全文获取类型
收费全文 | 329篇 |
免费 | 60篇 |
出版年
2023年 | 3篇 |
2022年 | 2篇 |
2021年 | 7篇 |
2020年 | 5篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2017年 | 6篇 |
2016年 | 17篇 |
2015年 | 11篇 |
2014年 | 18篇 |
2013年 | 18篇 |
2012年 | 25篇 |
2011年 | 26篇 |
2010年 | 8篇 |
2009年 | 14篇 |
2008年 | 22篇 |
2007年 | 19篇 |
2006年 | 17篇 |
2005年 | 8篇 |
2004年 | 10篇 |
2003年 | 12篇 |
2002年 | 13篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 7篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1993年 | 3篇 |
1992年 | 6篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 7篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1974年 | 6篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 4篇 |
1970年 | 5篇 |
1969年 | 2篇 |
1963年 | 2篇 |
排序方式: 共有389条查询结果,搜索用时 781 毫秒
101.
A. Lelania Bourgeois Thomas E. Rinderer Lorraine D. Beaman Robert G. Danka 《Journal of invertebrate pathology》2010,103(1):53-58
The incidence of nosemosis has increased in recent years due to an emerging infestation of Nosema ceranae in managed honey bee populations in much of the world. A real-time PCR assay was developed to facilitate detection and quantification of both Nosema apis and N. ceranae in both single bee and pooled samples. The assay is a multiplexed reaction in which both species are detected and quantified in a single reaction. The assay is highly sensitive and can detect single copies of the target sequence. Real-time PCR results were calibrated to spore counts generated by standard microscopy procedures. The assay was used to assess bees from commercial apiaries sampled in November 2008 and March 2009. Bees from each colony were pooled. A large amount of variation among colonies was evident, signifying the need to examine large numbers of colonies. Due to sampling constraints, a subset of colonies (from five apiaries) was sampled in both seasons. In November, N. apis levels were 1212 ± 148 spores/bee and N. ceranae levels were 51,073 ± 31,155 spores/bee. In March, no N. apis was detected, N. ceranae levels were 11,824 ± 6304 spores/bee. Changes in N. ceranae levels were evident among apiaries, some increasing and other decreasing. This demonstrates the need for thorough sampling of apiaries and the need for a rapid test for both detection and quantification of both Nosema spp. This assay provides the opportunity for detailed study of disease resistance, infection kinetics, and improvement of disease management practices for honey bees. 相似文献
102.
103.
Abstract We examined the effect of queen size on the probability of new colony establishment in the ant Pogonomyrmex occidentalis. Large queens are significantly more likely to survive than small queens through the initial stages of colony founding. These differences in individual fitness correlates have corresponding effects on colony fitness. In species in which individual queens vary in fitness, sexual allocation ratios should incorporate the individual fitness functions. 相似文献
104.
Using four highly polymorphic microsatellite markers (12-28 alleles), we gentoyped workers from 63 colonies of Pogonomyrmex occidentalis. Colonies have a single, multiply mated queen, and an average number of 6.3 patrilines per colony. Colony growth was measured over an 8-year period in the study population. Intracolonial relatedness and colony growth are correlated negatively, indicating a substantial fitness benefit to multiple mating. 相似文献
105.
106.
The structure of the SWI/SNF-remodeled nucleosome was characterized with single base-pair resolution by mapping the contacts of specific histone fold residues with nucleosomal DNA. We demonstrate that SWI/SNF peels up to 50 bp of DNA from the edge of the nucleosome, translocates the histone octamer beyond the DNA ends via a DNA bulge propagation mechanism, and promotes the formation of an intramolecular DNA loop between the nucleosomal entry and exit sites. This stable altered nucleosome conformation also exhibits alterations in the distance between contacts of specific histone residues with DNA and higher electrophoretic and sedimentation mobility, consistent with a more compact molecular shape. SWI/SNF converts a nucleosome to the altered state in less than 1 s, hydrolyzing fewer than 10 ATPs per event. 相似文献
107.
Ari E. Martínez José M. Ponciano Juan P. Gomez Thomas Valqui Jorge Novoa Mariamercedes Antezana Gabriela Biscarra Ettore Camerlenghi Blaine H. Carnes Renato Huayanca Munarriz Eliseo Parra Isabella M. Plummer John W. Fitzpatrick Scott K. Robinson Jacob B. Socolar John Terborgh 《Ecology letters》2023,26(2):335-346
Documenting patterns of spatiotemporal change in hyper-diverse communities remains a challenge for tropical ecology yet is increasingly urgent as some long-term studies have shown major declines in bird communities in undisturbed sites. In 1982, Terborgh et al. quantified the structure and organisation of the bird community in a 97-ha. plot in southeastern Peru. We revisited the same plot in 2018 using the same methodologies as the original study to evaluate community-wide changes. Contrary to longitudinal studies of other neotropical bird communities (Tiputini, Manaus, and Panama), we found little change in community structure and organisation, with increases in 5, decreases in 2 and no change in 7 foraging guilds. This apparent stability suggests that large forest reserves such as the Manu National Park, possibly due to regional topographical influences on precipitation, still provide the conditions for establishing refugia from at least some of the effects of global change on bird communities. 相似文献
108.
The cardiovascular effects of oral and intravenous administration of 0.05 and 0.1 mg/kg of the isosterically modified prostaglandin (PG) analog, (+)-4-{3-[3-[2-(1-hydroxycyclohexyl)ethyl]-4-oxo-thiazolidinyl]propy} benzoic acid were ascertained in conscious mongrels. After 0.05 mg/kg p.o., mean arterial pressure (MAP), obtained from indwelling catheters, fell from 105 ± 1 to 100 ± 4 mm Hg and total peripheral resistance (TPR) decreased from 0.062 ± 0.006 to 0.039 ± 0.002 mm Hg/ml/min. Cardiac output (CO), measured via electromagnetic flow probes, rose from 1.8 ± 0.2 to 2.6 ± 0.1 l/ml and heart rate from 109 ± 13 to 128 ± 8 beats/min. The 0.1 mg/kg p.o. dose produced similar results. Intravenous injection of 0.1 mg/kg immediately dropped MAP from 103 ± 6 to 58 ± 3 mm Hg and TRP from 0.049 ± .006 to .014 ± .002 mm Hg/ml/min. CO climbed from 2.3 ± 0.2 to 0.2 to 5.3 ± 0.5 l/ml and HR increased from 126 ± 9 to 254 ± 14 beats/min. Stroke volume was not affected by either oral or intravenous administration of the PG analog. Pretreatment with 100 μg/kg timolol blunted the CO and HR responses to 0.1 mg/kg iv of the PG analog without affecting the depressor response. Metaramidol infused during injection of 0.1 mg/kg iv of the PG analog diminished all responses. When compared to the cardiovascular effects of hydralazine and nitroprusside, the profile of the PG analog activity closely resembled that produced by the arterial vasodilator, hydralazine; in contrast, nitroprusside (which also dilates veins) reduced stroke volume, but did not significantly affect HR. In conclusion, dilation of the resistance vessels by the PG analog decreased MAP and TPR and reflexly elevated CO and HR in conscious dogs. 相似文献
109.
Increasing concentrations of malonaldehyde and beta-propiolactone were increasingly mutagenic with 7 mutants of Salmonella typhimurium, 5 of which mutated bya frameshift mechanism and 2 of which mutated through base-pair substitution. The antioxidants vitamin C, vitamin E, selenium and butylated hydroxytoluene (BHT) at 3 logarithmic concentrations markedly reduced mutagenesis in those strains which mutated by frameshift mechanism. 相似文献
110.
Topography of the ISW2-nucleosome complex: insights into nucleosome spacing and chromatin remodeling
下载免费PDF全文
![点击此处可从《The EMBO journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Linker DNA was found to be critical for the specific docking of ISW2 with nucleosomes as shown by mapping the physical contacts of ISW2 with nucleosomes at base-pair resolution. Hydroxyl radical footprinting revealed that ISW2 not only extensively interacts with the linker DNA, but also approaches the nucleosome from the side perpendicular to the axis of the DNA superhelix and contacts two disparate sites on the nucleosomal DNA from opposite sides of the superhelix. The topography of the ISW2-nucleosome was further delineated by finding which of the ISW2 subunits are proximal to specific sites within the linker and nucleosomal DNA regions by site-directed DNA photoaffinity labeling. Although ISW2 was shown to contact approximately 63 bp of linker DNA, a minimum of 20 bp of linker DNA was required for stable binding of ISW2 to nucleosomes. The remaining approximately 43 bp of flanking linker DNA promoted more efficient binding under competitive binding conditions and was functionally important for enhanced sliding of nucleosomes when ISW2 was significantly limiting. 相似文献