全文获取类型
收费全文 | 843篇 |
免费 | 124篇 |
出版年
2023年 | 7篇 |
2022年 | 5篇 |
2021年 | 17篇 |
2020年 | 10篇 |
2019年 | 20篇 |
2018年 | 20篇 |
2017年 | 25篇 |
2016年 | 29篇 |
2015年 | 40篇 |
2014年 | 35篇 |
2013年 | 45篇 |
2012年 | 51篇 |
2011年 | 44篇 |
2010年 | 31篇 |
2009年 | 30篇 |
2008年 | 38篇 |
2007年 | 40篇 |
2006年 | 45篇 |
2005年 | 35篇 |
2004年 | 32篇 |
2003年 | 35篇 |
2002年 | 27篇 |
2001年 | 38篇 |
2000年 | 23篇 |
1999年 | 19篇 |
1998年 | 14篇 |
1997年 | 9篇 |
1996年 | 12篇 |
1995年 | 11篇 |
1994年 | 19篇 |
1993年 | 9篇 |
1992年 | 19篇 |
1991年 | 17篇 |
1990年 | 9篇 |
1989年 | 18篇 |
1988年 | 14篇 |
1987年 | 10篇 |
1986年 | 13篇 |
1985年 | 15篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1968年 | 1篇 |
1966年 | 2篇 |
排序方式: 共有967条查询结果,搜索用时 15 毫秒
81.
Rose Monnerat Erica Martins Cristina Macedo Paulo Queiroz Lilian Pra?a Carlos Marcelo Soares Helio Moreira Isabella Grisi Joseane Silva Mario Soberon Alejandra Bravo 《PloS one》2015,10(4)
Brazil ranked second only to the United States in hectares planted to genetically modified crops in 2013. Recently corn producers in the Cerrado region reported that the control of Spodoptera frugiperda with Bt corn expressing Cry1Fa has decreased, forcing them to use chemicals to reduce the damage caused by this insect pest. A colony of S. frugiperda was established from individuals collected in 2013 from Cry1Fa corn plants (SfBt) in Brazil and shown to have at least more than ten-fold higher resistance levels compared with a susceptible colony (Sflab). Laboratory assays on corn leaves showed that in contrast to SfLab population, the SfBt larvae were able to survive by feeding on Cry1Fa corn leaves. The SfBt population was maintained without selection for eight generations and shown to maintain high levels of resistance to Cry1Fa toxin. SfBt showed higher cross-resistance to Cry1Aa than to Cry1Ab or Cry1Ac toxins. As previously reported, Cry1A toxins competed the binding of Cry1Fa to brush border membrane vesicles (BBMV) from SfLab insects, explaining cross-resistance to Cry1A toxins. In contrast Cry2A toxins did not compete Cry1Fa binding to SfLab-BBMV and no cross-resistance to Cry2A was observed, although Cry2A toxins show low toxicity to S. frugiperda. Bioassays with Cry1AbMod and Cry1AcMod show that they are highly active against both the SfLab and the SfBt populations. The bioassay data reported here show that insects collected from Cry1Fa corn in the Cerrado region were resistant to Cry1Fa suggesting that resistance contributed to field failures of Cry1Fa corn to control S. frugiperda. 相似文献
82.
Sara Garcia‐Serrano Carolina Gutiérrez‐Repiso Montserrat Gonzalo Juan Garcia‐Arnes Sergio Valdes Federico Soriguer Vidal Perez‐Valero Miguel A. Alaminos‐Castillo Juan Francisco Cobos‐Bravo Francisco J. Moreno‐Ruiz Alberto Rodriguez‐Cañete Francisca Rodríguez‐Pacheco Eva Garcia‐Escobar Eduardo García‐Fuentes 《Obesity (Silver Spring, Md.)》2015,23(8):1607-1615
83.
Paul J. Barr Isabelle Scholl Paulina Bravo Marjan J. Faber Glyn Elwyn Marion McAllister 《PloS one》2015,10(5)
BackgroundPatient empowerment has gained considerable importance but uncertainty remains about the best way to define and measure it. The validity of empirical findings depends on the quality of measures used. This systematic review aims to provide an overview of studies assessing psychometric properties of questionnaires purporting to capture patient empowerment, evaluate the methodological quality of these studies and assess the psychometric properties of measures identified.MethodsElectronic searches in five databases were combined with reference tracking of included articles. Peer-reviewed articles reporting psychometric testing of empowerment measures for adult patients in French, German, English, Portuguese and Spanish were included. Study characteristics, constructs operationalised and psychometric properties were extracted. The quality of study design, methods and reporting was assessed using the COSMIN checklist. The quality of psychometric properties was assessed using Terwee’s 2007 criteria.Findings30 studies on 19 measures were included. Six measures are generic, while 13 were developed for a specific condition (N=4) or specialty (N=9). Most studies tested measures in English (N=17) or Swedish (N=6). Sample sizes of included studies varied from N=35 to N=8261. A range of patient empowerment constructs was operationalised in included measures. These were classified into four domains: patient states, experiences and capacities; patient actions and behaviours; patient self-determination within the healthcare relationship and patient skills development. Quality assessment revealed several flaws in methodological study quality with COSMIN scores mainly fair or poor. The overall quality of psychometric properties of included measures was intermediate to positive. Certain psychometric properties were not tested for most measures.DiscussionFindings provide a basis from which to develop consensus on a core set of patient empowerment constructs and for further work to develop a (set of) appropriately validated measure(s) to capture this. The methodological quality of psychometric studies could be improved by adhering to published quality criteria. 相似文献
84.
Gustavo A. Bravo J. V. Remsen Jr. Robb T. Brumfield 《Evolution; international journal of organic evolution》2014,68(10):2757-2774
Phylogenetic niche conservatism (PNC) and convergence are contrasting evolutionary patterns that describe phenotypic similarity across independent lineages. Assessing whether and how adaptive processes give origin to these patterns represent a fundamental step toward understanding phenotypic evolution. Phylogenetic model‐based approaches offer the opportunity not only to distinguish between PNC and convergence, but also to determine the extent that adaptive processes explain phenotypic similarity. The Myrmotherula complex in the Neotropical family Thamnophilidae is a polyphyletic group of sexually dimorphic small insectivorous forest birds that are relatively homogeneous in size and shape. Here, we integrate a comprehensive species‐level molecular phylogeny of the Myrmotherula complex with morphometric and ecological data within a comparative framework to test whether phenotypic similarity is described by a pattern of PNC or convergence, and to identify evolutionary mechanisms underlying body size and shape evolution. We show that antwrens in the Myrmotherula complex represent distantly related clades that exhibit adaptive convergent evolution in body size and divergent evolution in body shape. Phenotypic similarity in the group is primarily driven by their tendency to converge toward smaller body sizes. Differences in body size and shape across lineages are associated to ecological and behavioral factors. 相似文献
85.
Brevis P Morales E Bravo JC Monasterio V Mánques B Zaror L Abaca P Toloza L 《Revista iberoamericana de micología》2010,27(4):183-185
BackgroundRhinosporidiosis is a chronic, granulomatous, and non-contagious infection, in which highly vascularized polyps (mainly present in the nasal cavity) appear. These polyps usually bleed easily.AimsTo present the case of a 14 year-old male suffering from an obstruction and injury of the right nostril due to a polypoid shaped-lesion with a raspberry-like appearance.MethodsA wide surgery resection of the base of the lesion was performed, as well as a standard histopathology procedure, including microscopic analysis with haematoxylin-eosin and Grocott staining.Results and conclusionsThe histopathology report indicated that the chronic inflammatory polyp was compatible with rhinosporidiosis. 相似文献
86.
Rafael E. Coopman Fernanda P. Fuentes-Neira Verónica F. Briceño Hernán M. Cabrera Luis J. Corcuera León A. Bravo 《Trees - Structure and Function》2010,24(2):247-259
Nothofagus nitida (Phil.) Krasser (Nothofagaceae) regenerates under the shade. Nonetheless, older seedlings are commonly found at full sun.
We tested the hypothesis that light capture and photochemical and non-photochemical energy dissipation of both photosystems
PSI and PSII adjust with ontogeny and brighter environment. Light energy partitioning in both photosystems was studied in
seedlings of different developmental stages (small 9.7 cm, tall 36 cm) under contrasting light environments (8–200 and 1,800–2,043 μmol
photons m−2 s−1) in the Chilean evergreen temperate forest. Higher A
max, dark respiration, and light compensation and saturation points in sun seedlings of both developmental stages were accompanied
by higher rates of electron transport. These seedlings also showed a high fraction of open PSII reaction centres and similar
non-photochemical quenching at high-light in both photosystems, showing no effect of developmental stage in these parameters.
Conversely, light capture, total thermal dissipation after photoinhibition, active down-regulation of antenna efficiency,
and state transitions were higher in smaller seedlings than in taller ones. These changes maintain photostasis, preventing
photodamage, while favouring a more oxidized quinone pool. There is an independent effect of seedling development and light
acclimation on this transition from shade to sun during early ontogeny. This transition reflects short-term responses of the
photosynthetic apparatus to light and longer term responses that depend on seedling developmental stage. 相似文献
87.
Crespo R de Bravo MG Colinas PA Bravo RD 《Bioorganic & medicinal chemistry letters》2010,20(22):6469-6471
A series of α-D-hex-2-enopyranosyl sulfonamides was evaluated for their antiproliferative activity against human hepatocellular liver carcinoma (HepG2) and human lung adenocarcinoma (A549) cell lines. The most potent compound (2,4,6-tri-O-acetyl-3-deoxy-α-D-erythro-hex-2-enopyranosyl ethanesulfonamide) showed antiproliferative properties in the micromolar range. The SARs of these sulfonamidoglycoside which includes the influence of carbohydrate rings and sulfonamide class are described. 相似文献
88.
Marie Gérard-Champod Stéphanie Blanquet-Diot Jean-Michel Cardot David Bravo Monique Alric 《Applied and environmental microbiology》2010,76(16):5592-5600
Following the January 2006 European ban of antibiotics used as growth promoters in the veal calf industry, new feed additives are needed in order to maintain animal health and growth performance. As an alternative to in vivo experiments in the testing of such additives, an in vitro system modeling the intestinal ecosystem of the veal calf was developed. Stabilization of the main cultured microbial groups and their metabolic activity were tracked in an in vitro continuous fermentor operated under anaerobiosis, at pH 6.5, and at a temperature of 38.5°C and supplied with one of three different nutritive media (M1, M2, or M3). These media mainly differed in their concentrations of simple and complex carbohydrates and in their lipid sources. In vitro microbial levels and fermentative metabolite concentrations were compared to in vivo data, and the biochemical composition of the nutritive media was compared to that of the veal calf intestinal content. All three nutritive media were able to stabilize anaerobic and facultative anaerobic microflora, lactate-utilizing bacteria, bifidobacteria, lactobacilli, enterococci, and Bacteroides fragilis group bacteria at levels close to in vivo values. The microbiota was metabolically active, with high concentrations of lactate, ammonia, and short-chain fatty acids found in the fermentative medium. Comparison with in vivo data indicated that M3 outperformed M1 and M2 in simulating the conditions encountered in the veal calf intestine. This in vitro system would be useful in the prescreening of new feed additives by studying their effect on the intestinal microbiota levels and fermentative metabolite production.European regulations introduced in January 2006 banned the use of antibiotics as growth promoters (AGP) at subtherapeutic levels in animal feed (regulation EC 1831/2003), particularly for veal calves. AGP generated significantly enhanced growth performance via complex processes. The mechanism of growth promotion is still speculative, but many studies suggest the involvement of the intestinal microbiota (7, 9). First of all, AGP did not promote the growth of germfree animals (6). Moreover, they strongly inhibited the bacterial catabolism of urea and amino acids and the fermentation of carbohydrates both in vitro and in vivo (10, 28, 35). AGP treatment thus provided the animal with higher nutrient availability and led to a decrease in the toxic metabolites produced by bacteria, like ammonia or amines, limiting the energy needed by the animal to detoxify the organism. Some authors also argue that another beneficial effect of AGP results from improved control of intestinal pathologies, such as necrotic enteritis in poultry (12). The January 2006 ban is thus expected to have an impact on veal calf health by leading to more frequent digestive disorders, as previously observed in pigs and poultry in the Nordic countries (36), where AGP have been totally prohibited since the 1990s. Even though no scientific study has yet been done on calves, there have already been reports of higher death rates on experimental commercial farms subsequent to the withdrawal of AGP. The main digestive diseases leading to veal calf deaths are enteritis and enterotoxemia, which are mainly triggered by pathogenic strains of Escherichia coli and Clostridium perfringens (22, 30).Veal calf producers are looking for new feed additives to allay the consequences of the AGP ban. Alternative approaches include the use of prebiotics, probiotics, or plant extracts. Several studies have reported both consistent improvements in weight gain and feed conversion and a reduction of the incidence of diarrhea with the addition of such additives to the veal calf diet (1, 11, 14). One of the hypotheses used to explain these beneficial effects involves the modulation of the intestinal microbiota. In particular, oligosaccharides containing mannose or fructose are known to selectively increase the growth of beneficial intestinal bacteria, including lactobacilli and bifidobacteria (21). Timmerman et al. (33) showed that a calf-specific probiotic containing six Lactobacillus species reduced the fecal counts of E. coli. Green tea extracts also improved the intestinal microbial balance by maintaining high fecal levels of Bifidobacterium and Lactobacillus spp. and decreasing those of C. perfringens (16).As indicated above, it is important to assess the action of newly developed feed additives on the veal calf intestinal microbiota. High interindividual variability makes it difficult and expensive to carry out in vivo studies. Alternatively, experiments can be conducted via in vitro systems modeling the intestinal environment of the animals, provided the model has been checked as pertinent. This approach should allow an economical and ethical way to prescreen feed additives by studying their effects on the intestinal microbiota cultured in the in vitro system and its metabolic activity. With this objective in mind, a necessary requirement is knowledge of the veal calf intestinal ecosystem. Thus, the bacterial and biochemical composition of the jejunoileal chyme of calves was previously characterized (13).The aims of the present study were (i) to set up an in vitro system where the main cultured microbial groups identified in the veal calf intestinal chyme are reproducibly stabilized and metabolically active and (ii) to validate our model by comparing the in vitro and in vivo levels of selected biotic and abiotic variables. 相似文献
89.
Susana B. Bravo Maria E.R. Garcia-Rendueles Sihara Perez-Romero Joana S. Rodrigues Clara V. Alvarez 《Analytical biochemistry》2010,400(2):219-228
Recently, it has been shown that commercial human thyroid lines were in fact derived from colon, mammary carcinoma, or melanoma. Others have demonstrated the absence of a common pattern of gene expression between available thyroid cancer cell lines and tumors from patients. Thus, it is important to use several primary cells with a common pathological origin to achieve reproducible results, and it is necessary to find common methods for manipulation of protein expression in such various cultures. We have standardized a transfection method for efficient expression of exogenous proteins in human primary thyroid cultures. We compared lipid-based techniques with three electroporation systems (Electroporator PulseAgile [PA]-4000, Microporator MP-100, and Nucleofector II). Nucleofection was unquestionably the most efficient even for promoter regulation studies, and it was effective in cultures from different origins as normal thyroid, papillary carcinoma, or lymphoid node metastasis. We also standardized, through lentiviral infection, the short hairpin RNA downregulation of protein expression generating human thyrocytes with low levels of p27KIP1 as a model system. 相似文献
90.
Annie Rochette Nicol Korner-Bitensky Duane Bishop Robert Teasell Carole White Gina Bravo Robert Côté Jean Lachaine Teri Green Louise-Hélène Lebrun Sylvain Lanthier Moira Kapral Sharon Wood-Dauphinee 《BMC neurology》2010,10(1):1-10