全文获取类型
收费全文 | 2484篇 |
免费 | 76篇 |
国内免费 | 13篇 |
专业分类
2573篇 |
出版年
2015年 | 15篇 |
2013年 | 54篇 |
2012年 | 59篇 |
2011年 | 49篇 |
2010年 | 66篇 |
2009年 | 109篇 |
2008年 | 84篇 |
2007年 | 64篇 |
2006年 | 60篇 |
2005年 | 55篇 |
2004年 | 52篇 |
2003年 | 26篇 |
2002年 | 16篇 |
2001年 | 14篇 |
2000年 | 16篇 |
1999年 | 27篇 |
1998年 | 36篇 |
1997年 | 41篇 |
1996年 | 36篇 |
1995年 | 27篇 |
1994年 | 24篇 |
1993年 | 19篇 |
1992年 | 34篇 |
1990年 | 24篇 |
1989年 | 23篇 |
1988年 | 18篇 |
1987年 | 22篇 |
1986年 | 20篇 |
1985年 | 21篇 |
1984年 | 14篇 |
1983年 | 18篇 |
1981年 | 21篇 |
1980年 | 14篇 |
1979年 | 22篇 |
1978年 | 14篇 |
1977年 | 15篇 |
1972年 | 13篇 |
1971年 | 16篇 |
1959年 | 49篇 |
1958年 | 123篇 |
1957年 | 137篇 |
1956年 | 134篇 |
1955年 | 149篇 |
1954年 | 150篇 |
1953年 | 119篇 |
1952年 | 104篇 |
1951年 | 98篇 |
1950年 | 59篇 |
1949年 | 14篇 |
1948年 | 23篇 |
排序方式: 共有2573条查询结果,搜索用时 15 毫秒
21.
22.
ANA MARTÍN GONZLEZ LAURA BENÍTEZ TRINIDAD SOTO RODRIGUEZ JOSEFINA DE LECEA JUAN CARLOS GUTÍERREZ 《Cell biology international》1997,21(4):213-216
Four different mycotoxins (patulin, T-2 toxin, diacetoxyscirpenol and roquefortine) were used to study growth inhibitory effects on a melanin precursor overproducer mutant of the ciliateTetrahymena thermophilaThis strain is especially sensitive to diacetoxyscirpenol and T-2 toxin. The secretion capacity of melanin precursors into the culture medium by this mutant and its biosensor capacity are very useful characteristics to elaborate a rapid bioassay to detect some specific mycotoxins. 相似文献
23.
24.
25.
ABSTRACT The vocal repertoire of Amazona amazonica during its breeding season has been recorded from wild individuals in Santa Bárbara do Pará, Pará State, Brazil. At individual nests, we continuously recorded vocalizations and behaviour for four hours in the early morning and three hours in the late afternoon, three times a week throughout the breeding season. We identified nine vocalizations that we classified in three behavioural categories: (1) Flight call—emitted when parrots arrive in the nest area; (2) Perched contact calls—two different vocalizations, one of them related to feeding, were emitted when the pair was perched in the nest area and interacted socially between themselves or with other individuals; (3) Aggressive calls—emitted when birds were in a dangerous situation, i.e. alarm (three types of calls), agonistic contact and distress calls (two types of call). The Orange-winged Parrot is a highly social species and the complexity of its social interactions is reflected in the diversity of its vocal repertoire. 相似文献
26.
27.
MIGUEL MENEZES DE SEQUEIRA JORGE HENRIQUE CAPELO JOSÉ CARLOS COSTA ROBERTO JARDIM 《Botanical journal of the Linnean Society. Linnean Society of London》2008,156(4):639-647
The species formerly recognized as Teucrium scorodonia in Madeira is here described as new: Teucrium francoi M. Seq., Capelo, J.C. Costa & R. Jardim. Morphologically close to species of Teucrium gr. scorodonia [ T. scorodonia L., T. pseudoscorodonia Desf., T. siculum (Raf.) Guss. and T. kotschyanum Poech], it exhibits, nonetheless, some distinct diagnostic characters. The indumentum density and type of hairs of T. francoi are clearly distinct from those of related species, as are the shape and dimensions of the leaves and bracts, calyx, and corolla, which are all taken as taxonomically significant diagnostic features. A diagnosis and a distribution map are presented for this new species. Morphology, ecology, biogeography, and conservation issues are discussed. Teucrium francoi , which is an endemic from Madeira (Portugal), is to be found mostly in the scope of the association Teucrio francoi–Origanetum virentis J.C. Costa, Capelo, Jardim, Sequeira, Lousã & Rivas-Martínez, but also occurs in somewhat humid habitats, such as open stands of Rosa mandonii Déségl. associated with small streams. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 156 , 639–647. 相似文献
28.
29.
Home range and association patterns of elephants Loxodonta africana in private nature reserves adjacent to the Kruger National Park, South Africa, were determined over a period of six years by using radio telemetry. The minimum convex polygon (MCP) and harmonic mean (HM) methods were used for data processing. The minimum and maximum range areas required by females were estimated at 115 and 465 km2 , respectively, whilst those of males varied between 157 and 342 km2 . Core areas of females comprised on average 10·1% of the range areas as calculated by the MCP method. Range areas between females in the Klaserie and Timbavati Private Nature Reserves differed significantly. A significant difference in range size was also found between the male population (pooled data) and the females of the Klaserie Private Nature Reserve. Range areas increased from the wet to the dry season. Three male elephant categories were established, namely males utilizing the same area during the study period, those who shifted their range areas and individuals with very large range areas which frequented the area on an irregular basis. A loose relationship existed between males. Association between females can be attributed to kinship and not to the overlapping of range areas. Results indicated avoidance behaviour between females in their core areas, which might partially explain the ability of elephants to tolerate high densities. It is concluded that male elephant hunting should be approached with caution. 相似文献
30.
MARÍA DE LOURDES MU
OZ MARCOS ROJKIND JESÚS CALDER
N MIGUEL TANIMOTO SERGIO ARIAS-NEGRETE ADOLFO MARTÍNEZ-PALOMO 《The Journal of eukaryotic microbiology》1984,31(3):468-470
Several axenic strains of pathogenic and nonpathogenic Entamoeba histolytica were tested for their capacity to digest native radioactive type I collagen gels and to produce liver abscesses when injected into the liver of newborn hamsters. The results demonstrate that the pathogenic strains of amebas (HM1:IMSS, HM3:IMSS, HM38:IMSS, and HK9) have a collagenolytic activity that closely correlates with their in vivo capacity to produce liver lesions. The nonpathogenic isolate (Laredo) did not show collagenolytic activity and failed to produce lesions in the liver of newborn hamsters. The results also demonstrate that type I collagen obtained from rodents and cats is degraded less by amebic collagenase than is bovine collagen, which is similar to human collagen. These findings suggest that species susceptibility to invasive infection may depend, among other factors, on the characteristics of the extracellular components of host tissues. 相似文献