全文获取类型
收费全文 | 156篇 |
免费 | 4篇 |
专业分类
160篇 |
出版年
2017年 | 1篇 |
2016年 | 1篇 |
2015年 | 2篇 |
2014年 | 2篇 |
2013年 | 6篇 |
2012年 | 7篇 |
2011年 | 9篇 |
2010年 | 7篇 |
2009年 | 15篇 |
2008年 | 12篇 |
2007年 | 10篇 |
2006年 | 10篇 |
2005年 | 6篇 |
2004年 | 1篇 |
2003年 | 2篇 |
2002年 | 2篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 6篇 |
1998年 | 1篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1973年 | 3篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1956年 | 1篇 |
1952年 | 1篇 |
排序方式: 共有160条查询结果,搜索用时 15 毫秒
1.
2.
FERNANDO DINI PAOLO BRACCHI ALESSANDRO GIANNÍ 《The Journal of eukaryotic microbiology》1987,34(2):236-243
A mating-type analysis was performed on 78 stocks of the marine hypotrich ciliate, Aspidisca sp., from a sufficient number of diverse geographic locations, some widely separated. Evidence is provided for the existence of a binary mating system in this "morphospecies." The collected stocks have been challenged by the most rigorous criterion, namely breeding affinity in the laboratory, and have yielded at least four reproductively, not necessarily geographically, isolated groups that are in fact "biological species," here referred to as "syngens." Different syngens contain different pairs of mating types. Syngens are morphologically indistinguishable; hence Aspidisca sp. can be considered a conservative taxon comprising a number of "cryptic" or "sibling species." Information is also presented about the mating behavior and the pattern of nuclear events at conjugation in Aspidisca sp. Search for soluble pheromones of the mating types gave only negative results. Hence, direct contact with potential partners is postulated to play a critical role in preparing individuals to mate. Mating reaction and mating which actually involves cross-fertilization (conjugation, sensu stricto) are completely inhibited by 10 μg/ml cycloheximide, suggesting the necessity of protein synthesis for recognition and union in conjugation of potential partners. 相似文献
3.
Dihydroxybenzoic acids (DBA), such as 3,4-DRA, 3,5-DBA, and 2,4-DBA—at all concentrations tested—inhibited the rate of DL-DOPA oxidation to dopachrome (λmax = 475 nm) by mushroom tyrosinase. 2,3-DBA and 2,5-DBA at relatively low concentration had a synergistic effect on the reaction, whereas at relatively high concentrations they inhibited the rate of DL-DOPA oxidation. The synergistic effect of 0.6-13.3 mM 2,3-DRA on the rate of DL-DOPA oxidation to dopachrome (λmax = 475 nm) was found to be due to the ability of 2,3-DBA-o-quinone (formed by the oxidation of 2,3-DBA by mushroom tyrosinase or by sodium periodate) to oxidize DL-DOPA to dopachrome (via dopaquinone) non-enzymatically. A similar explanation is likely to be valid for the synergism exerted by 2,5-DBA on the rate of DL-DOPA oxidation by mushroom tyrosinase. 相似文献
4.
1.Certain bacteria which are normally termed saprophytic, viz.Bacillus subtilis and B. megatherium, are able to parasitizeliving potato tissue at a suitably high temperature or whenthe tissue is injected with water. 2.Within the group of four bacteria tested, there is a correlationbetween capacity to attack potato tissue and amount of pectinaseenzyme excreted under standard conditions. 3.A qualitative difference between the pectinase enzymes ofBotrytis cinerea and Bacterium carotovorum has been demonstrated.Preparations of the bacterial enzyme, which when tested on turgidpotato discs of standard thickness were found to be weaker thanBotrytis enzyme, were able to attack normal (subturgid) potatotissue, whereas the Botrytis enzyme failed to do so. No explanationof this difference is yet forthcoming. It does not seem to restupon osmotic differences between the two enzymic preparations. 4.Rate of diffusion appears .to be a limiting factor in theattack of potato tissue by preparations of pectinase enzyme. 相似文献
5.
C. HOWARD C. BRUNTON FERNANDO ALVAREZ 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1989,22(3):247-250
Brunton, C. Howard C. & Alvarez, Fernando 1989 07 15: The relationship between major lamellae and epithelial regressions in some articulate brachiopods. Lethaia , Vol. 22, pp. 247–250. Oslo. ISSN 0024–1164.
Hiller (1988, Lethaia , Vol. 212) proposed three relationships between the secretory epithelium of articulate brachiopods and the shell surface ornamentations of growth lines, lamellae and spines. None of his models satisfy the growth of strongly lamellose athyrid shells and we propose a fourth involving strong regressions effecting both primary and secondary shell layers. In Recent Tegulorhynchia we suggest a growth function for the 'frayed' shell of Hiller occurring immediately in front of the spines. 相似文献
Hiller (1988, Lethaia , Vol. 212) proposed three relationships between the secretory epithelium of articulate brachiopods and the shell surface ornamentations of growth lines, lamellae and spines. None of his models satisfy the growth of strongly lamellose athyrid shells and we propose a fourth involving strong regressions effecting both primary and secondary shell layers. In Recent Tegulorhynchia we suggest a growth function for the 'frayed' shell of Hiller occurring immediately in front of the spines. 相似文献
6.
7.
FERNANDO CESAR CASCELLI DE AZEVEDO DENNIS L. MURRAY 《The Journal of wildlife management》2007,71(7):2379-2386
ABSTRACT Depredation of livestock by large carnivores is an important but poorly understood source of human-carnivore conflict. We examined patterns of livestock depredation by jaguars (Panthera onca) and pumas (Puma concolor) on a ranch-wildlife reserve in western Brazil to assess factors contributing to prey mortality. We predicted jaguars would kill a greater proportion of calves than yearling and adult cattle and that proximity to suitable habitat would increase mortality risk. We further speculated that exposure to predation risk would promote livestock grouping and increased movement distance. We recorded 169 cattle mortality incidents during 2003–2004, of which 19% were due to predation by jaguars and pumas. This level of mortality represented 0.2–0.3% of the total livestock holdings on the ranch. Jaguars caused most (69%) cattle predation events, and survival in allotments was lower for calves than for other age classes. Forest proximity was the only variable we found to explain patterns of livestock mortality, with predation risk increasing as distance to forest cover declined. Due to low predation risk, cattle movement patterns and grouping behavior did not vary relative to level of spatial overlap with radiocollared jaguars. The overall effect of predation on cattle was low and livestock likely constituted an alternative prey for large cats in our study area. However, selection of calves over other age cohorts and higher predation risk among cattle in proximity to forest cover is suggestive of selection of substandard individuals. Cattle ranchers in the Pantanal region may reduce cattle mortality rates by concentrating on losses due to nonpredation causes that could be more easily controlled. 相似文献
8.
9.
FERNANDO P. RODRIGUES FLVIA S. ROCHA JOS E. GARCIA JOS F. GARCIA MARIO DE VIVO SERGIO R. MATIOLI 《Molecular ecology resources》2006,6(3):686-688
Five microsatellite loci were isolated and characterized within the woolly mouse opossum (Micoureus paraguayanus), a Neotropical marsupial, using an enrichment cloning procedure. Between four and seven alleles were detected per locus, with expected heterozygosity ranging from 0.358 to 0.560. These microsatellites should provide useful markers in a variety of genetic analyses to examine parentage, inbreeding, population structure and population dynamics in fragmented forest habitats. 相似文献
10.
Light requirements and functional strategies of plants to cope with light heterogeneity in the field have a strong influence on community structure and dynamics. Shade intolerant plants often show a shade avoidance strategy involving a phytochrome‐mediated stem elongation in response to changes in red : far red ratio, while shade‐tolerant plants typically harvest light very efficiently. We measured plant size, stem diameter, internode and leaf lengths in randomly chosen saplings of 11 woody species differing in their shade tolerance in both a secondary forest and an old‐growth temperate evergreen rainforest in southern Chile. We also recorded the irradiance spectrum and the diffuse and direct light availabilities at each sampling point. Significant differences were found for the mean light environment of the saplings of each species, which also differed in basal stem diameter, internode length and leaf length, but not in plant height. Both plant slenderness (plant height/stem diameter) and mean internode length increased with increasing light availability, but no relationship was found between any of these two traits and red : far red ratio. The change in plant slenderness with light availability was of lesser magnitude with increasing shade tolerance of the species, while internode change with light availability increased with increasing shade tolerance of the species. Shade tolerators afford higher costs (thicker stems and plants), which render more biomechanically robust plants, and respond more to the light environment in a trait strongly influencing light interception (internode length) than shade intolerant species. By contrast, less shade‐tolerant plants afforded higher risks with a plastic response to escape from the understorey by making thinner plants that were biomechanically weaker and poorer light interceptors. Thus, species differing in their shade tolerances do differ in their plastic responses to light. Our results contribute to explain plant coexistence in heterogeneous light environments by improving our mechanistic understanding of species responses to light. 相似文献