全文获取类型
收费全文 | 557篇 |
免费 | 36篇 |
出版年
2023年 | 4篇 |
2022年 | 11篇 |
2021年 | 24篇 |
2020年 | 17篇 |
2019年 | 20篇 |
2018年 | 17篇 |
2017年 | 12篇 |
2016年 | 20篇 |
2015年 | 37篇 |
2014年 | 41篇 |
2013年 | 46篇 |
2012年 | 53篇 |
2011年 | 48篇 |
2010年 | 28篇 |
2009年 | 33篇 |
2008年 | 28篇 |
2007年 | 33篇 |
2006年 | 33篇 |
2005年 | 23篇 |
2004年 | 21篇 |
2003年 | 15篇 |
2002年 | 14篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1993年 | 1篇 |
1980年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有593条查询结果,搜索用时 31 毫秒
61.
Several insect species seem to persist not only in permanent but also in temporary ponds where they face particularly harsh conditions and frequent extinctions. Under such conditions, gene flow may prevent local adaptation to temporary ponds and may promote phenotypic plasticity, or maintain apparent population persistence. The few empirical studies on insects suggest the latter mechanism, but no studies so far quantified gene flow including both pond types. We investigated the effects of pond type and temporal variation on population genetic differentiation and gene flow in the damselfly Lestes viridis in northern Belgium. We report a survey of two allozyme loci (Gpi, Pgm) with polyacrylamide gel electrophoresis in 14 populations from permanent and temporary ponds, and compared these results with similar data from the same permanent populations one year before. The data suggested that neither pond-drying regime, nor temporal variation have a substantial effect on population genetic structuring and did not provide evidence for stable population differentiation in L. viridis in northern Belgium. Gene flow estimates were high within permanent and temporary ponds, and between pond types. Our data are consistent with a source-sink metapopulation system where temporary ponds act as sinks in dry years, and are quickly recolonized after local population extinction. This may create a pattern of apparent population persistence of this species in permanent and temporary ponds without clear local adaptation. 相似文献
62.
63.
64.
Van Laethem A Nys K Van Kelst S Claerhout S Ichijo H Vandenheede JR Garmyn M Agostinis P 《Free radical biology & medicine》2006,41(9):1361-1371
The p38 MAPK pathway controls critical premitochondrial events culminating in apoptosis of UVB-irradiated human keratinocytes, but the upstream mediators of this stress signal are not completely defined. This study shows that in human keratinocytes exposed to UVB the generation of reactive oxygen species (ROS) acts as a mediator of apoptosis signal regulating kinase-1 (Ask-1), a redox-sensitive mitogen-activated protein kinase kinase kinase (MAP3K) regulating p38 MAPK and JNK cascades. The NADPH oxidase antagonist diphenylene iodonium chloride and the EGFR inhibitor AG1487 prevent UVB-mediated ROS generation, the activation of the Ask-1-p38 MAPK stress response pathway, and apoptosis, evidencing the link existing between the early plasma membrane-generated ROS and the activation of a lethal cascade initiated by Ask-1. Consistent with this, Ask-1 overexpression considerably sensitizes keratinocytes to UVB-induced mitochondrial apoptosis. Although the JNK pathway is also stimulated after UVB, the killing effect of Ask-1 overexpression is reverted by p38 MAPK inhibition, suggesting that Ask-1 exerts its lethal effects mainly through the p38 MAPK pathway. Moreover, p38alpha(-/-) murine embryonic fibroblasts are protected from UVB-induced apoptosis even if JNK activation is fully preserved. These results argue for an important role of the UVB-generated ROS as mediators of the Ask-1-p38 MAPK pathway that, by culminating in apoptosis, restrains the propagation of potentially mutagenic keratinocytes. 相似文献
65.
Independent differentiation of mammotropes and somatotropes in the chicken embryonic pituitary gland
Zheng J Nakamura K Maseki Y Geelissen SM Berghman LR Sakai T 《Histochemistry and cell biology》2006,125(4):429-439
It has been reported that mammotropes in a rodent pituitary gland are derived from somatotropes via somatomammotropes (SMTs),
cells that produce both growth hormone (GH) and prolactin (Prl). However, no studies have been done on the transdifferentiation
of somatotropes in the chicken pituitary gland. In this study, in order to determine the origin of mammotropes, we studied
detail property of appearance of chicken somatotropes, mammotropes and pit-1 cells and then evaluated the existence of SMTs
in the chicken embryonic pituitary gland. Immunohistochemical analysis revealed that GH-immunopositive (GH-ip) cells appeared
on embryonic day (E) 14 and were mainly distributed in the caudal lobe, while Prl-immunopositive (Prl-ip) cells appeared in
the cephalic lobe of the pituitary gland on E16. In situ hybridization (ISH) and RT-PCR analysis showed that expression of
GH and Prl mRNA starts at E12 in the caudal lobe and at E14 in the cephalic lobe respectively. Pit-1 mRNA was first detected
on E5 by RT-PCR, and pit-1 mRNA-expressing cells were found in the cephalic lobe on E8. Then with the ontogeny of the chicken,
these cells spread into both lobes. Using a double staining method with ISH and immunohistochemistry, we could not detect
the existence of SMTs in the chicken embryonic pituitary gland even in the marginal region of either lobe. These results suggest
that chicken somatotropes and mammotropes independently appear in different lobes of pituitary gland and that transdifferentiation
from somatotropes to mammotropes is not the central route for differentiation of mammotropes in the embryonic chicken pituitary
gland. 相似文献
66.
Termont S Vandenbroucke K Iserentant D Neirynck S Steidler L Remaut E Rottiers P 《Applied and environmental microbiology》2006,72(12):7694-7700
Interleukin-10 (IL-10) is a promising candidate for the treatment of inflammatory bowel disease. Intragastric administration of Lactococcus lactis genetically modified to secrete IL-10 in situ in the intestine was shown to be effective in healing and preventing chronic colitis in mice. However, its use in humans is hindered by the sensitivity of L. lactis to freeze-drying and its poor survival in the gastrointestinal tract. We expressed the trehalose synthesizing genes from Escherichia coli under control of the nisin-inducible promoter in L. lactis. Induced cells accumulated intracellular trehalose and retained nearly 100% viability after freeze-drying, together with a markedly prolonged shelf life. Remarkably, cells producing trehalose were resistant to bile, and their viability in human gastric juice was enhanced. None of these effects were seen with exogenously added trehalose. Trehalose accumulation did not interfere with IL-10 secretion or with therapeutic efficacy in murine colitis. The newly acquired properties should enable a larger proportion of the administered bacteria to reach the gastrointestinal tract in a bioactive form, providing a means for more effective mucosal delivery of therapeutics. 相似文献
67.
68.
69.
70.
Martine Geraerts Sofie Willems Veerle Baekelandt Zeger Debyser Rik Gijsbers 《BMC biotechnology》2006,6(1):34