全文获取类型
收费全文 | 570篇 |
免费 | 31篇 |
国内免费 | 12篇 |
出版年
2014年 | 5篇 |
2013年 | 16篇 |
2012年 | 12篇 |
2011年 | 22篇 |
2010年 | 30篇 |
2009年 | 39篇 |
2008年 | 18篇 |
2007年 | 26篇 |
2006年 | 14篇 |
2005年 | 15篇 |
2004年 | 10篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 9篇 |
1997年 | 17篇 |
1996年 | 16篇 |
1995年 | 13篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 13篇 |
1990年 | 15篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 12篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1983年 | 6篇 |
1981年 | 4篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1974年 | 4篇 |
1973年 | 11篇 |
1972年 | 9篇 |
1971年 | 9篇 |
1968年 | 4篇 |
1959年 | 15篇 |
1958年 | 25篇 |
1957年 | 12篇 |
1956年 | 17篇 |
1955年 | 12篇 |
1954年 | 7篇 |
1953年 | 5篇 |
1952年 | 8篇 |
1951年 | 10篇 |
1950年 | 14篇 |
1949年 | 10篇 |
1948年 | 9篇 |
排序方式: 共有613条查询结果,搜索用时 93 毫秒
51.
52.
53.
54.
55.
56.
Multiple determinants influence root colonization and induction of induced systemic resistance by Pseudomonas chlororaphis O6 总被引:1,自引:0,他引:1
SONG HEE HAN ANNE J. ANDERSON KWANG YEOL YANG BAIK HO CHO KIL YONG KIM MYUNG CHUL LEE YONG HWAN KIM YOUNG CHEOL KIM 《Molecular Plant Pathology》2006,7(6):463-472
Colonization of the roots of tobacco by Pseudomonas chlororaphis O6 induces systemic resistance to the soft-rot pathogen, Erwinia carotovora ssp. carotovara SCC1. A screen of the transposon mutants of P. chlororaphis O6 showed mutants with about a fivefold reduction in ability to induce systemic resistance to the soft-rot disease. These mutations disrupted genes involved in diverse functions: a methyl-accepting chemotaxis protein, biosynthesis of purines, phospholipase C, transport of branched-chain amino acids and an ABC transporter. Additional mutations were detected in the intergenic spacer regions between genes encoding a GGDEF protein and fumarate dehydratase, and in genes of unknown function. The mutants in the ABC transporters did not display reduced root colonization. However, the other mutants had up to 100-fold reduced colonization levels. Generally the production of metabolites important for interactions in the rhizosphere, phenazines and siderophores, was not altered by the mutations. A reduced induction of systemic resistance by a purine biosynthesis mutant with a disrupted purM gene correlated with poor growth rate, lesser production of phenazines and siderophore and low levels of root colonization. These studies showed that multiple determinants are involved in the induction of systemic resistance, with there being a requirement for strong root colonization. 相似文献
57.
58.
SIRPA KAUNISTO PANU VÄLIMÄKI RAINE KORTET JANI KOSKIMÄKI SAULI HÄRKÖNEN ARJA KAITALA SAULI LAAKSONEN LAURA HÄRKÖNEN HANNU YLÖNEN 《Biological journal of the Linnean Society. Linnean Society of London》2012,106(2):275-286
The deer ked (Lipoptena cervi) is an ectoparasitic fly on cervids that has expanded its distribution rapidly in Northern Europe. However, the regulating biotic factors such as predation remain unknown. The host‐independent pupal stage of the fly lasts for several months. Blackish pupae are visible against snow, especially on the bedding sites of hosts, and are thus exposed to predators. To evaluate the role of predation on the invasion dynamics and evolution of L. cervi, we monitored pupal predation on artificial bedding sites in three geographical areas in Finland during winter. We explored: (1) possible predators; (2) magnitude of predation; and (3) whether predation risk is affected by host‐derived cues. We demonstrate that pupae are predated by a number of tit species. Any reddish brown snow discoloration on bedding sites, indicating heavy infestation of the host, serves as an exploitable cue for avian predators, thereby increasing the risk of pupal predation. The ability of tits to use this host‐derived cue seems to be dependent on the prevalence of L. cervi and the period of invasion history, which suggests that it may be a learned behavioural response. Predation by tits may potentially affect the L. cervi population dynamics locally. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 275–286. 相似文献
59.
MATTEO CAZZANELLI LAURA FORSSTRÖM MILLA RAUTIO ANDERS MICHELSEN KIRSTEN S. CHRISTOFFERSEN 《Freshwater Biology》2012,57(3):541-551
1. Shallow arctic lakes and ponds have simple and short food webs, but large uncertainties remain about benthic–pelagic links in these systems. We tested whether organic matter of benthic origin supports zooplankton biomass in a pond in NE Greenland, using stable isotope analysis of carbon and nitrogen in the pond itself and in a 13C‐enrichment enclosure experiment. In the latter, we manipulated the carbon isotope signature of benthic algae to enhance its isotopic discrimination from other potential food sources for zooplankton. 2. The cladoceran Daphnia middendorffiana responded to the 13C‐enrichment of benthic mats with progressively increasing δ13C values, suggesting benthic feeding. Stable isotope analysis also pointed towards a negligible contribution of terrestrial carbon to the diet of D. middendorffiana. This agreed with the apparent dominance of autochthonous dissolved organic matter in the pond revealed by analysis of coloured dissolved organic matter. 3. Daily net production by phytoplankton in the pond (18 mg C m?2 day?1) could satisfy only up to half of the calculated minimum energy requirements of D. middendorffiana (35 mg C m?2 day?1), whereas benthic primary production alone (145 mg C m?2 day?1) was more than sufficient. 4. Our findings highlight benthic primary production as a major dietary source for D. middendorffiana in this system and suggest that benthic organic matter may play a key role in sustaining pelagic secondary production in such nutrient‐limited high arctic ponds. 相似文献
60.
DONG‐SEOK KIM SOOK‐YOUNG KIM SEONG‐JOON MOON JIN‐HO CHUNG KYU‐HAN KIM KWANG‐HYUN CHO KYOUNG‐CHAN PARK 《Pigment cell & melanoma research》2001,14(2):110-115
Ceramide is a bioactive sphingolipid that mediates a variety of cell functions. However, the effects of ceramide on cell growth and the melanogenesis of melanocytes are not known. In the present study, we investigated the actions of cell‐permeable ceramide and its possible role in the signaling pathway of a spontaneously immortalized mouse melanocyte cell line, Mel‐Ab. Our results show that C2‐ceramide inhibits DNA synthesis in Mel‐Ab cells and G361 human melanoma cells in a dose‐dependent manner. Cell cycle analysis confirmed the inhibition of DNA synthesis by a reduction in the S phase. To investigate the ceramide signaling pathway, we studied whether C2‐ceramide is able to influence extracellular signal‐regulated kinase (ERK) and/or Akt/protein kinase B (PKB) activation. We demonstrated that phosphorylated Akt/PKB is decreased by C2‐ceramide, whereas phosphorylated ERK was only slightly affected. Therefore, the C2‐ceramide‐induced inactivation of Akt/PKB may be closely related to the reduced cell proliferation of Mel‐Ab cells. Furthermore, we assessed the effects of C2‐ceramide on the pigmentation of Mel‐Ab cells. The results obtained showed that the melanin content of cells was significantly reduced by C2‐ceramide at concentrations in the range of 1–10 μM, and that the pigmentation‐inhibiting effect of C2‐ceramide is much greater than that of kojic acid at 1–100 μM. In addition, we found that the activity of tyrosinase is reduced by C2‐ceramide treatment. Our results demonstrate that C2‐ceramide reduces the pigmentation of Mel‐Ab cells by inhibiting tyrosinase activity. 相似文献