全文获取类型
收费全文 | 326篇 |
免费 | 33篇 |
出版年
2022年 | 3篇 |
2021年 | 7篇 |
2020年 | 3篇 |
2019年 | 3篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 6篇 |
2015年 | 9篇 |
2014年 | 12篇 |
2013年 | 21篇 |
2012年 | 30篇 |
2011年 | 24篇 |
2010年 | 7篇 |
2009年 | 5篇 |
2008年 | 25篇 |
2007年 | 10篇 |
2006年 | 15篇 |
2005年 | 5篇 |
2004年 | 8篇 |
2003年 | 13篇 |
2002年 | 4篇 |
2001年 | 4篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1997年 | 3篇 |
1995年 | 5篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 7篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1981年 | 6篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1975年 | 8篇 |
1974年 | 7篇 |
1973年 | 3篇 |
1972年 | 6篇 |
1971年 | 2篇 |
1970年 | 4篇 |
1968年 | 3篇 |
1935年 | 2篇 |
1933年 | 2篇 |
排序方式: 共有359条查询结果,搜索用时 15 毫秒
61.
Tanner CJ 《Proceedings. Biological sciences / The Royal Society》2006,273(1602):2737-2742
The relationship between numerical advantage and competitive ability is a fundamental component in contests between groups of social animals. An individual's ability to correctly assess the numerical state of its group is of vital importance. In addition to numerical dominance, the group's fighting ability also plays an important role in competitive interactions. By staging experimental fights between two Formica ant species, I show that Formica xerophila are able to assess their own group's strength prior to any competitive encounter. Ants that perceive themselves as part of a large group act more aggressively toward a competitor than ants that perceive themselves as isolated individuals. This increase in aggression improves F. xerophila's competitive ability. Furthermore, the number of individuals in a contest was found to affect competitive ability. In contests with equal number of competitors, groups of F. xerophila were more successful than individual F. xerophila. Contrary to previous predictions using Lanchester's laws of fighting, F. xerophila's ability to kill competitors increased nonlinearly with group size. This nonlinearity was due to the collective fighting strategy of an F. xerophila group isolating and engaging a single Formica integroides competitors. 相似文献
62.
63.
Liu W Sheppeck JE Colby DA Huang HB Nairn AC Chamberlin AR 《Bioorganic & medicinal chemistry letters》2003,13(9):1597-1600
Analogues of the potent and moderately selective PP1/PP2A inhibitor tautomycin (TM) were prepared with modifications in the C1'-C7' anhydride moiety. While all retain varying degrees of activity within a 3000-fold range of potencies, they also show remarkable constancy in their IC(50) ratios, suggesting that the anhydride moiety is not critical in controlling the selectivity of inhibition. 相似文献
64.
Caroline Angelard Colby J Tanner Pierre Fontanillas Hélène Niculita-Hirzel Frédéric Masclaux Ian R Sanders 《The ISME journal》2014,8(2):284-294
Arbuscular mycorrhizal fungi (AMF) are among the most abundant symbionts of plants,
improving plant productivity and diversity. They are thought to mostly grow vegetatively,
a trait assumed to limit adaptability. However, AMF can also harbor genetically different
nuclei (nucleotypes). It has been shown that one AMF can produce genotypically novel
offspring with proportions of different nucleotypes. We hypothesized that (1) AMF respond
rapidly to a change of environment (plant host) through changes in the frequency of
nucleotypes; (2) genotypically novel offspring exhibit different genetic responses to
environmental change than the parent; and (3) genotypically novel offspring exhibit a wide
range of phenotypic plasticity to a change of environment. We subjected AMF parents and
offspring to a host shift. We observed rapid and large genotypic changes in all AMF lines
that were not random. Genotypic and phenotypic responses were different among offspring
and their parents. Even though growing vegetatively, AMF offspring display a broad range
of genotypic and phenotypic changes in response to host shift. We conclude that AMF have
the ability to rapidly produce variable progeny, increasing their probability to produce
offspring with different fitness than their parents and, consequently, their potential
adaptability to new environmental conditions. Such genotypic and phenotypic flexibility
could be a fast alternative to sexual reproduction and is likely to be a key to the
ecological success of AMF. 相似文献
65.
Victor Wong David Williams Christopher Colby David A. Saint 《Biotechnology letters》2000,22(24):1919-1924
Measuring uncoupled oxygen uptake rate (OUR) could provide a convenient method for quantifying changes in the metabolic activity of plant cultures caused by hydrodynamic shear. Experiments on Daucus carota (carrot) cells were performed in a novel O2-permeable Couette viscometer at varying levels of laminar shear (6 to 100 N m–2). When the uncoupled OUR of the cells was compared with mitochondrial activity (determined by 2,3,5-triphenyl tetrazolium chloride assay), a significant correlation was observed (R=0.91 by linear regression). 相似文献
66.
Curtin SJ Zhang F Sander JD Haun WJ Starker C Baltes NJ Reyon D Dahlborg EJ Goodwin MJ Coffman AP Dobbs D Joung JK Voytas DF Stupar RM 《Plant physiology》2011,156(2):466-473
We performed targeted mutagenesis of a transgene and nine endogenous soybean (Glycine max) genes using zinc-finger nucleases (ZFNs). A suite of ZFNs were engineered by the recently described context-dependent assembly platform--a rapid, open-source method for generating zinc-finger arrays. Specific ZFNs targeting dicer-like (DCL) genes and other genes involved in RNA silencing were cloned into a vector under an estrogen-inducible promoter. A hairy-root transformation system was employed to investigate the efficiency of ZFN mutagenesis at each target locus. Transgenic roots exhibited somatic mutations localized at the ZFN target sites for seven out of nine targeted genes. We next introduced a ZFN into soybean via whole-plant transformation and generated independent mutations in the paralogous genes DCL4a and DCL4b. The dcl4b mutation showed efficient heritable transmission of the ZFN-induced mutation in the subsequent generation. These findings indicate that ZFN-based mutagenesis provides an efficient method for making mutations in duplicate genes that are otherwise difficult to study due to redundancy. We also developed a publicly accessible Web-based tool to identify sites suitable for engineering context-dependent assembly ZFNs in the soybean genome. 相似文献
67.
Howard D. Colby Miriam Levitt Jeanne M. Bergstrom Harold Purcell 《The Journal of steroid biochemistry and molecular biology》1993,45(6):501-507
Studies were done to determine the effects of age on steroidogenesis in the inner (zona reticularis) and outer (zona fasciculta plus glomerulosa) zones of the guinea pig adrenal cortex. In 35-day-old animals, cortisol production by adrenal outer zone cells was approximately twice as great as that by inner zone cells. With aging, cortisol secretion by inner zone cells decreased to very low levels, but there was no detectable change in the capacity for cortisol production by the outer zone. However, the outer zone comprised a progressively decreasing fraction of the total adrenal mass in older animals. To determine the basis for the decline in cortisol production by inner zone cells with aging, the activities of several steroidogenic enzymes were determined. Microsomal 21-hydroxylase activity was greater in the inner than outer zone but was not significantly affected by age. By contrast, 17-hydroxylase activity was greater in the outer zone at all ages, and decreased with aging in the inner but not the outer zone. Mitochondrial cholesterol sidechain cleavage and 11β-hydroxylase activities were also higher in the outer than inner zone and declined in the zone only in older animals. The decrease in inner zone cholesterol sidechain cleavage activity with aging was proportionately greater than the age-dependent changes in other enzyme activities. The results indicate that the effects of aging on steroidogenesis are both zone- and enzyme-specific. The overall decline in cortisol secretion by the guinea pig adrenal cortex with aging is attributable to both a decrease in cortisol production by the cells of the zone reticularis and a disproportionate increase in the mass of the gland comprised by this zone. The decrease in cortisol secretion correlates closely with a decline in cholesterol sidechain cleavage activity in the zona reticularis, and may be causally related. 相似文献
68.
A variety of procedures were used to immobilise D-2-haloacid dehalogenase. Natural polymer supports were insufficiently robust to withstand degradation by high concentrations of 2-chloropropionate. The best results were obtained with enzyme covalently attached to controlled-pore glass via a diazo linkage. The immobilisation procedure was optimised with respect to enzyme loading, pH, temperature and the presence of substrate during attachment. Immobilisation significantly modified the kinetics of the enzyme, in particular improving its temperature stability and ability to withstand mildly alkaline conditions where it is most active. The performance of the immobilised preparation in batch and plug-flow bioreactors was assessed. Biocatalyst half-life in plug-flow reactors was better than in batch bioreactors whereas effectiveness factors, although concentration dependent in the batch reactor, were similar at least with 200 mM D,L-2-CPA as substrate. 相似文献
69.
In the past year research in the oculomotor system has concentrated on some hitherto neglected areas, and also caused a re-evaluation of several long-standing concepts. Careful studies of the translational (otolith) vestibulo-ocular reflex and the torsional system have demonstrated their importance. A re-evaluation of the role of the superior colliculus in the generation of saccades has provided evidence for its participation in the feedback process. New studies of the interaction of eye movements and visual processing have shown that the brain can compensate for the visual effects of eye movements and maintain a retinotopic representation of visual space for the saccadic system. 相似文献