全文获取类型
收费全文 | 499篇 |
免费 | 56篇 |
国内免费 | 1篇 |
出版年
2022年 | 5篇 |
2021年 | 8篇 |
2018年 | 7篇 |
2017年 | 9篇 |
2016年 | 8篇 |
2015年 | 10篇 |
2014年 | 11篇 |
2013年 | 19篇 |
2012年 | 24篇 |
2011年 | 20篇 |
2010年 | 10篇 |
2009年 | 16篇 |
2008年 | 17篇 |
2007年 | 18篇 |
2006年 | 11篇 |
2005年 | 14篇 |
2004年 | 15篇 |
2003年 | 13篇 |
2002年 | 12篇 |
2001年 | 12篇 |
2000年 | 16篇 |
1999年 | 12篇 |
1998年 | 13篇 |
1997年 | 4篇 |
1996年 | 9篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 11篇 |
1991年 | 9篇 |
1990年 | 14篇 |
1989年 | 11篇 |
1988年 | 7篇 |
1987年 | 21篇 |
1986年 | 13篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 17篇 |
1978年 | 4篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1975年 | 6篇 |
1971年 | 4篇 |
1970年 | 4篇 |
1968年 | 3篇 |
1966年 | 5篇 |
排序方式: 共有556条查询结果,搜索用时 31 毫秒
41.
An emerging generalization from theoretical and empirical studies on conservation biology is that high levels of environmental stochasticity increase the likelihood of population extinction. However, coexistence theory has illustrated that there are circumstances under which environmental stochasticity can increase the chance of population persistence. These theoretical studies have shown that the sign of the effect of environmental stochasticity on population persistence is determined by interactions between life history and environmental stochasticity. These interactions mean that the stochastic and deterministic rates of population growth might differ fundamentally. Although difficult to demonstrate in real systems, observed life histories and variance in the vital rates of populations suggest that this phenomenon is likely to be common, and is therefore of much relevance to conservation biologists. 相似文献
42.
Wu S Beier M Sztein MB Galen J Pickett T Holder AA Gómez-Duarte OG Levine MM 《Journal of biotechnology》2000,83(1-2):125-135
One strategy to develop a multi-antigen malaria vaccine is to employ live vectors to carry putative protective Plasmodium falciparum antigens to the immune system. The 19 kDa carboxyl terminus of P. falciparum merozoite surface protein 1 (MSP-1), which is essential for erythrocyte invasion and is a leading antigen for inclusion in a multivalent malaria vaccine, was genetically fused to fragment C of tetanus toxin and expressed within attenuated Salmonella typhi CVD 908. Under conditions in the bacterial cytoplasm, the fragment C-MSP-1 fusion did not form the epidermal growth factor (EGF)-like domains of MSP-1; monoclonal antibodies failed to recognize these conformational domains in immunoblots of non-denatured protein extracted from live vector sonicates. The MSP-1 was nevertheless immunogenic. One month following intranasal immunization of BALB/c mice with the live vector construct, four out of five mice exhibited > or =four-fold rises in anti-MSP-1 by ELISA (GMT=211); a single intranasal booster raised titers further (GMT=1280). Post-immunization sera recognized native MSP-1 on merozoites as determined by indirect immunofluorescence. These data encourage efforts to optimize MSP-1 expression in S. typhi (e.g. as a secreted protein), so that the EGF-like epitopes, presumably necessary for stimulating protective antibodies, can form. 相似文献
43.
44.
Improved tests for heterogeneity across a region of DNA sequence in the ratio of polymorphism to divergence 总被引:15,自引:9,他引:6
The neutral theory of molecular evolution predicts that the ratio of
polymorphisms to fixed differences should be fairly uniform across a region
of DNA sequence. Significant heterogeneity in this ratio can indicate the
effects of balancing selection, selective sweeps, mildly deleterious
mutations, or background selection. Comparing an observed heterogeneity
statistic with simulations of the heterogeneity resulting from random
phylogenetic and sampling variation provides a test of the statistical
significance of the observed pattern. When simulated data sets containing
heterogeneity in the polymorphism-to-divergence ratio are examined,
different statistics are most powerful for detecting different patterns of
heterogeneity. The number of runs is most powerful for detecting patterns
containing several peaks of polymorphism; the Kolmogorov-Smirnov statistic
is most powerful for detecting patterns in which one end of the gene has
high polymorphism and the other end has low polymorphism; and a newly
developed statistic, the mean sliding G statistic, is most powerful for
detecting patterns containing one or two peaks of polymorphism with reduced
polymorphism on either side. Nine out of 27 genes from the Drosophila
melanogaster subgroup exhibit heterogeneity that is significant under at
least one of these three tests, with five of the nine remaining significant
after a correction for multiple comparisons, suggesting that detectable
evidence for the effects of some kind of selection is fairly common.
相似文献
45.
46.
47.
Antony M. Hooper Muniru K. Tsanuo Keith Chamberlain Kay Tittcomb Julie Scholes Ahmed Hassanali Zeyaur R. Khan John. A. Pickett 《Phytochemistry》2010,71(8-9):904-908
In East African small-holder farming of maize, the cattle forage legume, Desmodium uncinatum is used as an intercrop due to its allelopathic inhibition of parasitism by Striga hermonthica, an obligate parasitic weed that can devastate the maize crop. Bioassay-guided fractionation of the root extract of D. uncinatum revealed isoschaftoside to be the main compound in the most potent fraction inhibiting growth of germinated S. hermonthica radicles. Bioassays repeated with isoschaftoside isolated from a different plant source, Passiflora incarnata, proved it to be a biologically active component. Analysis of the root exudates produced by hydroponically grown D. uncinatum showed isoschaftoside to be present in the hydroponic media at biologically active concentrations of 10–100 nM. 相似文献
48.
49.
50.
Intracellular parasitism of chlamydiae: specific infectivity of chlamydiaphage Chp2 in Chlamydophila abortus
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Skilton RJ Cutcliffe LT Pickett MA Lambden PR Fane BA Clarke IN 《Journal of bacteriology》2007,189(13):4957-4959
The obligate intracellular nature of chlamydiae presents challenges to the characterization of its phages, which are potential tools for a genetic transfer system. An assay for phage infectivity is described, and the infectious properties of phage Chp2 were determined. 相似文献