可从《Molecular and cellular biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
MacPherson D Sage J Crowley D Trumpp A Bronson RT Jacks T 《Molecular and cellular biology》2003,23(3):1044-1053
Targeted disruption of the retinoblastoma gene in mice leads to embryonic lethality in midgestation accompanied by defective erythropoiesis. Rb(-/-) embryos also exhibit inappropriate cell cycle activity and apoptosis in the central nervous system (CNS), peripheral nervous system (PNS), and ocular lens. Loss of p53 can prevent the apoptosis in the CNS and lens; however, the specific signals leading to p53 activation have not been determined. Here we test the hypothesis that hypoxia caused by defective erythropoiesis in Rb-null embryos contributes to p53-dependent apoptosis. We show evidence of hypoxia in CNS tissue from Rb(-/-) embryos. The Cre-loxP system was then used to generate embryos in which Rb was deleted in the CNS, PNS and lens, in the presence of normal erythropoiesis. In contrast to the massive CNS apoptosis in Rb-null embryos at embryonic day 13.5 (E13.5), conditional mutants did not have elevated apoptosis in this tissue. There was still significant apoptosis in the PNS and lens, however. Rb(-/-) cells in the CNS, PNS, and lens underwent inappropriate S-phase entry in the conditional mutants at E13.5. By E18.5, conditional mutants had increased brain size and weight as well as defects in skeletal muscle development. These data support a model in which hypoxia is a necessary cofactor in the death of CNS neurons in the developing Rb mutant embryo. 相似文献
52.
Bacterial functional redundancy along a soil reclamation gradient 总被引:10,自引:0,他引:10
Yin B Crowley D Sparovek G De Melo WJ Borneman J 《Applied and environmental microbiology》2000,66(10):4361-4365
A strategy to measure bacterial functional redundancy was developed and tested with soils collected along a soil reclamation gradient by determining the richness and diversity of bacterial groups capable of in situ growth on selected carbon substrates. Soil cores were collected from four sites along a transect from the Jamari tin mine site in the Jamari National Forest, Rondonia, RO, Brazil: denuded mine spoil, soil from below the canopy of invading pioneer trees, revegetated soil under new growth on the forest edge, and the forest floor of an adjacent preserved forest. Bacterial population responses were analyzed by amending these soil samples with individual carbon substrates in the presence of bromodeoxyuridine (BrdU). BrdU-labeled DNA was then subjected to a 16S-23S rRNA intergenic analysis to depict the actively growing bacteria from each site. The number and diversity of bacterial groups responding to four carbon substrates (L-serine, L-threonine, sodium citrate, and alpha-lactose hydrate) increased along the reclamation-vegetation gradient such that the preserved forest soil samples contained the highest functional redundancy for each substrate. These data suggest that bacterial functional redundancy increases in relation to the regrowth of plant communities and may therefore represent an important aspect of the restoration of soil biological functionality to reclaimed mine spoils. They also suggest that bacterial functional redundancy may be a useful indicator of soil quality and ecosystem functioning. 相似文献
53.
54.
Hawks, doves, and mixed-symmetry games 总被引:5,自引:0,他引:5
Crowley PH 《Journal of theoretical biology》2000,204(4):543-563
The hawk-dove game has proved to be an important tool for understanding the role of aggression in social interactions. Here, the game is presented in a more general form (GHD) to facilitate analyses of interactions between individuals that may differ in "size", where size is interpreted as a surrogate for resource holding power. Three different situations are considered, based on the availability and use of information that interacting individuals have about their sizes: the classical symmetric case, in which no information about sizes is used, the asymmetric case, in which the individuals know their relative sizes and thus their chances of prevailing in combat, and a mixed-symmetry case, in which each individual only knows its own size (or only knows its opponent's size). I describe and use some recently developed methods for multitype games-evolutionary games involving two or more categories of players. With these methods and others, the evolutionarily stable strategies (ESSs) that emerge for the three different cases are identified and compared. A proof of the form and uniqueness of the ESS for the mixed-symmetry case is presented. In this situation, one size category at most can play a mixed strategy; larger individuals are aggressive and smaller individuals are not. As the number of size categories approaches infinity and the size distribution becomes continuous, there is a threshold size, above which all individuals are aggressive, and below which they are not. 相似文献
55.
56.
Lauren A. Demers Elizabeth A. Olson David J. Crowley Scott L. Rauch Isabelle M. Rosso 《PloS one》2015,10(10)
Alexithymia, or “no words for feelings”, is highly prevalent in samples with childhood maltreatment and posttraumatic stress disorder (PTSD). The dorsal anterior cingulate cortex (dACC) has been identified as a key region involved in alexithymia, early life trauma, and PTSD. Functional alterations in the dACC also have been associated with alexithymia in PTSD. This study examined whether dACC morphology is a neural correlate of alexithymia in child maltreatment-related PTSD. Sixteen adults with PTSD and a history of childhood sexual abuse, physical abuse, or exposure to domestic violence, and 24 healthy controls (HC) completed the Toronto Alexithymia Scale 20 (TAS–20) and underwent magnetic resonance imaging. Cortical thickness of the dACC was measured using FreeSurfer, and values were correlated with TAS–20 scores, controlling for sex and age, in both groups. Average TAS–20 score was significantly higher in the PTSD than the HC group. TAS–20 scores were significantly positively associated with dACC thickness only in the PTSD group. This association was strongest in the left hemisphere and for TAS–20 subscales that assess difficulty identifying and describing feelings. We found that increasing dACC gray matter thickness is a neural correlate of greater alexithymia in the context of PTSD with childhood maltreatment. While findings are correlational, they motivate further inquiry into the relationships between childhood adversity, emotional awareness and expression, and dACC morphologic development in trauma-related psychopathology. 相似文献
57.
Amanda D. Melin Brooke E. Crowley Shaun T. Brown Patrick V. Wheatley Gillian L. Moritz Fred Tuh Yit Yu Henry Bernard Donald J. DePaolo Andrew D. Jacobson Nathaniel J. Dominy 《American journal of physical anthropology》2014,154(4):633-643
Calcium stable isotope ratios are hypothesized to vary as a function of trophic level. This premise raises the possibility of using calcium stable isotope ratios to study the dietary behaviors of fossil taxa and to test competing hypotheses on the adaptive origins of euprimates. To explore this concept, we measured the stable isotope composition of contemporary mammals in northern Borneo and northwestern Costa Rica, two communities with functional or phylogenetic relevance to primate origins. We found that bone collagen δ13C and δ15N values could differentiate trophic levels in each assemblage, a result that justifies the use of these systems to test the predicted inverse relationship between bioapatite δ13C and δ44Ca values. As expected, taxonomic carnivores (felids) showed a combination of high δ13C and low δ44Ca values; however, the δ44Ca values of other faunivores were indistinguishable from those of primary consumers. We suggest that the trophic insensitivity of most bioapatite δ44Ca values is attributable to the negligible calcium content of arthropod prey. Although the present results are inconclusive, the tandem analysis of δ44Ca and δ13C values in fossils continues to hold promise for informing paleodietary studies and we highlight this potential by drawing attention to the stable isotope composition of the Early Eocene primate Cantius. Am J Phys Anthropol 154:633–643, 2014. © 2014 Wiley Periodicals, Inc. 相似文献
58.
Andréia S Lessa Bruno D Paredes Juliana V Dias Adriana B Carvalho Luiz Fernando Quintanilha Christina M Takiya Bernardo R Tura Guilherme FM Rezende Antonio C Campos de Carvalho Célia MC Resende Regina CS Goldenberg 《BMC veterinary research》2010,6(1):1-10
Background
Atypical scrapie was first identified in Norwegian sheep in 1998 and has subsequently been identified in many countries. Retrospective studies have identified cases predating the initial identification of this form of scrapie, and epidemiological studies have indicated that it does not conform to the behaviour of an infectious disease, giving rise to the hypothesis that it represents spontaneous disease. However, atypical scrapie isolates have been shown to be infectious experimentally, through intracerebral inoculation in transgenic mice and sheep. The first successful challenge of a sheep with 'field' atypical scrapie from an homologous donor sheep was reported in 2007.Results
This study demonstrates that atypical scrapie has distinct clinical, pathological and biochemical characteristics which are maintained on transmission and sub-passage, and which are distinct from other strains of transmissible spongiform encephalopathies in the same host genotype.Conclusions
Atypical scrapie is consistently transmissible within AHQ homozygous sheep, and the disease phenotype is preserved on sub-passage. 相似文献59.
Brooke E. Crowley Melinda L. Carter Sarah M. Karpanty Adrienne L. Zihlman Paul L. Koch Nathaniel J. Dominy 《Oecologia》2010,164(3):611-626
Isotopic studies of wild primates have used a wide range of tissues to infer diet and model the foraging ecologies of extinct
species. The use of mismatched tissues for such comparisons can be problematic because differences in amino acid compositions
can lead to small isotopic differences between tissues. Additionally, physiological and dietary differences among primate
species could lead to variable offsets between apatite carbonate and collagen. To improve our understanding of the isotopic
chemistry of primates, we explored the apparent enrichment (ε*) between bone collagen and muscle, collagen and fur or hair
keratin, muscle and keratin, and collagen and bone carbonate across the primate order. We found that the mean ε* values of
proteinaceous tissues were small (≤1‰), and uncorrelated with body size or phylogenetic relatedness. Additionally, ε* values
did not vary by habitat, sex, age, or manner of death. The mean ε* value between bone carbonate and collagen (5.6 ± 1.2‰)
was consistent with values reported for omnivorous mammals consuming monoisotopic diets. These primate-specific apparent enrichment
values will be a valuable tool for cross-species comparisons. Additionally, they will facilitate dietary comparisons between
living and fossil primates. 相似文献
60.
van Beers JJ Raijmakers R Alexander LE Stammen-Vogelzangs J Lokate AM Heck AJ Schasfoort RB Pruijn GJ 《Arthritis research & therapy》2010,12(6):R219