全文获取类型
收费全文 | 1499篇 |
免费 | 75篇 |
出版年
2023年 | 19篇 |
2022年 | 26篇 |
2021年 | 60篇 |
2020年 | 34篇 |
2019年 | 43篇 |
2018年 | 48篇 |
2017年 | 53篇 |
2016年 | 72篇 |
2015年 | 88篇 |
2014年 | 104篇 |
2013年 | 113篇 |
2012年 | 134篇 |
2011年 | 109篇 |
2010年 | 87篇 |
2009年 | 57篇 |
2008年 | 89篇 |
2007年 | 75篇 |
2006年 | 49篇 |
2005年 | 41篇 |
2004年 | 45篇 |
2003年 | 38篇 |
2002年 | 29篇 |
2001年 | 13篇 |
2000年 | 17篇 |
1999年 | 18篇 |
1998年 | 12篇 |
1997年 | 10篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1993年 | 5篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1981年 | 3篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1971年 | 2篇 |
1970年 | 2篇 |
1968年 | 3篇 |
1967年 | 3篇 |
排序方式: 共有1574条查询结果,搜索用时 46 毫秒
91.
André M. Almeida Enrique Villalobos Susana S. Araújo Luis A. Cardoso Dulce M. Santos Maria A. Santos Pedro S. Fevereiro José M. Torné 《Acta Physiologiae Plantarum》2007,29(3):273-281
Trehalose is a non-reducing disaccharide of glucose that occurs in a large number of organisms, playing an important role
in desiccation and heat stress protection. Trehalose accumulation has proven to be an effective way of increasing drought
tolerance in both model plants such as tobacco and important crops such as potato or rice. In this work we aim to genetically
engineer maize with the Arabidopsis thaliana trehalose phosphate synthase gene (AtTPS1), involved in trehalose biosynthesis via electroporation. A cassette harboring the
AtTPS1 gene under the control of the CaMV35S promoter and the Bialaphos resistance gene Bar as a selective agent was inserted
in the plasmid vector pGreen0229 and used to transform maize inbred line Pa91 via electroporation. Fifteen putative transgenic
plants (T0 generation) were obtained. Transgene integration in T0 plants was analyzed by Southern-blot analysis. T0 plants
had normal phenotypes, although smaller than wild type plants. Contrary to wild type plants, when sexual organs emerged, tassels
appeared at least 15 days earlier than ears in the same plant, rendering impossible the self-pollination of the T0 plant.
These plants were then crossed with wild type plants and in some cases T1 seeds were obtained. T1 seeds presented deformities,
especially the lack of endosperm, but it was still possible to germinate some of these seeds. The so obtained plants were
tested by Northern blot but no AtTPS1 gene expression was detected, a fact possibly due to the incomplete insertion of the
AtTPS1 gene or an extremely low gene expression level. 相似文献
92.
Loss Ide O Fernandes LG Martins CD Cardoso LM Silva ME Dias-da-Silva VJ Moraes MF Chianca DA 《Life sciences》2007,81(11):944-950
Earlier studies from the authors' laboratory showed that malnourishment induces alterations in the cardiovascular homeostasis increasing the basal mean arterial pressure and heart rate. In this study, the authors evaluated whether the sympathetic and parasympathetic efferent activities contribute to changes in the cardiovascular homeostasis through altered modulation of the arterial baroreflex of malnourished rats. After weaning, male Fischer rats were given 15% (Normal Protein--NP) or 6% (Low Protein--LP) protein diet for 35 d. The baroreflex gain and latency were evaluated before and after selective autonomic blockades in control and malnourished rats. It was observed that malnourishment affected the baroreflex gain in response to activation and deactivation of the arterial baroreflex. Moreover, malnourished rats showed increased baroreflex latency as compared to that of control rats. Regarding the autonomic efferent activity directed to the heart, the data showed increased sympathetic and decreased parasympathetic efferent activities in malnourished rats, and such alterations could be related to the observed changes in the arterial baroreflex gain as well as in the basal mean arterial pressure and heart rate. 相似文献
93.
M. A. Nogueira U. Nehls R. Hampp K. Poralla E. J. B. N. Cardoso 《Plant and Soil》2007,298(1-2):273-284
Excess manganese (Mn) in soil is toxic to crops, but in some situations arbuscular mycorrhizal fungi (AMF) alleviate the toxic
effects of Mn. Besides the increased phosphorus (P) uptake, mycorrhiza may affect the balance between Mn-reducing and Mn-oxidizing
microorganisms in the mycorrhizosphere and affect the level of extractable Mn in soil. The aim of this work was to compare
mycorrhizal and non-mycorrhizal plants that received extra P in relation to alleviation of Mn toxicity and the balance between
Mn-oxidizing and Mn-reducing bacteria in the mycorrhizosphere. A clayey soil containing 508 mg kg−1 of extractable Mn was fertilized with 30 mg kg−1 (P1) or 45 mg kg−1 (P2) of soluble P. Soybean (Glycine max L. Merrill, cv. IAC 8-2) plants at P1 level were non-inoculated (CP1) or inoculated with either Glomus etunicatum (GeP1) or G. macrocarpum (GmP1), while plants at P2 level were left non-inoculated (CP2). Plants were grown in a greenhouse and harvested after 80 days.
In the mycorrhizosphere of the GmP1 and GeP1 plants a shift from Mn-oxidizing to Mn-reducing bacteria coincided with higher
soil extractability of Mn and Fe. However, the occurrence of Mn-oxidizing/reducing bacteria in the (mycor)rhizosphere was
unrelated to Mn toxicity in plants. Using 16S rDNA sequence homologies, the Mn-reducing isolates were consistent with the
genus Streptomyces. The Mn-oxidizers were homologous with the genera Arthrobacter, Variovorax and Ralstonia. While CP1 plants showed Mn toxicity throughout the whole growth period, CP2 plants never did, in spite of having Fe and
Mn shoot concentrations as high as in CP1 plants. Mycorrhizal plants showed Mn toxicity symptoms early in the growth period
that were no longer visible in later growth stages. The shoot P concentration was almost twice as high in mycorrhizal plants
compared with CP1 and CP2 plants. The shoot Mn and Fe concentrations and contents were lower in GmP1 and GeP1 plants compared
with the CP2 treatment, even though levels of extractable metals increased in the soil when plants were mycorrhizal. This
suggests that mycorrhiza protected its host plant from excessive uptake of Mn and Fe. In addition, higher tissue P concentrations
may have facilitated internal detoxification of Mn in mycorrhizal plants. The exact mechanisms acting on alleviation of Mn
toxicity in mycorrhizal plants should be further investigated. 相似文献
94.
Andrade MC Gabeira SC Abreu-Lopes D Esteves WT Vilardo Mde C Thomé JD Cabello PH Lauria-Filgueiras AL 《Memórias do Instituto Oswaldo Cruz》2007,102(1):53-57
Campylobacteriosis is an extremely important zoonosis, circulating freely in the environment. In nonhuman primates kept in open facilities and bred for experimental purposes, the presence of Campylobacter spp. could cause severe damage to the production and interfere with the results of scientific research. In this paper, we assessed the circulation of Campylobacter spp. in a colony of clinically healthy rhesus monkeys (Macaca mulatta) destined to research. The analysis was carried out during seven non-consecutive years. Data showed that despite several changes made in animal management along the studied years in order to control this zoonosis, reduction of bacterial charge did not occur. Significant differences among the age groups and sex were observed. Infants showed higher susceptibility than adult animals. In general males were more infected than females. Modifications adopted in the handling techniques need to be reviewed with the intent of improving the production, reducing bacterial infection of the stock and avoiding undesirable cross reactions in the research carried out with these animals. Therefore, this paper alerts professionals that work directly with captive rhesus monkeys about the risks of Campylobacter spp. infection and possible interference on the experimental procedures. 相似文献
95.
An affinity-enhanced neutralizing antibody against the membrane-proximal external region of human immunodeficiency virus type 1 gp41 recognizes an epitope between those of 2F5 and 4E10 下载免费PDF全文
Nelson JD Brunel FM Jensen R Crooks ET Cardoso RM Wang M Hessell A Wilson IA Binley JM Dawson PE Burton DR Zwick MB 《Journal of virology》2007,81(8):4033-4043
The membrane-proximal external region (MPER) of human immunodeficiency virus type 1 (HIV-1) gp41 bears the epitopes of two broadly neutralizing antibodies (Abs), 2F5 and 4E10, making it a target for vaccine design. A third Ab, Fab Z13, had previously been mapped to an epitope that overlaps those of 2F5 and 4E10 but only weakly neutralizes a limited set of primary isolates. Here, libraries of Fab Z13 variants displayed on phage were engineered and affinity selected against an MPER peptide and recombinant gp41. A high-affinity variant, designated Z13e1, was isolated and found to be approximately 100-fold improved over the parental Fab not only in binding affinity for the MPER antigens but also in neutralization potency against sensitive HIV-1. Alanine scanning of MPER residues 664 to 680 revealed that N671 and D674 are crucial for peptide recognition as well as for the neutralization of HIV-1 by Z13e1. Ab competition studies and truncation of MPER peptides indicate that Z13e1 binds with high affinity to an epitope between and overlapping with those of 2F5 and 4E10, with the minimal peptide epitope WASLWNWFDITN. Still, Z13e1 remained about an order of magnitude less potent than 4E10 against several isolates of pseudotyped HIV-1. The sum of our molecular analyses with Z13e1 suggests that the segment on the MPER of gp41 between the 2F5 and 4E10 epitopes is exposed on the functional envelope trimer but that access to the specific Z13e1 epitope within this segment is limited. Thus, the ability of MPER-bearing immunogens to elicit potent HIV-1-neutralizing Abs may depend in part on recapitulating the particular constraints that the functional envelope trimer imposes on the segment of the MPER to which Z13e1 binds. 相似文献
96.
Penitente AR Fernandes LG Cardoso LM Silva ME Pedrosa ML Silva AL Haibara AS Moraes MF Chianca DA 《Life sciences》2007,81(7):609-614
Several studies in the literature suggest that low-protein intake is associated with increases in sympathetic efferent activity and cardiovascular disease. Among the possible mechanisms, changes in the neurotransmission of cardiovascular reflexes have been implicated. Therefore, the present study comprised the evaluation of chemoreflex responsiveness in rats subjected to a low-protein diet during the 35 days after weaning. As a result, we observed that malnourished rats presented higher levels of baseline mean arterial pressure and heart rate and exhibited a mild increase in the pressor response to chemoreflex activation. They also exhibited a massive bradycardic response to chemoreflex activation. Interestingly, bilateral ligature of the carotid body arteries further increased baseline mean arterial pressure and heart rate in malnourished animals. The data suggest severe autonomic imbalance and/or change in the central interplay between neural and cardiovascular mechanisms. 相似文献
97.
The evolution, function and interaction of ligand-receptor pairs are of major pharmaceutical interest. Comparative sequence analysis approaches using data from phylogenetically distant organisms can provide insights into their origin and possible physiological roles. The present review focuses on the pituitary adenylate cyclase-activating polypeptide (PACAP), vasoactive intestinal polypeptide (VIP) and their receptors in the metazoa. A PACAP-like peptide is present in tunicates and chordates while VIP- and PACAP/VIP-specific receptors have only been isolated in the latter phyla. The apparently disparate evolution of the ligands and their specific receptors raises questions about their evolution during the metazoan radiation and also about how the ligands may have acquired new functions. 相似文献
98.
Phosphorus reference concentrations in European lakes 总被引:7,自引:5,他引:2
A. C. Cardoso A. Solimini G. Premazzi L. Carvalho A. Lyche S. Rekolainen 《Hydrobiologia》2007,584(1):3-12
99.
Peeter Nõges Wouter Van de Bund Ana Cristina Cardoso Anna-Stiina Heiskanen 《Hydrobiologia》2007,584(1):373-379
In most cases the negative impacts of climate change to aquatic ecosystems cannot be mitigated by measures in the river basin
management. Ignoring climate change by the Water Framework Directive may have strong implications for the typology and quality
assessment systems used for water bodies. As a result of climate change, water bodies, especially those located near the type
boundaries may change their type. Compared to typology characteristics, water quality parameters are even more labile and
may be easily affected by climate change. The paper exemplifies that the anticipated deterioration of water quality within
the time frame relevant for WFD implementation may be large enough to endanger the fulfillment of the set water quality objectives.
The review of the river basin characterization every six years, as required by the WFD, might also include re-evaluation of
reference conditions according to the changes observed at pristine reference sites. As a consequence, the restoration targets
(i.e., the good ecological status) would also need to be evaluated periodically. 相似文献
100.
siRNA delivery by a transferrin-associated lipid-based vector: a non-viral strategy to mediate gene silencing 总被引:1,自引:0,他引:1
Cardoso AL Simões S de Almeida LP Pelisek J Culmsee C Wagner E Pedroso de Lima MC 《The journal of gene medicine》2007,9(3):170-183
BACKGROUND: RNA interference provides a powerful technology for specific gene silencing. Therapeutic applications of small interfering RNA (siRNA) however require efficient vehicles for stable complexation, protection, and extra- and intracellular delivery of these nucleic acids. Here, we evaluated the potential of transferrin (Tf)-associated liposomes for siRNA complexation and gene silencing. METHODS: Cationic liposomes composed of DOTAP : Cholesterol associated with or without transferrin (Tf) were complexed with siRNA at different lipid/siRNA charge ratios. Complexation and protection of siRNA from enzymatic degradation was assessed with the PicoGreen intercalation assay and gel electrophoresis. Cellular internalization of these siRNA Tf-lipoplexes was detected by confocal microscopy. Luciferase assay, immunoblot and fluorescence-activated cell sorting (FACS) analysis were used to evaluate reporter gene silencing in Huh-7 hepatocarcinoma and U-373 glioma cells. c-Jun knockdown in HT-22 cells was evaluated by quantitative real-time polymerase chain reaction (RT-PCR). Cytotoxicity of the siRNA complexes was assessed by Alamar blue, lactate dehydrogenase and MTT assays. RESULTS: Complexation of siRNA with the cationic liposomes in the presence of Tf results in the formation of stable particles and prevents serum-mediated degradation. Confocal microscopy showed fast cellular internalization of the Tf-lipoplexes via endocytosis. In the GFP glioma cells Tf-lipoplexes showed enhanced gene silencing at minimum toxicity in comparison to Tf-free lipoplexes. Targeting luciferase in the hepatocarcinoma cell line resulted in more than 70% reduction of luciferase activity, while in HT-22 cells 50% knockdown of endogenous c-Jun resulted in a significant protection from glutamate-mediated toxicity. CONCLUSIONS: Cationic liposomes associated with Tf form stable siRNA lipoplexes with reduced toxicity and enhanced specific gene knockdown activity compared to conventional lipoplexes. Thus, such formulations may constitute efficient delivery systems for therapeutic siRNA applications. 相似文献