全文获取类型
收费全文 | 4958篇 |
免费 | 294篇 |
国内免费 | 2篇 |
专业分类
5254篇 |
出版年
2024年 | 3篇 |
2023年 | 43篇 |
2022年 | 76篇 |
2021年 | 154篇 |
2020年 | 114篇 |
2019年 | 131篇 |
2018年 | 137篇 |
2017年 | 130篇 |
2016年 | 236篇 |
2015年 | 288篇 |
2014年 | 283篇 |
2013年 | 376篇 |
2012年 | 441篇 |
2011年 | 400篇 |
2010年 | 300篇 |
2009年 | 205篇 |
2008年 | 305篇 |
2007年 | 292篇 |
2006年 | 255篇 |
2005年 | 226篇 |
2004年 | 176篇 |
2003年 | 170篇 |
2002年 | 165篇 |
2001年 | 37篇 |
2000年 | 43篇 |
1999年 | 37篇 |
1998年 | 39篇 |
1997年 | 25篇 |
1996年 | 20篇 |
1995年 | 17篇 |
1994年 | 17篇 |
1993年 | 14篇 |
1992年 | 6篇 |
1991年 | 12篇 |
1990年 | 14篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 7篇 |
1985年 | 5篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1974年 | 2篇 |
1970年 | 2篇 |
1966年 | 2篇 |
1960年 | 2篇 |
排序方式: 共有5254条查询结果,搜索用时 15 毫秒
51.
Cardoso AM Martins de Sousa E Viana-Niero C Bonfim de Bortoli F Pereira das Neves ZC Leão SC Junqueira-Kipnis AP Kipnis A 《Microbes and infection / Institut Pasteur》2008,10(14-15):1552-1557
A cluster of surgical site infection cases after arthroscopic and laparoscopic procedures occurred between 2005 and 2007 in Goiania, in the central region of Brazil. Nontuberculous mycobacteria (NTM) were isolated from samples (exudates from cutaneous abscesses) from 18 patients of seven private hospitals. There were no reports of post-surgical arthroscopic and laparoscopic mycobacterial infections in Goiania apart from this period. The 18 isolates were identified as Mycobacterium massiliense by PCR-restriction digestion of the hsp65 gene, pulsed-field gel electrophoresis (PFGE) comparisons, and rpoB partial gene sequencing. All isolates were typed as a single clone, indicating that they have the same origin, which suggests a common source of infection for all patients. 相似文献
52.
Nine indigenous cachaça Saccharomyces cerevisiae strains and one wine strain were compared for their trehalose metabolism characteristics under non-lethal (40°C) and lethal (52°C) heat shock, ethanol shock and combined heat and ethanol stresses. The yeast protection mechanism was studied through trehalose concentration, neutral trehalase activity and expression of heat shock proteins Hsp70 and Hsp104. All isolates were able to accumulate trehalose and activate neutral trehalase under stress conditions. No correlation was found between trehalose levels and neutral trehalase activity under heat or ethanol shock. However, when these stresses were combined, a positive relationship was found. After pre-treatment at 40°C for 60 min, and heat shock at 52°C for 8 min, eight strains maintained their trehalose levels and nine strains improved their resistance against lethal heat shock. Among the investigated stresses, heat treatment induced the highest level of trehalose and combined heat and ethanol stresses activated the neutral trehalase most effectively. Hsp70 and Hsp104 were expressed by all strains at 40°C and all of them survived this temperature although a decrease in cell viability was observed at 52°C. The stress imposed by more than 5% ethanol (v/v) represented the best condition to differentiate strains based on trehalose levels and neutral trehalase activity. The investigated S. cerevisiae strains exhibited different characteristics of trehalose metabolism, which could be an important tool to select strains for the cachaça fermentation process. 相似文献
53.
Analysis of nine characteristics on 1,205 males and 932 females from 12 tribes or groups of tribes indicated a poor relationship between morphology and language, as well as moderate agreement with the variability expected considering geography only. Two samples in the Xingu area studied during an interval of half a century (1897-1947) showed remarkable similarity. The conformity of the Caingang morphology with those of other tribes and the distinctiveness of the Xavante and Tenetehara has been amply confirmed. 相似文献
54.
Fernando P. F. Zorzenon Arthur F. Tomaseto Matthew P. Daugherty João R. S. Lopes Marcelo P. Miranda 《Journal of Applied Entomology》2021,145(4):326-335
Seasonality often influences multiple aspects of vector-borne plant diseases. With respect to the management of plant disease vectors, an understanding of the factors driving seasonal changes in vector flight activity may improve management outcomes by facilitating more proactive application of control measures. One of the most challenging issues for citrus Huanglongbing management is to forecast when disease primary spread by bacteriliferous Diaphorina citri will occur. We monitored the temporal patterns of immigrating psyllids, using upwards of 1,200 traps spread among 9 citrus farms and checked on a weekly basis over 4 years. This dataset was analysed with a set of hierarchical models to estimate the effect of climatic variables on citrus foliage production (i.e. flush), and effects of climatic variables and citrus foliage dynamics on D. citri catches over the season. The results showed substantial seasonal variability in immigrating D. citri abundance, with the critical dispersal/migration period occurring between end of winter and spring. During this period, 65% of the total psyllids were collected on sticky traps. Seasonality of immigrating D. citri coincided with changes in certain climate variables, with negative effects of humidity and daily maximum temperatures, and a positive effect of rainfall amount in prior weeks. Maximum temperature and both daily minimum temperature and rainfall during prior weeks were also associated with new citrus flush production, which itself was positively related to immigrating D. citri abundance. Based on these results, citrus growers should be aware and intensify the frequency of psyllid control tactics (i.e. insecticide and/or kaolin sprays) during this period in order to prevent Ca. L. asiaticus transmission. These results are an important step towards developing the predictive framework needed to refine D. citri and huanglongbing management. 相似文献
55.
Question: How do meteorological variations at seasonal, interannual scales differentially affect the canopy dynamics of four contrasting landscape units within a region? Location: Flooding Pampa, Buenos Aires, Argentina. 5000 km2. Central point: 35°15′S, 57°45′W. Methods: We used a 19‐year series of the normalized difference vegetation index (NDVI) derived from NOAA‐AVHRR PAL (Pathfinder AVHRR Land) images and meteorological data provided by a nearby weather station. The NDVI was used as surrogate of canopy photosynthetic status. The relationship between annually integrated NDVI and meteorological conditions was explored by stepwise multiple regressions for each defined unit. PC A was performed to compare units and growing seasons on a multivariate basis. Results: Mean seasonal NDVI curve was similarly shaped among landscapes. However, the absolute values differed widely. There was high interannual variation so that the mean seasonal pattern was seldom observed in any particular year. Annually integrated NDVI of all landscapes was negatively associated with summer temperature and positively with previous year precipitation. It was also directly related with current year winter precipitation in two landscapes and with summer precipitation in the others. NDVI response to September and March precipitation accounted for some of the differences in interannual variation among landscapes. Conclusions: Our results revealed a strong intra‐regional variation of canopy dynamics, closely linked to landscape (vegetation‐soil) and water availability (mainly in summer and during the previous year). These links may be used to predict forage production rates for livestock. 相似文献
56.
Marcelo De Franco Patrícia dos Santos Carneiro Luciana Carla Peters Francisca Vorraro Andrea Borrego Orlando Garcia Ribeiro Nancy Starobinas Wafa Koury Cabrera Olga Martinez Ibañez 《Mammalian genome》2007,18(4):263-269
Lines of mice were obtained by selective breeding for maximum (AIRmax) or minimum (AIRmin) acute inflammation. They present
distinct neutrophil influx and show frequency disequilibrium of the solute carrier family 11a member 1
(Slc11a1) alleles. This gene is involved in ion transport at the endosomes within macrophages and neutrophils, interfering in their
activation. Homozygous AIRmax and AIRmin sublines for the Slc11a1 gene were produced to examine the interaction of this gene with the acute inflammatory loci. The present work investigated
wound-healing traits in AIRmax and AIRmin mice, in F1 and F2 intercrosses, and in Slc11a1 sublines. Two-millimeter ear punches were made in the mice and hole closure was measured during 40 days. AIRmax mice demonstrated
significant tissue repair while AIRmin mice did not. Significant differences between the responses of male and female mice
were also observed. Wound-healing traits demonstrated a correlation with neutrophil influx in F2 populations. AIRmax
SS
showed higher ear-wound closure than AIRmax
RR
mice, suggesting that the Slc11a1
S allele favored ear tissue repair. QTL analysis has detected two inflammatory loci modulating ear wound healing on chromosomes
1 and 14. These results suggest the involvement of the acute inflammation modifier QTL in the wound-healing phenotype. 相似文献
57.
Mikovski Andréia Izabel da Silva Nayara Tayane Silva Lázara Aline Simões Machado Mariana de Souza Barbosa Lília Cristina Reis Aryane Campos de Matos Elyabe Monteiro Viccini Lyderson Facio da Silva Souza Claudinei Machado Marcelo Dias Otoni Wagner Campos de Carvalho Ilio Fealho Rocha Diego Ismael da Silva Maurecilne Lemes 《Plant Cell, Tissue and Organ Culture》2021,145(2):239-259
Plant Cell, Tissue and Organ Culture (PCTOC) - Somaclonal variation during in vitro culture is often an undesirable phenomenon but may also be a source of genetic variation useful for breeders. The... 相似文献
58.
Srgio Henrique Borges Fabricio Baccaro Marcelo Moreira Erik Lacerda Choueri 《Biotropica》2019,51(6):903-912
The principles of island biogeography are rarely applied to the animal assemblages of Amazonian river islands. Here, we compare bird assemblages of Amazonian river islands with a variety of mainland habitats. We also examine how bird species diversity and composition are related to island physical attributes. Birds were sampled with mist nets and qualitative censuses on 11 river islands and 24 mainland sites on the lower reaches of the Rio Negro in the Brazilian Amazon. Island bird assemblages were characterized by lower species richness and a higher abundance of a few dominant species. Additionally, the species composition of the islands was distinct from that of the mainland, including the nearby floodplain habitats. The number of bird species increased with island size and habitat diversity, and decreased with degree of isolation. In addition, small islands tended to harbor an impoverished subset of the species present on larger ones. Bird species diversity and composition on Amazonian river islands are likely influenced by the ecological succession and historical events affecting island formation. Considering their small total area across the Amazon basin, these insular fluvial communities could be disproportionately threatened by river channel disturbances related to climate change or hydroelectric dam development. Abstract in Portughese is available with online material. 相似文献
59.
Bingxin Wang Daniel G. Rocha Mark I. Abrahams Andr P. Antunes Hugo C. M. Costa Andr Luis Sousa Gonalves Wilson Roberto Spironello Milton Jos de Paula Carlos A. Peres Juarez Pezzuti Emiliano Ramalho Marcelo Lima Reis Elildo Carvalho Jr Fabio Rohe David W. Macdonald Cedric Kai Wei Tan 《Ecology and evolution》2019,9(9):5049-5062
Amazonia forest plays a major role in providing ecosystem services for human and sanctuaries for wildlife. However, ongoing deforestation and habitat fragmentation in the Brazilian Amazon has threatened both. The ocelot is an ecologically important mesopredator and a potential conservation ambassador species, yet there are no previous studies on its habitat preference and spatial patterns in this biome. From 2010 to 2017, twelve sites were surveyed, totaling 899 camera trap stations, the largest known dataset for this species. Using occupancy modeling incorporating spatial autocorrelation, we assessed habitat use for ocelot populations across the Brazilian Amazon. Our results revealed a positive sigmoidal correlation between remote‐sensing derived metrics of forest cover, disjunct core area density, elevation, distance to roads, distance to settlements and habitat use, and that habitat use by ocelots was negatively associated with slope and distance to river/lake. These findings shed light on the regional scale habitat use of ocelots and indicate important species–habitat relationships, thus providing valuable information for conservation management and land‐use planning. 相似文献