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   536篇
  免费   38篇
  2024年   1篇
  2023年   2篇
  2022年   1篇
  2021年   7篇
  2020年   14篇
  2019年   7篇
  2018年   16篇
  2017年   16篇
  2016年   14篇
  2015年   20篇
  2014年   16篇
  2013年   43篇
  2012年   16篇
  2011年   23篇
  2010年   14篇
  2009年   27篇
  2008年   48篇
  2007年   33篇
  2006年   28篇
  2005年   25篇
  2004年   33篇
  2003年   13篇
  2002年   29篇
  2001年   18篇
  2000年   16篇
  1999年   7篇
  1998年   11篇
  1997年   8篇
  1996年   11篇
  1995年   6篇
  1994年   3篇
  1993年   7篇
  1992年   4篇
  1991年   2篇
  1990年   4篇
  1989年   5篇
  1988年   5篇
  1987年   5篇
  1986年   1篇
  1985年   4篇
  1984年   1篇
  1982年   3篇
  1981年   1篇
  1980年   1篇
  1977年   1篇
  1976年   2篇
  1974年   1篇
  1973年   1篇
排序方式: 共有574条查询结果,搜索用时 859 毫秒
501.
502.
503.
504.
The octadecanoid pathway is responsible for producing jasmonic acid an important signaling molecule in plants, which controls the production of a variety of secondary metabolites. Previously the exogenous addition of jasmonic acid to Catharanthus roseus hairy roots caused an increase in terpenoid indole alkaloid (TIA) accumulation. The role of the endogenous production of jasmonic acid by the octadecanoid pathway in the production of TIAs in C. roseus hairy roots is examined. Feeding of octadecanoid pathway inhibitors suggests that the octadecanoid pathway does not actively control TIA production under normal growth conditions or during the UV‐B stress response in C. roseus hairy roots. Biotechnol. Bioeng. 2009;103: 1248–1254. © 2009 Wiley Periodicals, Inc.  相似文献   
505.
The breeding biology of the endemic Coquerel’s Coua (Coua coquereli), a non-parasitic cuckoo species for which few ecological data are available, was studied in the dry deciduous forest of western Madagascar. Nestling C. coquereli remain in the nest for only a short time after hatching. At approximately 9 days old and still unable to fly, they were observed to leave the nest and then remained on the ground where they were fed by both parents. This behaviour is probably a strategy used to reduce nestling predation.  相似文献   
506.
In this study, we use deterministic and stochastic models to analyze the demography of Verreaux’s sifaka (Propithecus verreauxi verreauxi) in a fluctuating rainfall environment. The model is based on 16 years of data from Beza Mahafaly Special Reserve, southwest Madagascar. The parameters in the stage-classified life cycle were estimated using mark-recapture methods. Statistical models were evaluated using information-theoretic techniques and multi-model inference. The highest ranking model is time-invariant, but the averaged model includes rainfall-dependence of survival and breeding. We used a time-series model of rainfall to construct a stochastic demographic model. The time-invariant model and the stochastic model give a population growth rate of about 0.98. Bootstrap confidence intervals on the growth rates, both deterministic and stochastic, include 1. Growth rates are most elastic to changes in adult survival. Many demographic statistics show a nonlinear response to annual rainfall but are depressed when annual rainfall is low, or the variance in annual rainfall is high. Perturbation analyses from both the time-invariant and stochastic models indicate that recruitment and survival of older females are key determinants of population growth rate.  相似文献   
507.
Mantella bernhardi is an endemic species of Malagasy poison frog threatened by loss and fragmentation of its natural habitat and collection for the pet trade. It is classified as threatened according to the International Union for Conservation of Nature and Natural Resources (IUCN) categories and included in Appendix II of the Convention on the International Trade of Endangered Species (CITES). A recent survey has increased the known distributional range of the species from one to eight populations across southeastern Madagascar, but little is known about its biology and genetic diversity. Here we estimate inter- and intrapopulation mitochondrial genetic variation of four populations. Populations from the northern and southern parts of the distributional range showed a high degree of divergence (maximum of 11.35% in cytochrome b) and were recovered as reciprocally monophyletic groups. Nine haplotypes were detected in the northern and 12 in the southern populations. The population from Ranomafana National Park showed the lowest number of haplotypes and nucleotide diversity, and shared its most common haplotype with the second northern population from Tolongoina. All the other detected haplotypes were unique to each of the four populations. This suggests the existence of important barriers to gene flow, pre-dating human colonization of Madagascar at about 2000 years ago, in distinct contrast to other Mantella species that show a high degree of haplotype sharing throughout their range. The continued habitat fragmentation within the distribution range of M. bernhardi prevents any connection between its populations. Our data indicate the existence of at least two different management units for conservation in this species, corresponding to the North and South of its distribution range, and highlight the existence of strong regional endemism in southeastern Madagascar.  相似文献   
508.
We review aspects of the distributional patterns of Malagasy scorpions belonging to the endemic genus Pseudouroplectes (family Buthidae), restricted to dry forests formations in the south and southwest. One species is described here as new to science. We propose that the observed distributional pattern of members of this genus is not only a consequence of recent ecological features of the landscape, but also of historical biogeographical factors associated with the antiquity of this scorpion lineage.  相似文献   
509.
I studied the foraging ecology of Coquerel's Coua (Coua coquereli) and Giant Coua (Coua gigas), which occur in the dry forest in west Madagascar. This kind of forest is characterised by an alternating of a dry and a rainy season. The foraging behaviour was described in several dimensions: i.e. height and proportion of perching, rate of capture (estimating the food availability), foraging techniques, substrates used, type and size of the captured prey. Their foraging behaviour was different according to the season and to the proximity of water. Habitat structure was important to take in consideration to study their foraging behaviour. They tended to use the same pattern of techniques and substrates, but differed by the proportions they used these variables and also by the possibility to climb into the dense understorey vegetation. Seasonal variation has probably an important effect on the prey availability and the nature of prey captured. The diet of both species is also discussed. I suggest that change in habitat structure and resources levels could be important to take in consideration for the conservation of these forest birds.  相似文献   
510.
The Verreaux's sifaka (Propithecus verreauxi) is one of the species of Propithecus, living in the dry forest of southwest Madagascar. This species is endangered due to the loss and fragmentation of its natural habitat, a consequence of deforestation. Thirteen novel nuclear microsatellite loci were isolated and characterized in three populations of Verreaux's sifaka. The marker suite proved informative with an average of 8.9 alleles per locus and observed heterozygosity across the three populations of 0.675.  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