全文获取类型
收费全文 | 626篇 |
免费 | 67篇 |
出版年
2023年 | 2篇 |
2021年 | 16篇 |
2020年 | 9篇 |
2019年 | 8篇 |
2018年 | 24篇 |
2017年 | 8篇 |
2016年 | 26篇 |
2015年 | 37篇 |
2014年 | 31篇 |
2013年 | 50篇 |
2012年 | 50篇 |
2011年 | 28篇 |
2010年 | 29篇 |
2009年 | 33篇 |
2008年 | 37篇 |
2007年 | 38篇 |
2006年 | 28篇 |
2005年 | 18篇 |
2004年 | 16篇 |
2003年 | 16篇 |
2002年 | 14篇 |
2001年 | 17篇 |
2000年 | 12篇 |
1999年 | 19篇 |
1998年 | 11篇 |
1997年 | 10篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 10篇 |
1991年 | 9篇 |
1990年 | 11篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 8篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 9篇 |
1976年 | 2篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1971年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有693条查询结果,搜索用时 93 毫秒
51.
X. Scheldeman L. Willemen G. Coppens d’Eeckenbrugge E. Romeijn-Peeters M. T. Restrepo J. Romero Motoche D. Jiménez M. Lobo C. I. Medina C. Reyes D. Rodríguez J. A. Ocampo P. Van Damme P. Goetgebeur 《Biodiversity and Conservation》2007,16(6):1867-1884
Vasconcellea species, often referred to as highland papayas, consist of a group of fruit species that are closely related to the common
papaya (Carica papaya). The genus deserves special attention as a number of species show potential as raw material in the tropical fruit industry,
fresh or in processed products, or as genetic resources in papaya breeding programs. Some species show a very restricted distribution
and are included in the IUCN Red List. This study on Vasconcellea distribution and diversity compiled collection data from five Vasconcellea projects and retrieved data from 62 herbaria, resulting in a total of 1,553 georeferenced collection sites, in 16 countries,
including all 21 currently known Vasconcellea species. Spatial analysis of species richness clearly shows that Ecuador, Colombia and Peru are areas of high Vasconcellea diversity. Combination of species occurrence data with climatic data delimitates the potential distribution of each species
and allows the modeling of potential richness at continent level. Based on these modeled richness maps, Ecuador appears to
be the country with the highest potential Vasconcellea diversity. Despite differences in sampling densities, its neighboring countries, Peru and Colombia, possess high modeled
species richness as well. A combination of observed richness maps and modeled potential richness maps makes it possible to
identify important collection gaps. A Principal Component Analysis (PCA) of climate data at the collection sites allows us
to define climatic preferences and adaptability of the different Vasconcellea species and to compare them with those of the common papaya. 相似文献
52.
This work shows in vitro processing of Bacillus thuringiensis svar. isralensis Cry toxins and the capacity of the active fragments to bind the midgut microvilli of Aedes aegypti larvae. Processing of Cry11Aa, Cry4Aa and Cry4Ba yielded double fragments of 38-30, 45-20 and 45-18 kDa, respectively. Competition assays showed that all active (125)I-Cry toxins are able to specifically bind to brush border membrane fractions and they might share a common class of binding sites. The values of IC(50) suggested that toxins do not display high affinity for the receptors from brush border membrane fractions, while dissociation assays showed that binding was irreversible, indicating the insertion of toxins in the cell membrane. 相似文献
53.
54.
55.
Demineralised, freeze-dried bone allografts (DFDBA) have been used extensively by dentists in the treatment of periodontal
and periapical osseous defects resulting from inflammatory diseases. Their use in India however, is limited by the availability
of quality allografts and the high cost of imported alternatives. A study was conducted to assess the osteogenic potential
of DFDBA prepared for the first time in India by the Tata Memorial Hospital (TMH) Tissue Bank. The DFDBA was used in the treatment
of osseous defects after removal of periapical lesions associated with devitalised teeth in 10 healthy patients. At the 6-month
recall visit all the patients showed a remarkable decrease in the grades of mobility, and 9 out of the 10 patients showed
radiographic evidence of complete healing of the osseous defects with evidence of normal bony trabaeculae. These findings
indicate that the indigenously prepared DFDBA is a cost effective, biocompatible material with osteogenic potential that can
be used effectively in treating osseous defects of periapical lesions associated with non vital teeth. 相似文献
56.
Leonel da Silveira Lobo Sternberg Su Yean Teh Sharon M. L. Ewe Fernando Miralles-Wilhelm Donald L. DeAngelis 《Ecosystems》2007,10(4):648-660
A
bstract
The boundaries between mangroves and freshwater hammocks in coastal ecotones of South Florida are sharp. Further, previous
studies indicate that there is a discontinuity in plant predawn water potentials, with woody plants either showing predawn
water potentials reflecting exposure to saline water or exposure to freshwater. This abrupt concurrent change in community
type and plant water status suggests that there might be feedback dynamics between vegetation and salinity. A model examining
the salinity of the aerated zone of soil overlying a saline body of water, known as the vadose layer, as a function of precipitation,
evaporation and plant water uptake is presented here. The model predicts that mixtures of saline and freshwater vegetative
species represent unstable states. Depending on the initial vegetation composition, subsequent vegetative change will lead
either to patches of mangrove coverage having a high salinity vadose zone or to freshwater hammock coverage having a low salinity
vadose zone. Complete or nearly complete coverage by either freshwater or saltwater vegetation represents two stable steady-state
points. This model can explain many of the previous observations of vegetation patterns in coastal South Florida as well as
observations on the dynamics of vegetation shifts caused by sea level rise and climate change. 相似文献
57.
Eric?Roberto?Guimar?es?Rocha Aguiar Roenick Proveti Olmo Simona Paro Flavia Viana Ferreira Isaque?Jo?o?da?Silva de?Faria Yaovi?Mathias?Honore Todjro Francisco Pereira Lobo Erna Geessien Kroon Carine Meignin Derek Gatherer Jean-Luc Imler Jo?o Trindade Marques 《Nucleic acids research》2015,43(13):6191-6206
Virus surveillance in vector insects is potentially of great benefit to public health. Large-scale sequencing of small and long RNAs has previously been used to detect viruses, but without any formal comparison of different strategies. Furthermore, the identification of viral sequences largely depends on similarity searches against reference databases. Here, we developed a sequence-independent strategy based on virus-derived small RNAs produced by the host response, such as the RNA interference pathway. In insects, we compared sequences of small and long RNAs, demonstrating that viral sequences are enriched in the small RNA fraction. We also noted that the small RNA size profile is a unique signature for each virus and can be used to identify novel viral sequences without known relatives in reference databases. Using this strategy, we characterized six novel viruses in the viromes of laboratory fruit flies and wild populations of two insect vectors: mosquitoes and sandflies. We also show that the small RNA profile could be used to infer viral tropism for ovaries among other aspects of virus biology. Additionally, our results suggest that virus detection utilizing small RNAs can also be applied to vertebrates, although not as efficiently as to plants and insects. 相似文献
58.
Francinaldo Soares Silva Jefferson Mesquita Brito Benedita Maria Costa Neta Shelre Emile Pereira Duarte Lobo 《Memórias do Instituto Oswaldo Cruz》2015,110(6):801-803
Hoover Pugedo light traps were modified for use with green and blue-light-emitting
diodes to trap phlebotomine sandflies in northeastern Brazil. A total of 2,267
specimens belonging to eight genera and 15 species were sampled. The predominant
species were Nyssomyia whitmani(34.41%) and Micropygomyia
echinatopharynx(17.25%).The green LED trap prevailed over the blue and
control lights; however, no statistically significant difference could be detected
among the three light sources. Even without statistical significance, we suggest
using LEDs as an attractant for the capture of sandflies because of several
advantages over the conventional method with incandescent lamps. 相似文献
59.
60.
Can we derive macroecological patterns from primary Global Biodiversity Information Facility data? 下载免费PDF全文