全文获取类型
收费全文 | 150篇 |
免费 | 2篇 |
国内免费 | 36篇 |
出版年
2016年 | 2篇 |
2015年 | 2篇 |
2014年 | 3篇 |
2013年 | 6篇 |
2012年 | 5篇 |
2011年 | 3篇 |
2010年 | 2篇 |
2009年 | 5篇 |
2007年 | 8篇 |
2006年 | 3篇 |
2004年 | 2篇 |
2003年 | 4篇 |
2002年 | 2篇 |
2001年 | 6篇 |
2000年 | 10篇 |
1999年 | 2篇 |
1996年 | 2篇 |
1994年 | 2篇 |
1993年 | 5篇 |
1991年 | 7篇 |
1990年 | 4篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 9篇 |
1983年 | 6篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 7篇 |
1976年 | 4篇 |
1975年 | 7篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1971年 | 4篇 |
1969年 | 2篇 |
1966年 | 1篇 |
1965年 | 4篇 |
1964年 | 2篇 |
1963年 | 1篇 |
1960年 | 1篇 |
1959年 | 1篇 |
1958年 | 2篇 |
1957年 | 3篇 |
1956年 | 1篇 |
1955年 | 2篇 |
1954年 | 3篇 |
1953年 | 2篇 |
排序方式: 共有188条查询结果,搜索用时 15 毫秒
1.
ASPECTS OF TRANSLOCATION OF CARBON IN THE TULIP 总被引:3,自引:2,他引:1
2.
本文对副华枝樇属Parasinophasma Chen et He进行了分类研究, 其中包括3新种--斑副华枝樇Parasinophasma maculatum sp. nov., 天目山副华枝樇Parasinophasma tianmushanense sp. nov.和单色副华枝樇Parasinophasma unicolor sp. nov.樇 新种模式标本保存于中国科学院动物研究所、上海昆虫博物馆、上海师范大学和香港昆虫学会。 相似文献
3.
1. In ant–hemipteran mutualisms, ants receive carbohydrates in the form of honeydew, while hemipterans receive protection from natural enemies. In the absence of natural enemies, however, the direct effects of tending are generally less well known. We hypothesised that with increasing tending intensity (ant to aphid ratio), aphid performance would increase initially, then decrease at high tending levels due to the metabolic cost of producing high quality honeydew. 2. We tested our hypothesis in a greenhouse experiment by manipulating Argentine ant (Linepithema humile Mayr) colony size while holding constant the initial size of aphid (Chaitophorus populicola Thomas) aggregations. The two parameters associated with survival, aphid survivorship to maturity and longevity, declined with increasing tending intensity, whereas per capita birth rate and time to first reproduction showed no relationship to attendance. The intrinsic rate of increase declined only at relatively high tending levels, suggesting a nonlinearity in the effect of tending intensity. 3. Tending intensity measured in the experiment was similar to that observed in free‐living aggregations of C. populicola. Furthermore, the per capita recruitment rate of ants to free‐living aphid aggregations was negatively density‐dependent, indicating that small aggregations tend to experience the highest levels of tending intensity. This finding suggests that the aphid's intrinsic rate of increase may be positively density‐dependent, mediated by the aphid's mutualistic interaction with the ant. 4. In the Argentine ant–C. populicola interaction, experimental manipulation of colony size revealed a direct cost of ant attendance that was conditional upon tending intensity. Experiments that manipulate only ant presence or absence may yield an incomplete understanding of the mutualistic interaction if underlying nonlinearities exist. 相似文献
4.
Changes in vegetative growing seasons are dominant indicators of the dynamic response of ecosystems to climate change. Therefore, knowledge of growing seasons over the past decades is essential to predict ecosystem changes. In this study, the long‐term changes in the growing seasons of temperate vegetation over the Northern Hemisphere were examined by analyzing satellite‐measured normalized difference vegetation index and reanalysis temperature during 1982–2008. Results showed that the length of the growing season (LOS) increased over the analysis period; however, the role of changes at the start of the growing season (SOS) and at the end of the growing season (EOS) differed depending on the time period. On a hemispheric scale, SOS advanced by 5.2 days in the early period (1982–1999) but advanced by only 0.2 days in the later period (2000–2008). EOS was delayed by 4.3 days in the early period, and it was further delayed by another 2.3 days in the later period. The difference between SOS and EOS in the later period was due to less warming during the preseason (January–April) before SOS compared with the magnitude of warming in the preseason (June–September) before EOS. At a regional scale, delayed EOS in later periods was shown. In North America, EOS was delayed by 8.1 days in the early period and delayed by another 1.3 days in the later period. In Europe, the delayed EOS by 8.2 days was more significant than the advanced SOS by 3.2 days in the later period. However, in East Asia, the overall increase in LOS during the early period was weakened in the later period. Admitting regional heterogeneity, changes in hemispheric features suggest that the longer‐lasting vegetation growth in recent decades can be attributed to extended leaf senescence in autumn rather than earlier spring leaf‐out. 相似文献
5.
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
6.
海南椰心叶甲病原菌金龟子绿僵菌的分离、鉴定及其生防潜力 总被引:3,自引:0,他引:3
椰心叶甲[Brontispa longissima(Gestro)]是椰子的重要害虫,近年来,该虫在海南岛发生普遍,椰子受害严重。由于椰心叶甲受到自然界中某些致病微生物的侵袭,在受害的椰子树心叶上常可发现椰心叶甲僵虫,并发现大部分僵虫表面长出了霉菌,本研究的目的在于从椰心叶甲僵虫表面的霉菌中分离出绿僵菌,并对分离菌株进行鉴定和致病性测定。从僵虫表面刮下孢子或菌丝体,置于绿僵菌选择性培养基(DOA)上培养,挑出真菌菌落,经纯化后,进行生物学特性、菌落生长速率及产孢量的测定,并从PPDA、OMA、VSA和PDA中筛选菌落生长及产孢最适培养基,同时对所分离的菌株进行对椰心叶甲的致病性测定。结果表明,所有分离菌株均鉴定为金龟子绿僵菌[Metarhizium anisopliae(Metschnikoff)],PPDA是菌落生长及产孢的最适培养基,大多数菌株对椰心叶甲有较强的致病力。选取强毒菌株MA4在田间进行防治效果的初步测定,结果表明,该菌株能显著降低椰心叶甲成虫的虫口密度。这些金龟子绿僵菌菌株是首次从海南的椰心叶甲僵虫中分离到的昆虫病原真菌,该菌对海南的椰心叶甲具有很好的生防潜能。 相似文献
7.
8.
9.
JIANQUAN LIU SHANGWU LIU TINGNONG HO ANMIN LU 《Botanical journal of the Linnean Society. Linnean Society of London》2001,135(2):107-112
Twenty-two populations of seven species of Cremanthodium from high altitude regions of western China were observed karyologically. C. ellisii, C. microglossum, C. brunneo-pilosum, C. stenoglossum, C. discoideum and C. lineare all had the same chromosome number of 2 n = 58 whereas C. humile had 2 n = 60. All chromosome numbers of these species are documented here for the first time. The basic number of x = 30 is new for this genus. The karyotypes of all species belong to 2A type according to Stebbins' asymmetry classification of karyotypes. Two basic chromosome numbers, x = 30 and x = 29 in Cremanthodium , correspond exactly to two branching patterns in this genus, sympodial versus monopodial. The systematic and taxonomic statuses of the sympodial species need further study. The karyomorphological data provide no support to the sectional subdivision in Cremanthodium . 相似文献
10.
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