首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   449篇
  免费   24篇
  473篇
  2023年   4篇
  2022年   2篇
  2021年   14篇
  2020年   3篇
  2019年   3篇
  2018年   4篇
  2017年   6篇
  2016年   7篇
  2015年   8篇
  2014年   17篇
  2013年   157篇
  2012年   23篇
  2011年   21篇
  2010年   13篇
  2009年   15篇
  2008年   13篇
  2007年   13篇
  2006年   8篇
  2005年   17篇
  2004年   15篇
  2003年   18篇
  2002年   11篇
  2001年   4篇
  2000年   7篇
  1999年   4篇
  1998年   4篇
  1996年   2篇
  1994年   5篇
  1993年   5篇
  1992年   2篇
  1991年   1篇
  1990年   5篇
  1989年   6篇
  1988年   1篇
  1986年   2篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
  1982年   4篇
  1981年   3篇
  1980年   2篇
  1979年   1篇
  1978年   4篇
  1977年   4篇
  1976年   1篇
  1975年   1篇
  1974年   1篇
  1972年   1篇
  1971年   2篇
  1969年   3篇
排序方式: 共有473条查询结果,搜索用时 0 毫秒
81.
82.
The primary goal of the 60th anniversary symposium of the Ecological Society of Japan (ESJ) was to re-examine the role of the Society. The first of five lectures, “Development of Long-term Ecological Research in Japan,” discussed the increasingly important role of long-term and networked research studies. Ecological research in Asia faces many challenges, because Asia features natural and anthropogenic landscapes with highly diverse ecosystems. “Developing Strategies of the Ecological Society of Japan for Worldwide Societies of Ecology with Special Reference to Strategies for Asia” emphasized the role of ESJ in promoting ecological research and outreach in Asia. Ecosystem sustainability is a key issue in both the theory and practice of ecosystem management. A framework concept of an environmental and biodiversity cycle was proposed in the session “Linking Community and Ecosystem Dynamics” for understanding the mechanisms driving the sustainability of ecosystems. Ecosystem services are essential aspects of land use and conservation planning and management. “Integrating Models of Ecosystem Services and Land Use Changes” reviewed recently-developed models that simulate patterns of land-use change and analyze its effects on ecosystem services and also recommended future directions for collaboration among researchers. “Disaster Resilience and Coastal Ecology” highlighted the contributions of ecologists to evaluating the resilience of damaged coastal ecosystems and provided sound proposals to local communities and governments for rehabilitation plans. The past achievements and future directions of ESJ were discussed by the panelists and the audience in “Past and Future of the Ecological Society of Japan.”  相似文献   
83.
Isohibalactone, the geometric isomer of hibalactone, was synthesized by the following route. Piperonylsuccinic acid anhydride was converted into thioethyl methyl ester ans was reduced to piperonylbutyrolactone by Raney nickel catalyst. Piperonylbutyrolactone was also prepared from piperonylsuccinic anhydride by the reduction with amalgamated aluminum. Condensation of piperdnal with the lactone in the presence of potassium amide afforded α-(3,4-methyIenedioxy-phenyl-hydroxymethyl)-β-(3,4-methylenedioxybenzyl)-butyrolactone, m.p. 151~2°C. Dehydration of the hydroxylactone with p-toluenesulfonic acid gave isohibalactone, m.p. 156~6.5°C.  相似文献   
84.
The synergistic action of phenolic lactones on allethrin and pyrethrin were investigated from the mortality of synergized pyrethroids against rice-weevil by petri-dish method.

In the series of α-benzylidene-γ-butyrolactones, (±) hibalactone and α-piperonylidenebutyrolactone were appreciably sy~ergistic on allethrin although less effective than piperonyl butoxide. (±) Hinokinin, 2-piperonylidene-3-piperonyl-l,4-butanediol also showed week activation, but α-benzylidene-, α-anisylidene-, α-veratrylidene-butyrolactone, α-piperonylidenea-α’-piperonyl-tetrahydrofuran, α-trirnethoxybenzylidene-β-trimethoxybenzyl-butyrolactone were not synergistic on the insecticidal action.

In the series of synergized pyrethrin, (±) hibalactone and α-piperonylidene-butyrolactone showed week synergism but the other test compounds showed no appreciable synergism.  相似文献   
85.
86.
Pschorr reaction of 4-[3-(3,4,5-trimethoxyphenyl)-propyl]-5-amino-tropolone (VII) gave desacetamidocolchiceine (IIa), though the oxidative coupling reaction of 4-[3-(3,4-dihydroxy- 5-methoxy phenyl)-propyl]-tropolone (Xa) failed to give the same compound (IIa).  相似文献   
87.
88.
Summary The deep-sea bioluminescent squid, Watasenia scintillans, has three visual pigments: The major one (A1 pigment) is based on retinal and has max = 484 nm, the second one (A2 pigment) is based on 3-dehydroretinal and has max = 500 nm, and the third one (A4 pigment) is based on 4-hydroxyretinal and has max = 470 nm. The distribution of these 3 visual pigments in the retina was studied by HPLC analysis of the retinals in retina slices obtained by microdissection. It was found that A1 pigment was not located in the specific region of the ventral retina receiving the down-welling light which contains very long photoreceptor cells, forming two strata. A2 and A4 pigment were found exclusively in the proximal pinkish stratum and in the distal yellowish stratum. The role of these pigments in the retina is hypothesized to involve spectral discrimination. The extraction and analysis of retinoids to determine the origin of 3-dehydroretinal and 4-hydroxyretinal in the mature squid showed only a trace amount of 4-hydroxyretinol in the eggs. Similar analysis of other cephalopods collected near Japan showed the absence of A2 or A4 pigment in their eyes.Abbreviations HPLC high-performance liquid chromatography - IS inner segment - OS outer segment  相似文献   
89.
Summary In vivo studies with galactokinase monitoring system demonstrated that the coliphage lambda PRPL promoter regions could be utilized in B. subtilis. These promoter regions were preferentially utilized during the stationary growth phase of B. subtilis. However, these promoter regions were not controlled by the cI857 gene at permissive or non-permissive temperature in B. subtilis, although the P RM promoter was utilized in B. subtilis. S1-nuclease mapping suggests that B. subtilis RNA polymerase recognizes specific sequences in P R promoter region that is not utilized in E. coli.  相似文献   
90.
Proton nuclear magnetic resonance (NMR) spectra have been recorded of various neurotoxins from snake venoms.pH dependence of the chemical shifts and resonance intensity has been followed for the functionally essential Trp-29. The indole N-1 proton of Trp-29 in -bungarotoxin, toxin B, and cobrotoxin exhibits appreciably large upfield shifts as thepH is lowered and the suppressed exchange with the solvent hydrogen atpH 3–4, but not inNaja haje annulifera 10 where Asp-31 is replaced with Gly-31. This observation strongly suggests the presence of a hydrogen bond between Trp-29 and Asp-31 that is probably important in stabilizing the arrangement of the functionally essential residues to form a distinct binding region for the receptor.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号