全文获取类型
收费全文 | 698篇 |
免费 | 35篇 |
专业分类
733篇 |
出版年
2024年 | 4篇 |
2023年 | 9篇 |
2022年 | 5篇 |
2021年 | 17篇 |
2020年 | 15篇 |
2019年 | 20篇 |
2018年 | 11篇 |
2017年 | 10篇 |
2016年 | 29篇 |
2015年 | 38篇 |
2014年 | 36篇 |
2013年 | 54篇 |
2012年 | 51篇 |
2011年 | 67篇 |
2010年 | 40篇 |
2009年 | 31篇 |
2008年 | 42篇 |
2007年 | 37篇 |
2006年 | 31篇 |
2005年 | 28篇 |
2004年 | 34篇 |
2003年 | 35篇 |
2002年 | 32篇 |
2001年 | 8篇 |
2000年 | 11篇 |
1999年 | 3篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1992年 | 3篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有733条查询结果,搜索用时 0 毫秒
1.
Juan J. Luque-Larena Pilar López† & Joaquim Gosálbez 《Ethology : formerly Zeitschrift fur Tierpsychologie》2002,108(3):273-285
We conducted a laboratory experiment to examine whether dominance status affects the use of locations occupied (i.e. scent-marked) by same-sex conspecifics among wild-caught snow vole males ( Chionomys nivalis ). Given that the costs of invading scent-marked areas should partially depend on the intruder's competitive ability, we hypothesised that, once a dominance relationship has been established with the owner of marks, the use of these areas by males would vary differently between dominant and subordinate individuals. Before any previous experience with the owner, scented substrates and nests were highly attractive to all males, indicating a general preference for recently occupied areas. However, after relative social status was established through direct interaction the subsequent response of males was altered differently, subordinate individuals reducing the use of marked areas to a much greater extent than dominants. Competitive relationships between male C. nivalis were found to be influenced by differences in body weight, larger males tending to display a more dominant pattern of behaviour. Our results reveal that male C. nivalis may require some direct experience with potential opponents to modulate their response towards occupied locations. Additionally, we suggest that the ability of males to conditionally respond to social signals from particular competing conspecifics might be used to lower the costs of prospective agonistic interactions. 相似文献
2.
Isolation from urine of two Serratia marcescens strains excreting a diffusible yellow pigment 总被引:1,自引:0,他引:1
Two bacterial strains excreting a yellow pigment were isolated from human urine and identified as Serratia marcescens. The pigment was produced in the late exponential and early stationary phases of growth. Minimal media supplemented with tyrosine, phenylalanine, 3,4-dihydroxyphenylacetate or tryptophan, as well as complex media, induced pigment production. UV-visible spectra of the extracted pigment had peaks characteristic of 2-hydroxy-5-carboxymethylmuconate semialdehyde, produced from meta-cleavage of 3,4-dihydroxyphenylacetate by the enzyme 3,4-dihydroxyphenylacetate 2,3-dioxygenase (EC 1.13.11.15). This enzyme was active when the bacteria were grown under conditions promoting pigment production. The kinetics and factors affecting pigment production are also reported. 相似文献
3.
Glutamate Oxidation by Soybean Cotyledon and Leaf Mitochondria 总被引:1,自引:0,他引:1
Day David A.; Salom Caroline L.; Azcon-Bieto Joaquim; Dry Ian B.; Wiskich Joseph T. 《Plant & cell physiology》1988,29(7):1193-1200
Mitochondria purified from cotyledons of soybean seedlings fiveto ten days old have the capacity to rapidly oxidize glutamate(measured as glutamate dependent oxygen consumption). This capacitywas greatest at ten days after planting but was very low priorto emergence of cotyledons from the vermiculite and during senescence.Solubilized glutamate dehydrogenase activity, on the other hand,was substantial at two days after planting, peaked at sevendays, then declined and rose again during senescence. It issuggested that mitochondrial glutamate oxidation plays a rolein reserve mobilization and amino acid metabolism during seedlinggrowth. Leaf mitochondria and those from senescing cotyledonscould not sustain rapid rates of glutamate oxidation despiteready oxidation of other substrates and high solubilized glutamatedehydrogenase activity, suggesting an alternative role for theenzyme in these tissues. Possible controlling factors are discussed.
2 Present address, Garvan Institute, Darlinghurst, N. S. W.,Australia.
3 Permanent address, Department de Biologia Vegetal, Facultatde Biologia, Universitat de Barcelona, Barcelona, Spain. (Received May 6, 1988; Accepted August 3, 1988) 相似文献
4.
5.
Rui L. Mendes Helena L. Fernandes José A.P Coelho Joaquim M.S Cabral António M. F. Palavra Júlio M. Novais 《Journal of applied phycology》1994,6(3):289-293
Samples of the microalgaBotryococcus braunii were submitted to supercritical fluid extraction with carbon dioxide at 40 °C and pressures of 12.5, 20.0 and 30.0 MPa. The extraction yield and the fraction of the hydrocarbons in the extracts both increased with pressure and at 30 MPa these compounds were obtained rapidly. This behaviour is associated with the localization of the hydrocarbons outside the cell wall. In the extracts, which are fluid, golden and limpid, chlorophyll and phospholipids were not detected.Author for correspondence 相似文献
6.
In this paper, we are dealing with the study of a case of multiple somatic malformations, with external female genitals and 46 XY caryotype. The anatomical and histological study of the genital organs, allows us to verify the existence of internal genital organs; consisting essentially in tubes, bicornous uterus, a gonadal ligament in a normotopical position, Wolffian remains and the absence of a vagina. The external female genitals are completely normal. When we interpreted these findings, we paid special attention to the relation existing between the abnormal presence of the Wolffian remains, male genotype, and typical female genital structures. Taking account of the latest scientific advances concerning genital development, we considered the possibility of the existence of secretions of a "masculinizing" substance from the gonad, before its morphological differentiation, which was interrupted by an etiological undetermined noxa. When this evolution was arrested, together with the secretions of the masculinizing substance, the genital development continued normally for a female. The terminal teratogenic period for this malformation is situated from the 5th to the 6th week of gestation (human embryos from 11 to 14 mm., Streeter Horizon XVII). 相似文献
7.
Jordi Mayneris-Perxachs María Arnoriaga-Rodríguez Josep Garre-Olmo Josep Puig Rafael Ramos Maria Trelis Aurelijus Burokas Cludia Coll Cristina Zapata-Tona Salvador Pedraza Vicente Prez-Brocal Lluís Rami Wifredo Ricart Andrs Moya Mariona Jov Joaquim Sol Manuel Portero-Otin Reinald Pamplona Rafael Maldonado Jos Manuel Fernndez-Real 《The ISME journal》2022,16(9):2181
Growing evidence implicates the gut microbiome in cognition. Blastocystis is a common gut single-cell eukaryote parasite frequently detected in humans but its potential involvement in human pathophysiology has been poorly characterized. Here we describe how the presence of Blastocystis in the gut microbiome was associated with deficits in executive function and altered gut bacterial composition in a discovery (n = 114) and replication cohorts (n = 942). We also found that Blastocystis was linked to bacterial functions related to aromatic amino acids metabolism and folate-mediated pyrimidine and one-carbon metabolism. Blastocystis-associated shifts in bacterial functionality translated into the circulating metabolome. Finally, we evaluated the effects of microbiota transplantation. Donor’s Blastocystis subtypes led to altered recipient’s mice cognitive function and prefrontal cortex gene expression. In summary, Blastocystis warrant further consideration as a novel actor in the gut microbiome-brain axis.Subject terms: Biomarkers, Pathogenesis, Diagnosis 相似文献
8.
Joaquim Jesus Maria Clara P. Amorim Paulo J. Fonseca Amílcar Teixeira Silvestre Natário João Carrola Simone Varandas Luís Torres Pereira Rui M. V. Cortes 《Journal of fish biology》2019,95(1):247-255
This study focused on the use of sound playbacks as acoustic deterrents to direct native potamodromous migratory species away from all kind of traps. The effects of two acoustic treatments, a repeated sine sweep up to 2 kHz (sweep-up stimulus) and an intermittent 140 Hz tone, were tested in three fish species native to Iberia: Salmo trutta, Pseudochondrostoma duriense and Luciobarbus bocagei. In contrast with S. trutta, the endemic cyprinids P. duriense and L. bocagei exhibited a strong repulse reaction to the frequency sweep-up sound. The 140 Hz stimulus did not seem to alter significantly the behaviour of any of the studied species. These results highlight the potential of acoustic stimuli as fish behavioural barriers and their application to in situ conservation measures of native Iberian fish populations, to protect them from hydropower dams. In addition, this study shows that acoustic deterrents can be used selectively on target species. 相似文献
9.
Gomes Helga Do R.; Goes Joaquim I.; Parulekar A.H. 《Journal of plankton research》1992,14(9):1307-1329
This study examines the spatial distribution and size structureof phytoplankton biomass and productivity in relation to thevertical structrure of the Andaman Sea (northeastern IndianOcean). This region was characterized by low concentrationsof nutrients and high levels of insolation. Nitrogen availabilityappeared to control overall productivity with nitrate-basednew production accounting for 824% of thetotal primary production. Euphotic column chlorophyll (chl a)averaged 52.5 mg m2 of which a major portion was locatedas a subsurface chl a maximum (SCM) at 相似文献
10.
Walter Rossi Cervi Rubens Augusto Camargo Lamparelli Joaquim Eugênio Abel Seabra Martin Junginger Sierk de Jong Floor van der Hilst 《Global Change Biology Bioenergy》2020,12(2):136-157
It is expected that Brazil could play an important role in biojet fuel (BJF) production in the future due to the long experience in biofuel production and the good agro‐ecological conditions. However, it is difficult to quantify the techno‐economic potential of BJF because of the high spatiotemporal variability of available land, biomass yield, and infrastructure as well as the technological developments in BJF production pathways. The objective of this research is to assess the recent and future techno‐economic potential of BJF production in Brazil and to identify location‐specific optimal combinations of biomass crops and technological conversion pathways. In total, 13 production routes (supply chains) are assessed through the combination of various biomass crops and BJF technologies. We consider temporal land use data to identify potential land availability for biomass production. With the spatial distribution of the land availability and potential yield of biomass crops, biomass production potential and costs are calculated. The BJF production cost is calculated by taking into account the development in the technological pathways and in plant scales. We estimate the techno‐economic potential by determining the minimum BJF total costs and comparing this with the range of fossil jet fuel prices. The techno‐economic potential of BJF production ranges from 0 to 6.4 EJ in 2015 and between 1.2 and 7.8 EJ in 2030, depending on the reference fossil jet fuel price, which varies from 19 to 65 US$/GJ across the airports. The techno‐economic potential consists of a diverse set of production routes. The Northeast and Southeast region of Brazil present the highest potentials with several viable production routes, whereas the remaining regions only have a few promising production routes. The maximum techno‐economic potential of BJF in Brazil could meet almost half of the projected global jet fuel demand toward 2030. 相似文献