全文获取类型
收费全文 | 434篇 |
免费 | 19篇 |
专业分类
453篇 |
出版年
2023年 | 4篇 |
2022年 | 10篇 |
2021年 | 8篇 |
2020年 | 4篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 11篇 |
2015年 | 19篇 |
2014年 | 15篇 |
2013年 | 28篇 |
2012年 | 27篇 |
2011年 | 25篇 |
2010年 | 16篇 |
2009年 | 17篇 |
2008年 | 32篇 |
2007年 | 23篇 |
2006年 | 21篇 |
2005年 | 23篇 |
2004年 | 18篇 |
2003年 | 13篇 |
2002年 | 20篇 |
2001年 | 7篇 |
2000年 | 15篇 |
1999年 | 4篇 |
1998年 | 5篇 |
1997年 | 9篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1978年 | 2篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 2篇 |
1970年 | 1篇 |
1969年 | 2篇 |
1948年 | 1篇 |
排序方式: 共有453条查询结果,搜索用时 15 毫秒
11.
12.
Effects of Lactococcus lactis on Composition of Intestinal Microbiota: Role of Nisin 总被引:1,自引:0,他引:1 下载免费PDF全文
Nete Bernbom Tine Rask Licht Carl-Henrik Brogren Birthe Jelle Anette H. Johansen Iker Badiola Finn K. Vogensen Birgit Nrrung 《Applied microbiology》2006,72(1):239-244
This study examined the ability of (i) pure nisin, (ii) nisin-producing Lactococcus lactis strain CHCC5826, and (iii) the non-nisin-producing L. lactis strain CHCH2862 to affect the composition of the intestinal microbiota of human flora-associated rats. The presence of both the nisin-producing and the non-nisin-producing L. lactis strains significantly increased the number of Bifidobacterium cells in fecal samples during the first 8 days but decreased the number of enterococci/streptococci in duodenum, ileum, cecum, and colon samples as detected by selective cultivation. No significant changes in the rat fecal microbiota were observed after dosage with nisin. Pearson cluster analysis of denaturing gradient gel electrophoresis profiles of the 16S rRNA genes present in the fecal microbial population revealed that the microbiota of animals dosed with either of the two L. lactis strains were different from that of control animals dosed with saline. However, profiles of the microbiota from animals dosed with nisin did not differ from the controls. The concentrations of nisin estimated by competitive enzyme-linked immunosorbent assay (ELISA) were approximately 10-fold higher in the small intestine and 200-fold higher in feces than the corresponding concentrations estimated by a biological assay. This indicates that nisin was degraded or inactivated in the gastrointestinal tract, since fragments of this bacteriocin are detected by ELISA while an intact molecule is needed to retain biological activity. 相似文献
13.
Transformation of Leuconostoc carnosum 4010 and Evidence for Natural Competence of the Organism 下载免费PDF全文
Sren Helmark Mette E. Hansen Birthe Jelle Kim I. Srensen Peter R. Jensen 《Applied microbiology》2004,70(6):3695-3699
Plasmid transformation in Leuconostoc carnosum 4010 was analyzed. A successful transformation protocol for L. carnosum was established by modifying an existing protocol for Lactococcus lactis. Several parameters, including the number of generations that the cells had grown at the time of harvest, glycine concentration, the time of incubation for phenotypic expression, and the electrical field strength, were investigated and proved to have influence on the transformation frequency. Electrocompetence was found to be transient and to peak in the early exponential growth phase. Optimized conditions resulted in transformation frequencies of up to 6.7 × 105 transformants per microgram of plasmid DNA. A total of five plasmids in L. carnosum were successfully introduced and maintained. Interestingly, we discovered that DNA uptake was of a frequency of 3 × 10−6 to 19 × 10−6 transformants per CFU in the absence of an applied electrical field. We concluded that L. carnosum is naturally competent. 相似文献
14.
The peptide segment corresponding to helix A4 in acyl-coenzyme-A-binding protein (ACBP) is an exceptionally stable helix in the denatured state of the protein as well as in its isolated form. Circular dichroism spectroscopy showed an alpha-helix content in the helix A4 peptide (HA4) of 45%, and under denaturing conditions at pH 2.3, helix conformations are still populated in 24% of the ensemble of molecules. The structure of HA4 at atomic resolution was assessed using nuclear magnetic resonance (NMR) spectroscopy. Long-range NOEs between remote residues at opposite peptide ends suggested the formation of an antiparallel homodimer, and the resulting structure was treated as the minimum higher-order structure. The dimerization property of helix A4 is maintained in the full-length protein under denaturing conditions. NMR diffusion studies and concentration-dependent experiments on ACBP at low pH proved the formation of dimers and revealed a cooperative stabilization of helix A4 in this process. This emphasizes its special role in the structure formation in the denatured state of ACBP. No dimers are formed in the presence of guanidine hydrochloride, which underlines the fundamental difference between the nature of these two denatured states. 相似文献
15.
16.
Banaz-Yaşar F Steffen G Hauschild J Bongartz BM Schumann GG Ergün S 《Histochemistry and cell biology》2010,134(6):581-589
Long interspersed nuclear element-1 (LINE-1, L1) is a retrotransposon which affects the human genome by a variety of mechanisms.
While LINE-1 expression is suppressed in the most somatic human cells, LINE-1 elements are activated in human cancer. Recently,
high accumulation of LINE-1-encoded ORF1p and ORF2p in endothelial cells of mature human blood vessels was described. Here,
we demonstrate that LINE-1 de novo retrotransposition events lead to a reduction of endothelial cell proliferation and migration
in a porcine aortic endothelial (PAE) cell model. Cell cycle studies show a G0/G1 arrest in PAE cells harboring LINE-1 de
novo retrotransposition events. Remarkably, in in situ analysis LINE-1-encoded ORF2p was not detectable in tumor blood vessels
of different human organs while vascular endothelial cells of corresponding normal organs strongly expressed LINE-1 ORF2p.
Quantitative RT-PCR analysis revealed that LINE-1 de novo retrotransposition influences selectively the expression of some
angiogenic factors such as VEGF and Tie-2. Thus, our data suggest that LINE-1 de novo retrotransposition events might suppress
angiogenesis and tumor vascularisation by reducing the angiogenic capacity of vascular endothelial cells. 相似文献
17.
Elizabeth C. White Jean-Thoussaint Dikangadissi Edmond Dimoto William B. Karesh Michael D. Kock Nathacha Ona Abiaga Ruth Starkey Tharcisse Ukizintambara Lee J. T. White Katharine A. Abernethy 《International journal of primatology》2010,31(4):627-645
The predicted relationship between home-range size and group mass in primates developed by Clutton-Brock and Harvey (1977) has proved extremely robust in describing the use of space by most primate species. However, mandrills (Mandrillus sphinx) are now known to have an extreme group mass in the wild, far larger than that of the species used originally to generate
that relationship, and so it was unknown whether this relationship would be robust for this species. We investigated the home-range
size and use of a wild horde of ca. 700 mandrills in Lopé National Park, Gabon, using radiotelemetry. The total area the horde used over a 6-yr period [100%
minimum convex polygon (MCP)] was 182 km2, including 89 km2 of suitable forest habitat. Mandrills used gallery forests and isolated forest fragments with high botanical diversity far
more intensively that the continuous forest and completely avoided savanna and marsh. Peeled polygons and fixed kernel contours
revealed multiple centres of use, with the horde spending more than half its time in <10% of the total documented range, typical
of a frugivore using a patchy environment. Home-range size and internal structure varied considerably between years, but total
home range fitted the predicted relationship between group mass and home range size, despite being an outlier to the dataset.
We discuss the conservation implications of the species’ space requirements, in light of current pressures on land use in
their range. 相似文献
18.
Birthe Tegtmeyer Gabrielle Vieyres Daniel Todt Chris Lauber Corinne Ginkel Michael Engelmann Maike Herrmann Christian K. Pfaller Florian W. R. Vondran Ruth Broering Ehsan Vafadarnejad Antoine-Emmanuel Saliba Christina Puff Wolfgang Baumgrtner Csaba Miskey Zoltn Ivics Eike Steinmann Thomas Pietschmann Richard J. P. Brown 《Journal of virology》2021,95(10)
19.
Kenneth J. Ferguson Sarah Cleaveland Daniel Thomas Haydon Alexandre Caron Richard A. Kock Tiziana Lembo J. Grant C. Hopcraft Bertrand Chardonnet Thomas Nyariki Julius Keyyu David James Paton Fredrick Mathias Kivaria 《EcoHealth》2013,10(3):314-322
Strategies to control transboundary diseases have in the past generated unintended negative consequences for both the environment and local human populations. Integrating perspectives from across disciplines, including livestock, veterinary and conservation sectors, is necessary for identifying disease control strategies that optimise environmental goods and services at the wildlife-livestock interface. Prompted by the recent development of a global strategy for the control and elimination of foot-and-mouth disease (FMD), this paper seeks insight into the consequences of, and rational options for potential FMD control measures in relation to environmental, conservation and human poverty considerations in Africa. We suggest a more environmentally nuanced process of FMD control that safe-guards the integrity of wild populations and the ecosystem dynamics on which human livelihoods depend while simultaneously improving socio-economic conditions of rural people. In particular, we outline five major issues that need to be considered: 1) improved understanding of the different FMD viral strains and how they circulate between domestic and wildlife populations; 2) an appreciation for the economic value of wildlife for many African countries whose presence might preclude the country from ever achieving an FMD-free status; 3) exploring ways in which livestock production can be improved without compromising wildlife such as implementing commodity-based trading schemes; 4) introducing a participatory approach involving local farmers and the national veterinary services in the control of FMD; and 5) finally the possibility that transfrontier conservation might offer new hope of integrating decision-making at the wildlife-livestock interface. 相似文献
20.
Einar Osland Vik-Mo Marta Nyakas Birthe Viftrup Mikkelsen Morten Carstens Moe Paulina Due-Tønnesen Else Marit Inderberg Suso Stein Sæbøe-Larssen Cecilie Sandberg Jan E. Brinchmann Eirik Helseth Anne-Marie Rasmussen Knut Lote Steinar Aamdal Gustav Gaudernack Gunnar Kvalheim Iver A. Langmoen 《Cancer immunology, immunotherapy : CII》2013,62(9):1499-1509